The present study is concerned with the aspects of stratosphere-troposphere dynamic interaction during major sudden stratospheric warming (SSW). The SSW observed in December 2018 – January 2019 was taken for consideration. The influence of the stratospheric polar vortex location on the position of the upper-level frontal zone (UFZ), changes in the steering flows in the middle troposphere, surface temperature anomalies, as well as on the characteristics of the tropopause have been studied using MERRA2 reanalysis data. Analysis has revealed that SSW events influence the location of the upper-level frontal zone (UFZ), subsequently altering steering flows in the troposphere and leading to the development of surface cold waves. Isentropic analysis has shown that SSW caused the intrusion of stratospheric air into the troposphere, which contributed to the intensification of the cold wave. Correlation analysis has demonstrated a statistically significant relationship between stratospheric processes and anomalies of geopotential height in the middle troposphere (500 hPa), exhibiting a two-week time lag following SSW events. Spatial distribution of the maximum correlation coefficient corresponds to the region with the UFZ deformation. In the cross-time interval of the formation of the SSW, 3-dimensional fluxes of planetary wave activity have been calculated. The enhanced reflection of wave activity over Canada during the SSW demonstrated the dynamic influence of the stratosphere on the troposphere, contributing to the formation of the cold wave. This confirms the role of stratospheric-tropospheric coupling in surface weather extremes.
In terms of the SSW impact on tropospheric circulation, according to the model studies, it is determined primarily by tropospheric variability. The presence of direct forcing from above, such as planetary wave reflection, tropopause folds, and stratospheric air invasion into the troposphere, should be combined with a stochastic component associated with internal tropospheric variability. This should enhance the SSW signal below, and in our case, it manifests itself in the UFZ deformation and the formation of the horizontal pressure advection. As a result, the processes under consideration lead to the establishment of a quasi-stationary wave structure that accompanied the intensification of the surface cold wave in the second half of January. The present work study of the features of vertical interactions of the stratosphere with the troposphere during the formation of such extreme external influences as SSW is important for understanding the processes, which must be taken into account in the long-range forecasting, including sub-seasonal to seasonal (S2S) forecasting.
This study is supported by Saint Petersburg State University (Project ID 124032000025-1).

SSW,cold air outbakes