Precipitation processes in an Antarctic moist air intrusion: insights from multi-frequency radar observations over a 1100-km transect

Abstract. In Antarctica, intrusions of coastal moist and warm air onto the high plateau play an important role in the mass balance of the ice sheet, due to their significant contribution to annual snowfall accumulation. The synoptic drivers of warm intrusions are well-established, in particular for extreme cases linked to atmospheric rivers. However, a lack of suitable observations means the micro-physical cloud and precipitation processes within intrusions remain uncertain. In the context of the Atmospheric WAter Cycle over Antarctica (AWACA) project, we investigate an intrusion associated with a coastal cyclone in East Antarctica in February 2025. Lagrangian trajectory analysis confirms that air masses within the intrusion pass over a 1100-km observational transect from the coast to the plateau, allowing precipitation properties to be tracked as the intrusion moves inland. At four sites along the transect, a multi-frequency, polarimetric, spectral radar dataset is used to investigate micro-physical processes. The reflectivity and dual frequency ratios indicate a decrease in particle size as the intrusion moves inland. Near the coast, high fall-velocities and spectral signatures point to riming of snowflakes, fuelled by ascending air masses above the coastal slope and the availability of supercooled water. On the plateau, dry and cold conditions lead to smaller particles, for which variation in the radar signal appears to arise from primary ice crystal habits. The case study illustrates the potential of multi-frequency radar data from an autonomous observational transect to investigate precipitation processes between the Antarctic coast and plateau.