Evaluation of a new multiple-Doppler tornado detection and characterization technique using real radar observations

A new multiple-Doppler radar analysis technique is presented for the objective detection and characterization of tornado-like vortices. 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 (representing the tornado). 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. Doing so avoids the need for time interpolation, moving reference frames or other ad-hoc procedures. The parameters in the low-order model are determined by minimizing this cost function.

The technique is first tested using analytically-simulated observations whose wind field and error characteristics are systematically varied. An ARPS (Advanced Regional Prediction System) high-resolution numerical simulation of a supercell and associated tornado is then used to emulate an observation data set. Finally, the technique is applied to real dual-Doppler observations of an F4 tornado which occurred in central Oklahoma on 8 May 2003. The technique shows skill in retrieving the tornado path and radar-grid-scale features of the horizontal wind field in and near the tornado. The best results are obtained using a two-step procedure in which the broadscale flow is retrieved first.