Extreme precipitation and atmospheric rivers over West Antarctic ice shelves: insights from kilometre-scale regional climate modelling

Extreme precipitation events in the Amundsen Sea Embayment, West Antarctica deposit significant precipitation amounts, often during atmospheric river (AR) events. In this work, we use observations, reanalysis, and three regional climate models (RCMs: MetUM, Polar-WRF, HCLIM) at a spatial resolution of 1 km to evaluate the characteristics of two AR cases: one in winter, and another in summer. We quantify the magnitude of snow and rain falling over the Thwaites and Pine Island ice shelves and explore the drivers and mechanisms of this extreme precipitation. The model results indicate that supercooled liquid precipitation fell during these cases, generated in particular by the interaction of the AR with steep topography. Model estimated snowfall compares well against observed snow height measurements, but ERA5 estimates for both events are severely underestimated (by 3-4 times) compared to the measurements. Our work highlights that kilometer-scale models are useful tools to investigate the total precipitation amount and its partitioning into rain and snow over this globally important and climatically sensitive region, and the critical need for in situ observations of rainfall.