Changes in the frequency and intensity of atmospheric severe convective events, including heavy rainfall, thunderstorm, hailstorm, squall, and tornado, in

Severe convective storms that produce tornadoes and straight-line winds usually develop under particular environmental conditions and have specific signatures on the cloud tops associated with intense updrafts. In this study, we performed a comparative analysis of satellite-derived characteristics, with a focus on cloud-top properties, and ERA5-based environmental parameters of convective storms in forested regions of the western part of Northern Eurasia in 2006–2021. The analyzed sample includes 128 different convective storms that produced 138 tornadoes and 143 linear windstorms. We found most tornadoes and linear windstorms are generated by quasi-linear convective storms or supercells. Such supercells form under lower convective instability and precipitable water content compared to those for other types of storms. We found a significant negative correlation of minimum temperature on the storm cloud top with instability parameters. In turn, the longevity of convective storms significantly correlates with wind shear and storm-relative helicity. About half of the tornadoes and 2/3 of linear windstorms are associated with the presence of cloud-top signatures, such as overshooting tops, cold-ring or cold U/V features. The events associated with such signatures are formed under high values of instability parameters. Our results can be used for further analysis of peculiarities of tornado and linear windstorm formation and to enhance the predictability of such severe events, especially in regions with a lack of weather radar coverage.

The effect of Moscow megapolis on precipitation of different intensity under contrasting physical–synoptic conditions was estimated. The analysis of long-term standard observations at weather stations in the Moscow Region and the data of high-resolution reanalysis ERA5 over 1988–2020 were used to demonstrate that the effect of the city on heavy precipitation is largest in the cases with higher static instability of the atmosphere, combined with a weak large-scale flow, high moisture content of the atmosphere, and the absence of pronounced frontal zones in the region. On the average over the study period, the excess of the total seasonal precipitation in Moscow relative to the background values over the Moscow region is 5.3%. It was found that the effect of the city on precipitation of various intensity is different: the precipitation of low and medium intensity was less in the city (statistically insignificant), while the heaviest precipitation (above 95 percentile) increased over the city by 11.6% above the background value.

Hazardous convective weather events (HCWE), such as heavy rainfall, large hail, squalls and tornadoes, are one of the substantial sources of natural emergencies in Russia. The territory of the Central Federal District (CFD) is characterized by the highest population density in Russia. On the one hand, this leads to increased risks associated with HCWE, but on the other hand, it provides the possibilities for collecting the most detailed information on them (including the events missed by the observation network and reported based on damage assessment). In this study, we consider the structure and information content of the GIS database of HCWE for the territory of the CFD. The main advantage of the developed database comparing with existing analogues is its structure, which includes information on both the events themselves and their consequences, and the conditions of their occurrence. This includes, in particular, the characteristics of meso-scale convective systems (convective storms) based on the images from meteorological satellites and diagnostic variables characterizing the atmospheric environments according to the data from ERA-5 and CFS reanalysis systems. Also, the developed database is associated with previously published databases on tornadoes in Northern Eurasia and large-scale windthrow events in European Russia. At present, we compiled the data on more than 2,000 cases of HCWE in the CFD for the period 2001–2020, most of which were reported based on damage assessment. The open-source PostgreSQL DBMS is used to manage and edit the database. Open access to the database on the Internet is implemented through an online web map service available at http://convective-storms.psu.ru/.

This paper considers physical and synoptic mechanisms of an extreme rainfall on June 30, 2017 in the central part of European Russia, which was the maximum of daily precipitation sum in Moscow (65 mm) since 1970. Based on meteorological observations, radar data, and ERA5 reanalysis data, we show that the rainfall was associated with three mesoscale convective systems (MCSs) that formed in the warm sector of a cyclone in a strip of anomalously high moisture content in the considered region, which developed further due to advection and evaporation. A numerical simulation with mesoscale model COSMO shows a significant contribution to the precipitation intensity of evaporation from the Earth’s surface: a 10-times decrease in soil the moisture in the initial conditions leads to a 3-times decrease in the amount of precipitation and its intensity. Additionally, we consider urban-induced effects on this rainfall event by switching on and off urban parametrization TERRA_URB. The application of the urban surface parametrization has not changed the average amount of precipitation in Moscow region. It causes, however, a redistribution of precipitation sums within it.

Large cities are especially vulnerable to heavy precipitation events, which can lead to significant economic losses. This topic is relevant both due to the observed increase in the frequency of dangerous weather phenomena (including extreme precipitation [Ye et al., 2017; Chernokulsky et al., 2019]) in midlatitudes in general, and due to the previously noted facts of intensification of deep atmospheric convection and associated rainfall over urban areas [Han et al., 2014; Liu, Niyogi, 2019]. Yet, despite the numerous studies, the magnitude of urban effects on intense precipitation and their physical drivers are not fully understood.In this study, we investigate urban effects on intensity and frequency of summer precipitation events exemplified by Moscow megacity, Russia. Previously, increase of mean summer precipitation amount by 10% over Moscow was revealed according to COSMO-CLM simulations for multiyear period [Varentsov et al., 2018]. Here we use long-term (1988-2021) observations at urban and rural weather stations. Statistical analysis is performed separately for categories of precipitation intensity. Moreover, using ERA5 reanalysis data [Hersbach et al, 2020] we estimated atmospheric convective instability and frontal parameters in order to classify precipitation cases according to the synoptic situation. This will help us to understand the physical mechanisms of precipitation intensification better. The assumption is that megacity influence on frontal systems is less noticeable than its influence on local convective clouds and convective systems in the low pressure gradient filed. Also we collected a catalogue of extreme precipitation cases in Moscow region exceeding 0.999 quantile values and studied most interesting cases among them.Eventually, we obtained qualitative and quantitative estimates of the Moscow impact on the characteristics of intense precipitation for various synoptic conditions.Acknowledgements:The study was supported by the Russian Ministry of Science and Higher Education (grant of President of Russian Federation for young PhD scientists No. МК-5988.2021.1.5, agreement No. 2020-220-08-5835).References:Chernokulsky, A., Kozlov, F., Zolina, O., Bulygina, O., Mokhov, I. I., & Semenov, V. A. (2019). Observed changes in convective and stratiform precipitation in Northern Eurasia over the last five decades. Environmental Research Letters, 14(4), 045001.Han, J. Y., Baik, J. J., & Lee, H. (2014). Urban impacts on precipitation. Asia-Pacific Journal of Atmospheric Sciences, 50(1), 17-30.Hersbach, H. et al. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146(730), 1999-2049.Liu, J., & Niyogi, D. (2019). Meta-analysis of urbanization impact on rainfall modification. Scientific reports, 9(1), 1-14.Varentsov M., Wouters H., Platonov V., & Konstantinov P. (2018). Megacity-Induced Mesoclimatic Effects in the Lower Atmosphere: A Modeling Study for Multiple Summers over Moscow, Russia. Atmosphere, 9(2), 50.Ye, H., Fetzer, E. J., Wong, S., & Lambrigtsen, B. H. (2017). Rapid decadal convective precipitation increase over Eurasia during the last three decades of the 20th century. Science advances, 3(1), e1600944.