Preliminary analyses of Dual-Doppler observations conducted with Ronsard and Monte-Lema radars during MAP

In autumn 1999, the Special Observing Period of the Mesoscale Alpine Program (7 September –15 November 1999) took place over the Alps. One of the main objectives was to investigate the mechanism of orographically induced heavy precipitation events with special emphasis on their dynamics, microphysics and hydrological consequences. In this context, the French Ronsard research radar located near Milan was operated in coordination with the Swiss SMA operational radar at Monte-Lema and the US NCAR S-POL Doppler and Polarimetric radar to provide multi-Doppler observations over the windward slope of the Alps. Since the past studies on precipitating systems were conducted over flat terrains, the data collected during the MAP/SOP provide a first opportunity to deduce three dimensional wind fields from Doppler data over mountainous regions. The first results about radar-derived wind and precipitation fields permit to emphasize the influence of the orography-induced air circulation (slope winds) on the structure and evolution of the observed precipitating systems. Also, this work permits to definitively insure the reliability of the procedure developed by the authors for multi-Doppler analyses over complex terrain.