Highlights on key polar processes driving the Antarctic surface mass balance and the added value of the regional climate model MAR compared to reanalyses

Séminaire de C. Agosta, jeudi 3 octobre à 11h, salle Lliboutry, bât de Glaciologie

Abstract :

Ice sheet mass balance results of the small imbalance between ice flow discharging in the ocean and net snow accumulation on the ice sheet surface, i.e. the surface mass balance (SMB). Past change in ice sheet mass can be assessed using satellite altimetry, gravimetry, or the input–output method, which all request SMB estimates.The input–output method, which consists in separately modeling ice dynamics and SMB, is also the only way to project future trends.

Here we show that, despite large spatial differences between SMB patterns from 7 reanalyses products (including ERA-5), we obtain mostly insignificant differences after downscaling them with the polar-oriented regional climate model MAR. Downscaled SMB is markedly closer to observations than the original reanalyses fields. We show that 1) processes related to clouds and precipitating particles in the atmosphere explain most of the divergences between reanalyses, MAR, and RACMO2 ground precipitation and consequently SMB, and that 2) resolution is a secondary order parameter. The temporal variability of downscaled SMB is however strongly related to the forcing reanalysis variability. We emphasis the interest of polar-oriented regional climate models to depict the Antarctic surface climate, particularly in view of atmosphere-ice sheet coupling. We also present application of the MAR model for quantifying snowmelt associated with atmospheric rivers, and for understanding the isotopic composition of water vapor in the boundary layer, toward new interpretation of the isotopic signal in firn cores.

By Cécile AGOSTA (LSCE)

Séminaire animé par Vincent Favier