Clarification on the generation of absolute and potential vorticity in mesoscale convective vortices
1Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
2WindLogics, Inc., Grand Rapids, Minnesota, USA
3Naval Postgraduate School, Monterey, California, USA
Abstract. The purpose of this paper is to clarify what we think are several outstanding issues concerning the predominant mechanism of vorticity generation in mesoscale convective vortices (MCVs). Using idealized mesoscale numerical simulations of MCV development, we examine here the vertical vorticity budgets in order to quantify the contributions of flux convergence of absolute vorticity versus tilting in the generation of MCV vorticity. In addition, we examine the corresponding diabatic heating profiles. By partitioning the diabatic heating between convective and stratiform regions, we elucidate the respective roles of convective and stratiform precipitation in the generation of potential vorticity (PV).
The analyses indicate that the horizontal flux convergence of vertical vorticity is the dominant mechanism for the spin-up and intensification of mid-level absolute vorticity. Indeed, diabatic heating and circulation budgets demonstrate that the vertical gradient of diabatic heating is supportive of low- to mid-level PV generation. During the early stages of MCV development, convective precipitation plays the dominant role in the PV generation; later on, the stratiform precipitation expands and becomes a larger contributor, particularly in low-CAPE background environments.