Modulation of a long-lasting extreme cold event in Siberia by a minor sudden stratospheric warming and the dynamical mechanism involved

Abstract

Previous studies have paid much attention to the impact of major sudden stratospheric warming (SSW) events on the tropospheric circulation. However, the attention to the modulation of minor SSW events on the extreme cold events is limited. In this study, the extreme cold event in Siberia in the winter of 2000/2001, the longest-lasting one from 1980/1981 to 2019/2020, and its linkages to the minor SSW event have been examined. Our results show that the largest cooling occurred in Siberia during 30 December 2000 − 10 January 2001, and then the cooling weakened and migrated to Northeast China from 11 to 18 January 2001. During the recovery stage of this minor SSW event, the stratospheric polar vortex gradually strengthened, along with strengthening of the zonal winds over the Ural region. The vertical distribution of positive zonal wind anomalies in the Ural region favored the reflection of stratospheric planetary wave in the Atlantic-Euro and Siberia region. The changes of planetary wave propagation were beneficial to the strengthening of the trough in the Atlantic-Euro and Siberia region during 26 December − 10 January, which facilitated the growth and maintenance of the Ural ridge in the same period by strengthening the meridional flow. The strengthened Ural ridge resulted in the extreme cold event breaking out and lasting from 30 December to 10 January. Because the stratospheric polar vortex did not continue to strengthen and a new ridge generated in the Atlantic region during 11 − 18 January, the Ural ridge decayed and the cold air moved to Northeast China.