北极冷空气爆发的识别及其对北欧海表面热通量的影响OACSTPCD

Cold Air Outbreaks(CAO)in the Arctic refer to the intermittent incursions of polar cold air masses southward across warmer ocean surfaces in lower latitudes and are often accompanied by intense air-sea heat exchange.The Nordic Seas are the largest year-round ice-free seas in the Arctic and play a crucial role in Arctic climate change.During winter,the Nordic Seas exhibit a complex sea-ice distribution comprising ice-covered,marginal ice zones,and open ocean surfaces.Accurate identification of CAO events impacting this critical Arctic zone and their implications on regional air-sea heat fluxes are crucial for enhancing our comprehension of Arctic climate change and capabilities of extreme weather forecast.Existing studies on Arctic CAO mainly focus on open ocean areas in the Nordic Seas,using lower-level potential temperature differences as indicators.Given the complex surface conditions of the wintertime Nordic Seas,this study explores the method of using a locally defined temperature standard deviation,a method commonly used in mid-to-high latitude cold wave research,to identify CAO events.A systematic comparison is conducted between this method and the conventional potential temperature difference method,by examining the spatiotemporal characteristics,atmospheric circulation evolutions and impacts on air-sea heat fluxes associated with CAO events of various intensities identified by both methods.Results from both identification methods show that,over the Nordic Seas,CAO events occur in approximately 30％days of the winter period,with the vast majority having life spans of less than three days and stronger events tending to persist longer.CAO events contribute to approximately 60％of the total wintertime air-sea heat fluxes in the region,with moderate-intensity CAO events exhibiting a large impact on these fluxes.Meanwhile,CAO events account for roughly 50％to 60％of the southward water vapor transport during winter in the concerned sectors of the Nordic Seas.The atmospheric circulations associated with the CAO events in the Labrador Sea-Greenland and Iceland Sea-Norwegian Sea-Barents Sea regions are notably different.The former is primarily influenced by the transformation of a transversal trough turning into a more meridional pattern,whereas the latter is associated with a dipole-like atmospheric circulation anomaly.