Abstract : 2E.15
Analysis of the 12-13 November 2004 heavy rainfall event over Southern Italy

Daniele Mastrangelo, Kristian Horvath, Angelo Riccio, Giorgio Budillon, Branka IvančAn-Picek
Parthenope University of Naples, Department of Environmental Sciences

During 12-13 November 2004 heavy rainfall affected Ionian regions of Southern Italy causing local floods with relevant impacts on human activities. Rain gauges data showed a non uniform spatial distribution of precipitation intensities with values up to 250 mm in 24 hr, on 12 November, over the northernmost coastal area of Gulf of Taranto and a peak of about 200 mm in 24 hr, on 13 November, recorded over the central part of Salentine Peninsula (the southeastern tip of Italian Peninsula).

The event was investigated by means of the Penn State/NCAR Mesoscale Model (MM5). The synoptic setting on 11 November was characterized by an upper-level cut-off low traversing the area of Atlas Mountains that interacted with a pre-existing low-level thermal anomaly in the lee. During 12 and 13 November the cyclone moved north-eastward and strongly deepened. The position and perdurability of the low-pressure system gave rise to intense south-easterly flow advecting warm and moist air that contributed to generate conditional instability over the Ionian Sea basin.

As revealed by the numerical mesoscale analysis, a mesofront embedded in the cyclonic circulation moved from Southern Ionian Sea towards Southern Italy; its interaction with local orography was responsible for persistent convective activity over the first maximum event area. At the same time, low-level convergence lines, related to the mesofront passage, were deflected and intensified by the blocking effect of Calabria region orography. In subsequent hours, due to the cyclone shifting, the convergence lines elongated north-eastward in the direction of the Salentine Peninsula and Southern Adriatic constituting the lifting mechanism necessary to trigger convection producing rainfall over the area.