DYNAMICS OF RAINFALL INTENSITY AND MESOSTRUCTURAL CHARACTERISTICS OF THEIR FIELDS IN THE WARM PERIOD OF THE YEAR IN THE PLAIN PART OF UKRAINE

Abstract

The research deals with the structure of temporal changes in rainfall intensity and the spatial distribution of magnitude within separate processes of fallout of dangerous and heavy rainfalls in the warm season. The analysis based on the data from the Ukrainian hydrometeorological observation network (2005-2017) and the data obtained during a special scientific experiment (Kyiv, Bagrynova Mt., warm period 1969). It has been determined 97 cases of such rainfalls, the characteristics of their spatial distribution, seasonal and daily variations. For individual processes, on the basis of pluviometric measurements there were determined the maximum rainfall intensities, the time of their occurrence, the presence and the number of waves (periods) of rainfall amplification and their temporal and spatial parameters. The mass of rainwater per unit area and the volumetric intensity were calculated for moments of maximum intensity or amplification waves. The analysis of spatial and temporal fluctuations of intensity values within a separate process allowed to distinguish three types of rainfall during the warm period of the year: heavy precipitations (maximum intensities greater than 1 mm/min., such intensities more often observed at the beginning of the process; it notes the presence of one/two waves of amplification of rainfall with different amplitudes), slight precipitations (maximum intensities are approximately equal to 0.1 mm/min, several (3-5) waves of amplification of rainfall with small but equal amplitudes), and a “mix” of heavy and slight precipitations during the development of frontal stratus with so-called “flooded” convection (maximum intensities less than 1 mm / min; there are several waves of amplification of different amplitude). Conditions for the formation of heavy precipitations of the last type are the combination of mechanisms of thermal and dynamic convection, which is manifested in the enhancement of vertical lifting of air masses due to the blocking processes. It was made a comparison of the intensity and nature of precipitation in the current climatic period and in previous periods. It was found that the values of the maximum intensity for the same type of precipitation during the different observation periods practically coincide. Obviously, there is a zone of “upper limit” of the intensity of the processes of precipitation and moisture storage of clouds, which ensures the constant intensity of rainfall over time. There is some increase in number and length of waves of rainfall amplification, as well as an increase in the frequency of rainfalls with “flooded” convection. The research shows the recurrence of rainfall intensity for certain types within certain gradations of their values. On this basis an integral providing curve is created, which makes it possible to estimate the probability or recurrence of given precipitation intensity values at different levels of providing.