The formation of a cooling-induced mesovortex in the trailing stratiform region of a midlatitude squall line

Abstract

This cooling-induced midlevel vortex originates from the preexisting cyclonic vorticity associated with a traveling meso-α-scale short wave. The vortex is intensified in the descending rear-to-front inflow as a result of continued sublimitative melting and evaporative cooling in the stratiform region. It decouples from the front-to-rear ascending and anticyclonic flow in the upper troposphere during the formative stage. The vortex tilts northward with height, resulting in a deep layer of cyclonic vorticity (up to 250 mb) near the northern end of the squall line. It has an across-line scale of 120-150 km and a longitudinal scale of more than 300 km, with its maximum intensity located above the melting level. A three-dimensional vorticity budget shows that the cooling-induced vortex is initially maintained through the vertical stretching of its absolute vorticity associated with the short-wave trough. -from Author