Midlevel Vorticity Structure of the 10–11 June 1985 Squall Line

Abstract

The comprehensive analysis of the kinematic structure of the mature phase of the 10?11 June 1985 squall-line system was used to examine the midlevel vertical-vorticity structure of the storm to show that relative vertical vorticity in the stratiform region at midlevels was organized into bands (both cyclonic and anticyclonic) oriented parallel to the convective line, with anticyclonic vorticity between the rear of the convective line and the heaviest stratiform precipitation and cyclonic vorticity farther back. Since previous studies have not found anticyclonic vorticity over such a large portion of the stratiform region at midlevels and since the concentration of anticyclonic vorticity may have been detrimental to the longevity of the storm by limiting the development of an inertially stable cyclonic circulation, the tilting and stretching terms of the vertical-vorticity equation were computed to determine how the observed vertical-vorticity pattern was maintained. Tilting of horizontal vorticity into vertical vorticity by gradients of vertical motion was a factor of 2?10 greater than the stretching of vertical vorticity. Below the melting level and at the rear of the stratiform region, tilting was associated with gradients of mesoscale vertical motion. Above the melting level, near the convective line, tilting was associated with gradients of mean convective motions.