DOPPLER RADAR OBSERVATIONS OF SUBSTORM-SCALE VORTICES IN A SUPERCELL

Counterrotating 500-m-scale vortices in the boundary layer are documen ted in the right-moving member of a splitting supercell thunderstorm i n northeastern Oklahoma on 17 May 1995 during the Verification of the Origins of Rotation in Tornadoes Experiment. A description is given of these vortices based upon data collected at close range by a mobile, 3-mm wavelength (95 GHz), pulsed Doppler radar. The vortices are relat ed to a storm-scale, pseudo-dual-Doppler analysis of airborne data col lected by the Electra Doppler radar (ELDORA) using the fore-aft scanni ng technique and to a boresighted video of the cloud features with whi ch the vortices were associated. The behavior of the storm is also doc umented from an analysis of WSR-88D Doppler radar data. The counterrot ating vortices, which were associated with nearly mirror image hook ec hoes in reflectivity, were separated by 1 km. The cyclonic member was associated with a cyclonically swirling cloud base. The vortices were located along the edge of a rear-flank downdraft gust front, southeast of a kink in the gust front boundary, a location previously found to be a secondary region for tornado formation. The kink was coincident w ith a notch in the radar echo reflectivity. A gust front located north of the kink, along the edge of the forward-flank downdraft, was chara cterized mainly by convergence and density current-like flow, while th e rear-flank downdraft boundary was characterized mainly by cyclonic v orticity. Previously documented vortices along gust fronts have had th e same sense of rotation as the others in the group and are thought to have been associated with shearing instabilities. The symmetry of the two vortices suggests that they may have been formed through the tilt ing of ambient horizontal vorticity. Although the vortices did not dev elop into tornadoes, it is speculated that similar vortices could be t he seeds from which some tornadoes form.