Processes leading to heavy precipitation associated with two Mediterranean cyclones observed during the HyMeX SOP1
Résumé
Two deep cyclones occurred in the Mediterranean between 25–31 October 2012, during the first Special Observation Period (SOP1) of the Hydrological cycle in Mediterranean Experiment (HyMeX). Both cyclones were associated with extreme rainfall covering a large part of the western Mediterranean Sea, where 24-h accumulated precipitation measurements exceeded 150 mm. We combine complementary observations from airborne radar and lidar systems, ZEUS lightning detection network and meteorological surface stations along with satellite diagnostics on deep convection, for a detailed microphysics and (thermo-)dynamical analysis of the two extreme rainfall cases. In addition, we use operational analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) for analyzing the synoptic conditions and diagnosing strongly ascending air masses in the vicinity of the cyclones, so-called warm conveyor belts (WCBs). The analysis revealed the different physical characteristics of the two cyclones responsible for the extreme rainfalls. Both cyclones were associated with a WCB and a comma cloud, but deep convection, intense lightning and very cold cloud tops occurred only for the first case while the second cyclone was mostly associated with stratiform rainfall, a strong WCB, and only few embedded cells of deep convection.