Climatology of Atmospheric Rivers-related precipitation over different surface types in the Southern Ocean

Antarctica experienced a rapid decline in sea ice extent in 2016 following a modest increase in annual sea ice extent. Rapid changes in Antarctic sea ice have consequences for the Antarctic climate system; however, the coupled atmosphere-ocean-ice processes driving these changes remain poorly understood. Precipitation is a key atmospheric variable influencing both the surface mass balance of the Antarctic ice sheet and the formation and persistence of Antarctic sea ice.  Two major moisture sources contribute to precipitation: local evaporation due to the reduced insulation effect of sea ice and poleward moisture transport from lower latitudes, often associated with atmospheric rivers (ARs) – long, narrow corridors that transport large amounts of heat and moisture from the mid-latitudes to the polar regions. 

Despite their rarity, ARs play an important role in the Antarctic climate system, contributing to surface melt on the West Antarctic Ice Sheet and extreme precipitation events across East Antarctica. However, the role of ARs and AR-related precipitation, particularly in relation to Antarctic sea ice, has been less explored. 

Here, we analyze ERA5 reanalysis data to investigate the contribution of ARs to precipitation over the Southern Ocean (60 – 90S), distinguishing between different surface characteristics (open ocean and sea ice) and precipitation phase (rain and snow). Our results show that ARs contribute more to rainfall (50%) than snowfall (25%). AR-related snowfall is relatively evenly distributed across the entire study region, whereas around 75% of AR-related rainfall occurs over the Ross Sea and Amundsen-Bellingshausen Seas. While AR-related snowfall exhibits weak seasonal variability, AR-related rainfall is more pronounced in winter and spring. Regarding different surface types, AR-related rainfall primarily occurs over the open ocean throughout the year but extends over sea ice during winter. In contrast, AR-related snowfall shifts seasonally, dominating over the open ocean in summer and autumn and over sea ice in winter and spring.  

Area-normalized precipitation reveals that AR-related precipitation events are more intense than non-AR events, with higher intensities in winter compared to summer.  These findings highlight the important role of ARs and their potential changes in Antarctica. Finally, we compare these results with simulations from the newly developed climate model ICON-XPP to assess its ability to represent AR characteristics over the Southern Ocean.