Loss of autumn Kara-East Siberian Sea ice intensifies winter Ural blocking and cold anomalies in high latitudes of Eurasia

Abstract

Sea ice in the Kara-East Siberian Sea (KESS) declined to the lowest record in the autumn of 2020 and has been suggested to affect the Eurasian climate in the following winter. By analyzing reanalysis data from 1979 to 2021 and performing model experiments, this study demonstrates that the loss of autumn KESS sea ice acts to intensify the Eurasian cold spells in winter. Low autumn KESS sea ice attenuates the stratospheric polar vortex through driving upward planetary wave activities. The weakening of polar vortex persists to winter and induces anomalies in tropospheric zonal wind and meridional gradient of potential vorticity through downward wave propagation. These intraseasonal to cross-seasonal processes lead to enhancement and prolonged duration of Ural blocking that aggravates Eurasian cold spells. A positive feedback likely exists between the weak stratospheric polar vortex induced by autumn sea ice loss and the wintertime Ural blocking via vertical wave propagation. The results establish a link between autumn KESS sea ice and Eurasian winter climate, with implications for seasonal prediction of Eurasian cold events.