Multiple tornadoes in the Italian Ionian regions: Observations, sensitivity tests and mesoscale analysis of convective storm environmental parameters

Abstract

In the months of November 2012, 2014 and 2018, four tornadic events affected southern Italy (Calabria and Apulia regions). Tornado-spawning supercells hit the same regions, had similar trajectories, and were characterized by common synoptic conditions.The events are analysed through the use of multiple observational tools; large-scale and mesoscale analysis are performed, in addition to high-resolution numerical simulations and sensitivity tests with the WRF model. In particular, the effect of changes in Sea Surface Temperature on the intensity and tracking of tornadic supercells in the Mediterranean is investigated, finding that small variations of SST may cause significant changes on instability parameters, consequently on the supercell intensity.Numerical simulations show that the structure and the track of the convective cells can be correctly reproduced, as well as the triggering of convection due to interaction of the flow with the topographic features, such as the land-sea interface and orography, within a relatively small temporal delay. The mesoscale analysis also reveals, in all cases, an environment highly favourable for tornado formation, with most simulated instability parameters/indices exceeding their critical thresholds.