Toy model simulations of horizontal momentum surges in supercells

Our full-physics simulations of supercells (see Dahl et al abstract submitted to this conference) suggest that surface vertical vorticity is rather unsteady and tied to surges of horizontal momentum emanating from downdrafts adjacent to the main updraft. The difficulty with full supercell simulations is that, when the environment is varied, many storm-scale features change. We are therefore also undertaking idealized sensitivity tests in which simple downdrafts, outflows, and horizontal momentum surges are introduced with various configurations into environments with different magnitudes and orientations of low-level shear. Our pilot tests successfully reproduce the horizontal momentum surges and vorticity that occur in the full-physics supercell simulations. We use a spectrum of initial wind profiles based on the simulated in-storm profiles from our full supercell simulations. By assessing sensitivities in these “toy” model simulations, we will isolate the downdraft processes from other storm-scale variability. Such work bears some resemblance to previous idealized studies (Walko 1993, Markowski et al. 2010), but here we undertake a broad matrix of sensitivity tests that specifically focus on the resulting structures of simulated horizontal momentum surges.