This study investigates how midlevel vorticity within convectively-generated mesovortices (MCVs) can amplify and grow downward to the surface by the redevelopment of deep convection. It is shown that the diabatic heating within the convection can increase the magnitude of the balanced warm core of the vortex, further lowering heights beneath the warm core and causing a cyclonic circulation closer to the surface. This cyclonic vorticity can develop in the lower troposphere even in the presence of the anomalously cold air of the low-level cold pool, given a sufficiently strong warm core aloft. The factors that play a key role in governing the downward penetration of vorticity to the surface are 1) onset of deep moist convection; 2) local reduction of the Rossby radius of deformation; and 3) weakening of the surface-based cold pool.
These concepts are explored by performing a 48-hour numerical simulation of an observed MCV that underwent multiple cycles of convective redevelopment, amplifying after each cycle. The model was successful in reproducing the creation and evolution of the MCV. The amplitude of the midlevel vortex increased considerably after each convective cycle, as cyclonic vorticity reached the surface during the third cycle. Conditions prior to the third cycle showed a strong southwesterly low-level jet that was transporting warm, moist air over an outflow boundary left from the previous convective cycle and underneath the existing MCV. Deep convection developed within the existing cyclonic circulation and intense latent heat release amplified the warm core. As a result of this warming, lower-tropospheric geopotential heights lowered, creating low-level convergence which increased cyclonic vorticity under the amplifying vortex. This convergence led to an intense vortex in the lower troposphere during the strongest periods of the convective cycle, despite the fact that the lower troposphere was anomalously cold during the entire period.
A conceptual model incorporating these ideas is presented. Since the MCV in this case was located over a midlatitude land mass, a discussion of the differences between midlatitude continental environments and tropical oceanic environments is also presented in order to assess the applicability of the concepts presented here to tropical cyclogenesis environments.