The influence of horizontal convective rolls on the morphology of low-level rotation in idealized simulations of supercell thunderstorms

In a suite of idealized numerical simulations including radiation and surface fluxes of heat, moisture and momentum, supercell thunderstorms are initiated in a convective boundary layer (CBL) environment characterized by horizontal convective rolls (HCRs) and compared with those simulated in a horizontally homogeneous environment. We examine and discuss the effects of inhomogeneities in the low-level environment on supercell evolution. Whereas bulk measures of storm strength such as maximum vertical velocity or vertical vorticity are largely unaffected by the presence of a CBL, results suggest that HCRs may influence small-scale features of the simulated storms. For instance, HCRs appear to be linked to the formation of periodic, misocyclone-like vertical vorticity maxima along the rear-flank gust front (RFGF). Furthermore, HCRs may provide a source of pre-existing vertical vorticity to the low-level mesocyclone previously unexplored in idealized simulations of supercells. The degree to which organized environmental inhomogenieties in vorticity, vertical velocity, temperature, and moisture associated with HCRs may enhance (or suppress) the development of significant low-level rotation, both in the mesocyclone and RFGF regions of the storm, is explored using analysis of parcel trajectories. The sensitivity of these results to the orientation of HCR axes relative to storm motion and horizontal grid spacing will be discussed.