Aerosol effects on precipitaiton in a multiscale aerosol climate model

Precipitation plays a key role in the energy and hydrological cycles of the climate system. By acting as cloud condensation nuclei, aerosol particles can affect precipitation efficiency and strength. By absorbing sunlight, the aerosol influences the atmospheric circulation and hence the convergence of moisture in precipitating cloud systems. While aerosol effects on precipitation have been studied by using cloud resolving models (CRM) and regional models, it is still a challenge to quantify aerosol effects on precipitation in global climate models (GCM) given that over the globe most precipitation is from convective clouds and aerosol effects on convective clouds are at best only very crudely represented in conventional GCMs. In this study, we use a multiscale aerosol climate model to examine aerosol effects on precipitation. In this multiscale model, a two-dimensional CRM is embedded within each grid column of the NCAR CAM5 GCM to replace the GCM's conventional cloud parameterizations, and radiative transfer is calculated on the CRM grid. Cloud statistics from the CRMs are used to drive trace gas and aerosol processing and removal by clouds, and aerosols are used when calculating droplet nucleation in the CRMs. This permits explicit simulation of interactions between aerosols and convective clouds in a global model for the first time. In this presentation we examine the relationship between aerosols and precipitation in the model, and investigate how atmospheric thermodynamics affect the aerosol-precipitation relationship. The model results are compared with observations (satellite data and in situ measurements).