Real-time wind synthesis from Doppler radar observations during the mesoscale alpine programme

A real-time and automated multiple-Doppler analysis method for ground-based radar data, with an emphasis on observations conducted over complex terrai n, is presented. It is the result of a joint effort of the radar groups of Centre National de Recherches Meteorologiques and Laboratoire d'Aerologie w ith a view to converging toward a common optimized procedure to retrieve ma ss-conserved three-dimensional wind fields in the presence of complex topog raphy. The multiple-Doppler synthesis and continuity adjustment technique i nitially proposed for airborne Doppler radar data, then extended to ground- based Doppler radars and nonflat orography, is combined with a variational approach aimed at improving the vertical velocity calculation over mountain ous regions. This procedure was successfully applied in real time during th e Mesoscale Alpine Programme Special Observing Period. The real-time proces sing and display of Doppler radar data were intended to assist nowcast and aircraft missions, and involved efforts of the United Sates, France, and Sw itzerland.