Diagnosis and modelling of two destructive derecho events in European Russia in the summer of 2010

Abstract In the summer of 2010, European Russia experienced an unprecedented high air temperature, catastrophic wildfires, heavy air pollution, but also several severe convective storms. Two of them occurring on June 27 and July 29 had a particularly high intensity and resulted in unprecedented forest damage. In this study, we estimate storm-related forest damage using Landsat images and analyse the synoptic-scale and mesoscale peculiarities of these storms formation and evolution using satellite and reanalyses data, surface observations, and mesoscale numerical simulation. The total area of stand-replacing windthrow caused by these two storms amounts to 1250 km2. We found for both events that dark-coniferous and pine forests were more impacted than deciduous and re-grown forests. Damage track length exceeds 500 km for one storm and 600 km for another; therefore, we classify them as derecho events, which are documented for the first time in Russia. Formation of both derecho-producing mesoscale convective systems (MCSs) was triggered by fast-moving waves formed on the polar front under conditions of substantial temperature gradients on a western flank of long-lived blocking anticyclones in their termination dates. Backward trajectories analysis shows that advection from the Caspian Sea was one of the sources of high atmospheric water content during the MCSs formation. Both MCSs developed within environments of moderate to strong convective instability and extremely high wind shear due to strong midlevel jet stream. We performed convection-permitting simulation of storms using the WRF model started with the initial data of CFS and ERA5 reanalysis. For the event of June 27, the simulations with both initial conditions underestimate the maximum wind gusts since the model reproduces only a squall line without dominating derecho-producing storm. For the event of July 29, the ERA5 based simulation successfully reproduced the main features of the storm life cycle, while the CFS-based simulation substantially underestimated the wind gusts and the storm-affected area. Our results highlight the importance of the atmospheric blocking influence on the convective severe storms formation and development, which deserves further research.