Abrupt Arctic Sea Ice Decline on the Synoptic Time Scale during Summer: Physical Processes and Background Condition Impacts

In this paper, the physical processes related to abrupt sea ice decline events on the synoptic time scale are explored over the Laptev Sea and the Eastern Siberian-Chukchi-Beaufort (EsCB) Seas in the summer during two periods, i.e., P1 (1979–2000) and P2 (2001–2021). Results show that abrupt sea ice decline events are closely associated with an atmospheric zonal dipole structure, charactering a cold cyclonic anomaly upstream of a warm anticyclonic anomaly, which correspondingly influences the primary surface energy components driving sea ice melt. The downstream anticyclonic anomaly usually results in decrease of low-level cloud cover, and therefore increased downward shortwave radiation (DSR), whereas, the anchored region between cyclonic and anticyclonic anomalies favors the transport of warm, moist air from the midlatitudes into the Arctic, leading to a positive total column water anomaly and therefore enhanced downward longwave radiation (DLR). To be specific, enhanced DSR is the primary contributor to triggering the abrupt sea ice decline. Afterwards, DLR and surface turbulent heat flux (STHF) start to take effect. From the perspective of accumulative effect of surface energy components, DSR plays a dominant role during the entire process of abrupt sea ice decline in the Laptev Sea, whether it is during P1 or P2. However, for abrupt sea ice decline events in the EsCB Seas, play a dominant role during P1, whereas DSR and STHF do so during P2. The background states associated with different phases of Pacific Decadal Oscillation (PDO) exert an influence on the structure and persistence of the atmospheric zonal dipole pattern over the EsCB Seas, thus leading to a greater sea ice decline in this region during P2. The above findings are beneficial for our understanding of the Arctic climate system.