SUMAK K. The current dynamics of the tropospheric frontal zones and regional synoptic processes over Eastern Europe.

The thesis is devoted to determining the spatial-temporal features of frontal and cyclonic activities over Eastern Europe and the territory of Belarus, in particular, in the period of 1995-2015. The physical-geographical and modern climatic conditions of Eastern Europe, characteristic features of atmospheric circulation in the region, and the role of the North Atlantic Oscillation on the weather conditions of Europe are considered. The analysis of modern methods for evaluating blocking processes in the atmosphere is performed, the role of trajectory analysis in assessing the meteorological characteristics of air masses is shown, and the basic principles of objective detection of atmospheric fronts are considered. The assessment of conditions for the formation and movement of cyclones of typical trajectories through the territory of Belarus in the period of 1995-2015 was carried out. A database of the main characteristics of cyclones was created, including the geographical coordinates of the beginning and the end of the trajectories, the date and the minimum pressure in the center, and maps of the trajectories were built. The main geographical areas of cyclone formation were determined. So, for the western cyclones these were the latitudes of 50-60° N above the Atlantic, north-western cyclones formed over the Norwegian sea and the Scandinavian Peninsula, and southern cyclonic formations reached the territory of Belarus from all regions of the Mediterranean, as well as the Balkan Peninsula and the Black sea. The interannual and seasonal variability of cyclones was analyzed. It was revealed that on average 15-16 cyclones of different types of trajectories move through the territory of Belarus every year. Most of the cyclones (57 %) belonged to the southern, western and north-western cyclones accounted for 20 % of cases. Analysis of the average pressure at the center of the cyclones showed that most cyclones deepened directly over the country's territory. The regional blocking index ECBI was used to assess macrocirculatory conditions during the evolution of cyclones. This index allowed determining the intensity of perturbation of the zonal flow in the processes of cyclogenesis. The predominance of the western component of the flow in any process of cyclogenesis over Eastern Europe was revealed. At the same time, southern cyclones formed and evolved most frequently in the blocking conditions. The frequency of dangerous weather phenomena in cyclones of different trajectories that moved through the territory of the Republic of Belarus during the period of 1995–2015 is considered. It is identified that southern and western cyclones caused dangerous weather events over the territory of Belarus. The interannual and seasonal frequency of cyclones causing dangerous weather phenomena in Belarus was analyzed. It is shown that the largest number of southern and western cyclones was characteristic mainly for the summer period and transitional seasons of the year, and the dangerous weather phenomena were associated mainly with the development of severe convection on atmospheric fronts. Such phenomena as very heavy rain, snowfall and wind had the highest frequency in cyclones, as in southern as western trajectories. The share of strong sticking of wet snow and large hail were isolated cases and these phenomena were recorded locally over the territory of country. The NOAA HYSPLIT Lagrangian transport model was used to estimate the main meteorological characteristics of air masses in different types of cyclones. Backward trajectories for a period of 24 h were calculated at the levels of 1500 and 3000 m for the most typical areas of origin and movement trajectories. It was revealed that relatively warm air masses entered the region of origin of both western and southern cyclones throughout the seasons of the year, while in the first case they were moist and cooled and became less saturated in the process of moving to Belarus, and in the second they were initially unsaturated, during the evolution of the cyclones experienced cooling and an increase of relative humidity. The character of the movement and transformation of air particles in northwestern cyclones for different seasons of the year has significant differences in connection with their formation under various conditions of the underlying surface.