Analysis of Tropospheric and Stratospheric Circulation Conditions That Contributed to the Formation of Cold Waves in the Northwest and Center of European Russia in December 2021

The peculiarities of the troposphere and stratosphere dynamic processes that accompanied cooling events (cold waves) with a duration of more than a week in the northwest of European Russia (on the example of St. Petersburg) and in its north and center (on the example of Moscow) in early and late December 2021, respectively, are analyzed using reanalysis data, station observations, and trajectory modeling. In both cases the daily temperatures dropped below −10°C, and cold waves were accompanied by the air mass transport from the northeast