The Entrainment of Air from Rainy Surface Regions and its Implications for Bioaerosol Transport in Three Deep Convective Storm Morphologies

Abstract. The rain produced by thunderstorms has been observed to coincide spatially and temporally with enhanced near-surface concentrations of warm-temperature ice nucleating particles (INPs) of biological origin. However, the air in rainy regions is evaporatively cooled and negatively buoyant, and so it is unclear if it is entrained into its parent storms. Despite bioaerosols being highly ice-nucleation active, the microphysical influence that rain-aerosolized bioaerosols exert on storm processes is therefore not well-understood. We use the RAMS cloud-resolving model to simulate high-resolution archetypal representations of three deep convective storm morphologies: isolated deep convection, a squall line, and a supercell. We measure the degree of entrainment of rainy and non-rainy surface air into its parent storm using passive tracers, as well as calculating measures of each storm’s characteristics that influence the timing and degree of this entrainment. We find different degrees of entrainment between storm morphologies and between rainy and non-rainy surface air, with the squall line and supercell entraining significantly more rainy air than the isolated convective storm for all but the lightest rain. These differences owe to variation between the storms in their degrees of entrainment of surface air, their proportions of entrained surface air that originate in rainy regions, and their amount of rain produced per updraft mass. This study finds a specific and previously unrecognized source of air potentially containing highly ice-active aerosols which is entrained to varying degrees in different convective storm morphologies, and which is likely to exert different microphysical impacts on each type of storm.