Аннотация:The paper considers the physical and synoptic causes of extreme rainfall on June 30, 2017 in the central part of the European territory of Russia, which determined the record precipitation amount per day in Moscow (65 mm) since 1970. Based on meteorological observations, radar data and reanalysis ERA5 [Hersbach et al., 2020] we showed that rainfall was associated with three mesoscale convective systems (two squall lines [Markowski, Richardson, 2010] and one meso-beta scale convective system [Veltishchev, 1990]).
These systems arose in the warm sector of the cyclone in a strip of anomalously high moisture content for the considered region (with a maximum value of 41.5 kg / m2 exceeding the 0.995 percentile in the data of sounding over Moscow [Durre et al., 2006] for the period 1957 – 2017). An analysis of the water vapor balance components using ERA5 reanalysis showed that advection of water vapor was the main factor in the appearance of the quasilinear region of an extremely high moisture content. A smaller but very noticeable role was played by evaporation from the surface of the earth.
For a more detailed study of an extreme precipitation’s formation mechanisms the mesoscale nonhydrostatic model COSMO 5.05 [Doms et al., 2015] with 3 km grid was used. The simulation result confirmed an idea of the significant role of evaporation from the earth’s surface in precipitation intensity: a 10 times decrease in soil moisture in the initial conditions led to a three times decrease in the daily amount of precipitation in the study area.
The impact of urban environment was also investigated. Coupling a bulk urban canopy model TERRA_URB [Wouters et al., 2016] to COSMO did not cause a noticeable increase in the amount of precipitation in the Moscow region, but led to some redistribution within it: a daily precipitation amount increased on the leeward
side of the Moscow.