The Influence of Convective Thermal Forcing on the Three-dimensional Circulation around Squall Lines

The present study suggests that the three-dimensional circulation in the trailing stratiform region behind squall lines is primarily determined by the time-mean pattern of heating and cooling in the leading convective line. Analysis of the line-normal circulations show that they develop as thermally generated gravity waves spread away from the leading line. Midlevel line-end vortices are the result of diabatically driven tilting of horizontal vorticity generated by the time-mean thermal forcing. In the presence of the Coriolis force, a symmetric thermal forcing generates an asymmetric stratiform circulation and a pattern of vertical displacement which resembles the comma-shaped stratiform anvil observed in real systems; this suggests that asymmetries in the cloud and circulation behind midlatitude squall lines are not necessarily the result of asymmetries in the convective leading line.