Exploring the Sensitivity of Tropical Oceanic Convective Clouds to Aerosol Characteristics under Differing Thermodynamic Environments

Aerosol influence on convective clouds has been an active, yet contentious, area of research over the past several decades. Previous studies on aerosol-cloud-precipitation interactions have shown that increased aerosol loading leads to smaller but more numerous cloud drops than there would be otherwise. Some studies have shown this to subsequently lead to a suppression of collision-coalescence processes, deeper convection, and stronger updrafts, while others have found a less monotonic response, or even inhibition of convective development with enhanced aerosol loading. These conflicting results may be due to a modulation of aerosol interactions by the environment, but at present, relatively little research has examined how different thermodynamic environments affect the sensitivity of convective clouds to aerosol loading. The goal of this research has therefore been to use numerical simulations to assess how the response of tropical, maritime boundary layer cumulus and cumulus congestus clouds to changes in aerosol content is modulated by different thermodynamic environments.

We have run high-resolution, cloud-resolving model simulations in the Regional Atmospheric Modeling System (RAMS) to address this research goal. Nine total experiments that were run include combinations of enhanced surface aerosol concentration (clean, moderate, and polluted) and reduced static stability (less stable, moderate, more stable). We used output from a larger-scale case study simulation covering the Maritime Continent and West Pacific Ocean to initialize and nudge these high-resolution simulations, and focused on a region in which primarily shallow convection was produced. We have examined the relative frequency of different convective cloud types, cloud dynamical and microphysical structural properties (e.g. updraft strength, cloud thickness, condensate distribution), and precipitation characteristics to quantify the response of the different cloud types to aerosol and thermodynamic perturbations on the initial state. The physical processes which led to these results will be presented and discussed.