CHANGES IN THE ATMOSPHERIC CIRCULATION TYPES OVER WESTERN UKRAINE IN THE 20th-21st CENTURIES

Abstract

Changes in regional atmospheric circulation can reflect or cause climate change over several decades and centuries. These changes are linked to both the anthropogenic factor and the cyclical fluctuations of the atmospheric circulation centers in the North Atlantic, which are distinctively manifested in different parts of the European continent. The study aims to identify changes in the atmospheric circulation types in the years 1881-2017 at different time spans in Western Ukraine, where the manifestation of regional atmospheric circulation is like the circulating patterns over Central Europe. For statistical analysis of regional circulation changes, a calendar of types of atmospheric circulation according to the Niedzwiedz T. classification, which identified 21 types of atmospheric circulation, was applied. The peculiarities are detected at the three-time spans (1881-1940, 1940-1970, 1970-2017) and compared to the course of air temperatures and precipitation in the seasonal and annual context. Between 1881 and 2017, there was no clear trend in changes in anticyclonic or cyclonic types, although anticyclonic types are predominant in the year (over 75 % of all the years). At shorter intervals, changes in the ratio of anticyclonic and anticyclonic types correspond to some long-term changes in air temperatures and precipitation amounts (periods of 1881-1940, 1970-2017). Some periods with several years of deviation, such as the years 1940-1970 and 1971-2017, are consistent with certain types of fluctuations in the North Atlantic Oscillation. The most evidenced is the increase in anticyclonic types of atmospheric circulation at the turn of the XX-XXI centuries corresponding to warming. More features in the temporal distribution of types of atmospheric circulation are observed in the seasonal context. In April – November, in 78 % of annual cases, the prevalence of anticyclonic weather was detected, but the predominance is much smaller (up to 16 %) than in terms of years. The anticyclonic type of wedge or high-pressure ridge (Ka) and the cyclonic type of the low-pressure trough (Bc) are invariably frequent in April – November. However, since the 1970s, an increase in anticyclonic types of the western sector (SWa, Wa, NWa) has been observed. In December – March, the number of anticyclonic types from the western sector has also increased. Instead, a decrease in the number of days typical for the region cyclonic situations from the west and northwest has been detected. In terms of months, since the 1970s, the biggest changes were observed in December and January. In December, the number of anticyclonic types increased, and in January the number of days with the western cyclonic type decreased. The multidecadal course of air temperatures and precipitation is associated with the changes in the ratio between the cyclonic and anticyclonic circulation types and NAO phases in three periods between 1881-2017. The changes and the peculiarities detected imply that the types of atmospheric circulation are appropriate to detect decadal climate changes in terms of seasons and months.