Utilizing the Divergent Component of Doppler Velocity Shear to Examine Tornadic Supercells

The ability to identify and track potentially tornadic supercells in real time and/or immediately following a severe weather event is one of the critical services provided by the Multi-Radar Multi-Sensor (MRMS) suite of algorithms. Traditionally, this has been accomplished through the generation of rotation tracks, a time accumulation of the radar-derived azimuthal (rotational) component of shear (AzShear). The same concept can be applied to calculate the other derivative component of the velocity field, radial (divergent) shear (DivShear).

Like AzShear, DivShear is computed using the linear, least-squares derivative (LLSD) estimate of gradients in the Doppler velocity field. It has only sparingly been utilized in severe weather applications, but recent work has greatly improved confidence in its ability to detect a variety of meteorological features, including strong circulations, which theoretically have distinct convergence/divergence characteristics. In this study, single-radar DivShear fields are calculated for Doppler velocity scans of a collection of tornadic supercells. Often, extreme divergence/convergence couplets are observed at or very near the tornado. Characteristics of these signatures, such as prevalence across cases, vertical continuity, and evolution over time, are investigated. In addition, DivShear is accumulated over time to generate divergence and convergence tracks which can track and trend the intensity of the features. Finally, DivShear and AzShear are compared at correlated times to investigate a possible relationship between the rotational and divergent components of the flow.