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Abstract

Combining datasets provided by Aura MLS, meteor radar, and reanalysis, we observed unusual changes in the thermal and dynamic regime in the upper stratosphere-lower mesosphere (USLM) and mesosphere-lower thermosphere (MLT) during ;winter of 2019–2020. A great majority of disturbances in the mesosphere occurred in early winter, creating specific configuration favored for strengthening and stability of the stratospheric polar vortex. Reduced temperature at 90;km accompanied by thermal inversions is observed in association with USLM warming in the eastern hemisphere. The meteor radar (67°N, 26°E) located under the ridge of wave 1 observes several successive pulses of ;eastward wind at high velocities up to 50;m/s. The wind core first appears at high altitudes and then descends abruptly, resulting in wind shears and stratification of zonal flow over a wide range of heights. Meridional component of MLT winds is dominated by the alternating north- and southward flows with a half-a-month period. Temperatures in MLT ;decrease due to USLM warming that begins in late December. This structure is interrupted by abrupt cooling throughout the entire middle atmosphere. During the initial formation of strong stratospheric polar vortex the MLT, USLM and lower stratosphere was largely decoupled from forcing below. High and strong “wall” surrounding the vortex is formed in association with high-altitude disturbances in lower latitudes.;Since the 21st century, only two strong Arctic polar vortex events occurred, one in 2019/2020 and the other in 2010/2011. Comparative analysis shows the high similarity in the winter evolution preceding the two strong polar vortex events.