A four year (2007-2010) analysis of long-lasting deep convective systems in the Mediterranean basin

Long-lasting, deep convective systems (DCS) occurring in the Mediterranean basin have been investigated for the 2007-2010 years using geostationary Meteosat Second Generation (MSG) satellite data, supported by the European Centre for Medium-Range Weather Forecasts (ECMWF) analyses and severe weather reports recorded by the European Severe Weather Database (ESWD). The spatial and seasonal variability of DCS occurrence have been investigated, as well as the most favourable synoptic precursors for their initiation. The analysis has shown the existence of some preferential areas of DCS genesis, mainly located in the western (i.e., around Balearic Islands) and central (i.e., Ionic and Tyrrhenian seas) Mediterranean, where these systems develop and grow preferentially in fall (i.e., September and October). The analysis of a selected set of Synoptic Precursors (SPs) has shown how the totality of the identified cases has occurred downstream a mid-tropospheric (500 hPa) disturbance (trough or cut-off) within a southerly flow, with high values of ?e (at 850 hPa) and precipitable water. Moreover, the approaching of an upper level tropopause dynamical anomaly coupled with a local maximum of upper and low level horizontal wind speed, seems to play a very important role in triggering convection. Finally, a careful crosscheck of the detected cases with the ESWD reports has allowed to investigate the severity of these systems, as they often affect population and produce significant damages. This study has to be considered a necessary step towards the development of a larger climatologic database of long-lasting, deep convective events occurring in the Mediterranean sea, as well as the definition of a specific conceptual model based on synoptic precursors, having the long-term issue of setting up an objective procedure to support regional meteorological services in early decisions and accurate nowcasting.