Using Gap-Filling Radars in Mountainous Regions to Complement a National Radar Network: Improvements in Multiple-Doppler Wind Syntheses

The existing French Application Radar à la Météorologie Infrasynoptique (ARAMIS) operational radar network covers a vast majority of the country of France, yet like many national networks, gaps in coverage are present in regions of mountainous and high terrain. Many of these areas are prone to extreme, orography-induced precipitation events, and therefore expansion of national radar networks into these regions is very important. The addition of small X-band radars, strategically placed to supplement the ARAMIS network, is discussed with emphasis on the ability to expand three-dimensional wind and reflectivity field retrieval. This expanded coverage is particularly important for terrain-related precipitation in the southern Alps. Successful dual- and multiple-Doppler syntheses were conducted using the existing ARAMIS network and two new radars located in mountainous terrain, installed within the context of the Risques Hydrométéorologiques en Territoires de Montagnes et Mediterranéens (RHYTMME) program. To illustrate the coverage and advantage that gap-filling radars can add to an existing national radar network, two case studies are presented, with multiple-Doppler syntheses revealing that terrain relief and low-level atmospheric stability influence the resulting wind field. In addition to the added coverage, the RHYTMME gap-filling radars improve wind-flow retrieval and the accuracy of reflectivity measurements over extreme southeast France and into the Mediterranean Sea.