Possible impact of sudden stratospheric warming on the intraseasonal reversal in winter

Abstract：The intraseasonal reversal of the temperature over East Asia and the sudden stratospheric warming (SSW) are two abrupt events during the winter of 2020/21. The characteristics of these two events and their relationship are the focused issues in this paper. In winter 2020/21, there was a transition from cold to warm over East Asia. The surface air temperature (SAT) in East Asia suddenly changed from cold to warm with long duration. The cold period lasted from 21 November 2020 to 11 January 2021, while the warm period lasted from 19 January to 28 February 2021. And the transition of the cold to the warm was from 12 to 18 January 2021.There are significant differences of the atmospheric circulations between the cold and warm periods in the upper and lower troposphere. During the cold period, both of Ural Mountain High(UH) and Siberian High(SH) were stronger than normal, the Westerly Jet (WJ) was weakened and located to the area farther southerly than usual, the northerly wind anomalies and the cold advection occurred in East Asian; vice versa during the warm period. The mutations of the atmospheric circulations in the upper and lower levels were obvious during the transition period, especially for UH and SH. A strong SSW event occurred in the stratosphere at the beginning of 2021. As a result, the stratospheric polar vortex was largely weakened and deviated to the areas over Ural Mountains and nearby, the polar westerly wind turned to easterly wind and the temperature gradient reversed. The abnormal changes of the temperature and the geopotential height over the Ural Mountains area in the stratosphere were closely related to the SSW. These abnormal signals caused by the SSW gradually transmitted from stratosphere to troposphere over the Ural Mountains and the polar region, leading to the weakening and collapse of tropospheric UH and further caused the transition from cold to warm in East Asia. The SSW may be the most critical factor leading to the turning from cold to warm over East Asia during the winter of 2020/21.