Unpacking Global Drivers of Extreme Precipitation over West Antarctica, using a Variable-Resolution Earth Systems Model with Explicit Moisture Tagging

The overall gain and loss of snow and ice on the surface of the Antarctic ice sheet is strongly driven by rare extreme events, some of which result from atmospheric rivers transporting both moisture and heat from the tropics towards the south pole. Moisture transport is strongly driven by large-scale patterns, e.g. the El Niño Southern Oscillation, the Southern Annular Mode, PSA1 and PSA2 patterns. Additionally, in recent years, the Southern Ocean region has witnessed major changes, including sequential record lows for sea ice extent and warming oceans, with direct impacts on the Antarctic ice sheet and Southern Ocean. Previous research has highlighted the strong sensitivity of precipitation in West Antarctica to large-scale patterns, and especially the importance of atmospheric rivers. However, atmospheric rivers are only one mechanism of transport, and estimates are subject to the reliability of detection algorithms. Additionally, the ability to fully-capture drivers and impacts of extreme events are limited by spatiotemporal resolution in Earth Systems Models.

Here, we employ a variable-resolution version of the global Community Earth Systems Model (VR-CESM2) with enhanced resolution over Antarctica over the historical period (1990-2020), run at a high time-resolution capable of capturing extremes and calculating atmospheric rivers. We additionally employ moisture-tagging (linking precipitation to a moisture source region), which can quantify links between sources and sinks of extreme precipitation directly and identify mechanisms which drive transport. Here, we will focus on drivers of extremes in West Antarctica, comparing mechanisms identified via direct moisture tagging with those concurrent with atmospheric rivers.