Abstract: Using a snow/atmosphere coupled model, the evolution of the surface and near-surface snow temperature is modeled at Dome C, Antarctica, during the period 20-30 January 2010. Firstly, the detailed multilayer snow model Crocus is run in stand-alone mode, with meteorological input forcing data provided by local meteorological observations. The snow model is able to simulate the evolution of surface temperature with good accuracy. It reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well. Secondly, a fully coupled 3-D snow/atmosphere simulation is performed with the AROME regional meteorological model, for which the standard single-layer snow parameterization is replaced by Crocus. In spite of a poor simulation of clouds, the surface and near-surface snow temperatures are correctly simulated, showing neither significant bias nor drifts during the simulation period. The model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower. This study highlights the potential of snow/atmosphere coupled models over the Antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions.

Abstract: l y a 25 ans était organisée une campagne d'observation et d'analyse des vents catabatiques en Terre Adélie, l'une des régions du monde où ces vents se manifestent de façon particulièrement fréquente et violente. Frappés par une conséquence majeure de ces vents, la neige soufflée, les promoteurs de cette campagne affublaient alors la Terre Adélie du titre de Royaume du Blizzard. Depuis 2009, le CNRS et le CEMAGREF de Grenoble, avec le soutien de l'Institut polaire Fançais (IPEV) et du programme cadre de l'Europe pour la recherche, déploient des instruments de mesure de la neige soufflée en Terre Adélie afin de mieux caractériser ce phénomène, mieux le modéliser, et ainsi mieux prévoir sa contribution à l'accumulation de la neige en Antarctique. Une évolution éventuelle de l'accumulation en réponse au changement climatique aura un impact sur le niveau global des mers.
Twenty five years ago, a field campaign was designed to observe an analyze the catabatic winds of Adélie Land, a region where these winds are particularly strong and persistent. Impressed by one major consequence of the winds, the investigators then tagged Adélie Land, the Blizzard Kingdom. Since 2009, with support from the french polar institute and the European framework program for research, the CNRS and CEMAGREF in Grenoble deploy and maintain instruments in Adélie Land to measure blowing snow, increase our understanding of the processes involved, improve blowing snow modeling, and better assess the contribution of blowing snow to surface accumulation. If Antarctic snow accumulation changes in response to climate change, this will have global consequences on global sea-level.

Abstract: For the first time a simulation of blowing snow events was validated in detail using one-month long observations (January 2010) made in Adélie 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 ranged from 2 m 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 Adélie Land only when the half-hourly wind speed value at 2 m a.g.l. is higher than 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.