Synoptic Drivers of Atmospheric River Induced Precipitation Near Dronning Maud Land, Antarctica
Atmospheric Rivers (AR) precipitation occurs when a warm moist air mass travels meridionally and is lifted by the sloping topography of the Antarctic coast. While topography plays a vital role in lifting AR air masses and determining the mesoscale variability in precipitation impacts across the Antarctic continent, this study aims to diagnose complementary atmospheric mechanisms that contribute to AR precipitation and the extent to which those mechanisms are responsible for variability in AR precipitation intensity. We choose a focus region near Donning Maud Land (DML) from 30°W to 30°E where AR precipitation represents 15 ± 7% of total annual precipitation. Although ARs reach this region only up to ∼3 days per year, they account for 77% of the interannual variability of total precipitation. DML serves as a particularly suitable focus region for investigating the mechanisms that generate AR precipitation because snowfall is the only significant AR impact on SMB and is a controlling factor of interannual precipitation variability.
ARs that reach the Antarctic Ice Sheet (AIS) transport moisture in the atmosphere from lower latitudes and can result in significant precipitation on the ice sheet. Around Dronning Maud Land, East Antarctica, the precipitation associated with ARs has a substantial impact on the year-to-year variability in the amount of water stored by the ice sheet. As the climate warms, changing AR impacts may modulate future global sea level changes as more or less water is stored in the AIS. Assessing the environmental factors driving AR precipitation around Dronning Maud Land will ultimately help us understand, predict, and project precipitation, water storage, and impacts on the AIS. Our findings on the impacts of moisture availability and atmospheric forcing for AR precipitation intensity suggest that anomalous atmospheric moisture is necessary for the occurrence of an AR, but that an increase in moisture will not necessarily result in high precipitation intensity unless suitable synoptic-scale forcing is present.
ARs that reach the Antarctic Ice Sheet (AIS) transport anomalous moisture from lower latitudes and can impact the AIS via extreme precipitation and increased downward longwave radiation. ARs contribute significantly to the interannual variability of precipitation over the AIS and, thus, are likely to play a key role in understanding future changes in the surface mass balance of the AIS. Dronning Maud Land (DML) is one of four maxima in AR frequency over coastal East Antarctica, with AR precipitation explaining 77% of the interannual variability in precipitation for this region. We employ a 16-node self-organizing map (SOM) trained with MERRA-2 sea-level pressure anomalies to identify synoptic-scale environments associated with landfalling ARs in and around DML. Node composites of atmospheric variables reveal common drivers of precipitation associated with ARs reaching DML, including anomalous high-low surface pressure couplets, anomalously high integrated water vapor, and coastal barrier jets. Using a quasi-geostrophic framework, we find that upward vertical motion associated with the occlusion process of attendant cyclones dominates atmospheric lift in AR environments. We further identify mechanisms that explain the variability in AR precipitation intensity across nodes, such as the lift associated with the occlusion process of attendant cyclones and the spatial coincidence of ascent induced by the occlusion process and frontogenesis. The latter suggests that ARs making landfall during the mature phase of cyclogenesis result in higher precipitation intensity compared to landfalling ARs that occur during the occluded phase.