Regime transitions in the nighttime atmosphere

Séminaire de Bas van de Wiel (Université de Delft), Mercredi 11 Octobre 2017 à 11h en Salle Lliboutry, Bât. Glaciologie

Seminar by  : Bas van de Wiel (Université de Delft , Pays-Bas)

Summary : Results on our fascinating nocturnal atmosphere will be presented.
In particular we will discuss a new conceptual model, which is used in combination with observational analysis to understand regime transitions of near surface temperature inversions at night as well as in Antarctic conditions. The model combines a surface energy budget with a bulk parameterization for turbulent heat transport. Energy fluxes or feedbacks due to soil and radiative heat transfer are accounted for by a ‘lumped parameter closure’, which represents the ‘coupling strength’ of the system.
Observations from Cabauw, Netherlands and Dome C, Antarctica, are analyzed. As expected, inversions are weak for strong winds, whereas large inversions are found under weak wind conditions. However, a sharp transition is found between those regimes, as it occurs within a narrow wind range. This results in a typical, S-shaped dependency.
The conceptual model explains why this characteristic must be a robust feature.
Differences between the Cabauw and Dome C cases are explained from differences in coupling strength (being weaker in the Antarctic). For comparison, a realistic column model is run. As findings are similar to the simple model and the observational analysis, it suggests generality of the results.
In the future we will therefore further explore this intriguing phenomenon with respect to its practical implications and also perform 3D simulations using turbulence resolving models (DNS/LES).

Animation : E. Vignon (GLACE)