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Abstract

Remote sensing observations point out that snow grain size in Antarctica follows a clear seasonal evolution, a summer increase and a winter decrease, which is conditioned by atmospheric processes, namely temperature, wind, snowfall, and by mechanisms acting inside the snowpack leading to water vapour transport causing the coarsening of the grains. This study focuses on the evolution of the grain size in the interior part of East Antarctica, where dry metamorphism occurs. For this, we use AMSU-B passive microwave radiometer observations collected from 2020 to 2022. The highest ridges in East Antarctica are the regions where the grain size increases the most in the summer, mainly because the wind speed is low. Moreover, some extreme weather events in this regions, where the grain size increased to large values with respect to the averages (over +3 sigma), were identified. In these cases, the ERA5 reanalysis revealed an atmospheric blocking/ridge situation around the onsets of the summer growing of the grain size, conveying the relatively warm and moist air coming from the mid latitudes, often associated with atmospheric rivers. If the following weeks feature weak wind, low temperature and low snowfall conditions, snow dry metamorphism is facilitated, leading to grain growth, and determining anomalous high value of the snow grain size at the end of the summer season. These grain size changes impact the albedo and have consequence on the energy budget of the surface.