The thesis’ task is to determine the impact of different synoptic patterns on the occurrence of anomalous phenomena in different regions of Ukraine, taking into account a season and features of regional orographic conditions.
In recent decades, much attention has been paid to climate change due to it affects all aspects of human life. On the other hand, against the background of rising temperature and increasing aridity of Ukraine's climate, it is important to study the features of synoptic patterns causing certain extreme weather events, such as high or low temperatures, heavy rainfall, or, conversely, long dry periods, etc. Usually, such studies are done for separate parts of Ukraine, for example, its southern regions, but the dependence of particular anomalous weather phenomena on the type of synoptic pattern was not comprehensively analyzed, and therefore the thesis is relevant and innovative.
Hess-Brezovsky's concept of Großwetterlage (GWL), although was initially developed for Central Europe, has been adapted for Ukraine – certain synoptic conditions directly over Ukraine were defined for each type of GWL.
The climatic indices were calculated by using the daily mean, minimum, maximum temperatures, the daily precipitation – frost days, ice days, summer days, tropical nights, wet days, heavy precipitation days, very heavy precipitation days, dry days, cold dry days, cold wet days, warm dry days, and warm wet days. Also, since synoptic conditions of precipitation differ depending on the season, the precipitation indices were calculated separately for summer, winter and the whole year.
The temperature and precipitation data from the ERA-Interim re-analysis were used in order to calculate climatic indices for the period 01.01.1979–31.12.2001, which is 8401 days (23 years). The step of the horizontal grid in the re-analysis is 0.75° × 0.75°, and the grid covers the territory of Ukraine (21.75°–40.50° E, 44, 25°–52.50° N).
A methodology for comprehensive definition of synoptic pattern impact on anomalous weather phenomena for Ukraine was developed. The methodology uses two approaches. The first approach determined the number of days for each weather phenomenon with each GWL type registered for this phenomenon. The GWL types were ranked for each grid node covering the territory of Ukraine, and maps were built on which the GWL types that were most characteristic were plotted at the grid nodes. According to the second approach, maps of the most characteristic anomalous weather phenomena were created for each synoptic pattern determined by each GWL type. As in the previous approach, weather phenomena were ranked.
The analysis of the frequency for the different types of synoptic patterns in Ukraine revealed the five most frequent GWL types, which are observed in 75% of cases. Seasonal variability was also studied and the types of most frequent synoptic patterns for each season were identified.
The results of the study showed that the temperature extremes of hot or cold weather are mostly formed by the same types of circulation processes in Ukraine. The explanation for the fact that temperature and precipitation anomalies are determined by some types of GWL is not only that these types are most common, but also that these types of circulating conditions can be physically explained as contributing to extreme precipitation or temperatures.
Certain regional features related to the influence of the underlying surface - the Carpathian Mountains and the Black and Azov Seas – were identified. The features in the occurrence of various anomalous weather phenomena in Ukraine under different synoptic conditions are also determined.
Our analysis showed that certain synoptic patterns can determine certain, quite original, weather conditions in Ukraine. An example is type 10, in which mostly ‘summer’ weather conditions are observed, or type 8 with predominantly ‘winter’ weather conditions, despite the fact that both these types are determined by the influence of anticyclones on weather conditions in Ukraine.
