Cloud-aerosol interactions in a mutiscale aerosol climate model

Anthropogenic aerosol effects on clouds produce one of the largest uncertainties in estimates of radiative forcing of past and future climate change. Much of this uncertainty arises from the multiscale nature of the interactions between aerosols, clouds and large-scale dynamics, which are difficult to represent in conventional global climate models. In this study, we use a multiscale aerosol climate model to examine the aerosol indirect effect. This multiscale aerosol climate model is an extension of a multiscale climate model (SPCAM) that embeds a cloud-resolving model (CRM) within each grid cell of a global climate model. In this extension a two-moment cloud microphysics scheme replaces the simple bulk microphysics scheme in the CRM, and a third-order turbulence scheme is implemented in the CRM to better represent boundary layer clouds. The effects of clouds on aerosols are treated by using an explicit cloud-parameterized pollution approach that links aerosol and chemical processes on the large-scale grid with statistics of cloud properties and processes resolved by the CRM. With these extensions, our multiscale aerosol climate model improves the representation of multiscale interactions between aerosols, clouds and large-scale dynamics. This enables us to study the aerosol indirect effect on all major cloud types in a global climate model for the first time. Here, we examine simulated aerosol and cloud fields with a focus on the relationship between aerosol and cloud properties. These relationships are compared with those derived from in-situ and satellite data.