Climatology and Surface Impacts of Atmospheric Rivers on West Antarctica

Abstract. Atmospheric rivers (ARs) transport large amounts of moisture from the mid- to high-latitudes and they are a primary driver of the most extreme snowfall events on Antarctica. ARs also raise surface temperatures when they make landfall over Antarctica, leading to surface melting. In this study, we characterize the climatology and surface impacts of ARs on West Antarctica, focusing on the Amundsen Sea Embayment and Marie Byrd Land. First, we develop a climatology of ARs in this region, using an Antarctic-specific AR detection tool combined with MERRA-2 and ERA5 atmospheric reanalyses. We find that while ARs are infrequent, they cause intense precipitation in short periods of time and account for 11 % of the annual surface accumulation. They are driven by the coupling of a blocking high over the Antarctic Peninsula with a low--pressure system known as the Amundsen Sea Low. Next, we use observations from automatic weather stations on Thwaites Eastern Ice Shelf to examine a case study of 3 ARs that made landfall in rapid succession from February 2 to 8, known as an AR family event. We use snow height observations to force the firn model SNOWPACK to reconstruct accumulation and surface melting during the event, and compare these results with accumulation higher up on the glacier derived from surface height changes using interferometric reflectometry. While accumulation dominates the surface impacts of the event on Thwaites Eastern Ice Shelf (>100 kg m⁻²), we find small amounts of surface melt as well (<5 kg m⁻²). West Antarctica currently experiences minimal surface melting, most of which is absorbed by the firn, but future atmospheric warming could lead to more widespread surface melting in West Antarctica. Combined with a future increase in AR intensity or frequency, this could limit the ability of the firn layer to absorb melt water, which could harm ice shelf stability, and ultimately accelerate mass loss of the West Antarctic Ice Sheet. The results presented here enable us to quantify the past impacts of ARs on West Antarctic surface mass balance and characterize their interannual variability and trends, enabling a better assessment of future AR-driven changes in the surface mass balance.