2012-2013

Abstract: About 75 % of the Antarctic surface mass gain occurs over areas below 2,000 m asl, which cover 40 % of the grounded ice-sheet. As the topography is complex in many of these regions, surface mass balance modelling is highly dependent on horizontal resolution, and studying the impact of Antarctica on the future rise in sea level requires physical approaches. We have developed a computationally efficient, physical downscaling model for high-resolution (15 km) long-term surface mass balance (SMB) projections. Here, we present results of this model, called SMHiL (surface mass balance high-resolution downscaling), which was forced with the LMDZ4 atmospheric general circulation model to assess Antarctic SMB variability in the twenty first and the twenty second centuries under two different scenarios. The higher resolution of SMHiL better reproduces the geographical patterns of SMB and increase significantly the averaged SMB over the grounded ice-sheet for the end of the twentieth century. A comparison with more than 3200 quality-controlled field data shows that LMDZ4 and SMHiL reproduce the observed values equally well. Nevertheless, field data below 2,000 m asl are too scarce to efficiently show the added value of SMHiL and measuring the SMB in these undocumented areas should be a future scientific priority. Our results suggest that running LMDZ4 at a finer resolution (15 km) may give a future increase in SMB in Antarctica that is about 30 % higher than by using its standard resolution (60 km) due to the higher increase in precipitation in coastal areas at 15 km. However, a part (similar to 15 %) of these discrepancies could be an artefact from SMHiL since it neglects the foehn effect and likely overestimates the precipitation increase. Future changes in the Antarctic SMB at low elevations will result from the competition between higher snow accumulation and runoff. For this reason, developing downscaling models is crucial to represent processes in sufficient detail and correctly model the SMB in coastal areas.

Abstract: Dam flushing is conducted regularly on the Arc River (Northern French Alps) to remove sediments from dam reservoirs. This paper presents the analysis of five field campaigns carried out during dam flushing events in the upper Arc River basin (in June 2006, 2007, 2009, 2010 and 2011). Measurements of suspended sediment concentrations (SSC) and discharges were performed at several sampling sites along the river channel. To complete the discharge data set, a 1D numerical hydraulic model, MASCARET, was calibrated and used to estimate the instantaneous discharge at any position along the river system. Following the temporal integration of the instantaneous suspended sediment fluxes, a spatial distribution of the suspended load along the Arc and Isere Rivers was obtained. The classical error propagation method was used to quantify errors resulting from the method employed to estimate the integrated fluxes, by taking into account the relative errors introduced by both the measurements and the model. It appears that the response of the river's sediment transport differs from one year to another. The quantity of fine sediments removed from the reservoirs varied from 10,000 tons in 2007 to 40,000 tons in 2006. Over the 120 kilometers of river network, the suspended load could either increase significantly (30,000 tons in 2007) or else remain exactly the same (in 2009 and 2011). The mean relative standard deviation on the integrated fluxes is equal to 11 %. Taking into account these uncertainty values, it appears that the global tendencies are significant, but the local mass balances are more difficult to interpret.

Abstract: Particulate Flux estimation (suspended sediment and associated substances such as organic matter or micropolutants) is a major issue in mountain rivers. A database of high-frequency (30 minutes) discharge, suspended solids (TSS) and particulate organic carbon (POC) on Isere River in Grenoble was used for the calculation of annual fluxes and during major floods over 6 years (2006-2011). Fluxes were calculated by summing the 30 minutes fluxes. The study presents a method for calculating uncertainty fluxes based on Monte Carlo simulations using the errors on the relationships between continuous measurement / experimental measurements (height / flow, TSS / Turbidity, TSS / POC). In particular, the effect of discharge for the calculation of uncertainty is analyzed for different error scenarios (0, 3, 10, 20, 30 % and using a mean daily discharge). The method allowed estimating uncertainties < 10 % for annual fluxes of TSS and POC whatever the scenario. However, uncertainties are more important for flood events (up to 30 % with the use of a mean daily discharge). It appears from the study that the influence of the error on the discharge is relatively less important than the errors on the parameters MES and POC. It is also shown that the mean daily discharge should be avoided for flux calculations and that high frequency database remains the best alternative for a good estimate of the fluxes.

Abstract: We have analysed the trends of total aerosol particle number concentrations (N) measured at long-term measurement stations involved either in the Global Atmosphere Watch (GAW) and/or EU infrastructure project ACTRIS. The sites are located in Europe, North America, Antarctica, and on Pacific Ocean islands. The majority of the sites showed clear decreasing trends both in the full-length time series, and in the intra-site comparison period of 2001-2010, especially during the winter months. Several potential driving processes for the observed trends were studied, and even though there are some similarities between N trends and air temperature changes, the most likely cause of many northern hemisphere trends was found to be decreases in the anthropogenic emissions of primary particles, SO2 or some co-emitted species. We could not find a consistent agreement between the trends of N and particle optical properties in the few stations with long time series of all of these properties. The trends of N and the proxies for cloud condensation nuclei (CCN) were generally consistent in the few European stations where the measurements were available. This work provides a useful comparison analysis for modelling studies of trends in aerosol number concentrations.

Abstract: The features associated with modern synchrotron radiation machines (intense and coherent beams) result in a substantial extension of X-ray imaging capabilities in terms of spatial and temporal resolution, phase contrast and 3D images. This allows crystal growth-related information to be obtained which is not available otherwise. After briefly describing the main synchrotron radiation based imaging techniques of interest, we give original examples illustrating the new capabilities for crystal growth: characterisation of crystals grown for applications, such as ice tri-crystals produced for mechanical deformation studies; SiC; crystalline silicon for solar photovoltaic cells; in situ and in real time studies of quasicrystal growth (AlPdMn); and ultrafast tomography for the study of the growth of dendrites in metallic alloys. (C) 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Abstract: An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale had been developed based on an inverse dating method (Datice), combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousands of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2013), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120-800 ka. In this framework, new measurements of delta O-18(atm) over Marine Isotope Stage (MIS) 11-12 on EDC and a complete delta O-18(atm) record of the TALDICE ice cores permit us to derive additional orbital gas age constraints. The coherency of the different orbitally deduced ages (from delta O-18(atm), delta O-2/N-2 and air content) has been verified before implementation in AICC2012. The new chronology is now independent of other archives and shows only small differences, most of the time within the original uncertainty range calculated by Datice, when compared with the previous ice core reference age scale EDC3, the Dome F chronology, or using a comparison between speleothems and methane. For instance, the largest deviation between AICC2012 and EDC3 (5.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

Abstract: To improve both precision and accuracy of cosmic-ray exposure dating methods, there is a crucial need of calibration sites constraining the production rate of cosmogenic isotopes. This is particularly true in the high tropical area, where existing scaling models present significant discrepancies. This study presents a new calibration site for cosmogenic He-3, located at 3800 m in the tropical Altiplano (19.9 degrees S, 67.6 degrees W), on the southern flank of the Tunupa volcano, in the vicinity of the Salar de Uyuni. It consists in a fluvio-glacial outwash that is stratigraphically bracketed by two successive lacustrine shorelines. These shorelines are well-dated by C-14 and U-series dating (n = 57), allowing determination of the age of the boulder field at the surface of the delta, at 15.3 +/- 0.5 ka (let). Eleven andesitic boulders were sampled on this fluvio-glacial surface and the cosmogenic He-3 contents of their pyroxene phenocrysts and amphiboles was analyzed. The nucleogenic contribution from Li-6 capture is well-constrained by determining the (U-Th-Sm)/He-4 age of these rocks. This correction is minimal (<2%) and does not represent a significant source of uncertainty. Cosmogenic He-3 (He-c) concentrations are characterized by a very high reproducibility: 10 samples overlap within 10- analytical error. This suggests that pre- or post-deposition processes have minimal impact on the 3Hec data. Furthermore, there is no correlation between the Li and the He-3(c) content of the mineral, indicating that He-3(c) production from cosmogenic thermal neutron is here negligible. Combined with the absolute dating of the delta, these He-3(c) data yield a local production rate of 999 +/- 38 (1 sigma) at g(-1) yr(-1), at 3800 m and 19.89 S. After scaling with the time dependent scaling scheme of (Stone, 2000), this result yields a rate of 121 +/- 5 (1 sigma) at g(-1) yr(-1) at high latitude and sea level. This new calibration is the highest among the existing global dataset It will thus permit the establishment of new robust glacial chronologies in the high Tropics, with an uncertainty lower than 5% at 1 sigma. Such precision may have important implications in paleoclimatology, notably because it will allow comparison with other well-dated paleoclimatic archives. Including this new data, the updated global He-3(c) production rate is 122 +/- 15 at g(-1) yr(-1), using the time-dependent scaling of Stone (2000). The new site-specific He-3(c) production rate is used here to refine glacier fluctuations on Cerro Tunupa, confirming that the local last glacial maximum was synchronous with the Lake Tauca highstand (15.5 ka). Data also suggest that a dramatic glacial retreat occurred at about 15 ka, few hundred years before the Lake Tauca regression, synchronously with the onset of the Bolling-Allerod. (C) 2013 Elsevier B.V. All rights reserved.

Abstract: In this study, it is shown (i) that, as a result of the nonlinearity of the seawater equation of state, unresolved scales represent a major source of uncertainties in the computation of the large-scale horizontal density gradient from the large-scale temperature and salinity fields, and (ii) that the effect of these uncertain ties can be simulated using random processes to represent unresolved temperature and salinity fluctuations. The results of experiments performed with a low resolution global ocean model show that this parameterization has a considerable effect on the average large-scale circulation of the ocean, especially in the regions of intense mesoscale activity. The large-scale flow is less geostrophic, with more intense associated vertical velocities, and the average geographical position of the main temperature and salinity fronts is more consistent with observations. In particular, the simulations suggest that the stochastic effect of the unresolved temperature and salinity fluctuations on the large-scale density field may be sufficient to explain why the Gulf Stream pathway systematically overshoots in non-stochastic low resolution ocean models. (c) 2013 Elsevier Ltd. All rights reserved.

Abstract: In recent years, there has been an increase in flash flood impacts, even as our ability to forecast events and warn areas at risk increases. This increase results from a combination of extreme events and the exposure of vulnerable populations. The issues of exposure and vulnerability to flash floods are not trivial because environmental circumstances in such events are specific and complex enough to challenge the general understanding of natural risks. Therefore, it seems essential to consider physical processes of flash floods concurrently with the impacts they trigger. This paper takes a first step in addressing this need by creating and testing the coherence of an impact-focused database based on two pre-existing public and expert-based survey datasets: the Severe Hazards Analysis and Verification Experiment (SHAVE) and the US National Weather Service (NWS) Storm Data. The SHAVE initiative proposes a new method for collecting near-real-time high-resolution observations on both environmental circumstances and their disastrous consequences (material and human losses) to evaluate radar-based forecasting tools. Forecast verification tools and methods are needed to pursue improving the spatial and temporal accuracy of forecasts. Nevertheless by enhancing SHAVE and NWS datasets with socially and spatially relevant information, we aim at improving future forecast ability to predict the amount and types of impacts. This paper describes the procedures developed to classify and rank the impacts from the least to the most severe, then to verify the coherence and relevance of the impact-focused SHAVE dataset via cross-tabulation analysis of reported variables and GIS-sampled spatial characteristics. By crossing impact categories with socio-spatial characteristics, this analysis showed first benchmarks for the use of exposure layers in future flash flood impact forecasting models. The enhanced impact-focused datasets were used to test the capabilities of flash flood forecasting tools in predicting different categories of impacts for two extreme cases of flash flooding in Oklahoma, USA. Results showed a general tendency for the more severe impacts to be associated to higher mean exceedances over tool values. This means that, at least for these particular case studies, the tools were able to make a distinction between less severe and more severe impacts. Finally, a critical analysis of the NWS and SHAVE data collection methodologies was completed and challenges for future work were identified. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: The broadband albedo of surface snow is determined both by the near-surface profile of the physical and chemical properties of the snowpack and by the spectral and angular characteristics of the incident solar radiation. Simultaneous measurements of the physical and chemical properties of snow were carried out at Summit Camp, Greenland (72 degrees 36' N, 38 degrees 25' W, 3210m a.s.l.) in May and June 2011, along with spectral albedo measurements. One of the main objectives of the field campaign was to test our ability to predict snow spectral albedo by comparing the measured albedo to the albedo calculated with a radiative transfer model, using measured snow physical and chemical properties. To achieve this goal, we made daily measurements of the snow spectral albedo in the range 350-2200 nm and recorded snow stratigraphic information down to roughly 80 cm. The snow specific surface area (SSA) was measured using the DUFISSS instrument (DUal Frequency Integrating Sphere for Snow SSA measurement, Gallet et al., 2009). Samples were also collected for chemical analyses including black carbon (BC) and dust, to evaluate the impact of light absorbing particulate matter in snow. This is one of the most comprehensive albedo-related data sets combining chemical analysis, snow physical properties and spectral albedo measurements obtained in a polar environment. The surface albedo was calculated from density, SSA, BC and dust profiles using the DISORT model (DIScrete Ordinate Radiative Transfer, Stamnes et al., 1988) and compared to the measured values. Results indicate that the energy absorbed by the snowpack through the whole spectrum considered can be inferred within 1.10 %. This accuracy is only slightly better than that which can be obtained considering pure snow, meaning that the impact of impurities on the snow albedo is small at Summit. In the near infrared, minor deviations in albedo up to 0.014 can be due to the accuracy of radiation and SSA measurements and to the surface roughness, whereas deviations up to 0.05 can be explained by the spatial heterogeneity of the snowpack at small scales, the assumption of spherical snow grains made for DISORT simulations and the vertical resolution of measurements of surface layer physical properties. At 1430 and around 1800 nm the discrepancies are larger and independent of the snow properties; we propose that they are due to errors in the ice refractive index at these wavelengths. This work contributes to the development of physically based albedo schemes in detailed snowpack models, and to the improvement of retrieval algorithms for estimating snow properties from remote sensing data.

Abstract: Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Determining the influence of glacial runoff to streams is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose quantifying the diurnal cycle amplitude of the stream-flow to determine the glacial influence in glacierized catchments. We performed water-level measurements using water pressure loggers over 10 months at 30 min time steps in 15 stream sites in 2 glacier-fed catchments in the Ecuadorian Andes (> 4000 m a.s.l.) where no perennial snow cover is observed outside the glaciers. For each stream site, we performed wavelet analyses on water-level time series, determined the scale-averaged wavelet power spectrum at 24 h scale and defined three metrics, namely the power, frequency and temporal clustering of the diurnal flow variation. The three metrics were then compared to the percentage of the glacier cover in the catchments, a metric of glacial influence widely used in the literature. As expected, we found that the diurnal variation power of glacier-fed streams decreased downstream with the addition of non-glacial tributaries. We also found that the diurnal variation power and the percentage of the glacier cover in the catchment were significantly positively correlated. Furthermore, we found that our method permits the detection of glacial signal in supposedly non-glacial sites, thereby revealing glacial meltwater resurgence. While we specifically focused on the tropical Andes in this paper, our approach to determine glacial influence may have potential applications in temperate and arctic glacierized catchments. The measure of diurnal water amplitude therefore appears as a powerful and cost-effective tool to understand the hydrological links between glaciers and hydrosystems better and assess the consequences of rapid glacier shrinking.

Abstract: The Greenland NEEM (North Greenland Eemian Ice Drilling) operation in 2010 provided the first opportunity to combine trace-gas measurements by laser spectroscopic instruments and continuous-flow analysis along a freshly drilled ice core in a field-based setting. We present the resulting atmospheric methane (CH4) record covering the time period from 107.7 to 9.5 ka b2k (thousand years before 2000 AD). Companion discrete CH4 measurements are required to transfer the laser spectroscopic data from a relative to an absolute scale. However, even on a relative scale, the high-resolution CH4 data set significantly improves our knowledge of past atmospheric methane concentration changes. New significant sub-millennial-scale features appear during interstadials and stadials, generally associated with similar changes in water isotopic ratios of the ice, a proxy for local temperature. In addition to the midpoint of Dansgaard-Oeschger (D/O) CH4 transitions usually used for cross-dating, sharp definition of the start and end of these events brings precise depth markers (with +/- 20 cm uncertainty) for further cross-dating with other palaeo- or ice core records, e. g. speleothems. The method also provides an estimate of CH4 rates of change. The onsets of D/O events in the methane signal show a more rapid rate of change than their endings. The rate of CH4 increase associated with the onsets of D/O events progressively declines from 1.7 to 0.6 ppbv yr(-1) in the course of marine isotope stage 3. The largest observed rate of increase takes place at the onset of D/O event #21 and reaches 2.5 ppbv yr(-1).

Abstract: Stochastic modelling is a useful way of simulating complex hard-rock aquifers as hydrological properties (permeability, porosity etc.) can be described using random variables with known statistics. However, very few studies have assessed the influence of topological uncertainty (i.e. the variability of thickness of conductive zones in the aquifer), probably because it is not easy to retrieve accurate statistics of the aquifer geometry, especially in hard rock context. In this paper, we assessed the potential of using geophysical surveys to describe the geometry of a hard rock-aquifer in a stochastic modelling framework. The study site was a small experimental watershed in South India, where the aquifer consisted of a clayey to loamy-sandy zone (regolith) underlain by a conductive fissured rock layer (protolith) and the unweathered gneiss (bedrock) at the bottom. The spatial variability of the thickness of the regolith and fissured layers was estimated by electrical resistivity tomography (ERT) profiles, which were performed along a few cross sections in the watershed. For stochastic analysis using Monte Carlo simulation, the generated random layer thickness was made conditional to the available data from the geophysics. In order to simulate steady state flow in the irregular domain with variable geometry, we used an isoparametric finite element method to discretize the flow equation over an unstructured grid with irregular hexahedral elements. The results indicated that the spatial variability of the layer thickness had a significant effect on reducing the simulated effective steady seepage flux and that using the conditional simulations reduced the uncertainty of the simulated seepage flux. As a conclusion, combining information on the aquifer geometry obtained from geophysical surveys with stochastic modelling is a promising methodology to improve the simulation of groundwater flow in complex hard-rock aquifers. (C) 2013 Elsevier B.V. All rights reserved.

Abstract: An 800 year volcanic record is constructed from high-resolution chemical analysis of recently obtained West Antarctica and central Greenland ice cores. The high accuracy and precision of the ice core chronologies are a result of dating by annual ice layer counting. Nineteen bipolar volcanic signals in this record represent large, explosive eruptions in the tropics with probable climatic impact. One of the two bipolar volcanic signals dated at 1453 and 1459 is probably left by the eruption of the submarine volcano Kuwae in the tropical Pacific, one of the largest volcanic eruptions in the last millennium. The discovery of the two signals in the 1450s casts doubt on the eruption year of 1452 or 1453 for Kuwae based on previous ice core records. The volcanic sulfate deposition patterns in this bipolar record suggest that the later signal is likely from the Kuwae eruption in 1458, although a firm attribution is not possible. Sulfur isotope composition in the volcanic sulfate in the central Greenland cores indicates that both eruptions in the 1450s injected sulfur gases into the stratosphere with probable impact on the global climate. These results are in agreement with tree ring records showing two short cold episodes during that decade. The bipolar volcanic record supports the hypothesis that unusually active volcanism in the thirteenth century contributed to the onset of the Little Ice Age and another active period in the mid fifteenth century may have helped to sustain the Little Ice Age.

Abstract: We propose a new simplified vision of flood dynamics through temporal and spatial scales to enhance understanding of potential and limits of human responses to flash floods. Based on data from a set of extreme flash floods that occurred in Europe, we analyze both the runoff response time of flash floods and the asynchronous character of flood peak time generation. We introduce the concept of “timeliness” to quantify the balance in time between the hydrological response of catchments to heavy storms and the human reactions. Timeliness is investigated across the range of spatial scales of concern for flash floods and for various types of anticipation actions. Results are reported for four extreme flash flood events occurred since 2002 in France, Italy and Slovenia. These results indicate that human actions adapt their pace to the physical context and are in a kind of “hurrying” process as the flood danger approaches in time. They show the importance of self-organization and 'unofficial' warning in response to flash flooding by individuals and groups. The work draws on flood hazard research findings from hydrology, meteorology and social science and put forward a framework for interdisciplinary collaboration between hydrologists and social scientists. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Within the frame of the European Aerosol Cloud Climate and Air Quality Interactions (EUCAARI) project, the Meteo-France aircraft ATR-42 performed 22 research flights over central Europe and the North Sea during the intensive observation period in May 2008. For the campaign, the ATR-42 was equipped to study the aerosol physical, chemical, hygroscopic and optical properties, as well as cloud microphysics. For the 22 research flights, retroplume analyses along the flight tracks were performed with FLEXPART in order to classify air masses into five sectors of origin, allowing for a qualitative evaluation of emission influence on the respective air parcel. This study shows that the extensive aerosol parameters (aerosol mass and number concentrations) show vertical decreasing gradients and in some air masses maximum mass concentrations (mainly organics) in an intermediate layer (1-3 km). The observed mass concentrations (in the boundary layer (BL): between 10 and 30 μg m(-3); lower free troposphere (LFT): 0.8 and 14 μg m(-3)) are high especially in comparison with the 2015 European norms for PM2.5 (25 μg m(-3)) and with previous airborne studies performed over England (Morgan et al., 2009; McMeeking et al., 2012). Particle number size distributions show a larger fraction of particles in the accumulation size range in the LFT compared to BL. The chemical composition of submicron aerosol particles is dominated by organics in the BL, while ammonium sulphate dominates the submicron aerosols in the LFT, especially in the aerosol particles originated from north-eastern Europe (similar to 80 %), also experiencing nucleation events along the transport. As a consequence, first the particle CCN acting ability, shown by the CCN/CN ratio, and second the average values of the scattering cross sections of optically active particles (i.e. scattering coefficient divided by the optical active particle concentration) are increased in the LFT compared to BL.

Abstract: Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.

Abstract: High-elevation sites from the inner part of the East Antarctic plateau sample windborne dust representative of large portions of the Southern hemisphere, and are sensitive to long-range atmospheric transport conditions to polar areas. On the periphery of the ice sheet, conversely, the aeolian transport of particles from high-elevation ice-free areas can locally represent a relatively important additional input of dust to the atmosphere, and the interplay of atmospheric dynamics, dust transport and deposition is strictly related to the regional atmospheric circulation behaviour both at present-day and in the past. The understanding of the spatial extent where local sources can influence the mineral dust budget on the ice sheet is fundamental for understanding the atmospheric dust cycle in Antarctica and for the interpretation of the dust history in marginal glaciological settings. In this work we investigate the spatial variability of dust flux and provenance during modern (pre-industrial) and Holocene times along a transect connecting Tabs Dome to the internal sites of the Antarctic plateau and we extend the existing documentation of the isotopic (Sr-Nd) fingerprint of dust-sized sediments from Victoria Land source areas. Dust flux, grain size and isotopic composition show a marked variability between Tabs Dome, Mid Point, D4 and Dome C/Vostok, suggesting that local sources play an important role on the periphery of the ice sheet. Microscope observations reveal that background mineral aerosol in the TALDICE core is composed by a mixture of dust, volcanic particles and micrometric-sized fragments of diatoms, these latter representing a small but pervasive component of Antarctic sediments. A set of samples from Victoria Land, mostly consisting of regolith and glacial deposits from high-elevation areas, was collected specially for this work and the isotopic composition of the dust-sized fraction of samples was analyzed. Results reveal a close relationship with the parent lithologies, but direct comparison between source samples and firn/ice core dust is problematical because of the ubiquitous volcanic contribution to the environmental particulate input in the Tabs Dome area. The frequency of events potentially suitable for peripheral dust transport to Tabs Dome appears relatively high for present-day conditions, according to back trajectories calculations, and the related air flow pattern well-defined from a seasonal and spatial perspective. Also, as expected from palaeo-data, these events appear extremely uncommon for internal sites. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: In this paper, monitoring results of two cross tunnel sections are presented. This underground work has been realized for a subway in an urban area (Lyon, France). By comparison with measurements of other projects, it appears that the face instability and the annular gap identified after the shield release are the main sources of short-term settlements. These observations of vertical and horizontal movements during the tunnel excavation by a slurry pressurized tunnel boring machine are then compared with several numerical approaches. The 2D numerical approach uses the concept of volume loss and is applied to each excavation stage. It simulates approximately the observed movements but requires the use of empirical coefficients to represent in two dimensions the three-dimensional problem. The 3D approach considers more directly the physics of the problem and permits to take into account: the slurry pressure at the tunnel face, the shield conicity, the grout injection in the annular void and the grout consolidation. Three dimensional numerical calculations are the most accurate approaches to simulate all the physical processes occurring during tunneling. However this type of model assumes that all the parameters that control the movements induced by the excavation are well known. Due to the complexity of a tunneling boring machine, it is not necessarily the case. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: The main soil properties related to the leaching of naphthalene in soils are particle size, organic matter content and the mineralogical composition of silt and clay fractions. The aim of this study was to evaluate naphtalene reactive transfer in soil columns determinated by the dispersion and retardation of naphthalene in soil samples collected from the surroundings of fuel storage tanks in Recife, Brazil. Leaching experiments were carried out in columns containing disturbed soils and were modeled using the convection-dispersion equation, which was adjusted to the experimental data with the CXTFIT software 2.0. The results indicated that sandy soils offer less resistance to leaching of naphthalene and that the presence of goethite, together with organic matter appeared to be the main factors responsible for the retardation of naphtalene transport in the studied samples.

Abstract: The application field of shield tunneling has extended in recent years. Most shield-driven tunnels are supported by segmental concrete linings. Although many well documented experimental, numerical and analytical results exist in literature concerning the functioning of segmental tunnel linings, their behavior under the influence of joints is still not clear. This paper presents a numerical study that has been performed to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The longitudinal joint between segments in a ring has been simulated through double node connections, with six degrees of freedom, represented by six springs. The proposed model allows the effect of not only the rotational stiffness but also the radial stiffness and the axial stiffness of the longitudinal joints to be taken into consideration. The numerical results show a significant reduction in the bending moment induced in the tunnel lining as the joint number increases. The tunnel behavior in terms of the bending moment considering the effect of joint distribution, when the lateral earth pressure factor K-0 is equal to 0.5, 1.5 and 2, is almost similar and differs when K0 is equal to unity. It has been seen that the influence of joint rotational stiffness, the reduction in joint rotation stiffness under the negative bending moment, the lateral earth pressure factor and Young's modulus of ground surrounding the tunnel should not be neglected. On the other hand, the results have also shown an insignificant influence of the axial and radial stiffness of the joints on segmental tunnel lining behavior. (c) 2013 Elsevier Ltd. All rights reserved.

Abstract: A method to acquire three dimensional diffraction data and orientation mapping with the 2D imaging setup of Hasylab beamline G3 is presented. The method has been successfully applied to undeformed large grains extracted from ice samples and extended to the 2D determination of lattice misorientation and lattice orientation distribution within deformed grains. (c) 2013 Elsevier B.V. All rights reserved.

Abstract: Marine ice-sheet stability is mostly controlled by the dynamics of the grounding line, i.e. the junction between the grounded ice sheet and the floating ice shelf. Grounding line migration has been investigated within the framework of MISMIP (Marine Ice Sheet Model Intercomparison Project), which mainly aimed at investigating steady state solutions. Here we focus on transient behaviour, executing short-term simulations (200 yr) of a steady ice sheet perturbed by the release of the buttressing restraint exerted by the ice shelf on the grounded ice upstream. The transient grounding line behaviour of four different flowline ice-sheet models has been compared. The models differ in the physics implemented (full Stokes and shallow shelf approximation), the numerical approach, as well as the grounding line treatment. Their overall response to the loss of buttressing is found to be broadly consistent in terms of grounding line position, rate of surface elevation change and surface velocity. However, still small differences appear for these latter variables, and they can lead to large discrepancies (> 100 %) observed in terms of ice sheet contribution to sea level when cumulated over time. Despite the recent important improvements of marine ice-sheet models in their ability to compute steady state configurations, our results question the capacity of these models to compute short-term reliable sea-level rise projections.

Abstract: The current positive trend in the Southern Annular Mode (SAM) is thought to reduce the growth rate of the Southern Ocean CO2 sink because enhanced wind-driven upwelling of dissolved inorganic carbon (DIC) increases outgassing of natural CO2. However, no study to date has quantified the potentially large role of mesoscale eddies in compensating intensified upwelling nor the mixed-layer processes in terms of their effects on CO2 fluxes. Here we report on results from two new simulations in a regional 0.5 degrees eddying model of the Southern Ocean. The first simulation is forced with interannually varying atmospheric reanalysis and coupled to a biogeochemistry model run under constant preindustrial atmospheric CO2. The second simulation is like the first except that superimposed on the forcing is a poleward shifted and intensified westerlies wind anomaly consistent with the positive phase of the SAM. In response to the SAM, the Southern Ocean's sea-to-air CO2 flux is enhanced by 0.1PgCyr(-1) per standard deviation of the SAM, mostly from the Antarctic Zone (AZ), where enhanced surface DIC is only partly compensated by enhanced surface alkalinity. Increased mixed-layer DIC in the AZ results from a combination of increased upwelling below the mixed layer and increased vertical diffusion at the base of the mixed layer. Previous studies overlooked the latter. Thus, upward supply of DIC and alkalinity depends on associated vertical gradients just below the mixed layer, which are affected by interior ocean transport. Our eddying model study suggests that about one third of the SAM enhancement of the Ekman-induced northward DIC transport is compensated by southward transport from standing and transient eddies.

Abstract: As part of the FORMES summer 2008 experiment, an Aerodyne compact time-of-flight aerosol mass spectrometer (cToF-AMS) was deployed at an urban background site in Marseille to investigate the sources and aging of organic aerosols (OA). France's second largest city and the largest port in the Mediterranean, Marseille, provides a locale that is influenced by significant urban industrialized emissions and an active photochemistry with very high ozone concentrations. Particle mass spectra were analyzed by positive matrix factorization (PMF2) and the results were in very good agreement with previous apportionments obtained using a chemical mass balance (CMB) approach coupled to organic markers and metals (El Haddad et al., 2011a). AMS/PMF2 was able to identify for the first time, to the best of our knowledge, the organic aerosol emitted by industrial processes. Even with significant industries in the region, industrial OA was estimated to contribute only similar to 5% of the total OA mass. Both source apportionment techniques suggest that oxygenated OA (OOA) constitutes the major fraction, contributing similar to 80% of OA mass. A novel approach combining AMS/PMF2 data with C-14 measurements was applied to identify and quantify the fossil and non-fossil precursors of this fraction and to explicitly assess the related uncertainties. Results show with high statistical confidence that, despite extensive urban and industrial emissions, OOA is overwhelmingly non-fossil, formed via the oxidation of biogenic precursors, including monoterpenes. AMS/PMF2 results strongly suggest that the variability observed in the OOA chemical composition is mainly driven in our case by the aerosol photochemical age. This paper presents the impact of photochemistry on the increase of OOA oxygenation levels, formation of humic-like substances (HULIS) and the evolution of alpha-pinene SOA (secondary OA) components.

Abstract: Here we report the measurement of the comprehensive isotopic composition (delta N-15, Delta O-17 and delta O-18) of nitrate at the air-snow interface at Dome C, Antarctica (DC, 75 degrees 06'S, 123 degrees 19'E), and in snow pits along a transect across the East Antarctic Ice Sheet (EAIS) between 66 degrees S and 78 degrees S. In most of the snow pits, nitrate loss (either by physical release or UV photolysis of nitrate) is observed and fractionation constants associated are calculated. Nitrate collected from snow pits on the plateau (snow accumulation rate below 50 kg m(-2)a(-1)) displays average fractionation constants of (-59 +/- 10) parts per thousand, (+2.0 +/- 1.0)parts per thousand and (+8.7 +/- 2.4)parts per thousand for delta N-15, Delta O-17 and delta O-18, respectively. In contrast, snow pits sampled on the coast show distinct isotopic signatures with average fractionation constants of (-16 +/- 14) parts per thousand, (-0.2 +/- 1.5)parts per thousand and (+3.1 +/- 5.8) parts per thousand, for delta N-15, Delta O-17 and delta O-18, respectively. Our observations corroborate that photolysis (associated with a N-15/N-14 fractionation constant of the order of -48 parts per thousand according to Frey et al. (2009)) is the dominant nitrate loss process on the East Antarctic Plateau, while on the coast the loss is less pronounced and could involve both physical release and photochemical processes. Year-round isotopic measurements at DC show a close relationship between the Delta O-17 of atmospheric nitrate and Delta O-17 of nitrate in skin layer snow, suggesting a photolytically driven isotopic equilibrium imposed by nitrate recycling at this interface. Atmospheric nitrate deposition may lead to fractionation of the nitrogen isotopes and explain the almost constant shift of the order of 25 parts per thousand between the delta N-15 values in the atmospheric and skin layer nitrate at DC. Asymptotic delta N-15(NO3-) values calculated for each snow pit are found to be correlated with the inverse of the snow accumulation rate (ln(delta N-15(as.) + 1) = (5.76 +/- 0.47) . (kg m(-2) a(-1)/A)+(0.01 +/- 0.02)), confirming the strong relationship between the snow accumulation rate and the degree of isotopic fractionation, consistent with previous observations by Freyer et al. (1996). Asymptotic Delta O-17(NO3-) values on the plateau are smaller than the values found in the skin layer most likely due to oxygen isotope exchange between the nitrate photoproducts and water molecules from the surrounding ice. However, the apparent fractionation in Delta O-17 is small, thus allowing the preservation of a portion of the atmospheric signal.

Abstract: Stochastic point processes for rainfall are known to be able to preserve the temporal variability of rainfall on several levels of aggregation (e.g. hourly, daily), especially when the cluster approach is used. One major assumption in most of the applications todate is the stationarity of the rainfall properties in time, which must be reconsidered under a climate change hypothesis. Here, we propose new theoretical developments of a Poisson-based model with cluster, namely the Neyman-Scott Rectangular Pulses Model, which treats storm frequency as a nonstationary function. In this paper, storm frequency is modelled as a linear function of time in order to reproduce an increase (or decrease) of the mean annual precipitation. The basic theory is reconsidered and the moments are derived up to the third order. Then, a calibration method based on the generalized method of moments is proposed and discussed. An application to a rainfall time series from Uccle illustrates how this model can reproduce a trend for the average rainfall. This work opens new avenues for future developments on transient stochastic rainfall models and highlights the major challenges linked to this approach.

Abstract: Gaseous elemental mercury (GEM) was monitored at the Niwot Ridge (NWT) Long-Term Ecological Research (LTER) site (Colorado, USA, 40 degrees N) from interstitial air extracted from the snowpack at depths ranging from the snow surface to 10 cm above the soil. A highly dynamic cycling of mercury (Hg) in this mid-latitude snowpack was observed. Patterns were driven by both GEM production in surface snow and GEM destruction in the deeper snowpack layers. Thorough mixing and vertical transport processes were observed through the snowpack. GEM was photochemically produced near the snow-air interface throughout the entire winter, leading to enhanced GEM levels in interstitial air of surface snow of up to 8 ng m(-3). During low-wind periods, GEM in surface snow layers remained significantly above ambient air levels at night as well, which may indicate a potential weak GEM production overnight. Analyses of vertical GEM gradients in the snowpack show that surface GEM enhancements efficiently propagated down the snowpack, with a temporal lag in peak GEM levels observed with increasing depth. Downward diffusion was responsible for much of these patterns, although vertical advection also contributed to vertical redistribution. Destruction of GEM in the lower snowpack layers was attributed to dark oxidation of GEM. Analysis of vertical GEM/CO2 flux ratios indicated that this GEM destruction occurred in the snow and not in the underlying soil. The strong, diurnal patterns of photochemical GEM production at the surface ultimately lead to re-emission losses of deposited Hg back to the atmosphere. The NWT data show that highest GEM surface production and re-emissions occur shortly after fresh snowfall, which possibly resupplies photoreducible Hg to the snowpack, and that photochemical GEM reduction is not radiation-limited as it is strong even on cloudy days.

Abstract: We present an updated and quality controlled surface mass balance (SMB) database for the Antarctic ice sheet. Importantly, the database includes formatted metadata, such as measurement technique, elevation, time covered, etc, which allows any user to filter out the data. Here, we discard data with limited spatial and temporal representativeness, too small measurement accuracy, or lack of quality control. Applied to the database, this filtering process gives four times more reliable data than when applied to previously available databases. New data with high spatial resolution are now available over long traverses, and at low elevation in some areas. However, the quality control led to a considerable reduction in the spatial density of data in several regions, particularly over West Antarctica. Over interior plateaus, where the SMB is low, the spatial density of measurements remains high. This quality controlled dataset was compared to results from ERA-Interim reanalysis to assess whether field data allow us to reconstruct an accurate description of the main SMB distribution features in Antarctica. We identified large areas where data gaps impede model validation: except for very few areas (e. g., Adelie Land), measurements in the elevation range between 200 m and 1000 m above sea level are not regularly distributed and do not allow a thorough validation of models in such regions with complex topography, where the highest scattering of SMB values is reported. Clearly, increasing the spatial density of field measurements at low elevations, in the Antarctic Peninsula and in West Antarctica is a scientific priority.

Abstract: Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990s. The last two decades are characterized by an increase of negative phases of the North Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June-July-August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that similar to 70% of the 1993-2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990s, which induces more frequent southerly warm air advection along the western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long-term climate warming but are more a consequence of NAO variability affecting atmospheric heat transport. Although no global model from the CMIP5 database projects subsequent significant changes in NAO through this century, we cannot exclude the possibility that the observed NAO changes are due to global warming.

Abstract: Earth system models (ESMs) are increasing in complexity by incorporating more processes than their predecessors, making them potentially important tools for studying the evolution of climate and associated biogeochemical cycles. However, their coupled behaviour has only recently been examined in any detail, and has yielded a very wide range of outcomes. For example, coupled climate-carbon cycle models that represent land-use change simulate total land carbon stores at 2100 that vary by as much as 600 Pg C, given the same emissions scenario. This large uncertainty is associated with differences in how key processes are simulated in different models, and illustrates the necessity of determining which models are most realistic using rigorous methods of model evaluation. Here we assess the state-of-the-art in evaluation of ESMs, with a particular emphasis on the simulation of the carbon cycle and associated biospheric processes. We examine some of the new advances and remaining uncertainties relating to (i) modern and palaeodata and (ii) metrics for evaluation. We note that the practice of averaging results from many models is unreliable and no substitute for proper evaluation of individual models. We discuss a range of strategies, such as the inclusion of pre-calibration, combined process- and system-level evaluation, and the use of emergent constraints, that can contribute to the development of more robust evaluation schemes. An increasingly data-rich environment offers more opportunities for model evaluation, but also presents a challenge. Improved knowledge of data uncertainties is still necessary to move the field of ESM evaluation away from a “beauty contest” towards the development of useful constraints on model outcomes.

Abstract: Atmospheric nitrogen oxides (NO and NO2) were observed at Dome C, East Antarctica (75.1 degrees S, 123.3 degrees E, 3233 m), for a total of 50 days, from 10 December 2009 to 28 January 2010. Average (+/- 1 sigma) mixing ratios at 1.0m of NO and NO2, the latter measured for the first time on the East Antarctic Plateau, were 111 (+/- 89) and 98 (+/- 89) pptv, respectively. Atmospheric mixing ratios are on average comparable to those observed previously at South Pole, but in contrast show strong diurnal variability: a minimum around local noon and a maximum in the early evening coincide with the development and collapse of a convective boundary layer. The asymmetric diurnal cycle of NOx concentrations and likely any other chemical tracer with a photolytic surface source is driven by the turbulent diffusivity and height of the atmospheric boundary layer, with the former controlling the magnitude of the vertical flux and the latter the size of the volume into which snow emissions are transported. In particular, the average (+/- 1 sigma) NOx emission flux from 22 December 2009 to 28 January 2010, estimated from atmospheric concentration gradients, was 8.2 (+/- 7.4) x 10(12) molecule m(-2) s(-1) belongs to the largest values measured so far in the polar regions and explains the 3-fold increase in mixing ratios in the early evening when the boundary layer becomes very shallow. Dome C is likely not representative for the entire East Antarctic Plateau but illustrates the need of an accurate description of the boundary layer above snow in atmospheric chemistry models. A simple nitrate photolysis model matches the observed median diurnal NOx flux during the day but has significant low bias during the night. The difference is significant taking into account the total random error in flux observations and model uncertainties due to the variability of NO3- concentrations in snow and potential contributions from NO2- photolysis. This highlights uncertainties in the parameterization of the photolytic NOx source in natural snowpacks, such as the poorly constrained quantum yield of nitrate photolysis. A steadystate analysis of the NO2 : NO ratios indicates that peroxy (HO2 + RO2) or other radical concentrations in the boundary layer of Dome C are either higher than measured elsewhere in the polar regions or other processes leading to enhanced NO2 have to be invoked. These results confirm the existence of a strongly oxidising canopy enveloping the East Antarctic Plateau in summer.

Abstract: The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

Abstract: For the first time a simulation of blowing snow events was validated in detail using one-month long observations (January 2010) made in Ad,lie Land, Antarctica. A regional climate model featuring a coupled atmosphere/blowing snow/snowpack model is forced laterally by meteorological re-analyses. The vertical grid spacing was 2 m from 2 to 20 m above the surface and the horizontal grid spacing was 5 km. The simulation was validated by comparing the occurrence of blowing snow events and other meteorological parameters at two automatic weather stations. The Nash test allowed us to compute efficiencies of the simulation. The regional climate model simulated the observed wind speed with a positive efficiency (0.69). Wind speeds higher than 12 m s (-1) were underestimated. Positive efficiency of the simulated wind speed was a prerequisite for validating the blowing snow model. Temperatures were simulated with a slightly negative efficiency (-0.16) due to overestimation of the amplitude of the diurnal cycle during one week, probably because the cloud cover was underestimated at that location during the period concerned. Snowfall events were correctly simulated by our model, as confirmed by field reports. Because observations suggested that our instrument (an acoustic sounder) tends to overestimate the blowing snow flux, data were not sufficiently accurate to allow the complete validation of snow drift values. However, the simulation of blowing snow occurrence was in good agreement with the observations made during the first 20 days of January 2010, despite the fact that the blowing snow flux may be underestimated by the regional climate model during pure blowing snow events. We found that blowing snow occurs in Ad,lie Land only when the 30-min wind speed value at 2 m a.g.l. is > 10 m s (-1). The validation for the last 10 days of January 2010 was less satisfactory because of complications introduced by surface melting and refreezing.

Abstract: The ice volume evolution of a frozen waterfall (or ice cascade) was studied using a thermodynamic model. The model was developed from meteorological data collected in the vicinity of the waterfall and validated from ice volume measurements estimated from terrestrial lidar images. The ice cascade forms over a 45 m high rock wall located in northern Gaspesie, Quebec, Canada. Two stages of formation were identified. During the first stage, the growth is mainly controlled by air convection around the flowing and free-falling water. The ice cascade growth rate increases with decreasing air temperature below 0 degrees C and when the water flow reaches its lowest level. During the second stage, the ice cascade covers the entire rock-wall surface, water flow is isolated from the outside environment and ice volume increases asymptotically. Heat is evacuated from the water flow through the ice cover by conduction. The growth is controlled mainly by the conductive heat loss through the ice cover but also by the longwave radiation emitted at the ice surface during the night. In spring, melting of the ice cascade is dependent on the air convection over the ice surface but also on the sensible heat carried by the increasing water flow and the solar radiation received during the day.

Abstract: The lower atmospheric boundary layer at Dome C on the Antarctic plateau has been continuously monitored along a 45-m tower since 2009. Two years of observations (2009 and 2010) are presented. A strong diurnal cycle is observed near the surface in summer but almost disappears at the top of the tower, indicating that the summer nocturnal inversion is very shallow. Very steep inversions reaching almost 1 degrees C m(-1) on average along the tower are observed in winter. They are stronger and more frequent during the colder 2010 winter, reaching a maximum in a layer similar to 10-15 m above the surface. Winter temperature is characterized by strong synoptic variability. An extreme warm event occurred in July 2009. The temperature reached -30 degrees C, typical of midsummer weather. Meteorological analyses which agree with the observations near the surface confirm that heat is propagated downward from higher elevations. A high total water column indicates moist air masses aloft originating from the lower latitudes. The coldest temperatures and strongest inversions are associated with characteristic synoptic patterns and a particularly dry atmosphere. Measurement of moisture in the clean and cold Antarctic plateau atmosphere is a challenging task. Supersaturations are very likely but are not revealed by the observations. This is possibly an instrumental artifact that would affect other moisture measurements made in similar conditions. In spite of this, such observations offer a stringent test of the robustness of the polar boundary layer in meteorological and climate models, addressing a major concern raised in the IPCC 2007 report.

Abstract: Given the paucity of observations, a great deal of uncertainty remains concerning temperature changes at very high altitudes over the last century. Englacial temperature measurements performed in boreholes provide a very good indicator of atmospheric temperatures for very high elevations although they are not directly related to air temperatures. Temperature profiles from seven deep boreholes drilled at three different sites between 4240 and 4300mabove sea level in the Mont Blanc area (French Alps) have been analyzed using a heat flow model and a Bayesian inverse modeling approach. Atmospheric temperature changes over the last century were estimated by simultaneous inversion of these temperature profiles. A mean warming rate of 0.14 degrees C/decade between 1900 and 2004 was found. This is similar to the observed regional low altitude trend in the northwestern Alps, suggesting that air temperature trends are not altitude dependent.

Abstract: The evaluation of rainfall products over the West African region will be an important component of the Megha-Tropiques (MT) Ground Validation (GV) plan. In this paper, two dense research gauge networks from Benin and Niger, integrated in the MT GV plan, are presented and are used to evaluate several currently available global or regional satellite-based rainfall products. Eight productsthe Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), Climate Prediction Center Morphing method (CMORPH), Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) 3B42 real-time and gauge-adjusted version, Global Satellite Mapping of Precipitation (GSMaP), Climate Prediction Center (CPC) African Rainfall Estimate (RFE), Estimation des Precipitation par SATellite (EPSAT), and Global Precipitation Climatology Project One Degree Daily estimate (GPCP-1DD)are compared to the ground reference. The comparisons are carried out at daily, 1 degrees resolution, over the rainy season (June-September), between the years 2003 and 2010. The work focuses on the ability of the various products to reproduce salient features of the rainfall regime that impact the hydrological response. The products are analysed on a multi-criteria basis, focusing in particular on the way they distribute the rainfall within the season and by rain rate class. Standard statistical diagnoses such as the correlation coefficient, bias, root mean square error and Nash skill score are computed and the inter-annual variability is documented. Two simplified hydrological models are used to illustrate how the nature and structure of the product error impact the model output in terms of runoff (calculated using the Soil Conservation Service method, SCS, in Niger) or outflow (calculated with the modele du Genie Rural a 4 parametres Journalier', GR4J model, in Benin). Copyright (c) 2013 Royal Meteorological Society

Abstract: IO, BrO, and NO2 were measured for the first time at Dumont d'Urville (East Antarctic coast) during summer 2011/2012 by using a near-UV-Visible laser spectrometer based on mode-locked cavity-enhanced absorption spectroscopy. IO mixing ratios ranged from the 2 sigma detection limit (0.04 pptv) up to 0.15 pptv. BrO remained close or below the detection limit (2 pptv) of the instrument. Daily averaged NO2 values ranged between the detection limit (10 pptv) and 60 pptv being far higher than levels of a few pptv commonly observed in the remote marine boundary layer. Data are discussed and compared with those available for another coastal Antarctic station (Halley, West Antarctica). It is shown that the oxidative capacity of the atmospheric boundary layer at coastal Antarctic sites is quite different in nature from West to East Antarctica, with the halogen chemistry being promoted at West and the OH chemistry at East. Citation: Grilli, R., M. Legrand, A. Kukui, G. Mejean, S. Preunkert, and D. Romanini (2013), First investigations of IO, BrO, and NO2 summer atmospheric levels at a coastal East Antarctic site using mode-locked cavity enhanced absorption spectroscopy, Geophys. Res. Lett., 40, 791-796, doi: 10.1002/grl.50154.

Abstract: Air and water stable isotope measurements from four Greenland deep ice cores (GRIP, GISP2, NGRIP and NEEM) are investigated over a series of Dansgaard Oeschger events (DO 8, 9 and 10), which are representative of glacial millennial scale variability. Combined with firn modeling, air isotope data allow us to quantify abrupt temperature increases for each drill site (1 sigma = 0.6 degrees C for NEEM, GRIP and GISP2, 1.5 degrees C for NGRIP). Our data show that the magnitude of stadial interstadial temperature increase is up to 2 degrees C larger in central and North Greenland than in northwest Greenland: i.e., for DO 8, a magnitude of +8.8 degrees C is inferred, which is significantly smaller than the +11.1 degrees C inferred at GISP2. The same spatial pattern is seen for accumulation increases. This pattern is coherent with climate simulations in response to reduced sea-ice extent in the Nordic seas. The temporal water isotope (delta O-18) temperature temperature relationship varies between 0.3 and 0.6 (+/- 0.08) %degrees C-1 and is systematically larger at NEEM, possibly due to limited changes in precipitation seasonality compared to GISP2, GRIP or NGRIP. The gas age ice age difference of warming events represented in water and air isotopes can only be modeled when assuming a 26 % (NGRIP) to 40 % (GRIP) lower accumulation than that derived from a Dansgaard Johnsen ice flow model.

Abstract: The first reported seasonal O-17 anomaly in sulfate aerosols and measurements of radioactive (SO42-)-S-35 activities collected from Dome C, Antarctica, are reported. O-17 values exhibit minima during summer (as low as 0.91) when tropospheric oxidation patterns are dominated by OH/H2O2 mechanisms. Significant enrichment during autumn and spring is observed (up to 2.40) as ozone oxidation increases in the troposphere relative to summer and both stratospheric sources and long-range transport become more significant to the total sulfate budget. An unexpected decrease in O-17 is seen as winter progresses. This decline is concluded to potentially arise due to a reduction in vertical mixing in the troposphere or linked to variations in the long-range transport of sulfur species to Antarctica. (SO42-)-S-35 activities exhibit maxima during summer (up to 1219 atoms S-35/m(3)) that correlate with the peak in stratospheric flux and minima during winter (as low as 146 atoms S-35/m(3)) when the lack of solar radiation substantially reduces photochemical activity. It is shown that S-35 offers the potential to be used as an additional tracer to study stratospheric and tropospheric interactions and is used to estimate stratospheric input of sulfur (combination of SO2 and SO42-). Stratospheric sulfur input produces maxima during summer/autumn with an upper limit of 5.5ng/m(3) and minima during winter/spring with an upper limit of 1.1ng/m(3). From these results, it is concluded that the variation in O-17 is more reliant upon shifts in tropospheric oxidation mechanisms and long-range transport than on changes in the stratospheric flux.

Abstract: Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on the northeast saddle of Mt. Qomolangma (Everest) (28 degrees 01'N, 86 degrees 58'E, 6518m above sea level) give access to a tentative record of past Himalayan atmospheric mixing ratio of CH4 spanning the past 1200 yr. The major part of the record is affected by artifacts probably due to in situ production. After selecting what may represent the true atmospheric mixing ratio, an average of 749 +/- 25 ppbv of CH4 is estimated for the late preindustrial Holocene, which is similar to 36 +/- 17 (similar to 73 +/- 18) ppbv higher than the atmospheric levels recorded in the Greenland (Antarctic) ice cores. A comparison of these new data with model simulations of the CH4 latitudinal gradient suggests either that the models do not get a correct balance between high and low latitude CH4 sources, or that the filtered CH4 profile from the ER cores remains biased by small artifacts.

Abstract: A regional numerical model of the tropical Atlantic Ocean and observations are analyzed to investigate the intraseasonal fluctuations of the sea surface temperature at the equator in the Gulf of Guinea. Results indicate that the seasonal cooling in this region is significantly shaped by short-duration cooling events caused by wind-forced equatorial waves: mixed Rossby- gravity waves within the 12-20-day period band, inertia gravity waves with periods below 11 days, and equatorially trapped Kelvin waves with periods between 25 and 40 days. In these different ranges of frequencies, it is shown that the wave-induced horizontal oscillations of the northern front of the mean cold tongue dominate the variations of mixed layer temperature near the equator. But the model mixed layer heat budget also shows that the equatorial waves make a significant contribution to the mixed layer heat budget through modulation of the turbulent cooling, especially above the core of the Equatorial Undercurrent (EUC). The turbulent cooling variability is found to be mainly controlled by the intraseasonal modulation of the vertical shear in the upper ocean. This mechanism is maximum during periods of seasonal cooling, especially in boreal summer, when the surface South Equatorial Current is strongest and between 2 degrees S and the equator, where the presence of the EUC provides a background vertical shear in the upper ocean. It applies for the three types of intraseasonal waves. Inertia-gravity waves also modulate the turbulent heat flux at the equator through vertical displacement of the core of the EUC in response to equatorial divergence and convergence.

Abstract: The isotopic composition of precipitation, in deuterium, oxygen 18 and oxygen 17, depends on the climatic conditions prevailing in the oceanic regions where it originates, mainly the sea surface temperature and the relative humidity of air. This dependency applies to present-day precipitation but also to past records which are extracted, for example, from polar ice cores. In turn, coisotopic measurements of deuterium and oxygen 18 offer the possibility to retrieve information about the oceanic origin of modern precipitation as well as about past changes in sea surface temperature and relative humidity of air. This interpretation of isotopic measurements has largely relied on simple Rayleigh-type isotopic models and is complemented by Lagrangian back trajectory analysis of moisture sources. It is now complemented by isotopic General Circulation Models (IGCM) in which the origin of precipitation can be tagged. We shortly review published results documenting this link between the oceanic sources of precipitation and their isotopic composition. We then present experiments performed with two different IGCMs, the GISS model II and the LMDZ model. We focus our study on marine water vapor and its contribution to precipitation over Antarctica and over the Andean region of South America. We show how IGCM experiments allow us to relate climatic conditions prevailing in the oceanic source of precipitation to its isotopic composition. Such experiments support, at least qualitatively, the current interpretation of ice core isotopic data in terms of changes in sea surface temperature. Additionally, we discuss recent studies clearly showing the added value of oxygen 17 measurements.

Abstract: The vertical profile of reflectivity (VPR) must be identified to correct estimations of rainfall rates by radar for the nonuniform beam filling associated with the vertical variation of radar reflectivity. A method for identifying VPRs from volumetric radar data is presented that takes into account the radar sampling. Physically based constraints on the vertical structure of rainfall are introduced with simple VPR models within a rainfall classification procedure defining more homogeneous precipitation patterns. The model parameters are identified in the framework of an extended Kalman filter to ensure their temporal consistency. The method is assessed using the dataset from a volume-scanning strategy for radar quantitative precipitation estimation designed in 2002 for the Bollene radar (France). The physical consistency of the retrieved VPR is evaluated. Positive results are obtained insofar as the physically based identified VPR (i) presents physically consistent shapes and characteristics considering beam effects, (ii) shows improved robustness in the difficult radar measurement context of the Cevennes-Vivarais region, and (iii) provides consistent physical insight into the rain field.

Abstract: We study fluid-particle motion in the velocity field induced by a quasi-stationary point vortex structure consisting of one upper-layer vortex and two identical vortices in the bottom layer of a rotating two-layer fluid. The regular regimes are investigated, and the possibility of chaotic regimes (chaotic advection) under the effect of quite small non-stationary disturbances of stationary configurations has been shown. Examples of different scenarios are given for the origin and development of chaos. We analyse the role played by the stochastic layer in the processes of mixing and in the capture of fluid particles within a vortex area. We also study the influence of stratification on these effects. It is shown that regular and chaotic advection situations exhibit significant differences in the two layers.

Abstract: The interface friction coefficient is an important design parameter for reinforced soil structures where the friction between the soil and reinforcement elements is mobilized. The pull-out test is the most commonly adopted method to identify this friction coefficient. In this paper, 18 pull-out tests were conducted on two types of welded steel meshes (normal and dense mesh) embedded in a sand to investigate the soil/reinforcement interaction. The tests were conducted under vertical stresses ranging from 20 to 140 kPa on the reinforcement. The French standard (NF P 94-270, 2009) uses an analytical method to predict the friction coefficient. The comparison with the experimental results agrees reasonably well. Ju et al. (2004) developed a new test method based on a staged pull-out test for extensible reinforcements. In this study and for inextensible reinforcement, this new test method has also been used. In a usual pull-out test, only one vertical stress has been used. For a staged pull-out test, several vertical stresses are used. The results of staged pull-out tests are in good agreement with results of usual pull-out test. (C) 2013 Elsevier Ltd. All rights reserved.

Abstract: The Arctic environment is undergoing changes due to climate shifts, receiving contaminants from distant sources and experiencing increased human activity. Climate change may alter microbial functioning by increasing growth rates and substrate use due to increased temperature. This may lead to changes of process rates and shifts in the structure of microbial communities. Biodiversity may increase as the Arctic warms and population shifts occur as psychrophilic/psychrotolerant species disappear in favor of more mesophylic ones. In order to predict how ecological processes will evolve as a function of global change, it is essential to identify which populations participate in each process, how they vary physiologically, and how the relative abundance, activity and community structure will change under altered environmental conditions. This review covers aspects of the importance and implication of snowpack in microbial ecology emphasizing the diversity and activity of these critical members of cold zone ecosystems.

Abstract: We investigated the interactions between snowpack chemistry, mercury (Hg) contamination and microbial community structure and function in Arctic snow. Snowpack chemistry (inorganic and organic ions) including mercury (Hg) speciation was studied in samples collected during a two-month field study in a high Arctic site, Svalbard, Norway (79 degrees N). Shifts in microbial community structure were determined by using a 16S rRNA gene phylogenetic microarray. We linked snowpack and meltwater chemistry to changes in microbial community structure by using co-inertia analyses (CIA) and explored changes in community function due to Hg contamination by q-PCR quantification of Hg-resistance genes in metagenomic samples. Based on the CIA, chemical and microbial data were linked (p=0.006) with bioavailable Hg (BioHg) and methylmercury (MeHg) contributing significantly to the ordination of samples. Mercury was shown to influence community function with increases in merA gene copy numbers at low BioHg levels. Our results show that snowpacks can be considered as dynamic habitats with microbial and chemical components responding rapidly to environmental changes.

Abstract: Understanding hydro-sedimentary dynamics at the catchment scale requires high temporal resolution data on suspended sediments such as their origin, in addition to the common measurements of sediment concentrations and discharges. Some rapid and low-cost fingerprinting methods based on spectroscopy have recently been developed. We investigated how visible spectra could be used to predict the proportion of various source materials in suspended sediment samples, paying particular attention to the potential alteration of spectrocolorimetric signatures between soils and suspended sediments during transport. The 22-km(2) Galabre catchment, France, is composed of black marls, limestones, molasses, undifferentiated deposits and gypsum. Forty-eight source materials were sampled and 328 suspended sediment samples were collected at the outlet during 23 runoff events. Measurements were taken with a diffuse reflectance spectrophotometer on dried samples. As the erosion processes are particle size selective, five particle size fractions of source material were measured in order to assess the potential alteration of the fingerprint signatures. As the biogeochemical processes occurring in the river could also affect the signatures, source materials were immersed in the river for durations ranging from 1 to 63 days and subsequently measured. Finally, partial least-squares regression models were constructed on 81 artificial laboratory mixtures to predict the proportions of source materials. The spectrocolorimetric measurements discriminated the primary source materials but not the Quaternary deposits. As the gypsum was not conservative, only the black marls, molasses and limestones were used in the fingerprinting procedure. The construction of the partial least-squares regression models led to a median absolute error of 1.1%. This error increased to 3.9% when the models were applied to source samples with: (1) different particle sizes; (2) different durations spent in the river; or (3) different origins than those used for their construction. The effect of particle size on the fingerprinting procedure was larger than the effect of biogeochemical reactions or the spatial variability of the spectrocolorimetric signatures. Half of the 23 runoff events analysed exhibited huge variations in the source proportions from one sediment sample to another. The spectrocolorimetric fingerprinting approach was able to quantify routinely the proportion of primary source materials in all suspended sediment samples collected during runoff events. The high temporal resolution of the predicted proportions revealed that only analysing three or four suspended sediment samples during a runoff event could lead to a misunderstanding of the hydro-sedimentary processes for more than half of the investigated runoff events.

Abstract: Dissolved organic carbon (DOC) and an extended array of organic compounds were investigated in an Alpine ice core covering the 1920-1988 time period. Based on this, a reconstruction was made of the long-term trends of water-soluble organic carbon (WSOC) aerosol in the European atmosphere. It is shown that light mono- and dicarboxylates, humic-like substances, and formaldehyde account together for more than half of the DOC content of ice. This extended chemical speciation of DOC is used to estimate the DOC fraction present in ice that is related to WSOC aerosol and its change over the past. It is suggested that after World War II, the WSOC levels have been enhanced by a factor of 2 and 3 in winter and summer, respectively. In summer, the fossil fuel contribution to the enhancement is estimated to be rather small, suggesting that it arises mainly from an increase in biogenic sources of WSOC.

Abstract: Debris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.

Abstract: This paper reports on bedload flux and texture monitored in a natural, steep, sandy ephemeral channel draining a small gullied sandy watershed, the Barranca de los Pinos (1.32 ha), Spain. Bedload flux was continuously monitored with two independent Reid-type slot samplers; bedload texture was determined from the sediment collected in the samplers. Channel morphology was surveyed with a high spatial resolution with a Terrestrial Laser Scanner. The monitored instantaneous bedload fluxes are among the highest measured in natural rivers, characterized by high temporal and spatial variability related to the presence of bedforms, shallow bars and sand sheets, and to the reworking of the dry bed between and at the end of individual flow events. The grain size distribution of the bedload indicates equal mobility; but bedload texture fluctuates, depicting the transport of coarser bar surfaces and of finer-grained anabranch surfaces as well as of the overall bed subsurface. (C) 2013 Elsevier B.V. All rights reserved.

Abstract: The Peak-Over-Threshold (POT) approach is an interesting alternative to the one based on Annual Maxima (AM) series since it gives the opportunity to take into consideration extreme events that would not be considered otherwise. It has also been recognized that the regional approach improves statistical inference when compared to the local approach, assuming that the region is statistically homogeneous. A regional POT approach was developed and applied to the network stations located in southern Quebec. POT series for 5-, 10-, 15-, 30-min and 1-, 2-, 6- and 12-h durations were constructed assuming a fixed exceedance rate. An analysis of local POT series showed that the intra-annual variability of the Generalized Pareto Distribution (GPD) parameters needs to be taken into consideration. Models of various complexities were defined combining local and regional representations as well as the intra-annual variability of GPD parameters. Regional likelihood was estimated and models were compared based on the Akaike Information Criterion (AIC). Models with regional shape and scale parameters and accounting for intra-annual variability were selected for all durations. Spatial covariates were also introduced through a simple model linking GPD parameters to latitude, longitude and altitude. The sensitivity of results to threshold values and selected models was also investigated. Interpolated maps of intense rainfall over the studied area are finally proposed. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: The objective of this work was to evaluate the transport of Escherichia coli cells in undisturbed cores of a brown leached soil collected at La Cote St Andre (France). Two undisturbed soil cores subjected to repeated injections of bacterial cells and/or bromide tracer were used to investigate the effect of soil hydrodynamics and ionic strength on cell mobility. Under the tested experimental conditions, E. coli cells were shown to be transported at the water velocity (retardation factor close to 1) and their retention appeared almost insensitive to water flow and ionic strength variations, both factors being known to control bacterial transport in model saturated porous media. In contrast, E. coli breakthrough curves evolved significantly along with the repetition of the cell injections in each soil core, with a progressive acceleration of their transport. The evolution of E. coli cells BTCs was shown to be due to the evolution of the structure of soil hydraulic pathways caused by the repeated water infiltrations and drainage as may occur in the field. This evolution was demonstrated through mercury intrusion porosimetry (MIP) performed on soil aggregates before and after the repeated infiltrations of bacteria. MIP revealed a progressive and important reduction of the soil aggregate porosity, n, that decreased from approximately 0.5 to 0.3, along with a decrease of the soil percolating step from 27 to 2 μm. From this result a clear compaction of soil aggregates was evidenced that concerned preferentially the pores larger than 2 μm equivalent diameter, i.e. those allowing bacterial cell passage. Since no significant reduction of the global soil volume was observed at the core scale, this aggregate compaction was accompanied by macropore formation that became progressively the preferential hydraulic pathway in the soil cores, leading to transiently bi-modal bacterial BTCs. The evolution of the soil pore structure induced a modification of the main hydrodynamic processes, evolving from a matrix-dominant transfer of water and bacteria to a macropore-dominant transfer. This work points out the importance of using undisturbed natural soils to evaluate the mobility of bacteria in the field, since the evolving hydrodynamic properties of soils appeared to dominate most physicochemical factors.

Abstract: This study compares different methods to retrieve the specific surface area (SSA) of snow from satellite radiance measurements in mountainous terrain. It aims at addressing the effect on the retrieval of topographic corrections of reflectance, namely slope and aspect of terrain, multiple reflections on neighbouring slopes and accounting (or not) for the anisotropy of snow reflectance. Using MODerate resolution Imaging Spectrometer (MODIS) data for six different clear sky scenes spanning a wide range of snow conditions during the winter season 2008-2009 over a domain of 46 x 50 km in the French Alps, we compared SSA retrievals with and without topographic correction, with a spherical or non-spherical snow reflectance model and, in spherical case, with or without anisotropy corrections. The retrieved SSA values were compared to field measurements and to the results of the detailed snowpack model Crocus, fed by driving data from the SAFRAN meteorological analysis. It was found that the difference in terms of surface SSA between retrieved values and SAFRAN-Crocus output was minimal when the topographic correction was taken into account, when using a retrieval method assuming disconnected spherical snow grains. In this case, the root mean square deviation was 9.4 m(2) kg(-1) and the mean difference was 0.1 m(2) kg(-1), based on 3170 pairs of observation and simulated values. The added-value of the anisotropy correction was not significant in our case, which may be explained by the presence of mixed pixels and surface roughness. MODIS retrieved data show SSA variations with elevation and aspect which are physically consistent and in good agreement with SAFRAN-Crocus outputs. The variability of the MODIS retrieved SSA within the topographic classes of the model was found to be relatively small (3.9 m(2) kg(-1)). This indicates that semi-distributed snowpack simulations in mountainous terrain with a sufficiently large number of classes provides a representation of the snowpack variability consistent with the scale of MODIS 500 m pixels.

Abstract: This work examines the relevance of the inclusion of ground-based gravity data in the calibration process of a global rainfall-discharge reservoir model. The analysis is performed for the Durzon karst system (Larzac, France). The first part of the study focuses on the hydrological interpretation of the ground-based gravity measurements. The second part of the study investigates further the information content of the gravity data with respect to water storage dynamics modelling. The gravity-derived information is found unable to either reduce equifinality of the single-objective, discharge-based model calibration process or enhance model performance through assimilation.

Abstract: In ocean general circulation models, near-surface atmospheric variables used to specify the atmospheric boundary condition remain one of the main sources of error. The objective of this research is to constrain the surface forcing function of an ocean model by sea surface temperature (SST) data assimilation. For that purpose, a set of corrections for ERAinterim (hereafter ERAi) reanalysis data is estimated for the period of 1989-2007, using a sequential assimilation method, with ensemble experiments to evaluate the impact of uncertain atmospheric forcing on the ocean state. The control vector of the assimilation method is extended to atmospheric variables to obtain monthly mean parameter corrections by assimilating monthly SST and sea surface salinity (SSS) climatological data in a low resolution global configuration of the NEMO model. In this context, the careful determination of the prior probability distribution of the parameters is an important matter. This paper demonstrates the importance of isolating the impact of forcing errors in the model to perform relevant ensemble experiments. The results obtained for every month of the period between 1989 and 2007 show that the estimated parameters produce the same kind of impact on the SST as the analysis itself. The objective is then to evaluate the long-term time series of the forcing parameters focusing on trends and mean error corrections of air-sea fluxes. Our corrections tend to equilibrate the net heat-flux balance at the global scale (highly positive in ERAi database), and to remove the potentially unrealistic negative trend (leading to ocean cooling) in the ERAi net heat flux over the whole time period. More specifically in the intertropical band, we reduce the warm bias of ERAi data by mostly modifying the latent heat flux by wind speed intensification. Consistently, when used to force the model, the corrected parameters lead to a better agreement between the mean SST produced by the model and mean SST observations over the period of 1989-2007 in the intertropical band.

Abstract: We applied a Regional Climate Model (RCM) to simulate precipitation and snow cover over the Himalaya, between March 2000 and December 2002. Due to its higher resolution, our model simulates a more realistic spatial variability of wind and precipitation than those of the reanalysis of the European Centre of Medium range Weather Forecast (ECMWF) used as lateral boundaries. In this region, we found very large discrepancies between the estimations of precipitation provided by reanalysis, rain gauges networks, satellite observations, and our RCM simulation. Our model clearly underestimates precipitation at the foothills of the Himalaya and in its eastern part. However, our simulation provides a first estimation of liquid and solid precipitation in high altitude areas, where satellite and rain gauge networks are not very reliable. During the two years of simulation, our model resembles the snow cover extent and duration quite accurately in these areas. Both snow accumulation and snow cover duration differ widely along the Himalaya: snowfall can occur during the whole year in western Himalaya, due to both summer monsoon and mid-latitude low pressure systems bringing moisture into this region. In Central Himalaya and on the Tibetan Plateau, a much more marked dry season occurs from October to March. Snow cover does not have a pronounced seasonal cycle in these regions, since it depends both on the quite variable duration of the monsoon and on the rare but possible occurrence of snowfall during the extramonsoon period.

Abstract: Tunneling-induced ground movements are investigated in this paper using both deterministic and probabilistic analyses. The deterministic model is based on three-dimensional (3D) numerical simulations using the commercial code FLAC(3D). This model attempts to reproduce some major phenomena during a typical slurry-shield tunnel excavation (ground movements due to the applied face pressure, the overcutting, the shield conicity, the annular void behind the shield, and the grout injection in this void). Moreover, the model provides useful information about the nature and magnitude of the soil movements at the ground surface. A probabilistic study is then undertaken in order to evaluate the impact of the variability of several input variables on the ground movements. An efficient probabilistic method called CSRSM is used to assess this uncertainty propagation. In a last section, the output variables of the model are linked to failure criteria. This allows one to determine probabilities of failure, depending on the probabilistic properties of the input variables and on the admissible threshold of each criterion.

Abstract: The purpose of this work is to evaluate the performance of an optimization algorithm from the field of evolutionary computation, namely an Evolution Strategy, in back analysis of geomechanical parameters in underground structures. This analysis was carried out through a parametric study of a synthetic case of a tunnel construction. Different combinations of parameters and measurements were carried out to test the performance of the algorithm. In order to have a comparison base for its performance also three classical optimization algorithms based on the gradient of the error function and a Genetic Algorithm were used. It was concluded that the Evolution Strategy algorithm presents interesting capabilities in terms of robustness and efficiency allowing the mitigation of some of the limitations of the classical algorithms. Moreover a back analysis study of geomechanical parameters using real monitoring data and a 3D numerical model of a hydraulic underground structure being built in the North of Portugal was performed using the Evolution Strategy algorithm, in order to reduce the uncertainties about the parameters evaluated by in situ and laboratory tests. It was verified that the low quantity of monitoring data available hinders the possibility to identify the parameters of interest. The existence of information of only one additional extensometer perpendicular to the existing one would allow this identification to succeed. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: The specific surface area of snow (SSA) is a useful variable to describe the physical and chemical properties of snow, including a quantitative link to snow metamorphism and the optical properties of snow. Here we present a series of 16 weekly profiles of snow physical properties including SSA measured using the DUFISSS instrument spanning the period from January to April 2010 at the Col de Porte field site in the French Alps near Grenoble. Measured SSA values for dry snow ranged between ca. 5 and 80 m(2) kg(-1), and generally decreased over time in a given snow layer. Wet snow conditions encountered towards the end of the snow season show SSA values between 3 and 10 m(2) kg(-1). This unique dataset is compared with simulations carried out using the Crocus snowpack model, using two parameterizations of snow SSA: one simply derived from the internal computation of the optical radius in Crocus, and the other one determined from density and snow type. Both parameterizations perform rather satisfactorily qualitatively and quantitatively, compared to the performance in terms of snow density profile. Ample room for improvement exists, in particular through the implementation of SSA as a fully fledged prognostic variable in Crocus, which is currently in progress. (c) 2012 Elsevier Ltd. All rights reserved.

Abstract: Carbon and total suspended sediment (TSS) loads were investigated from April 2006 to March 2008 in the mountainous watershed of the Isere River, French Alps (5570km(2)). The river bed has been highly impounded for hydroelectricity production during the last century. Hydraulic flushes are managed every year to prevent TSS storage within upstream dams. The Isere River has been instrumented for high-frequency monitoring of water, TSS by turbidity and carbon (organic, inorganic, dissolved and particulate) in order to evaluate the impact of natural floods and hydraulic flushes on annual loads. Annual TSS load which was estimated between 1.3 and 2.3 MT y(-1) (i.e. 233 to 413Tkm(-2) y(-1)) highlighted the high erodibility of the Isere watershed. Annual carbon load was estimated between 173 10(3)T y(-1) and 199 10(3)T y(-1) (i.e 31 to 36Tkm(-2) y(-1)). About 80% of the annual carbon loads were inorganic. The impact of hydraulic flushes on annual loads appeared limited (less than 3% for annual TSS load and about 1.5% for annual carbon load), whereas the most important natural flood event contributed to 20% of the annual TSS load and 10% of the annual carbon load. Copyright (c) 2012 John Wiley & Sons, Ltd.

Abstract: The reinforcement of soils using rigid inclusions is a technique used to reduce settlements and to ensure the stability of an embankment built over soft soils. This technique reduces construction delays and is an economical and reliable solution, which has led to its widespread use. Thus, many design methods have been developed to assess the performance of these reinforced structures. These methods are mainly based on results from small scale models and numerical analyses. The reliability of these methods must be validated under in-situ conditions. This paper presents an analytical and numerical study of full-size experiments at the Chelles test site (France). The work presented in this paper is part of the ASIRI French National Research Project. The experiment consisted of a 5-m-high embankment built over soft alluvial ground improved by rigid vertical piles. The embankment is divided into four zones that illustrate the influence of the piles and the geosynthetic reinforcements on the soil's behavior. The performance of the embankment support system is assessed by monitoring data (total stresses, horizontal and vertical displacements). Several in-situ and laboratory soil investigations were performed using two axially loaded test piles. These tests verified the geotechnical hypothesis used for the numerical model and defined the soil-pile interaction parameters. Several analytical methods and numerical models were tested to assess the arching effect. Comparisons between the experimental data and these design methods are presented in terms of stress and the settlement efficacy of the improved system. The results show that these methods overestimate the stress efficacy but that the settlement efficacy is a reliable parameter to assess the overall performance of the rigid inclusion technique. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Understanding the role of atmospheric CO2 during past climate changes requires clear knowledge of how it varies in time relative to temperature. Antarctic ice cores preserve highly resolved records of atmospheric CO2 and Antarctic temperature for the past 800,000 years. Here we propose a revised relative age scale for the concentration of atmospheric CO2 and Antarctic temperature for the last deglacial warming, using data from five Antarctic ice cores. We infer the phasing between CO2 concentration and Antarctic temperature at four times when their trends change abruptly. We find no significant asynchrony between them, indicating that Antarctic temperature did not begin to rise hundreds of years before the concentration of atmospheric CO2, as has been suggested by earlier studies.

Abstract: Predictions of marine ice-sheet behaviour require models able to simulate grounding-line migration. We present results of an intercomparison experiment for plan-view marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no buttressing effects from lateral drag). Perturbation experiments specifying spatial variation in basal sliding parameters permitted the evolution of curved grounding lines, generating buttressing effects. The experiments showed regions of compression and extensional flow across the grounding line, thereby invalidating the boundary layer theory. Steady-state grounding-line positions were found to be dependent on the level of physical model approximation. Resolving grounding lines requires inclusion of membrane stresses, a sufficiently small grid size (<500 m), or subgrid interpolation of the grounding line. The latter still requires nominal grid sizes of <5 km. For larger grid spacings, appropriate parameterizations for ice flux may be imposed at the grounding line, but the short-time transient behaviour is then incorrect and different from models that do not incorporate grounding-line parameterizations. The numerical error associated with predicting grounding-line motion can be reduced significantly below the errors associated with parameter ignorance and uncertainties in future scenarios.

Abstract: Recent studies have demonstrated the possibility to use surface soil moisture satellite products in order to correct precipitation estimates. The overall approaches are generally based on adjusting the precipitation rate into a water balance model in order to match observed and simulated soil moisture. In the present study, a recently proposed approach was improved and assessed over a 4-year period in West Africa. Three different satellite precipitation products (CMORPH, TRMM-3B42 and PERSIANN) were used in this study. The new algorithm was evaluated over three 0.25 x 0.25 degrees areas in Niger, Mali and Benin and precipitation estimates (before and after correction) were compared to observed ground-based precipitation measurements. An assessment was also conducted at the regional scale using 48 independent rainfall stations located in Togo, Niger and Burkina Faso. The proposed methodology showed that, after correction, the three satellite precipitation products converge to the ground-based precipitation measurements, demonstrating the robustness of the methodology. In addition, soil moisture estimates derived from the methodology were found to be in good agreement with ground-based soil moisture measurements (R-2 > 0.78 in Niger, R-2 > 0.54 in Mali and R-2 > 0.64 in Benin). (C) 2013 Elsevier Inc. All rights reserved.

Abstract: We present the first reconstruction of the Northern Hemisphere (NH) high latitude atmospheric carbon monoxide (CO) mole fraction from Greenland firn air. Firn air samples were collected at three deep ice core sites in Greenland (NGRIP in 2001, Summit in 2006 and NEEM in 2008). CO records from the three sites agree well with each other as well as with recent atmospheric measurements, indicating that CO is well preserved in the firn at these sites. CO atmospheric history was reconstructed back to the year 1950 from the measurements using a combination of two forward models of gas transport in firn and an inverse model. The reconstructed history suggests that Arctic CO in 1950 was 140-150 nmol mol(-1), which is higher than today's values. CO mole fractions rose by 10-15 nmol mol(-1) from 1950 to the 1970s and peaked in the 1970s or early 1980s, followed by a approximate to 30 nmol mol(-1) decline to today's levels. We compare the CO history with the atmospheric histories of methane, light hydrocarbons, molecular hydrogen, CO stable isotopes and hydroxyl radicals (OH), as well as with published CO emission inventories and results of a historical run from a chemistry-transport model. We find that the reconstructed Greenland CO history cannot be reconciled with available emission inventories unless unrealistically large changes in OH are assumed. We argue that the available CO emission inventories strongly underestimate historical NH emissions, and fail to capture the emission decline starting in the late 1970s, which was most likely due to reduced emissions from road transportation in North America and Europe.

Abstract: The acquisition of reliable data sets representative of hydrological regimes and their variations is a critical concern for water resource assessment. For the subsurface, traditional approaches based on probe measurements, core analysis, and well data can be laborious, expensive, and highly intrusive, while only yielding sparse data sets. For this study, an innovative field survey, merging relative microgravimetry, magnetic resonance soundings, and hydrological measurements, was conducted to evaluate both surface and subsurface water storage variations in a semiarid Sahelian area. The instrumental setup was implemented in the lower part of a typical hillslope feeding to a temporary pond. Weekly measurements were carried out using relative spring gravimeters during 3 months of the rainy season in 2009 over a 350 x 500 m(2) network of 12 microgravity stations. Gravity variations of small to medium amplitude <= 220 nm s(-2)) were measured with accuracies better than 50 nm s(-2), revealing significant variations of the water storage at small time (from 1 week up to 3 months) and space (from a couple of meters up to a few hundred meters) scales. Consistent spatial organization of the water storage variations were detected, suggesting high infiltration at the outlet of a small gully. The comparison with hydrological measurements and magnetic resonance soundings involved that most of the microgravity variations came from the heterogeneity in the vadose zone. The results highlight the potential of time lapse microgravity surveys for detecting intraseasonal water storage variations and providing rich space-time data sets for process investigation or hydrological model calibration/evaluation.

Abstract: DMRT-ML is a physically based numerical model designed to compute the thermal microwave emission of a given snowpack. Its main application is the simulation of brightness temperatures at frequencies in the range 1-200 GHz similar to those acquired routinely by space-based microwave radiometers. The model is based on the Dense Media Radiative Transfer (DMRT) theory for the computation of the snow scattering and extinction coefficients and on the Discrete Ordinate Method (DISORT) to numerically solve the radiative transfer equation. The snowpack is modeled as a stack of multiple horizontal snow layers and an optional underlying interface representing the soil or the bottom ice. The model handles both dry and wet snow conditions. Such a general design allows the model to account for a wide range of snow conditions. Hitherto, the model has been used to simulate the thermal emission of the deep firn on ice sheets, shallow snowpacks overlying soil in Arctic and Alpine regions, and overlying ice on the large ice-sheet margins and glaciers. DMRT-ML has thus been validated in three very different conditions: Antarctica, Barnes Ice Cap (Canada) and Canadian tundra. It has been recently used in conjunction with inverse methods to retrieve snow grain size from remote sensing data. The model is written in Fortran90 and available to the snow remote sensing community as an open-source software. A convenient user interface is provided in Python.

Abstract: This article presents the results of an experimental study which aimed to evaluate the effect of surface wear on the friction properties of geosynthetic interfaces constituted of geomembranes and geospacers. The tests were performed in ramp test device, and the results showed the different sensitivities of the interfaces to the wear process. For the particular types of interfaces considered in the experiment, the surface wear can increase, decrease or maintain the original friction properties of the geosynthetic interface, with direct effects on the stability under service condition.

Abstract: HCHO was monitored throughout the year 2009 at the coastal East Antarctic site of Dumont d'Urville (DDU) using Aerolaser AL-4021 analyzers. The accurate determination of less than 100 pptv required optimization of the analyzers, in particular, to minimize effects of changing ambient temperatures. The impact of station activities and of the presence of large penguin colonies at the site in summer was scrutinized. The obtained contamination-free record indicates monthly means close to 50 pptv from May to September and a maximum of 200 pptv in January. Zero-dimensional and 2-D calculations suggest that in summer, the largest HCHO source is the gas-phase photochemistry (80%) mainly driven by methane oxidation, which is considerably greater than from snow emissions (20%). The influence of light alkenes, dimethyl sulfide, and halogens remains weak. In winter, snow emissions represent the main HCHO source (70%). These findings are compared to previous studies conducted at the West Antarctic coast. It is shown that in summer the HCHO production from methane chemistry is 3 times more efficient at DDU than at the west coast due to more frequent arrival of oxidant-rich air masses from inland Antarctica. Halogen chemistry is found to represent a weak HCHO sink at both West and East Antarctica. Compared to DDU, the shallower atmospheric boundary layer and the less efficient gas-phase production at the west coast make the snow pack the dominant HCHO source (85%) compared to gas-phase photochemistry (15%) there in summer.

Abstract: As pointed out by the forth assessment report of the Intergovernmental Panel on Climate Change, IPCC-AR4 (Meehl et al., 2007), the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise, is a subject of key importance for the scientific community. By the end of the next century, a 3-5 degrees C warming is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period, 130-115 ka BP, due to a change in orbital configuration rather than to an anthropogenic forcing. Ice core evidence suggests that the Greenland ice sheet (GIS) survived this warm period, but great uncertainties remain about the total Greenland ice reduction during the LIG. Here we perform long-term simulations of the GIS using an improved ice sheet model. Both the methodologies chosen to reconstruct palaeoclimate and to calibrate the model are strongly based on proxy data. We suggest a relatively low contribution to LIG sea level rise from Greenland melting, ranging from 0.7 to 1.5m of sea level equivalent, contrasting with previous studies. Our results suggest an important contribution of the Antarctic ice sheet to the LIG highstand.

Abstract: The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age (LIA, mid-17th-early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the one computed on a global scale. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from -0.2mw. e. in the period 1964-1975 to -0.76mw. e. in the period 1976-2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia show that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance at the decadal timescale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10 degrees C decade(-1) in the last 70 yr. The higher frequency of El Nino events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world.

Abstract: This study focuses on the contribution of annual glacier ice melt to streamflow along two rivers in two watersheds situated in the monsoon-influenced part of the Nepal Himalaya (Trishuli and Dudh Kosi basins). We used a simple elevation-dependent ice ablation model based on glacier areas from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and IKONOS remote-sensing data combined with hypsometry from the Shuttle Radar Topography Mission (SRTM). Long-term hydrologic measurements were used to calculate the percent contribution of the glacier ice melt component of the water balance to discharge at various elevations and distances from glacier outlets. Glacier ice melt was positively correlated with the basin glacierized area and contributed 58.3% to annual flow in the small Langtang Khola watershed in the Trishuli basin (43.5% glacierized area) and 21.2% in the Hinku watershed in Dudh Kosi basin (34.7% glacierized area). Of this, 17.7% and 4.1% of streamflow, respectively, was due to the contribution of debris-covered glaciers in Langtang Khola and Hinku. The contribution of glacier ice melt to measured discharge decreased substantially toward lowland locations in both study sites, i.e., 9.5% of the streamflow measured at Betrawati (600 m) and 7.4% at Rabuwa Bazaar (470 m), about 50 km from glacier termini. Glacier ice melt contribution decreased to 4.5% of annual discharge further downstream in Trishuli basin (at 325 m, about 75 km from glacier termini). At low elevations, debris-covered tongues contributed a small percent (1.1% and 3.0%) to measured discharge at Betrawati and Rabuwa Bazaar stations, respectively. We independently evaluated the ice ablation approach with synoptic sampling of stable water isotopes (O-18 and D) collected during the post-monsoon season to quantify the contribution of various sources of water to river flow. Mixing models showed groundwater to be an important component of river flow within only tens of kilometers of the glacier outlets in the post-monsoon season.

Abstract: Understanding the climate dynamics in mountainous areas still remains a challenge. For Peruvian areas situated above 3000 m three aspects concerning the temperatures are developed with in-situ and NCEP NCAR Reanalysis from National Center for Environmental Prediction and National Center for Atmospheric Research (NNR) data: a) Based on in-situ temperature records of about 30 years for 27 stations, no trend was identified at 99% of confidence level in the Northern Andes (Cordillera Blanca y Negra) of Peru, contrary to regions in the south of Central Andes of Peru where it was identified local trends in the Andean valleys near to Vilcanota node with maximum values of 0.03 degrees C/year. b) Taking into account the importance of temperature and data scarcity in mountainous regions, in-situ records were compared with other data source such as NNR. The comparison was made according to the geographical location, the common periods of the records and grid coverage. We conclude that NNR at 700 hPa level (similar to 3000 m asl) and 600 hPa level (similar to 4000 m asl) offer an approximation to terrain elevation of stations, however that comparison has variations from 10 degrees C in Northern Andes to 0.4 degrees C in Central Andes. c) Considering the differences between in-situ and NNR data, a correction of NNR data is proposed with monthly regional lapse rate. The methodology considers the use of one base in-situ station into a NNR grid with an altitudinal gradient, thus we generate mean monthly temperatures records in other areas into the NNR grid. The reliability of corrections are evaluated is terms of the correlation coefficient and the root mean squared error and the results offer very acceptable results in Northern and Central Andes.

Abstract: It is now accepted that one of the important pathways of secondary organic aerosol (SOA) formation occurs through aqueous phase chemistry in the atmosphere. However, the chemical mechanisms leading to macromolecules are still not well understood. It was recently shown that oligomer production by OH radical oxidation in the aerosol aqueous phase from alpha-dicarbonyl precursors, such as methylglyoxal and glyoxal, is irreversible and fast. Methyl vinyl ketone (MVK) was chosen in the present study as it is an alpha,beta-unsaturated carbonyl that can undergo radical oligomerization in the aerosol aqueous phase. We present here experiments on the aqueous phase OH-oxidation of MVK, performed under various conditions. Using NMR and UV absorption spectroscopy, high and ultra-high resolution mass spectrometry, we show that the fast formation of oligomers up to 1800 Da is due to radical oligomerization of MVK, and 13 series of oligomers (out of a total of 26 series) are identified. The influence of atmospherically relevant parameters such as temperature, initial concentrations of MVK and dissolved oxygen are presented and discussed. In agreement with the experimental observations, we propose a chemical mechanism of OH-oxidation of MVK in the aqueous phase that proceeds via radical oligomerization of MVK on the olefin part of the molecule. This mechanism highlights in our experiments the paradoxical role of dissolved O-2: while it inhibits oligomerization reactions, it contributes to produce oligomerization initiator radicals, which rapidly consume O-2, thus leading to the dominance of oligomerization reactions after several minutes of reaction. These processes, together with the large range of initial concentrations investigated show the fundamental role that radical oligomerization processes likely play in polluted fogs and atmospheric aerosol.

Abstract: The HAMSTRAD microwave instrument operates at 60 and 183 GHz and measures temperature and water vapor, respectively, from 0- to 10-km altitude with a time resolution of 7 min. The radiometer has been successfully deployed at Dome C (Concordia Station), Antarctica (75 degrees 06' S, 123 degrees 21' E, 3233 m amsl) during the first summertime campaign for 12 days in January-February 2009. The radiometer has been continuously running since January 2010, hosted within a dedicated shelter. We have used the very first set of HAMSTRAD data, recorded when the instrument was outdoors, to assess its potential to sound the troposphere over Dome C, from the planetary boundary layer (PBL) up to the tropopause (similar to 6 km above surface, similar to 9 km amsl). We have compared the HAMSTRAD measurements to several sets of measurements performed at the Dome-C station or in its vicinity: meteorological radiosondes, in situ PT100 and Humicap sondes along the vertical extent of a 45-m tower, meteorological sensor attached to the HAMSTRAD instrument, and the space-borne Infrared Atmospheric Sounding Interferometer (IASI) instrument onboard the EUMETSAT MetOp-A satellite in polar orbit. The variability of integrated water vapor (IWV) observed by HAMSTRAD with extremely low values of 0.5 kg . m(-2) was also measured by the radiosondes (very high HAMSTRAD versus radiosonde correlation of 0.98), whereas IASI cloud-free measurements did not reproduce well the HAMSTRAD IWV variation (weak HAMSTRAD versus IASI correlation of 0.58). The measurements of absolute humidity (H2O) from HAMSTRAD at Dome C cover a large vertical extent from the surface to about 6 km above surface with a high sensitivity in the free troposphere. The strong diurnal variation of H2O observed by the in situ sensors in the PBL is not well detected by the radiometer. In the free troposphere, the HAMSTRAD versus radiosonde H2O correlation can reach 0.8-0.9. Around the tropopause, HAMSTRAD shows the same variability as IASI and radiosondes but with a dry bias of 0.01 g . m(-3). HAMSTRAD tends to show a wetter atmosphere by 0.1-0.3 g . m(-3) compared with radiosondes from the surface to similar to 2-km altitude and a drier atmosphere above by similar to 0.1 g . m(-3). The sensitivity of the temperature profiles from HAMSTRAD is very high in the PBL and in the free troposphere but degrades around the tropopause. The strong diurnal signal measured above the surface by HAMSTRAD (3-6 K) is consistent with all the other in situ data sets. The temporal evolution over the 12-day period in the PBL is also consistent with all other data sets (radiosondes, IASI, in situ sondes, and meteorological sensors). In the free troposphere and around the tropopause, the HAMSTRAD temporal evolution is consistent with that observed by radiosondes and IASI, although a cold bias exists compared with IASI and radiosondes around the tropopause. For heights less than 4 km above surface, HAMSTRAD correlates very well with radiosondes and in situ sensors (correlation better than 0.8) but less well with IASI (0.4). Below the tropopause, the IASI and HAMSTRAD correlation reaches 0.9, whereas above the tropopause, the correlation of IASI and radiosondes with HAMSTRAD is rather low (< 0.5). Throughout the 12-day period (except on January 23), in the lowermost troposphere for heights less than 500 m above surface, the HAMSTRAD temperature profiles agree with the profiles measured by the radiosondes. From 500 m up to 5 km above the surface, the HAMSTRAD temperature profile has a cold bias from 1 to 5 K compared with the radiosondes, but for some dates (e. g., on January 25 and 29), the HAMSTRAD temperature is very close to the radiosonde temperature. HAMSTRAD generally measures a tropopause lower and warmer than the radiosondes except on some occasions, for instance, on January 23, 30, and 31. In the lower stratosphere, HAMSTRAD measurements of H2O and temperature have little sensitivity. Based upon 5-day back trajectory analyses, the great variability of H2O and temperature above Dome C as measured by the different instruments from the surface up to the tropopause over the 12-day period can be explained by the origin of air masses. The Dome-C site is found to be under the influence of the oceanic middle latitudes and the Antarctic coastal latitudes, but on some occasions, the air masses originated from the Antarctic continent are associated with colder and drier episodes.

Abstract: A Hierarchical Ascending Classification is used to regionalize monthly temperature anomalies measured at 24 weather stations in Antarctica and the Sub-Antarctic and mid-latitude southern islands from 1973 to 2002. Three principal regions are identified that are geographically coherent: Eastern Antarctica, the Antarctic Peninsula and the Sub-Antarctic and mid-latitude islands. Within each region, consistent trends are observed: namely, stationary temperatures in East-Antarctica'; a robust warming in the Sub-Antarctic and mid-latitude islands', most pronounced in austral summer (nearly 0.5 degrees C per decade); and a strong but more recent warming in the Antarctic Peninsula'. Austral summer temperature anomalies are related to (1) the Southern Annular Mode (SAM) indexes computed using two reanalysis products (20th Century Reanalyses and ERA40) over two periods (1958-2002 and 1973-2002), (2) the seasonal frequencies of four recurrent daily weather regimes identified with a k-means algorithm applied on the 500hPa geopotential height (DJF 1958-2002) and (3) HadSST2 sea surface temperature (SST) anomalies (DJF 1958-2002). East-Antarctica interannual temperature anomalies are associated with the SAM variability. In the Antarctic Peninsula, only the long-term trend is common with the SAM. The SAM does impact significantly the temperature anomalies of the Sub-Antarctic and mid-latitude islands. Trend and interannual variability of the islands' temperatures are associated with the nearby SST. For the Indian Ocean stations, warming in the Agulhas Current system could also have led to these changes. Copyright (c) 2012 Royal Meteorological Society

Abstract: Cluster particles (0.8-1.9 nm) are key entities involved in nucleation and new particle formation processes in the atmosphere. Cluster ions were characterized in clear sky conditions at the Puy de Dome station (1465 ma.s.l.). The studied data set spread over five years (February 2007-February 2012), which provided a unique chance to observe seasonal variations of cluster ion properties at high altitude. Statistical values of the cluster ion concentrations and diameters are reported for both positive and negative polarities. Cluster ions were found to be ubiquitous at the Puy de Dome and displayed an annual variation with lower concentrations in spring. Positive cluster ions were less numerous than negative, but were larger in diameter. Negative cluster ion properties were not sensitive to the occurrence of a new particle formation (NPF) event, while positive cluster ions appeared to be significantly more numerous and larger on event days. The parameters of the balance equation for the positive cluster concentration are reported separately for the different seasons and for the NPF event days and non-event days. The steady-state assumption suggests that the ionization rate is balanced with two sinks: the ion recombination and the attachment onto background aerosol particles, referred to as “aerosol ion sink”. The aerosol ion sink was predominant compared to the recombination sink. The positive ionization rates derived from the balance equation (Q(calc)) were well correlated with the ionization rates obtained from radon measurement (Q(meas)). When ignoring the gamma radiation contribution to the ion production, Q(calc) is on average higher than Q(meas) during the warm season. In contrast, when a seasonal gamma contribution is taken into account, Q(meas) always exceeds Q(calc). We found that neither the aerosol ion sink nor the ionization rate (calculated or measured, with or without the gamma contribution) were significantly different on event days compared to non-event days, and thus, they were not able to explain the different positive cluster concentrations between event and non-event days. Hence, the excess of positive small ions on event days may derive from an additional constant source of ions leading to a non-steady state.

Abstract: A multi-isotope approach has been used in the Marano lagoon (NE Italy) and parts of its catchment area to identify causes of increased NO3- pollution. The hydrogeochemical features of different water types and potential sources of NO3- were characterized using the isotopic composition of NO3- (delta N-15, delta O-18, and Delta O-17) and other source-related species such as B (delta B-11), water (delta H-2 and delta O-18) and SO42- (delta S-34 and delta O-18). Water samples from the lagoon, its tributary rivers, the groundwater up-welling line, groundwater, sewer pipes, and open sea water have been collected at quarterly intervals in the years 2009-2010. The results indicate that the NO3- load in the lagoon was not only derived from agricultural activities but also from other sources such as urban waste water, in situ nitrification and atmospheric deposition. The delta S-34 signature in the lagoon clearly denotes the largely prevailing origin of aqueous SO42- from seawater, and practically points to the absence of any appreciable redox process involving S species in the lagoon. It also supports the existence of a connection between the lagoon and the nearby Tagliamento river. (c) 2013 Elsevier Ltd. All rights reserved.

Abstract: Methane is a strong greenhouse gas and large uncertainties exist concerning the future evolution of its atmospheric abundance. Analyzing methane atmospheric mixing and stable isotope ratios in air trapped in polar ice sheets helps in reconstructing the evolution of its sources and sinks in the past. This is important to improve predictions of atmospheric CH4 mixing ratios in the future under the influence of a changing climate. The aim of this study is to assess whether past atmospheric delta C-13(CH4) variations can be reliably reconstructed from firn air measurements. Isotope reconstructions obtained with a state of the art firn model from different individual sites show unexpectedly large discrepancies and are mutually inconsistent. We show that small changes in the diffusivity profiles at individual sites lead to strong differences in the firn fractionation, which can explain a large part of these discrepancies. Using slightly modified diffusivities for some sites, and neglecting samples for which the firn fractionation signals are strongest, a combined multisite inversion can be performed, which returns an isotope reconstruction that is consistent with firn data. However, the isotope trends are lower than what has been concluded from Southern Hemisphere (SH) archived air samples and high-accumulation ice core data. We conclude that with the current datasets and understanding of firn air transport, a high precision reconstruction of delta C-13 of CH4 from firn air samples is not possible, because reconstructed atmospheric trends over the last 50 yr of 0.3-1.5 parts per thousand are of the same magnitude as inherent uncertainties in the method, which are the firn fractionation correction (up to similar to 2 parts per thousand at individual sites), the Kr isobaric interference (up to similar to 0.8 parts per thousand, system dependent), inter-laboratory calibration offsets (similar to 0.2 parts per thousand) and uncertainties in past CH4 levels (similar to 0.5 parts per thousand).

Abstract: Detailed insight into natural variations of the greenhouse gas nitrous oxide (N2O) in response to changes in the Earth's climate system is provided by new measurements along the ice core of the North Greenland Ice Core Project (NGRIP). The presented record reaches from the early Holocene back into the previous interglacial with a mean time resolution of about 75 years. Between 11 and 120 kyr BP, atmospheric N2O concentrations react substantially to the last glacial-interglacial transition (Termination 1) and millennial time scale climate variations of the last glacial period. For long-lasting Dansgaard/Oeschger (DO) events, the N2O increase precedes Greenland temperature change by several hundred years with an increase rate of about 0.8-1.3 ppbv/century, which accelerates to about 3.8-10.7 ppbv/century at the time of the rapid warming in Greenland. Within each bundle of DO events, the new record further reveals particularly low N2O concentrations at the approximate time of Heinrich events. This suggests that the response of marine and/or terrestrial N2O emissions on a global scale are different for stadials with and without Heinrich events.

Abstract: The ability of sulfate aerosols to reflect solar radiation and simultaneously act as cloud condensation nuclei renders them central players in the global climate system. The oxidation of S(IV) compounds and their transport as stable S(VI) in the Earth's system are intricately linked to planetary scale processes, and precise characterization of the overall process requires a detailed understanding of the linkage between climate dynamics and the chemistry leading to the product sulfate. This paper reports a high-resolution, 22-y (1980-2002) record of the oxygen-triple isotopic composition of sulfate (SO4) aerosols retrieved from a snow pit at the South Pole. Observed variation in the O-isotopic anomaly of SO4 aerosol is linked to the ozone variation in the tropical upper troposphere/lower stratosphere via the Ozone El-Ni o Southern Oscillations (ENSO) Index (OEI). Higher Delta O-17 values (3.3%, 4.5%, and 4.2%) were observed during the three largest ENSO events of the past 2 decades. Volcanic events inject significant quantities of SO4 aerosol into the stratosphere, which are known to affect ENSO strength by modulating stratospheric ozone levels (OEI = 6 and Delta O-17 = 3.3%, OEI = 11 and Delta O-17 = 4.5%) and normal oxidative pathways. Our high-resolution data indicated that Delta O-17 of sulfate aerosols can record extreme phases of naturally occurring climate cycles, such as ENSOs, which couple variations in the ozone levels in the atmosphere and the hydrosphere via temperature driven changes in relative humidity levels. A longer term, higher resolution oxygen-triple isotope analysis of sulfate aerosols from ice cores, encompassing more ENSO periods, is required to reconstruct paleo-ENSO events and paleotropical ozone variations.

Abstract: The results presented here examine the quasi-geostrophic dynamics of a point vortex structure with one upper-layer vortex and two identical bottom-layer vortices in a two-layer fluid. The problem of three vortices in a barotropic fluid is known to be integrable. This fundamental result is also valid in a stratified fluid, in particular a two-layer one. In this case, unlike the barotropic situation, vortices belonging to the same layer or to different layers interact according to different formulae. Previously, this occurrence has been poorly investigated. In the present work, the existence conditions for stable stationary (translational and rotational) collinear two-layer configurations of three vortices are obtained. Small disturbances of stationary configurations lead to periodic oscillations of the vortices about their undisturbed shapes. These oscillations occur along elliptical orbits up to the second order of the Hamiltonian expansion. Analytical expressions for the parameters of the corresponding ellipses and for oscillation frequencies are obtained. In the case of finite disturbances, vortex motion becomes more complicated. In this case we have made a classification of all possible movements, by analysing phase portraits in trilinear coordinates and by computing numerically the characteristic trajectories of the absolute and relative vortex motions.

Abstract: Iron deposition influences primary production and oceanic sequestration of atmospheric carbon dioxide (CO2). Iron has two oxidation states, Fe(II) and Fe(III), with Fe(II) being more soluble and available for oceanic phytoplankton uptake. The past proportions of soluble iron in aerosol dust remain unknown. Here we present iron speciation (Fe2+ and Fe3+) in the Antarctic Talos Dome ice core over millennial time scales. We demonstrate that iron speciation over the last 55 kyr is linked to increasing quantities of fine dust (FD) (0.75 μm) and intensified long-range dust transport. We propose that Fe(II) and Fe2+ production is principally enhanced in FD by photoreduction, although pH and organic complexation may also contribute to the speciation dynamics. During the Last Glacial Maximum, Fe2+ concentrations in dust increased by up to seven times more than interglacial levels, while Fe3+ only doubled. Cold and dusty climatic periods may increase the percentage of biologically available Fe(II) and Fe2+ deposited in the nutrient-limited Southern Ocean, allowing greater phytoplankton uptake and perhaps increased CO2 drawdown.

Abstract: Sea ice is an integral part of the earth's climate system because it affects planetary albedo, sea-surface salinity, and the atmosphere-ocean exchange of reactive gases and aerosols. Bromine and iodine chemistry is active at polar sea ice margins with the occurrence of bromine explosions and the biological production of organoiodine from sea ice algae. Satellite measurements demonstrate that concentrations of bromine oxide (BrO) and iodine oxide (IO) decrease over sea ice toward the Antarctic interior. Here we present speciation measurements of bromine and iodine in the TALDICE (TALos Dome Ice CorE) ice core (159 degrees 11'E, 72 degrees 49'S; 2315 m a.s.l.) spanning the last 215 ky. The Talos Dome ice core is located 250 km inland and is sensitive to marine air masses intruding onto the Antarctic Plateau. Talos Dome bromide (Br-) is positively correlated with temperature and negatively correlated with sodium (Na). Based on the Br-/Na seawater ratio, bromide is depleted in the ice during glacial periods and enriched during interglacial periods. Total iodine, consisting of iodide (I-) and iodate (IO3-), peaks during glacials with lower values during interglacial periods. Although IO3- is considered the most stable iodine species in the atmosphere it was only observed in the TALDICE record during glacial maxima. Sea ice dynamics are arguably the primary driver of halogen fluxes over glacial-interglacial timescales, by altering the distance between the sea ice edge and the Antarctic plateau and by altering the surface area of sea ice available to algal colonization. Based on our results we propose the use of both halogens for examining Antarctic variability of past sea ice extent.

Abstract: Refined temporal signals extracted from a winter and summer mass balance series recorded at Glacier de Sarennes (French Alps) using variance decomposition are related to local meteorological data and large-scale North Atlantic Oscillation (NAO) anomalies in terms of interannual variability, trends of the low-frequency signals, and breaks in the time series. The winter balance has increased by +23% since 1976 due to more precipitation in early and late winter. The summer balance has decreased since 1982 due to a 43% increase in snow and ice melt. A 24-day lengthening of the ablation period – mainly due to longer ice ablation – is the main component in the overall increase in ablation. In addition, the last 25 yr have seen increases in ablation rates of 14 and 10% for snow and ice, respectively. A simple degree-day analysis can account for both the snow/ice melt rate rise and the lengthening of the ablation period as a function of higher air temperatures. From the same analysis, the equilibrium-line altitude of this 45 degrees N latitude south-facing glacier has a sensitivity to temperature of +93m degrees C-1 around its mean elevation of 3100 ma.s.l. over 6 decades. The sensitivity of summer balance to temperature is -0.62 m w.e. yr(-1) degrees C-1 for a typical 125-day-long ablation season. Finally, the correlation of winter and summer mass balance terms with NAO anomalies is investigated. Singularly, highest values are obtained between winter NAO anomalies and summer balance. Winter NAO anomalies and winter balance and precipitation are almost disconnected. However, these results strongly depend on how the NAO signal is smoothed, so that the link between Sarennes mass balance seasonal terms and NAO signal remains tenuous and hard to interpret.

Abstract: A large set of ice ablation data from a glacier in the French Alps is used to investigate the sensitivity of ice melting to solar radiation and temperature. The data come from 7 years of observations on a small network of 16 stakes set up on Glacier de Saint-Sorlin. The high spatial variability of ice ablation is shown to be strongly dependent on potential solar radiation. On the other hand, temporal variations are highly correlated with air temperatures measured both at a nearby and at a remote meteorological station, but poorly correlated with incoming shortwave radiation measured at an automatic weather station located close to the glacier terminus. Spatial variations of ice ablation therefore appear to be mainly driven by potential solar radiation, while temporal variations are driven by temperature. This result suggests that minimizing the influence of temperature in an enhanced temperature-index melt model may compromise the model's ability to simulate interannual changes in melt. These new results may help to improve the calibration, and thus the performance, of these empirical melt models used for long-term simulations of glacier mass balances.

Abstract: This study investigates the size and concentration effects on the transport of silica colloids in columns of sandy aquifer material. Colloid transport experiments were performed with specifically developed fluorescent labeled silica colloids in columns of a repacked natural porous medium under hydro-geochemical conditions representative of sandy aquifers. Breakthrough curves and vertical deposition profiles of colloids were measured for various colloid concentrations and sizes. The results showed that for a given colloid concentration injected, deposition increased when increasing the size of the colloids. For a given colloid size, retention was also shown to be highly concentration-dependent with a non-monotonous pattern presenting low and high concentration specificities. Deposition increases when increasing both size and injected concentration, until a threshold concentration is reached, above which retention decreases, thus increasing colloid mobility. Results observed above the threshold concentration agree with a classical blocking mechanism typical of a high concentration regime. Results observed at lower colloid concentrations were not modeled with a classical blocking model and a depth-and time-dependent model with a second order kinetic law was necessary to correctly fit the experimental data in the entire range of colloid concentrations with a single set of parameters for each colloidal size. The colloid deposition mechanisms occuring at low concentrations were investigated through a pore structure analysis carried out with Mercury Intrusion Porosimetry and image analysis. The determined pore size distribution permitted estimation of the maximal retention capacity of the natural sand as well as some low flow zones. Altogether, these results stress the key role of the pore space geometry of the sand in controlling silica colloids deposition under hydro-geochemical conditions typical of sandy aquifers. Our results also showed originally that colloid mobility in porous media is not only favored at high colloid concentrations, but also at very low concentrations, which are more likely to be observed in groundwater.

Abstract: Snow plays an important role in land surface models (LSM) for climate and model applied over Fran studies, but its current treatment as a single layer of constant density and thermal conductivity in ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems) induces significant deficiencies. The intermediate complexity snow scheme ISBA-ES (Interaction between Soil, Biosphere and Atmosphere-Explicit Snow) that includes key snow processes has been adapted and implemented into ORCHIDEE, referred to here as ORCHIDEE-ES. In this study, the adapted scheme is evaluated against the observations from the alpine site Col de Porte (CDP) with a continuous 18year data set and from sites distributed in northern Eurasia. At CDP, the comparisons of snow depth, snow water equivalent, surface temperature, snow albedo, and snowmelt runoff reveal that the improved scheme in ORCHIDEE is capable of simulating the internal snow processes better than the original one. Preliminary sensitivity tests indicate that snow albedo parameterization is the main cause for the large difference in snow-related variables but not for soil temperature simulated by the two models. The ability of the ORCHIDEE-ES to better simulate snow thermal conductivity mainly results in differences in soil temperatures. These are confirmed by performing sensitivity analysis of ORCHIDEE-ES parameters using the Morris method. These features can enable us to more realistically investigate interactions between snow and soil thermal regimes (and related soil carbon decomposition). When the two models are compared over sites located in northern Eurasia from 1979 to 1993, snow-related variables and 20cm soil temperature are better reproduced by ORCHIDEE-ES than ORCHIDEE, revealing a more accurate representation of spatio-temporal variability.

Abstract: A high-resolution sedimentological and geochemical study of a high-altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 8001300) and the current period of global warming. On a multi-decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi-centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multi-decadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns. Copyright (c) 2013 John Wiley & Sons, Ltd.

Abstract: The last glacial period has been punctuated by two types of abrupt climatic events, the Dansgaard-Oeschger (DO) and Heinrich (HE) events. These events, recorded in Greenland ice and in marine sediments, involved changes in the Atlantic Meridional Overturning Circulation (AMOC) and led to major changes in the terrestrial biosphere. Here we use the dynamical global vegetation model ORCHIDEE to simulate the response of vegetation to abrupt changes in the AMOC strength. We force ORCHIDEE offline with outputs from the IPSL_CM4 general circulation model, in which the AMOC is forced to change by adding freshwater fluxes in the North Atlantic. We investigate the impact of a collapse and recovery of the AMOC, at different rates, and focus on Western Europe, where many pollen records are available for comparison. The impact of an AMOC collapse on the European mean temperatures and precipitations simulated by the GCM is relatively small but sufficient to drive an important regression of forests and expansion of grasses in ORCHIDEE, in qualitative agreement with pollen data for an HE event. On the contrary, a run with a rapid shift of the AMOC to a hyperactive state of 30 Sv, mimicking the warming phase of a DO event, does not exhibit a strong impact on the European vegetation compared to the glacial control state. For our model, simulating the impact of an HE event thus appears easier than simulating the abrupt transition towards the interstadial phase of a DO. For both a collapse or a recovery of the AMOC, the vegetation starts to respond to climatic changes immediately but reaches equilibrium about 200 yr after the climate equilibrates, suggesting a possible bias in the climatic reconstructions based on pollen records, which assume equilibrium between climate and vegetation. However, our study does not take into account vegetation feedbacks on the atmosphere.

Abstract: The overturning circulation of the Southern Ocean has been investigated using eddying coupled ocean-sea ice models. The circulation is diagnosed in both density-latitude coordinates and in depth-density coordinates. Depth-density coordinates follow streamlines where the Antarctic Circumpolar Current is equivalent barotropic, capture the descent of Antarctic Bottom Water, follow density outcrops at the surface, and can be interpreted energetically. In density-latitude coordinates, wind-driven northward transport of light water and southward transport of dense water are compensated by standing meanders and to a lesser degree by transient eddies, consistent with previous results. In depth-density coordinates, however, wind-driven upwelling of dense water and downwelling of light water are compensated more strongly by transient eddy fluxes than fluxes because of standing meanders. Model realizations are discussed where the wind pattern of the southern annular mode is amplified. In density-latitude coordinates, meridional fluxes because of transient eddies can increase to counter changes in Ekman transport and decrease in response to changes in the standing meanders. In depth-density coordinates, vertical fluxes because of transient eddies directly counter changes in Ekman pumping.

Abstract: Daily rain gauge data over Europe for the period from 1950 to 2009 were used to analyze changes in the duration of wet and dry spells. The duration of wet spells exhibits a statistically significant growth over northern Europe and central European Russia, which is especially pronounced in winter when the mean duration of wet periods increased by 15%-20%. In summer wet spells become shorter over Scandinavia and northern Russia. The duration of dry spells decreases over Scandinavia and southern Europe in both winter and summer. For the discrimination between the roles of a changing number of wet days and of a regrouping of wet and dry days for the duration of the period, the authors suggest a fractional truncated geometric distribution. The changing numbers of wet days cannot explain the long-term variability in the duration of wet and dry periods. The observed changes are mainly due to the regrouping of wet and dry days. The tendencies in duration of wet and dry spells have been analyzed for a number of European areas. Over the Netherlands both wet and dry periods are extended in length during the cold and the warm season. A simultaneous shortening of wet and dry periods is found in southern Scandinavia in summer. Over France and central southern Europe during both winter and summer and over the Scandinavian Atlantic coast in summer, opposite tendencies in the duration of wet and dry spells were identified. Potential mechanisms that might be responsible for the changing durations of wet and dry periods and further perspectives are discussed.

Abstract: The GLACIOCLIM-SAMBA (GS) Antarctic accumulation monitoring network, which extends from the coast of Adelie Land to the Antarctic plateau, has been surveyed annually since 2004. The network includes a 156-km stake-line from the coast inland, along which accumulation shows high spatial and interannual variability with a mean value of 362 mm water equivalent a(-1). In this paper, this accumulation is compared with older accumulation reports from between 1971 and 1991. The mean and annual standard deviation and the km-scale spatial pattern of accumulation were seen to be very similar in the older and more recent data. The data did not reveal any significant accumulation trend over the last 40 years. The ECMWF analysis-based forecasts (ERA-40 and ERA-Interim), a stretched-grid global general circulation model (LMDZ4) and three regional circulation models (PMM5, MAR and RACMO2), all with high resolution over Antarctica (27-125 km), were tested against the GS reports. They qualitatively reproduced the meso-scale spatial pattern of the annual-mean accumulation except MAR. MAR significantly underestimated mean accumulation, while LMDZ4 and RACMO2 overestimated it. ERA-40 and the regional models that use ERA-40 as lateral boundary condition qualitatively reproduced the chronology of interannual variability but underestimated the magnitude of interannual variations. Two widely used climatologies for Antarctic accumulation agreed well with the mean GS data. The model-based climatology was also able to reproduce the observed spatial pattern. These data thus provide new stringent constraints on models and other large-scale evaluations of the Antarctic accumulation.

Abstract: The effects of an ice-shelf collapse on inland glacier dynamics have recently been widely studied, especially since the breakup of the Antarctic Peninsula's Larsen-B ice shelf in 2002. Several studies have documented acceleration of the ice streams that were flowing into the former ice shelf. The mechanism responsible for such a speed-up lies with the removal of the ice-shelf backforce. Independently, it is also well documented that during the last glacial period, the Northern Hemisphere ice sheets experienced large discharges into the ocean, likely reflecting ice flow acceleration episodes on the millennial time scale. The classic interpretation of the latter is based on the existence of an internal thermo-mechanical feedback with the potential to generate oscillatory behavior in the ice sheets. Here we would like to widen the debate by considering that Larsen-B-like glacial analog episodes could have contributed significantly to the registered millennial-scale variablity.

Abstract: Mass-balance and dynamic behaviour of Chhota Shigri glacier, western Himalaya, India, has been investigated between 2002 and 2010 and compared to data collected in 1987-89. During the period 2002-10, the glacier experienced a negative glacier-wide mass balance of -0.67 +/- 0.40 m w.e.a(-1). Between 2003 and 2010, elevation and ice-flow velocities slowly decreased in the ablation area, leading to a 24-37% reduction in ice fluxes, an expected response of the glacier dynamics to its recent negative mass balances. The reduced ice fluxes are still far larger than the balance fluxes calculated from the 2002-10 average surface mass balances. Therefore, further slowdown, thinning and terminus retreat of Chhota Shigri glacier are expected over the next few years. Conversely, the 2003/04 ice fluxes are in good agreement with ice fluxes calculated assuming that the glacier-wide mass balance is zero. Given the limited velocity change between 1987-89 and 2003/04 and the small terminus change between 1988 and 2010, we suggest that the glacier has experienced a period of near-zero or slightly positive mass balance in the 1990s, before shifting to a strong imbalance in the 21st century. This result challenges the generally accepted idea that glaciers in the Western Himalaya have been shrinking rapidly for the last few decades.

Abstract: Soot, which is produced from biomass burning and the incomplete combustion of fossil and biomass fuels, has been linked to regional and global climate change and to negative health problems. Scientists measure the properties of soot using a variety of methods in order to quantify source emissions and understand its atmospheric chemistry, reactivity under emission conditions, interaction with solar radiation, influence on clouds, and health impacts. A major obstacle currently limiting progress is the absence of established standards or reference materials for calibrating the many instruments used to measure the various properties of soot. The current state of availability and practicability of soot standard reference materials (SRMs) was reviewed by a group of 50 international experts during a workshop in June of 2011. The workshop was convened to summarize the current knowledge on soot measurement techniques, identify the measurement uncertainties and limitations related to the lack of soot SRMs, and identify attributes of SRMs that, if developed, would reduce measurement uncertainties. The workshop established that suitable SRMs are available for calibrating some, but not all, measurement methods. The community of users of the single-particle soot-photometer (SP2), an instrument using laser-induced incandescence, identified a suitable SRM, fullerene soot, but users of instruments that measure light absorption by soot collected on filters did not. Similarly, those who use thermal optical analysis (TOA) to analyze the organic and elemental carbon components of soot were not satisfied with current SRMs. The workshop, and subsequent, interactive discussions, produced a number of recommendations for the development of new SRMs, and their implementation, that would be suitable for the different soot measurement methods.

Abstract: The ozone molecule possesses a unique and distinctive O-17 excess (Delta O-17), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO2 + O-3 reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Delta O-17 from ozone to nitrate radical (NO3) during the gas-phase NO2 + O-3 -> NO3 + O-2 reaction was investigated in a series of laboratory experiments. The isotopic composition (delta O-17, delta O-18) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Delta O-17 transfer function for the NO2 + O-3 reaction was determined to be: Delta O-17(O-3*) = (1.23 +/- 0.19) x Delta O-17(O-3)(bulk) + (9.02 +/- 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Delta O-17 values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen. (C) 2012 American Institute of Physics. [doi:10.1063/1.3666852]

Abstract: In relation to Arctic warming, the possible occurrence of methane hydrate degassing events has attracted an increasing interest in recent years. We evaluate the atmospheric impact of rapid and massive emissions of methane and how they are imprinted in ice core records, by combining for the first time models of atmospheric chemistry and trace gas transport in firn. Different emission characteristics as well as climatic conditions (present, pre-industrial, glacial) are considered. The delta isotopic signatures characterizing stable isotopologues of methane DCH3 and (CH4)-C-13 are also analysed. Our results suggest little effect of clathrate degassing on the main methane oxidant: OH radicals. Due to the relatively short atmospheric lifetime of methane, the simulated clathrate-induced perturbations last for less than a century. This time scale is comparable to or shorter than the duration of air bubble closure in polar ice sheets. As a consequence, rapid methane perturbations in the atmosphere are strongly smoothed in ice core records. This smoothing mostly depends on the snow accumulation rate at the site of ice core drilling. We propose a methodology to identify a potential clathrate degassing event in ice core records. Continuous CH4 records from high accumulation rate sites could allow to decipher short time scale events. delta D of CH4 should reveal a typical “lying S” shape at high accumulation rate sites, reflecting the combined effects of the clathrate source signature (negative excursion) and subsequent OH fractionation in the atmosphere (positive excursion). The amplitude ratio of the negative and positive delta D swings recorded in Greenland and Antarctica under similar accumulation rate conditions could also indicate the latitude of a clathrate degassing event. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Gas transfer experiments on claystone and numerical simulations have been conducted to enhance the knowledge of gas transport in nuclear waste repositories in the Callovo-Oxfordian clay formation in Bure, France. Laboratory Gas transfer experiments were performed with a specific device dedicated to very low permeability measurement (10(-23) to 10(-20) m(2)). Experiments were performed on both dry and close to saturation claystone. The Dusty Gas Model, based on multi-component gas transfer equations with Knudsen diffusion, was used to describe the experimental results. The parameters obtained are the effective permeability, the Knudsen diffusion (Klinkenberg effect) and molecular diffusion coefficients and the porosity accessible to gas. Numerical simulations were carried with various boundary conditions and for different gases (helium vs hydrogen) and were compared with experiments to test the reliability of the model parameters and to better understand the mechanisms involved in clays close to saturation. The numerical simulation fitted the experimental data well whereas simpler models cannot describe the complexity of the Knudsen/Klinkenberg effects. Permeabilities lie between 10(-22) and 10(-20) m(2). Claystones close to saturation have an accessible porosity to gas transfer that is lower than 0.1-1% of the porosity. Analysis of the Klinkenberg effect suggests that this accessible pore network should be made of 50-200 nm diameter pores. It represents pore networks accessible at capillary pressure lower than 4 MPa.

Abstract: The objective of this paper is to investigate if the description of ocean uncertainties can be significantly improved by applying a local anamorphic transformation to each model variable, and by making the assumption of joint Gaussianity for the transformed variables, rather than for the original variables. For that purpose, it is first argued that a significant improvement can already be obtained by deriving the local transformations from a simple histogram description of the marginal distributions. Two distinctive advantages of this solution for large size applications are the conciseness and the numerical efficiency of the description. Second, various oceanographic examples are used to evaluate the effect of the resulting piecewise linear local anamorphic transformations on the spatial correlation structure. These examples include (i) stochastic ensemble descriptions of the effect of atmospheric uncertainties on the ocean mixed layer, and of wind uncertainties or parameter uncertainties on the ecosystem, and (ii) non-stochastic ensemble descriptions of forecast uncertainties in current sea ice and ecosystem pre-operational developments. The results indicate that (i) the transformation is accurate enough to faithfully preserve the correlation structure if the joint distribution is already close to Gaussian, and (ii) the transformation has the general tendency of increasing the correlation radius as soon as the spatial dependence between random variables becomes nonlinear, with the important consequence of reducing the number of degrees of freedom in the uncertainties, and thus increasing the benefit that can be expected from a given observation network.

Abstract: Air was sampled from the porous firn layer at the NEEM site in Northern Greenland. We use an ensemble of ten reference tracers of known atmospheric history to characterise the transport properties of the site. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the depth-diffusivity reconstruction. We define an objective root mean square criterion that is minimised in the model tuning procedure. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1 sigma Gaussian distribution. A comparison between two replicate boreholes drilled 64 m apart shows differences in measured mixing ratio profiles that exceed the experimental error. We find evidence that diffusivity does not vanish completely in the lock-in zone, as is commonly assumed. The ice age- gas age difference (Delta age) at the firn-ice transition is calculated to be 182(-9)(+3) yr. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore, diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records.

Abstract: The orbital-scale transition from the last interglacial to glacial climate corresponds to the progressive organization of global millennial-scale climate variability. Here, we investigate the structure and the global fingerprint of the first warming event occurring during the last glacial inception, the Greenland InterStadial 25 (GIS 25). Using centennial to decadal-resolution measurements of delta O-18 and delta D in the ice together with delta N-15, delta O-18(2) and CH4 in the trapped air, we show that GIS 25 does not coincide with large environmental changes at lower latitudes. Such an equivocal fingerprint questions whether GIS 25 is simply a smaller amplitude version of later rapid events or whether it reflects a more regional northern hemisphere origin for the initiation of the millennial-scale climatic variability. After this ambiguous first rapid event, the onset of the global millennial-scale variability – characteristic of the last glacial period-occurs as a short (300 years) event ending GIS 25.

Abstract: Extreme rainfall is classically estimated using raingauge data at raingauge locations. An important related issue is to assess return levels of extreme rainfall at ungauged sites. Classical methods consist in interpolating extreme-value models. In this paper, such methods are referred to as regionalization schemes. Our goal is to evaluate three classical regionalization schemes. Each scheme consists of an extreme-value model (block maxima, peaks over threshold) taken from extreme-value theory plus a method to interpolate the parameters of the statistical model throughout the Cevennes-Vivarais region. From the interpolated parameters, the 100-yr quantile level can be estimated over this whole region. A reference regionalization scheme is made of the couple block maxima/kriging, where kriging is an optimal interpolation method. The two other schemes differ from the reference by replacing either the extreme-value model block maxima by peaks over threshold or kriging by a neural network interpolation procedure. Hyper-parameters are selected by cross-validation and the three regionalization schemes are compared by double cross-validation. Our evaluation criteria are based on the ability to interpolate the 100-yr return level both in terms of precision and spatial distribution. It turns out that the best results are obtained by the regionalization scheme combining the peaks-over-threshold method with kriging.

Abstract: This paper presents a model of Andean glacier hydrology which can be used to assess the water management implications of possible future glacier retreat. The approach taken uses the Water Evaluation and Planning (WEAP) system and integrates both hydrologic processes and representations of the operations of built infrastructure. The model is applied in the Rio Santa watershed in Peru to illustrate how alternative water management strategies can be simulated. The WEAP platform built for this study has been used to engage with local stakeholders for water management.

Abstract: The description of soil structure is primordial to determine the effects of management practices on soil environment. Different techniques were developed to determine the pore structure, each with its own limitations. In this study mercury intrusion porosimetry (MIP) and X-ray microtomography (micro-CT) were used to study the total porosity and pore size distribution of soil aggregates (5-6 mm) treated with different fertilisations (organic, mixed and mineral). The network model Pore-Con was applied to pore distribution curves to highlight subtle structural properties affecting the aggregates. The combination of these techniques highlighted that: (1) MIP was fundamental to reveal the small pores that were not detected by micro-CT and that represented up to 70% of total porosity; (2) micropores (30-6.25 μm) detected by MIP were underestimated with respect to micro-CT (-9.4%) probably due to the “ink bottle” effect, whereas meso- and macropores were overestimated; (3) only micro-CT highlighted the effects of organic amendants on pore morphology. These outcomes were compared with modelling results of the network model Pore-Cor that proved its ability to predict the pore structure organisation and the differences between fertilisations. Further improvement of micro-CT will allow to cover a wider range of pores, but at present the integration with different techniques is still fundamental. (C) 2011 Elsevier B.V. All rights reserved.

Abstract: We present here the first profiles of acetate and formate concentrations in Antarctic ice for time periods that include the great climatic changes of the past. Data are from two Antarctic deep ice cores recovered on the central East Antarctic Plateau (EDC) and in the Dronning Maud Land (EDML) facing the Atlantic Ocean (European EPICA Project). Except the sporadic arrival of diluted continental plumes during glacial extrema, the main source of acetate deposited over the EDC does not seem to have changed significantly over the past 300 kyr and is related to marine biogenic activity. A more detailed study of the past 55 kyr leads to the conclusion that acetate reaching the EDML during a large part of the last glacial maximum was emitted by the Patagonian continental biomass and was uptaken along with nitric acid at the surface of mineral dust. Changes in formate concentrations are characterised by less scattered and lower values at both sites during glacial periods. We propose that the present marine source of formic acid (Legrand et al., 2004) drastically decreased but did not completely vanish under cold climate conditions, whereas the share of methane oxidation in formic acid production became prominent.

Abstract: Changes in the hydrological regime of Sahelian Rivers are considered based upon the example of the Middle Niger River and its exceptional flood in 2010 near the city of Niamey. It is shown that rainfall in 2010 was only average with respect to the long term record, with neither the monthly rainfall distribution in terms of the amount of rainfall nor the distribution of rainy events changing significantly in the last few decades. Particularly, no increase in the number of extreme rainfall events is observed. In spite of this, the Niger River's right bank tributaries have shown a sharp increase in runoff since the 1970s, which is still ongoing, and has resulted in a modification of the Niger River's regime from a single hydrograph to a two flood hydrograph, the local flood, occurring during the rainy season being the more pronounced one. This modification is likely due to an increase of bare soils and crusted soil areas as a consequence of human pressure, resulting mostly from the spatial extension of crop areas and the shortening of fallow periods. Changes in connectivity of the river networks on both banks of the Niger such as endorheism bursting events also caused an increase in the contributing basin area. Policy makers should be alerted to the effects of intensive cropping, land clearing and overgrazing in some areas, on the hydrological regimes of Sahelian Rivers. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: Clay-based landfill covers often have a geomembrane (GM) layer sandwiching between the clay barrier and the cover soil. The knowledge pertaining to the deformation behaviour of a clay barrier along with geomembrane subjected to differential settlements is very limited. Hence, the main objective of this paper is to examine the influence of GM on the integrity of clay-based landfill covers subjected to differential settlements in a geotechnical centrifuge. First, scaling considerations required for modelling geomembrane in a centrifuge are presented. A series of centrifuge tests were performed at 40 gravities using a 4.5 m radius beam centrifuge having a capacity of 2500 g-kN available at IIT Bombay on model clay-based landfill covers with and without GM. By maintaining type moist-compacted conditions of the clay barrier as constant, the thickness of the clay barrier was varied as 0.6 m and 1 m. The performance of the clay barrier with and without GM was monitored by measuring water breakthrough at the onset of differential settlements. The analysis and interpretation of centrifuge test results reveal that with the provision of a GM and an overburden pressure equivalent to that of a landfill cover, the sealing efficiency of the cover system was found to be maintained even after the formation of full-depth cracks within 0.6 m and 1 m thick clay barriers subjected to a maximum distortion level of 0.125. This observed behaviour is attributed to the downward thrust exerted by the deformed geomembrane at the zone of maximum curvature which hinders the infiltration of water through cracks. This indicates the significant influence of GM in maintaining the sealing efficiency of a landfill cover system. (C) 2012 Elsevier Ltd. All rights reserved.

Abstract: Gaseous elemental mercury (Hg-0) was investigated in the troposphere and in the interstitial air extracted from the snow at Dome Concordia station (alt. 3320 m) on the Antarctic Plateau during January 2009. Measurements and modeling studies showed evidence of a very dynamic and daily cycling of Hg-0 inside the mixing layer with a range of values from 0.2 ng m(-3) up to 2.3 ng m(-3). During low solar irradiation periods, fast Hg-0 oxidation processes in a confined layer were suspected. Unexpectedly high Hg-0 concentrations for such a remote place were measured under higher solar irradiation due to snow photochemistry. We suggest that a daily cycling of reemission/oxidation occurs during summer within the mixing layer at Dome Concordia. Hg-0 concentrations showed a negative correlation with ozone mixing ratios, which contrasts with atmospheric mercury depletion events observed during the Arctic spring. Unlike previous Antarctic studies, we think that atmospheric Hg-0 removal may not be the result of advection processes. The daily and dramatic Hg-0 losses could be a consequence of surface or snow induced oxidation pathways. It remains however unclear whether halogens are involved. The cycling of other oxidants should be investigated together with Hg species in order to clarify the complex reactivity on the Antarctic plateau.

Abstract: This review is the result of a series of multidisciplinary meetings organised by the Arctic Monitoring and Assessment Programme as part of their 2011 Assessment 'Mercury in the Arctic'. This paper presents the state-of-the-art knowledge on the environmental fate of mercury following its entry into the Arctic by oceanic, atmospheric and terrestrial pathways. Our focus is on the movement, transformation and bioaccumulation of Hg in aquatic (marine and fresh water) and terrestrial ecosystems. The processes most relevant to biological Hg uptake and the potential risk associated with Hg exposure in wildlife are emphasised. We present discussions of the chemical transformations of newly deposited or transported Hg in marine, fresh water and terrestrial environments and of the movement of Hg from air, soil and water environmental compartments into food webs. Methylation, a key process controlling the fate of Hg in most ecosystems, and the role of trophic processes in controlling Hg in higher order animals are also included. Case studies on Eastern Beaufort Sea beluga (Delphinapterus leucas) and landlocked Arctic char (Salvelinus alpinus) are presented as examples of the relationship between ecosystem trophic processes and biologic Hg levels. We examine whether atmospheric mercury depletion events (AMDEs) contribute to increased Hg levels in Arctic biota and provide information on the links between organic carbon and Hg speciation, dynamics and bioavailability. Long-term sequestration of Hg into non-biological archives is also addressed. The review concludes by identifying major knowledge gaps in our understanding, including: (1) the rates of Hg entry into marine and terrestrial ecosystems and the rates of inorganic and MeHg uptake by Arctic microbial and algal communities; (2) the bioavailable fraction of AMDE-related Hg and its rate of accumulation by biota and (3) the fresh water and marine MeHg cycle in the Arctic, especially the marine MeHg cycle.

Abstract: To refine the understanding of how the Southern Ocean responds to recent intensification of the southern annular mode (SAM), a regional ocean model at two eddy-permitting resolutions was forced with two synthetic interannual forcings. The first forcing corresponds to homogeneously intensified winds, while the second concerns their poleward intensification, consistent with positive phases of the SAM. Resulting wind-driven responses differ greatly between the nearly insensitive Antarctic Circumpolar Current (ACC) and the more sensitive meridional overturning circulation (MOC). As expected, eddies mitigate the response of the ACC and MOC to poleward-intensified winds. However, transient eddies do not necessarily play an increasing role in meridional transport with increasing resolution. As winds and resolution increase, meridional transport from standing eddies becomes more efficient at balancing wind-enhanced overturning. These results question the current paradigms on the role of eddies and present new challenges for eddy flux parameterization. Results also indicate that spatial patterns of wind anomalies are at least as important as the overall change in intensity in influencing the Southern Ocean's dynamic response to wind events. Poleward-intensified wind anomalies from the positive trend in the SAM are far more efficient in accelerating the ACC than homogeneous wind anomalies.

Abstract: Albedo is one of the variables controlling the mass balance of temperate glaciers. Multispectral imagers, such as MODerate Imaging Spectroradiometer (MODIS) on board the TERRA and AQUA satellites, provide a means to monitor glacier surface albedo. In this study, different methods to retrieve broadband glacier surface albedo from MODIS data are compared. The effect of multiple reflections due to the rugged topography and of the anisotropic reflection of snow and ice are particularly investigated. The methods are tested on the Saint Sorlin Glacier (Grandes Rousses area, French Alps). The accuracy of the retrieved albedo is estimated using both field measurements, at two automatic weather stations located on the glacier, and albedo values derived from terrestrial photographs. For summers 2008 and 2009, the root mean square deviation (RMSD) between field measurements and the broadband albedo retrieved from MODIS data at 250m spatial resolution was found to be 0.052 or about 10% relative error. The RMSD estimated for the MOD10 daily albedo product is about three times higher. One decade (2000-2009) of MODIS data were then processed to create a time series of albedo maps of Saint Sorlin Glacier during the ablation season. The annual mass balance of Saint Sorlin Glacier was compared with the minimum albedo value (average over the whole glacier surface) observed with MODIS during the ablation season. A strong linear correlation exists between the two variables. Furthermore, the date when the average albedo of the whole glacier reaches a minimum closely corresponds to the period when the snow line is located at its highest elevation, thus when the snow line is a good indicator of the glacier equilibrium line. This indicates that this strong correlation results from the fact that the minimal average albedo values of the glacier contains considerable information regarding the relative share of areal surfaces between the ablation zone (i.e. ice with generally low albedo values) and the accumulation zone (i.e. snow with a relatively high albedo). As a consequence, the monitoring of the glacier surface albedo using MODIS data can provide a useful means to evaluate the interannual variability of the glacier mass balance. Finally, the albedo in the ablation area of Saint Sorlin Glacier does not exhibit any decreasing trend over the study period, contrasting with the results obtained on Morteratsch Glacier in the Swiss Alps.

Abstract: The role of long-range elastic interactions in discontinuous dynamic recrystallization is assessed using a simple analytical model, taking into account dislocation pileup relaxation during embryo formation. Long-range dislocation pileup rearrangements following absorption of leading dislocations by a dislocation-free embryo provides an additional driving force that results in a drastic decrease of both nucleation critical radius and saddle point energy. A very sharp transition between a saddle point behavior and spontaneous grain nucleation is evidenced. The role of long-range internal stresses on grain nucleation during dynamic discontinuous recrystallization of ice, metals and minerals is shortly discussed. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: The rise and spread of Anopheles gambiae s.l. (the major malaria vector sub-Saharan Africa) resistance to pyrethroids is of great concern owing to the predominant role of pyrethroid-treated nets in the WHO global strategy for malaria control. Use of pyrethroids for agricultural purposes may exert a strong selection pressure, favouring the emergence of insecticide resistance. The objective of this study was to evaluate the efficacy of alpha-cypermethrin treated nets in settings where insecticides are used against pests. This was assessed in two ways, i.e. under laboratory conditions using the WHO standard cones test technique and in experimental huts, on Anopheles gambiae s.l. collected in two Malian rural sites, Koumantou characterised by cotton crops and high insecticide use and Selingue, a rice field area with low insecticide use. According to the WHO standard cones test technique, there was no difference between mosquitoes collected in the two sites: KD50 time was less than 3 min and the KD95 time below 30 min. Nevertheless, in the experimental huts with alpha-cypermethrin treated bed nets, the mosquito mortality rate was significantly lower in Koumantou (102/361, 28.2%) than in Selingue (122/233, 52.3%) (RR: 0.65, 95%CI: 0.56-0.76) (p < 0.001). In addition, in Koumantou the percentage of unfed mosquitoes found in the veranda was much lower in the huts with untreated (26.0%, 33/127) than in those with treated nets (92.2%, 118/128) (p < 0.01) while in Selingue there was no difference between huts with treated and untreated bed nets. Alpha-cypermethrin treated bed nets had a significant effect on mortality and repelling behaviour of Anopheles gambiae s.l. though in Koumantou treated bed nets were less efficacious, possibly due to the intense use of pesticide for agriculture. (C) 2012 Elsevier B.V. All rights reserved.

Abstract: This letter assesses the quality of temperature and rainfall daily retrievals of the European Climate Assessment and Dataset (ECA&D) with respect to measurements collected locally in various parts of the Euro-Mediterranean region in the framework of the Hydrological Cycle in the Mediterranean Experiment (HyMeX), endorsed by the Global Energy and Water Cycle Experiment (GEWEX) of the World Climate Research Program (WCRP). The ECA&D, among other gridded datasets, is very often used as a reference for model calibration and evaluation. This is for instance the case in the context of the WCRP Coordinated Regional Downscaling Experiment (CORDEX) and its Mediterranean declination MED-CORDEX. This letter quantifies ECA&D dataset uncertainties associated with temperature and precipitation intra-seasonal variability, seasonal distribution and extremes. Our motivation is to help the interpretation of the results when validating or calibrating downscaling models by the ECA&D dataset in the context of regional climate research in the Euro-Mediterranean region.

Abstract: Most of oceanographic operational centers use three-dimensional data assimilation schemes to produce reanalyses. We investigate here the benefits of a smoother, i.e. a four-dimensional formulation of statistical assimilation. A square-root sequential smoother is implemented with a tropical Atlantic Ocean circulation model. A simple twin experiment is performed to investigate its benefits, compared to its corresponding filter. Despite model's non-linearities and the various approximations used for its implementation, the smoother leads to a better estimation of the ocean state, both on statistical (i.e. mean error level) and dynamical points of view, as expected from linear theory. Smoothed states are more in phase with the dynamics of the reference state, an aspect that is nicely illustrated with the chaotic dynamics of the North Brazil Current rings. We also show that the smoother efficiency is strongly related to the filter configuration. One of the main obstacles to implement the smoother is then to accurately estimate the error covariances of the filter. Considering this, benefits of the smoother are also investigated with a configuration close to situations that can be managed by operational center systems, where covariances matrices are fixed (optimal interpolation). We define here a simplified smoother scheme, called half-fixed basis smoother, that could be implemented with current reanalysis schemes. Its main assumption is to neglect the propagation of the error covariances matrix, what leads to strongly reduce the cost of assimilation. Results illustrate the ability of this smoother to provide a solution more consistent with the dynamics, compared to the filter. The smoother is also able to produce analyses independently of the observation frequency, so the smoothed solution appears more continuous in time, especially in case of a low frenquency observation network.

Abstract: PM10 speciation data from various sites in Switzerland for two time periods (January 1998-March 1999 and August 2008 July 2009) have been analysed for major sources by receptor modelling using Positive Matrix Factorisation (PMF). For the 2008/2009 period, it was found that secondary aerosols (sulphate- and nitrate-rich secondary aerosols, SSA and NSA) are the most abundant components of PM10 at sites north of the Alps. Road traffic and wood combustion were found to be the largest sources of PM10 at these sites. Except at the urban roadside site where road traffic is dominating (40% of PM10 – including road salt), the annual average contribution of these two sources is of similar importance (17% and 14% of PM10, respectively). At a rural site south of the Alps wood combustion and road traffic contributions to PM10 were higher (31% and 24%, respectively), and the fraction of secondary aerosols lower (29%) than at similar site types north of the Alps. Comparison of PMF analyses for the two time periods (1998/1999 and 2008/2009) revealed decreasing average contributions of road traffic and SSA to PM10 at all sites. This indicates that the measures that were implemented in Switzerland and in neighbouring countries to reduce emissions of sulphur dioxide and PM10 from road traffic were successful. On the other hand, contributions of wood combustion did not change during this ten year period, and the contribution of nitrate-rich secondary aerosols has even increased. It is shown that PMF can be a helpful tool for the assessment of long-term changes of source contributions to ambient particulate matter. (C) 2012 Elsevier Ltd. All rights reserved.