Development of Parameterizations of Aerosol/Cloud Interactions and Assessment of Their Potential Climatic Impacts

Colorado State University, Fort Collins CO

Investigators

Abstract

This is a modeling-based investigation of the interactions of clouds and aerosols and the effects of these interactions on cloud dynamics, precipitation, and radiative transfer. It is an extension of a recent study of the cloudy boundary layer, based on what is called the assumed probability density function (PDF) method. Within every computational grid box of the cloud model, it is assumed that the joint probability of vertical velocity, potential temperature, and liquid water content satisfies a parametric form such as the multivariate Gaussian. Large-eddy simulation (LES) provides information on the small-scale variability of these quantities, enabling the estimation of the parameters of the distribution. The cloud model predicts the development in time of the mean values of the quantities in the grid boxes and the PDF model characterizes the subgrid-scale variability. In this project, the previous work will be extended to include precipitation processes and the estimation of the effects of variable concentrations of cloud condensation nuclei and ice forming nuclei on the microphysical, dynamic, and radiative properties of clouds. The feasibility of applying the technique to large cumulonimbus clouds (deep convection) will be investigated. Sensitivity studies will determine the extent to which changes in aerosol characteristics can affect the clouds and influence regional climate.