Evaluation of the Vortex Detection and Characterization (VDAC) technique using multiple-Doppler observations of tornadoes and low-level mesocyclones

The Vortex Detection and Characterization (VDAC) technique (Potvin et al. 2009) is designed to identify intense sub-storm scale vortices in multiple-Doppler radar data and retrieve their size, strength and translational velocity. The technique consists of fitting radial wind data from two or more radars to a simple analytical model of a vortex and its near-environment. The model combines a uniform flow, linear shear flow, linear divergence flow (all of which comprise a broadscale flow), and modified combined Rankine vortex. The vortex and its environment are allowed to translate. A cost-function accounting for the discrepancy between the model and observed radial winds is evaluated over space and time so that observations can be used at the actual times and locations they were acquired. The parameters in the low-order model are determined by minimizing this cost function.

The technique has been extensively tested and modified using dual-Doppler observations of tornadoes and other convective vortices. The technique exhibits skill in detecting these vortices and estimating their size and strength. The latest results will be presented, including tests with Collaborative Adaptive Sensing of the Atmosphere (CASA) radar observations of the 14 May 2009 Anadarko, OK tornado, as well as tests with single-mobile-Doppler observations of larger (> 1 km diameter) vortices.