Extreme Precipitation in the Cyrosphere: Atmospheric River Interaction with Antarctic Sea Ice

In 2016, Antarctic sea ice experienced a regime shift when a persisting decreasing trend emerged from a relatively stable annual cycle. Drivers of the sea ice regime shift and future projections of Southern Ocean sea ice remain unresolved. One possible contributing phenomena are atmospheric rivers (ARs), which are long, narrow, and transient features responsible for the majority of global poleward water vapor transport. Though infrequent over Antarctica, ARs wield a substantial influence on the Antarctic ice mass balance. Previous studies highlight their significance, attributing 35% of the interannual precipitation variability over the Antarctic Ice Sheet (AIS) to ARs. The interaction between ARs and Antarctic sea ice has not been as clearly defined. Our ongoing work uses ERA5 reanalysis data, results from an AR tracking algorithm, and passive microwave sea ice concentration data from 1980 to 2023 to examine the relationship between ARs and Antarctic sea ice, especially in the context of the changing sea ice state. In this study, we explore the relationship between AR activity and sea ice area at a region and seasonal scale, then analyse the contribution of ARs to precipitation over sea ice and how that contribution has changed through the 40-year study period. On average, ARs can be attributed with 11% of total precipitation, 11% of snowfall, and 13% of rain over Antarctic sea ice. While the AR contribution to sea ice snowfall is fairly consistent through the year, the predominant AR contribution to rain rotates around the Southern Ocean sequentially by season. The strongest signal of AR precipitation over sea ice is in the Weddell Sea winter, when ARs constitute 25% of winter rain. The trends of these contributions vary by season and by region. For example, while AR precipitation on sea ice has an increasing trend across all types of precipitation in each season in the Weddell Sea, the opposite is true for the Ross Sea. These findings underscore the importance of the AR interaction with Antarctic sea ice, particularly in the context of seasonal and regional variability and change. This work will improve our understanding of the spatiotemporal variability and trends of ARs as precipitation mechanisms, which is vital for understanding and predicting sea ice mass balance in a changing climate.