SEASONAL FEATURES OF CIRCULATION PROCESSES AND CHANGES IN CLOUD HEIGHT OVER THE TERRITORY OF THE SOUTH OF WESTERN SIBERIA

Abstract

Basing on the ERA5 reanalysis data, the amount of precipitation, and the cloud base, we assessed seasonal differences in circulation processes that determined the transfer of moisture and pollutants by air masses to the
territory of the south of Western Siberia in 2014-2023. The paper shows that the cold season is characterized by unidirectional movement of air masses, both in the lower layers of the atmosphere and in the middle troposphere, which is associated with western and southwestern flows. In contrast to the cold season, the warm season is characterized by multidirectional movements in the lower layers of the atmosphere and in the middle troposphere: for the middle troposphere, as
in the cold season, western and southwestern flows are predominant, while for the lower layers northwestern flows are
predominant. Using the HYSPLIT model, trajectories corresponding to the cloud layer height were constructed for the
dates of precipitation, which also showed differences in different seasons, both in direction and duration: in the warm
season the average direction of air masses movement to the study area is northwestern, in the cold season – southwesternwestern.
The study has found that for the cold period the height of the cloud base at which precipitation predominantly
occurred (70.1% in terms of the number of days with precipitation and 60.0% in terms of precipitation volume) was ≥2500
m, while for the warm period the maximum precipitation amount was recorded at the height of the cloud base in the range
of 600-1000 m (85.3% and 87.5% respectively). It is concluded that for the cold period of the year, the contribution of
long-range transboundary transport to the supply of moisture and pollutants to the underlying surface of the study area
will be significantly higher than for the warm period, when air masses of long-range transboundary transport will transit
over the study area.