Mesocyclones in Romania – characteristics and environments

The last three years had a record of unusual severe weather events in Romania: flash floods, hail, intense cloud to ground strokes, tornadic and severe straight-line wind damage. As an example, during 2005, 13 tornadic events were reported across the country and many of them were documented. The majority of these occurred in the southeastern part of Romania (see Figure). The damage did not reach nor exceed the historical F3+ Facaeni tornado in 2002, and there were no victims, but the societal impact was very important due to little previous experience among the population with respect to these unusual events in the climatology of Romania. Another example is that at least 14 severe flash-flood cases were recorded in the last three years, with at least 20 deaths and very significant damages. Also, severe hail cases were reported frequently in the last years. This paper presents the mesoscale conditions that sustained the development of the convective storms responsible for these events, of which many were supercells. The use of the SIMIN Romanian radar network, consisting of five S-band Doppler radars (WSR-98D type), enabled the Romanian forecasters to easily identify presence of rotation and thus to discriminate and focus on the most severe cases. The mesocyclone's life cycle was studied in order to compare the Romanian supercell characteristics with those from other countries, mainly with those from US, and to define specific adaptable parameters for radar algorithms. In this paper we present the first conclusions about the specific environment that supports mesocyclone development in Romania and also the interaction with local circulations and orography. Among the conclusions of this study, we have found that the southeastern region of Romania brings together the main ingredients for mesocyclonic events in a more frequent manner than other parts of the country. Numerical model output, sounding and surface data, SAFIR lightning data, S-band and C-band Doppler radar, and satellite data were used to identify the sources of these ingredients. The main mesoscale patterns that produced mesocyclones in southeastern Romania are also compared with those identified in other regions of the country.