THE NATIONAL SEVERE STORMS LABORATORY MESOCYCLONE DETECTION ALGORITHMFOR THE WSR-88D

The National Severe Storms Laboratory (NSSL) has developed a mesocyclo ne detection algorithm (NSSL MDA) for the Weather Surveillance Radar-1 988 Doppler (WSR-88D) system designed to automatically detect and diag nose the Doppler radar radial velocity patterns associated with storm- scale (1-10-km diameter) vortices in thunderstorms. The NSSL MDA is an enhancement to the current WSR-88D Build 9.0 Mesocyclone Algorithm (8 8D B9MA). The recent abundance of WSR-88D observations indicates that a variety of storm-scale vortices are associated with severe weather a nd tornadoes, and not just those vortices meeting previously establish ed criteria for mesocyclones observed during early Doppler radar studi es in the 1970s and 1980s in the Great Plains region of the United Sta tes. The NSSL MDA's automated vortex detection techniques differ from the 88D B9MA, such that instead of immediately thresholding one-dimens ional shear segments for strengths comparable to predefined mesocyclon e parameters, the initial strength thresholds are set much lower, and classification and diagnosis are performed on the properties of the fo ur-dimensional detections. The NSSL MDA also includes multiple range d ependent strength thresholds, a more robust two-dimensional feature id entifier, an improved three-dimensional vertical association technique , and the addition of time association and trends of vortex attributes . The goal is to detect a much broader spectrum of storm-scale vortice s (so that few vortices are missed), and then diagnose them to determi ne their significance. The NSSL MDA is shown to perform better than th e 88D B9MA at detecting storm-scale vortices and diagnosing significan t vortices. Operational implications of the NSSL MDA are also presente d. In light of the new WSR-88D observations of storm-scale vortices an d their association with severe weather and tornadoes, it is clear tha t the operational paradigms of automated vortex detection require chan ges.