Axis 2 : Study of the exchange processes at the surface-atmosphere interface

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An essential activity of the C2H team concerns the analysis of energy and mass exchanges at the surface of seasonal snow-covers and glaciers. This analysis is carried out on the basis of in-situ measurements of the processes in relation with local and regional meteorological forcing. This analysis takes into account the diversity of mechanisms at work, the interactions with other components (e.g., forest) and the extreme spatial heterogeneity in mountains, which raises the question of changes of scales (from the micrometer for snow, to the scale of large ice ? caps and mountain massifs/catchment areas).

The specificity of cryospheric surfaces is the omnipresence of snow, whose metamorphism and feedbacks to the atmosphere must be considered precisely (e.g., albedo feedback, stable boundary layers). These loops and specific conditions are crucial to quantify the response of the cryosphere to climatic variations, and consequently that of the hydrosphere in mountain regions.

The team aims at describing and modeling series of processes operating at the surface such as :
(i) radiative and turbulent energy exchanges with the atmosphere,
(ii) heat exchanges with the subsoil (permafrost, ground, glacier, ice pack, ...) or with rock debris when these cover the glaciers (so-called "black" glaciers),
(iii) exchanges of matter (snow accumulation, wind transport of snow, water flows, avalanches), and
(iv) interactions with vegetation (e.g., forest).

For this, C2H carries out specific observations allowing to describe and quantify the spatio-temporal variabilities of surface characteristics (snow depth, roughness, optical properties, topography, thickness/heterogeneity of debris, presence of supra-glacial lakes or cliffs etc.), as well as thermodynamic processes.