Fine scale simulations of the MAP-IOP2a precipitating system: comparison with radar data and sensitivity to the hail category

Overview & Synopsis

During Intensive Observing Periods (IOP) of the Mesoscale Alpine Programme (MAP, see Bougeault et al. 2001) a network of three Doppler radars was operated in the Lago Maggiore Target Area (LMTA). In the afternoon and evening of Sept. 17, 1999 (MAP-IOP2a), a major squall line formed on the foothills of the southeastward facing slopes of the Lago Maggiore region and intensified during its propagation to the east as a three-dimensional con­vective cluster. This intense orogenic system with lots of lightning impacts and precipitation amounts of more than 70 mm in 6 hours, was well observed by the radars. Additional polarimetric data from radar S-POL (NCAR) revealed rich regions of grau­pel/hail mixture in convective cells where the verti­cal velocity, w 2: 4 ms-1 and the radar reflectivity, Z 2: 45 dBZ (Tabary et al., 2001).