Influences of Anvil Shading on the Evolution of the Supercell Environment and Updraft Accelerations during the Nocturnal Transition

The effects of anvil cloud shading on the near-storm environment and subsequent updraft accelerations remain relatively unexplored in the scientific literature, especially regarding storms encountering the nocturnal planetary boundary layer (PBL) transition. Past observational and idealized simulation studies have documented afternoon baroclinic vorticity generation along anvil shading edges and associated effects on updraft rotation. Additionally, studies have analyzed differences in afternoon PBL thermodynamic and wind shear characteristics between near-storm environments influenced by anvil shading and unaffected far-field environments. We hypothesize that anvil shading prior to sunset reduces buoyancy in the near-storm environment and weakens buoyancy accelerations in the updraft. Meanwhile, after sunset, downwelling longwave radiation from the anvil slows the decrease in buoyancy beneath the anvil compared to the far field, thus retarding reductions in buoyancy acceleration through the nocturnal transition. We expect wind shear to increase in the anvil-shaded region due to reduced vertical momentum flux and an associated dynamic updraft acceleration increase, which may be hodograph dependent. Initial tests of our hypotheses will use two idealized simulations of supercells through the nocturnal transition. Both simulations will include surface fluxes of heat, moisture, and momentum in addition to shortwave and longwave radiation. The distinguishing factor between the simulations will be the inclusion (exclusion) of cloud-radiation interactions, thus allowing us to isolate the anvil-shading effects on the nocturnal evolution of the near-storm environment relative to the far-field environment.