The effect of aerosols on the onset of precipitation

This work examines the theory of the Second Indirect Effect of Aerosols through analysis of cloud and aerosol properties at the onset of precipitation, specifically using observational data. The data used include many cases from four DOE ARM (Department of Energy Atmospheric Radiation Measurement Program) mobile and permanent facilities in order to test the robustness of the results in different locations and climates around the world. Cloud properties such as cloud thickness, liquid water contents and drop size distributions (retrieved from the radar and radiometer data using an optimal estimation scheme) are statistically correlated with CCN (Cloud Condensation Nuclei) concentrations in order to determine the effects of aerosols on the onset of precipitation. These trends are also tested against changing environmental factors, including relative humidity, wind speed and stability parameters in order to see if these can affect the results. In order to show the sensitivity of results to changing environmental conditions, case studies will be presented along with the statistical analysis. Preliminary results have been relatively consistent with theories in this field that have been developed from modeling studies, however, it does seem that environmental conditions may play a larger role than was previously considered in these theories.