The influence of convective thermal forcing on the three-dimensional circulation around squall lines

Midlatitude squall lines are typically trailed by a large region of stratif orm cloudiness and precipitation with significant mesoscale flow features, including an ascending front to rear flow; a descending rear inflow jet; li ne-end vortices; and, at later times, mesoscale convective vortices. The pr esent study suggests that the mesoscale circulation in the trailing stratif orm region is primarily determined by the time-mean pattern of heating and cooling in the leading convective line. Analysis of the line-normal circula tion shows that it develops as thermally generated gravity waves spread awa y from the leading line. Midlevel line-end vortices are the result of diaba tically driven tilting of horizontal vorticity generated by the time-mean t hermal forcing. Ln the presence of the Coriolis force, a symmetric thermal forcing generates an asymmetric stratiform circulation and a pattern of ver tical displacement that resembles the comma-shaped stratiform anvil observe d in real systems; this suggests that asymmetries in the cloud and circulat ion behind midlatitude squall lines are not necessarily the result of asymm etries in the convective leading line.