Characteristics of the Wind Field in Three Nontornadic Low-Level Mesocyclones Observed by the Doppler On Wheels Radars

Abstract

The three-dimensional wind fields within three nontornadic supercell thunderstorms are retrieved from dual-Doppler radar observations obtained by a pair of Doppler on Wheels (DOW) radars. The observations focus on the low-level mesocyclone regions of the storms near the time of strongest low-level rotation. All three storms display strong low-level rotation (e.g., the vertical vorticity maxima exceed 0.05 s-1 in the lowest 1000 m AGL in each storm). A principal finding is that the nontornadic mesocyclones possess many of the same signatures found in tornadic supercells, even those viewed in similarly fine resolution; e.g., rear-flank gust fronts wrapping around the circulation centers, multiple cyclonic vertical vorticity maxima along the gust front that spiral inward toward the circulation center, and arching vortex lines joining the cyclonic vorticity maxima to regions of anticyclonic vertical vorticity on the opposite side of the hook echo. The nontornadic mesocyclones possess less circulation than most of the tornadic mesocyclones that have been observed by the DOW radars, particularly within 1 km of the axis of rotation. Another finding is that the trajectories of air parcels passing through the near-surface vertical vorticity maxima have relatively shallow upward vertical excursions, suggesting that these parcels do not enter the overlying midlevel updraft and mesocyclone.