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

The ERC Synergy funded project AWACA aims to understand the atmospheric branch of the water cycle over Antarctica. It relies on innovative observations of the tropospheric meteorological conditions and the isotopic composition of water vapor and hydrometeors along a 1100-km transect between Dumont d’Urville station at the coast and Concordia station on the high inner Antarctic plateau. The deployment of instruments was completed in the austral summer season from November 2024 to February 2025. The instruments will remain in place for three years. At four locations along the transect, temporary container-stations were deployed. Each container includes, among other instruments, a Metek MIRA 35 GHz cloud radar, an MRR-PRO 24 GHz precipitation radar, and a BASTA 95 GHz cloud radar. Adjacent to each container is a comprehensive surface weather station.

This contribution will present a case study of a coastal cyclone and resulting moist air intrusion in February 2025, focusing on the radar data. Trajectory analysis confirmed that air parcels within the same intrusion traveled inland over multiple sites of the observational transect. However, the mechanisms by which the moisture of the intrusion is converted into precipitation differ between the coast and the high plateau. Taking advantage of the multi-frequency, spectral, polarimetric radar dataset, differences in the microphysics of snowfall along the transect have been investigated. On the coastal slope of the ice sheet, uplift, turbulence and the presence of liquid water lead to riming and aggregation of snowflakes. On the high plateau, dry and cold conditions lead to smaller snow particles, for which the variation in the radar signal appears to arise from variations in primary production and ice crystal habit.