Examining aerosol indirect effects on tropical deep convection
A series of model simulations have been conducted under a radiative-convective equilibrium framework, which has been utilized in the past to successfully simulate the tropics. These model simulations are large-scale, three-dimensional channel runs (approximately 5,000 km x 250 km) using a cloud resolving model with 1 km spacing in the horizontal and variable vertical grid spacing. The model being used is the Regional Atmospheric Modeling System (RAMS), which allows for the prognosis of ccn number concentration based on background aerosol concentration and various environmental conditions. The set of simulations differ only in the background aerosol concentration, so as to simulate the response of tropical convection to changes in the amount of aerosols that are available to act as ccn. The typical tri-modal cloud distribution that has been observed in the tropics is well represented in these model simulations, but given the focus of this study, only deep convective clouds are considered.
Preliminary findings have shown significant differences resulting from increases in aerosols available to act as ccn. Deep convective clouds forming in polluted simulations have increased cloud water content, likely due to a decrease in warm rain efficiency. The larger available cloud water content allows an increase in riming efficiency, and so more graupel can be found within the clouds. Some evidence exists for convective invigoration, or enhanced updrafts due to an increase in latent heat release, but the full response is not yet fully understood. These findings will be investigated in more detail by analyzing aspects such as the latent heating profiles through these deep convective systems and examining specific microphysical processes related to precipitation formation. The results of these analyses will be presented.