Structure of a Midtropospheric Vortex Induced by a Mesoscale Convective System

Abstract

On 9 June 1988 a mesoscale (?200-km diameter) convectively generated vortex (MCV) passed through the Colorado wind-profiling network. The generating convective system, which was too small to meet Maddox?s mesoscale convective complex criteria, developed beneath a high-amplitude mid- and upper-level ridge axis. Profiler winds obtained within the stratiform region of the convective system and near the center of the ensuing MCV form the basis of this study. With the addition of satellite (including rapid scan) images and conventional and Doppler radar data, this vortex was well observed over its entire life cycle. The slowly moving vortex was observed by the Flagler 50-MHz profiler for more than 16 h. For a portion of this period the circulation was quasi-steady; hence, the spatial structure of the vortex was depicted by time-to-space conversion of the profiler data. The results show a strong, coherent circulation with maximum tangential speeds greater than 16 m s?1 at 6 km above mean sea level (MSL) and at radii of 50?70 km; corresponding relative vorticity was more than three times as large as the local Coriolis parameter. The long duration and the apparent dominance of vorticity over divergence suggest that the flow in the vortex was in a quasi-balanced state. Hence, the temperature perturbation necessary to support the tangential velocity distribution was computed assuming gradient balance in the radial direction. The resulting estimated temperature structure showed a warm core with a magnitude of 2.3°C at 7.3 km MSL and a cold core below 6.3 km MSL. The associated potential vorticity (PV) structure at the vortex center consisted of a lens of high PV with a maximum at 6.3 km MSL and relative minima above and below this height.