Mesoscale Convective System Anvil Cloud Response to Aerosol Loading

Abstract:

Mid-latitude mesoscale convective systems (MCS) are large convective engines that redistribute heat and moisture throughout the atmosphere. Upper level divergence and detrainment above the level of maximum vertical motion and below the vicinity of the tropopause leads to the formation of horizontally and vertically expansive anvil clouds. These are composed largely of weakly precipitating ice species and potentially supercooled liquid water that may homogeneously freeze at higher anvil altitudes. Because of the tremendous horizontal expanse of anvil cloud decks they can impact the radiation budget by reflecting incoming shortwave and outgoing longwave radiation, and potential changes to anvil extent or characteristics are thus important factors in climate change scenarios.

Increasing the number concentration of cloud droplet nucleating aerosols within various cloud systems has been shown to alter cloud droplet size distributions which leads to changes in warm rain formation, vertical distributions of cloud water, latent heating profiles, riming rates, and precipitation rates. If additional cloud water is generated and lofted higher within MCSs under scenarios of high aerosol concentration, then there is the potential for modification of anvil cloud microphysical and radiative properties and anvil dynamics. Results will be presented from cloud resolving numerical simulations of an MCS that occurred May 23 during the MC3E field project based in Oklahoma in 2011. Aerosol effects on MCS anvil characteristics will be contrasted within the range of observed clean and polluted aerosol conditions. The focus will be to address the range of response in anvil ice distributions, ice microphysical processes, anvil areal coverage, and local changes in short and longwave radiation to variations in aerosol number concentration.