Atmospheric Rivers, Warm Air Intrusions, and Surface Radiation Balance in the Amundsen Sea Embayment

Over recent decades the primary climatic forcing on the ice shelves in the Amundsen Sea Embayment (ASE) has been the influx of warm water into sub-ice-shelf ocean cavities. By contrast, the contribution of a globally warming atmosphere has been negligible but may play a more significant role in the future. Warm, moist air intrusions from the ocean onto the ice sheet surface play an essential role in the surface energy budget and constitute the primary driver for surface melting in West Antarctica. This study employs observations from automatic weather stations deployed on the Pine Island Glacier and numerical model outputs from the Antarctic Mesoscale Prediction System to investigate warm air intrusion (WAI) events and examine their impacts on surface glacier melt in the ASE. A deep low-pressure center over the Amundsen/Ross Seas and a blocking ridge over the southeast Pacific created favorable conditions for developing an atmospheric river that directs warm and moist air toward the ASE. An analysis of meteorological observations through 2013-2014 shows that 2013 received two times higher frequency WAI events than 2014. 2013 year coincides with more substantial pressure gradients in the western Ross Sea and the eastern Amundsen Sea. The February and March 2013 WAI events induce about 3 days of surface melting over the Pine Island Glacier and the Thurston Island area. A continued increase in the large-scale advection of warm air from the midlatitudes toward the ASE could lead to an increased surface melting frequency with implications for ice shelves in the study area.