The Relative Impact of Aerosols and Environmental Moisture on the Characteristics of Low-Precipitation Supercells

Due to their unique precipitation distribution and atypical radar signature, low-precipitation (LP) supercells are the most difficult of the three main supercell storm archetypes to identify. Consequently, observational studies of LPs are somewhat limited, and very few modeling studies of LPs have been reported in the literature. Physical processes leading to the differences in supercell morphology are therefore not well understood. LPs frequently form near the dryline or in the high plains of the U.S., and they are typically isolated or are the most upwind of storms in lines of supercell development. Since high aerosol concentrations and dry layers are more common in such environments, the goal of this research is to investigate the relative sensitivity of LP supercell characteristics both to the background aerosol concentrations and environmental moisture profile.

High-resolution, idealized, cloud-resolving modeling simulations have been performed with the Regional Atmospheric Modeling System in order to achieve this goal. Supercell storms were simulated under a range of aerosol concentrations and environmental moisture profiles. A classic supercell was first simulated using a moist profile and clean aerosol conditions. Sensitivity tests then demonstrate that LP supercells can form under clean or polluted conditions when elevated dry layers are present, such as may be seen near the dryline or within environmental conditions unmodified by previous convection. Mechanisms that distinguish between LP and classic supercells will be presented, including the relative roles played by enhanced aerosol concentrations and dry layers. More specifically, the relative influence of aerosols vs. environmental moisture on supercell storm dynamical and microphysical characteristics, including updraft and vorticity structure, hail formation mechanisms, and precipitation distribution, will be discussed.