Convective Microphysics and the Interaction of Aerosols, Convection and Large-scale Circulation in the NCAR CAM5

Description

Observations and cloud-resolving model simulations show that aerosols have significant effects on convection. While aerosol-cloud interaction and its effect on climate have been studied extensively, aerosol effects on convection have only been explored recently. It was believed that aerosols can invigorate convection by suppressing warm rain and enhancing ice production in convective updrafts, thereby releasing more latent heat from freezing. Recently we implemented a two-moment convective microphysics scheme that we developed through ASR support into the NCAR CAM5. It enables us to investigate the interaction between aerosols, convection and climate. For this purpose, we carried out several multi-year numerical experiments using CAM5 with prescribed aerosols. We examine how aerosols affect convection under given large-sale meteorological conditions, to what extent this interaction depends on convection regime or thermodynamic environment, and how it affects the climate simulation through convection-large-scale feedbacks. It is found that for fixed meteorological conditions, the CAM5 model with the convective microphysics scheme is able to simulate the aerosol invigoration effect on convection. However, when the response of large-scale circulation to the invigorated convection is accounted for, much of the local aerosol effect on convection invigoration is negated by convection response to circulation change, leaving a much smaller net aerosol effect on convection.