29 March 2014

Investigation of Aerosol Indirect Effects Using a Cumulus Microphysics Parameterization in a Regional Climate Model


Previous studies show that aerosols affect microphysical and dynamical processes in both stratiform clouds and convective clouds; however, cumulus parameterizations for deep convective clouds do not include cloud microphysics. DOE scientists at Pacific Northwest National Laboratory led collaborative research to investigate aerosol indirect effects using a cumulus parameterization incorporated with cloud microphysics in a regional climate model. The team linked aerosols with cloud droplet nucleation and ice nucleation processes in a cumulus parameterization that incorporates cloud microphysics–recently developed by scientists at Scripps Institution of Oceanography. They first investigated the impacts of aerosols on the East Asian summer monsoon using this new cumulus parameterization in the Weather Research & Forecasting model. Their findings clarified the role of cloud microphysics and aerosol-cloud interactions in deep convective clouds, and provided a comprehensive view of how aerosols affect regional climate. They found that the cumulus parameterization, including microphysical processes, improves the simulation of precipitation and radiative properties as more cloud condensates are detrained from the convective clouds. They further found that increasing aerosols lead to reductions in precipitation and cloud fraction as convection is suppressed except during some heavy precipitation periods. They also noted that parameterizing microphysics in a cumulus parameterization has larger effects than increasing aerosols on regional climate simulations. Their findings underline the importance of considering cloud microphysics in cumulus parameterization and suggests a need for new approaches in parameterizing microphysical feedback to cloud dynamics for better simulation of aerosol impacts on convective clouds in climate models.