Spatial Variability in the Occurrence of Summer Precipitation over a 30 km Transect in the Sør Rondane Mountains, Antarctica

Despite its role as the main contributor to the surface mass balance of the Antarctic ice sheet, precipitation remains poorly characterized over the continent. Direct measurements of snowfall are particularly scarce inland, more so in mountainous terrain and farther away from scientific bases. The deployment of multiple ground-based instruments in the complex terrain south of the Belgian base Princess Elisabeth Antarctica (PEA) during the PEA Orographic Precipitation Experiment (POPE) is a unique opportunity to study snowfall in a region where observations were previously unavailable. In particular, a transect of three vertically-pointing K-band Doppler radars (MRR-PRO), reaching a distance of 30 km from PEA, allowed us to investigate the spatial variability in the occurrence of precipitation over a specific region of the mountain chain. Using the measurements collected between December 2019 and January 2020, the occurrence of virga (i.e. precipitation that does not reach the ground) and surface precipitation has been characterized over the three MRR-PRO sites. The analysis reveals that virgae represent a higher fraction of the events recorded at lower altitudes. Moreover, the profiles of attenuated equivalent reflectivity from all sites suggest the presence of sublimation below 3.5 km above mean sea level. We used high-resolution simulations from the WRF model, forced by the ERA5 reanalysis, to investigate the profiles of meteorological fields over the transect. The analysis reveals the presence of a relatively drier layer below 3.5 km, which is likely responsible for the sublimation observed in the radar data. Since the height of the top of this dry layer is approximately constant over the region, the terrain height controls its depth. The simulations also suggest that orographic lifting may be responsible for the enhancement of precipitation over the highest MRR-PRO sites. Finally, we used measurements from automatic weather stations (AWS) at the ground and the ERA5 reanalysis to study the link between the location of low-pressure systems over the Southern Ocean and the occurrence of virga and surface precipitation over the transect. A low-pressure system directly south of PEA is usually associated with surface precipitation. Virgae, typically occurring before and after surface precipitation, are instead associated with locations further to the East and West, respectively. Overall, this study highlights the large spatial variability in precipitation (and virgae) at a relatively small scale (10s of km) due to the interactions between the synoptic flow and the complex Antarctic terrain around the PEA station.