A Simulation of a Supercell Thunderstorm with Emulated Radiative Cooling beneath the Anvil

Abstract

This note reports the preliminary results of an ongoing numerical study designed to investigate what effects, if any, radiative transfer processes can have on the evolution of convective storms. A pair of idealized three-dimensional simulations are conducted to demonstrate the potential dynamical importance of shortwave radiation reductions within the large shadows cast by storms. One of the simulations (the control) is run without surface physics and radiation. In the other simulation, radiative cooling due to cloud shading is emulated by prescribing a cooling rate to the skin temperature at any grid point at which cloud water was present overhead. The imposed skin cooling rate is consistent with past observations. Low-level air temperatures are coupled to the skin cooling in this second simulation by the inclusion of surface sensible heat fluxes using simple bulk aerodynamic drag laws (latent and soil heat fluxes are not included). Significant differences are observed between the two simulated storms, particularly in the evolution of the vertical vorticity field and gust fronts. The storm simulated with emulated cloud shading develops substantially weaker low-level rotation than the storm in the control simulation.