The Influences of Low-Level Stability on Bow Echo Mesovortex Genesis

The purpose of this work is to test whether current theories regarding the generation of low-level rotation in supercells is analogous to the development of bow echo mesovortices. Straka et al. (2007) propose that low-level rotation develops in supercells by tilting baroclinically-generated low-level vorticity originating in the rear flank region. A relationship exists between the strength of the rear flank downdraft (RFD) and the ability of a supercell to generate low-level rotation. It is believed that bow echo mesovortices develop through similar processes by tilting baroclinically-generated vorticity that is along the gust front, which is similar to the hypothesized processes by which low-level rotation forms in supercells. It is believed that strong RFDs generate relatively large amounts of vorticity at the expense of increased stability and resistance to tilting and stretching. However, weak RFDs do not resist the vertical motion necessary for tilting and stretching at the expense of weaker baroclinic vorticity generation. Therefore, an intermediate state is preferred to maximize the generation of vertical vorticity. We believe that the same relationship holds true for the development of bow echo mesovortices. Idealized simulations were performed using the CM1 non-hydrostatic cloud model with a variety of cold pool strengths and vertical velocities, both upward and downward, to test whether model simulations support the hypothesized relationship between cold pool strength and bow echo mesovortices. Results of the simulations will be presented.