These investigators will use a new coupled model to study how aerosols influence the properties of clouds. This study thus addresses one of the major uncertainties in climate simulations, the "indirect effect of aerosols" that arising from their influence on the radiative properties of clouds. It is expected that higher concentrations of particles lead to more cloud droplets and so to brighter clouds as well as clouds with longer lifetime and reduced probability of producing precipitation, but it has proven difficult to formulate a quantitative prediction based on this expectation. In this study, the investigators will attempt to isolate cases where the influence is expected to be prominent and will then use their model to separate the influence of aerosols on those clouds from other factors that also affect the same cloud properties. The effort requires coupling of several models in order to represent realistic cloud fields, cloud elements, cloud-droplet sizes, and chemical and aerosol transport. This coupled model will then be applied to conditions appropriate for Houston, Texas, where there is significant urban pollution expected to affect the properties of clouds that form downwind of the city.
The expected result of this research will be an assessment of how urban pollution or other sources of aerosols affects cloud properties like reflectivity, probability of forming precipitation, and lifetime. The product of this research will apply to Cumulus clouds, and so will need eventual extension to other cloud types that also influence the global radiation balance. This information is needed by climate scientists who seek to predict how the increasing aerosol content of the atmosphere will affect the radiative balance and the precipitation distribution of the Earth.
