Case study of the 20 May 2008 tornadic storm in Hungary — Remote sensing features and NWP simulation

Abstract This paper discusses a case study of a tornadic thunderstorm event that occurred over Hungary on 20 May 2008. The paper presents both remote sensing measurements and numerical simulations of the storm system, and the synoptic situation is also described. The pre-convective environment was analyzed using satellite retrieved instability indices and total precipitable water content. The evolution of the convective system was described using 5-minute satellite imagery, 15-minute radar data, and continuous lightning observations. A high resolution MODIS image was also examined. The analysis of cloud top characteristics using satellite imagery revealed numerous cloud top features typically associated with severe storms: cold-ring and cold-U shapes in the infrared images, as well as longer lasting series of strong overshooting tops, gravity waves, above-anvil plumes, and radial cirrus. The cloud top microphysical properties indicated severe updraft — the imagery showed many small ice crystals within the cloud tops. The analysis of retrieved effective radius and brightness temperature profiles also pointed to a strong updraft. Some of the radar images displayed bow echo features often associated with severe storms. Some radar cross-sections showed WER echoes. The total lightning rate was extremely high. The event was simulated using the MM5 non-hydrostatic numeric model, with two goals. First, we wanted to test the model's ability to predict the event. Second, we hoped to improve our knowledge of dynamic processes related to mesocyclogenesis and increased vorticity within this type of thunderstorms. An analysis of the vorticity equation terms indicate that at mid-tropospheric levels vorticity was generated mainly by the tilting of streamwise horizontal vorticity in the thunderstorm updraft. The ambient horizontal vorticity substantially increased near intense thunderstorm cells. At low levels, rotation intensified as a result of vertical acceleration and the stretching of the air column. Overall, the results suggest that in similar conditions (moderate values of CAPE and Storm-Relative Environmental Helicity of the ambient air), explicit numerical forecasts of thunderstorms can warn about the likely development of mesocyclones and other severe weather features such as rear inflow jets.