Features of the atmospheric circulation during extreme floods in Cisbaikalia
O.P. OSIPOVA, N.V. KICHIGINA
V.B. Sochava Institute of Geography, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
Keywords: extreme rainfall floods, synoptic processes, atmospheric precipitation, HYSPLIT backward trajectories, Cisbaikalia
Abstract
The article presents the results of studies of the relationship between atmospheric circulation and floods in Southern Cisbaikalia. During the floods (in July 1971, June and July 2019), precipitation at the meteorological stations of the study area was significantly higher than the norm: on average 229 %, 163 % and 156 % of the norm, respectively. A comprehensive synoptic analysis was carried out to identify the main causes of extremely high precipitation values, which provoked a rise in water levels on the left-bank tributaries of the Angara river and on the rivers of Southern Baikal in July 1971, June and July 2019. Synoptic processes were classified by weather types according to the Jenkinson and Collison method. Six and fifteen weather types were identified for the July 1971 flood and for the June and July 2019 flood, respectively. These were mainly cyclonic and advective types with eastern components, correlating with humid weather conditions. The directions of air mass transfer were determined based on the analysis of 5-day HYSPLIT backward trajectories. It was found that the main factors determining the intensity of catastrophic floods were as follows: 1) active process of cyclogenesis; 2) sharp increase in meridional cold and heat flows and development of blocking processes; 3) the presence of a high content of potentially accumulated moisture, a field of upward vertical movements and forced convection in the foothills, and 4) local orographic conditions.
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