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.
The statistical estimation of changes of the cloud cover characteristics was made by the data of the meteorological observations over Ukraine during 1961-2017. Such characteristics as the quantity of total and lower cloudiness, the frequency of clear and overcast sky, the frequency of main cloud forms were analyzed. Monthly, seasonal and annual observational data were used for computation of the trends, the sliding of thirty years (1961-1990, 1971-2000, 1981-2010, 2001-2017) and the fluctuations between successive decades in regions (west, north, central, east and south). The clear sky frequency for total cloudiness was decreasing with different intensity in all regions. This decreasing was forcing all time on west and east and against the gradually stopping on central and south and forcing in third sliding of thirty years and stopping in fourth on north. The clear sky frequency for lower cloudiness was more complex and indeterminate. The overcast sky frequency for total and lower cloudiness was decreasing all time in all regions with different intensity in space and time. The half-clear sky frequency for total and lower cloudiness was forcing all time in all regions with different intensity in space and time. The quasi-periodicity changes of the cloud cover characteristics for total and lower cloudiness confirm the fluctuations of the changes between the successive decades. These changes agree with the corresponding changes of air pressure on level sea. The decreasing of the frequency of main cloud forms was 55 %, the increasing was 45 %. The increasing of the frequency Cb, Ac, Cc and Ci was all time over all territory
The investigations of connection between the different meteorological processes, for example, the circulation indexes with the quantity of the total and lower cloudiness during 1961-2018 over Ukraine were made. The spatial distributions of the total and lower cloudiness were received for 73 years (1946-2018) at first. The quantity of cloudiness is diminished from west to east and with north to south. The declinations of the annual data of total and lower cloudiness from the historical (1961-1990) and the present (1981-2010) norms were calculated. The great variations were characterized for the lower cloudiness. The linear trends showed that the diminish of the lower cloudiness was on 90 % of the all territory, this changes were important on 70 % of the territory. The trends of the monthly variations were showed on the diminish of the lower cloudiness in during all year only on north, on other territory was the increasing in the separate months, frequently in January and September. The variations of the total cloudiness were insignificant, the increase or decrease were nearly in equal parts. North Atlantic Oscillation (NAO), Arctic Oscillation (AO), East-Atlantic Oscillation (EA), Scandinavian Oscillation (SCAND), Greenlandic Oscillation (GBI) and South Oscillation (El-Niño) were used for the investigation of relationship between the circulation indexes and cloud cover. It was shown that different circulation indexes have influence on climate of Northern Hemisphere and on Ukraine too. The relation with each other and their variations in period of global warming were showed. The quantity estimation of the total and lower cloudiness variations was made by the frequencies of clear, semi clear and overcast sky in the successive decades and by the relative variations of frequencies between decades (1961-1970 and 1971-1980; 1971-1980 and 1981-1990; 1981-1990 and 1991-2000; 1991-2000 and 2001-2010; 2001-2010 and 2011-2018). The parallel analyze of the variations of circulation was estimated in that time. The difference between the circulating processes during 1961-1970 and 1971-1980 contributed to a decrease in the relative frequency of the clear sky (on 5.4%) and a slight increase of the overcast sky (on 1.6%) by total cloud cover and a slight increase of the clear sky (on 0.8 %) and a decrease of the overcast sky (on 5.2%) by lower cloudiness. At the same time, the relative frequency of the semi-clear sky by lower cloudiness almost in three times increased in comparison to total cloudiness (on 10.2% and 3.8%, respectively). In the third decade of 1981-1990 the relative frequency of clear sky by lower cloudiness increased on 5.1% and did not change by total cloudiness (0%). During this decade the relative frequency of overcast sky decreased the most in the whole period under study: by total cloudiness on 6.4% and by lower cloudiness on 13.3%. At the same time, the relative frequency of semi-clear sky had largest increasing: on 22.4% for total cloudiness and 13% for lower cloudiness. Then, during 1991-2000, the frequency of clear sky decreased significantly both for total cloudiness (on 6.5%) and for lower cloudiness (on 3.1%). The frequency of overcast sky decreased also, but less significantly (on 1.3% and 2.3%, respectively), thereby the number of clouds of the middle and upper levels increased. From 2001 to 2010, the frequency of clear sky by total cloudiness and by lower cloudiness continued to decrease (on 5.3 and 3.2%, respectively), but the frequency of overcast sky increased (on 0.9 and 1.7%, respectively), thereby the number of clouds for all levels increased. During 2011-2018 the frequency of clear sky by total cloudiness increased (on 0.9%) and by lower cloudiness did not change. The frequency of overcast sky decreased on 3.6% (by total cloudiness) and on 0.7% (by lower cloudiness). The variations of the relative frequencies of the different state sky between the successive decades are agreed with the changes of the circulation indexes.
The distribution of drop effective radius on cloud upper level was defined and analyzed for main cloud forms over Ukraine during two years (2014-2015) using satellite observations. The effective radius values of isolated cumulonimbus on cloud top and its dependency on optical thickness was estimated in measurements during April-September 2014 over Kyiv area. For cumulonimbus clouds with precipitation the dependence of effective radius on the type, precipitation intensity and liquid water path was defined. The distribution of drop effective radius on cloud top in the strength frontal systems with heavy showers area over all territory of Ukraine was defined for two systems and it dependence on the cloud height and the precipitation type, their intensity and the liquid water path was estimated. For all types of clouds the size of effective radius of the droplets was 6 μm. In St and As cloud system droplets with this size of effective radius were observed in 100%, in Sc and As cloud system – 91-92%. The values of effective radius in Ns and Cb cloud system was close to 6 μm (71 and 89% respectively). Larger droplets (8 μm) in Ns were observed in 29% and in Cb in 9%. However, in Cb, accompanied by rainfalls and powerful thunderstorms, the values of effective radius were 10-15 μm (1.5%) and 25-45 μm (0.5%). In 75% of moderate precipitation cases were formed by drops with an effective radius of 6 μm and in 25% with an effective radius of 8 μm. For the heavy precipitated clouds, the drops with an effective radius of 8 μm (62%) had the highest frequency, in 33% the effective radius of 6 μm were observed. The larger droplets (≥10 μm) had a small frequency (5%). The drop effective radius for cases of heavy rainfalls was 8 μm in 75%, in 25% larger droplets were observed (10, 15 and 30 μm). More intense rainfall was accompanied by greater values of cloud water content and, accordingly, greater effective radius values. The cases with large values of microphysical parameters and precipitation were observed as streaks in frontal cloud systems.
Information of water content of frontal clouds produced strong precipitation has important practical applications. Such type of data is necessary for the estimation of electromagnetic waves attenuation, the calculation of aircrafts' icing possibility, the estimation of necessity of an increase of precipitation or clouds dissipation (for the cases when thick cloudiness is observed over airports and astronomical observatories) by using of weather modification technologies and so on. This information can be obtained by aircrafts' sounding, but not for the whole area of cloud frontal system and not for the all-time of their existence. Nowadays the satellites can provide measurements of cloud systems parameters continuously and on a large scale. The main objective of this research is to define the water content, water balance and liquid water losses for different precipitation intensity levels (especially heavy) of frontal cloud systems in cold period. The analysis of water contents and water balances for the three synoptic situations: 08-13 January, 30 January – 06 February, 27-31 March 2015 have been done. Initial data included: the hourly water content estimated by satellite measurements (P), the precipitation amount (Q) and duration (T) observed on 40 meteorological stations and the wind speed on the cloud level (V) derived from air soundings. Other characteristics as precipitation generation ability (K), the water balance (Q*=0.36×P×V×T) and water balance recovery (Q/Q*) were defined. Some specific values of the typical water content for different precipitation intensity levels were defined. The dependence K on Q is manifested in the form of two straight-line dependencies for each synoptic situation, which is probably due to the peculiarities of the formation of the water content of clouds. For clouds with crystal precipitation the maximal value of water balance was 25 tons and for clouds with liquid water precipitation – 80 tons. The data of water balance recovery during process of precipitation are interesting. For this purpose, the amount of water transported by the clouds over the meteorological stations was calculated during the time of precipitation. The ratio of Q to the value of Q* characterizes the process of water balance recovery. It was shown, that the distribution of Q/Q*was the same for all synoptic situations. For most cases (75-80%) water loses due to precipitation were no more than 0.4 Q*. The all water balance recovery (Q/Q* equals 1.0…1.5) was in 1 % cases.
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