The Terminal Doppler Weather Radar Tornadic Vortex Signature Detection Algorithm

An algorithm for real-time detection of tornadoes, using single- Doppler radar data, is described. This algorithm searches for tornadic vortex signatures TVSs which are characterized by strong azimuthal shear in Doppler velocity fields. A TVS usually indicates that a tornado is occurring. The algorithm searches for azimuthal radial velocity differences, above a certain threshold, between adjacent gates at constant range. It then builds these pattern vectors into features for each scan in elevation, and finally determines the vertical correlation among features. When at least three features are vertically correlated and the lowest one is below a prescribed minimum-height threshold, a TVS is declared, indicating that a tornado is occurring. If the lowest feature is not below the height threshold, a potential TVS PTVS is declared, indicating that a tornado may soon occur. The TVS algorithm has been tested on five tornados that occurred in Colorado and Missouri. Each tornado had an associated TVS, which was detected by the algorithm. In all cases, either a PTVS or TVS preceded each tornado, resulting in a 4-minute average lead time. Evaluated on a scan-by-scan basis, the Probability of Detection POD is 78. No TVS false alarms and only 3PTVS false alarms occurred for these 5 cases. The algorithm was also tested on two rotating microbursts with no detections occurring.