A numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines

Abstract

The physical processes that generate and maintain the mesoscale inflow at the rear of squall-line-type mesoscale convective systems are examined. Horizontal potential temperature gradients generated by a combination of latent heat release in the convective region and unsaturated mesoscale descent, both modulated by evaporation, cause a horizontal pressure gradient and generate horizontal, line-parallel vorticity. The rear inflow is a consequence of these processes. The system-scale organization is examined by using Lagrangian conservation properties. First, passive tracer analyses quantify the relative importance of individual transports. Second, the vorticity field is analyzed by using a nonlinear steady state conservation theorem that, despite being applied to a system containing transient convective cells, adequately represents the persistent nature of the vorticity dynamics and demonstrates the strong interaction between the convective and stratiform regions. It is demonstrated that the vorticity structure in the COPT81 lines is much more complex than a balance between the inflow shear and the vorticity generated in the vicinity of the cold pool mainly because the system-scale (convective and stratiform) baroclinic vorticity generation cannot be neglected. -from Authors