Origin of Near-Surface Vertical Vorticity of Mesovortices in a Quasi-Linear Convective System

The mechanisms of genesis of low-level mesovortices within quasi-linear convective systems (QLCS) are not well understood and, therefore, mesovortex formation and the locations of large values of near-surface vertical vorticity are difficult to predict. These mesovortices have been associated with damaging winds and tornadoes within QLCSs. The strength of mesovortices within the same system is highly variable and it is unknown why there is such variability between individual mesovortices. Mesovortices have been observed and modeled in simulations, but there is considerable disagreement on their genesis and strengthening. It has been speculated that the strength of the mesovortex is highly dependent on low-level environmental shear, Coriolis forcing, and the superposition of the descending rear inflow jet (RIJ). It is important to understand the rearrangement of baroclinic vortex lines and frictionally generated vortex lines within the mesovortex. As in supercells, the baroclinic generation and subsequent upward tilting of vertical vorticity by a downdraft is likely to play a role in the production vertical vorticity near the surface.

In this study, we will explore mesovortices and the dynamics associated with them within a QLCS storm mode using the Bryan Cloud Model 1 (CM1). QLCSs are simulated using the idealized Weisman-Klemp sounding to help better understand mesovortex genesis and their favored position along the gust front. Parcel trajectories are implemented to diagnose the origin of vertical vorticity within the mesovortex as they descend to the surface and tilt into the vertical. From these simulations, similarities will be analyzed between the origins of vertical vorticity within both QLCS mesovortices and supercell mesocyclones.