This proposal addresses the critical need for an accurate representation of aerosol indirect effect in climate and Earth system models. One of the most important and least understood climate feedbacks that controls climate response to increasing CO₂ forcing is related to aerosols and their influence on the energy and water cycles in the Earth systems. This proposal addresses critical gaps in representations of aerosol properties and processes, and their indirect effects on cloud and precipitation in climate models, with an emphasis on deep convective clouds and the associated anvils and cirrus clouds. Our overall objective is to reduce uncertainties associated with indirect effect of aerosols by improving parameterizations for aerosol cloud precipitation feedbacks in regional and global climate models and conducting high resolution regional climate simulations to estimate aerosol indirect effects. This research will produce improved treatments of climatically-relevant aerosols and fully link aerosol, cloud microphysics, and cumulus convection to better represent aerosol-cloud-precipitation interactions and their influence on the radiative balance and hydrological cycle in climate models. Our specific tasks are as follows:

1. Improve parameterizations for formation and early growth of new particles as well as model treatments for secondary organic aerosol formation and dust effects.
2. Improve and evaluate the Zhang and McFarlane (ZM) convective parameterization with consideration of aerosol and cloud microphysical effects on convection and precipitation as well as ice nucleation schemes that link ice formation to aerosols to better represent the influence of aerosols on clouds and precipitation.
3. Conduct and evaluate coupled aerosol-climate simulations using WRF/Chem over East China at 4-12 km horizontal resolution and analyze aerosol indirect effects under different cloud regimes and their interannual variability.

The proposed research will produce an integrated climate model framework with improved and unified aerosol, convection, and cloud microphysics to better represent aerosol-cloud-precipitation climate interactions. It directly addresses the NSF area of interest on improving climate models or components of Earth System Models by enhancing model representations of aerosols, clouds, and precipitation. It also addresses DOE's interest in reducing uncertainties in estimating aerosol indirect effect by quantifying uncertainties of aerosol indirect effects in different types of clouds and intercomparing various existing schemes at regional scales. The modules developed or improved in this project will be made available to the regional and global climate modeling community.

The results of this work will be of tremendous benefit to the scientific community. It will improve representations of aerosol-cloud-climate interactions in coupled chemistry-climate models and enhance our understanding of how model sensitivities/uncertainties impact climate predictions. The proposed unified climate modeling framework will provide a powerful tool and advance the community modeling paradigm for long-term climate simulations to understand the impact of human-induced pollution on climate system. The outcomes and findings can be of direct benefit to other areas such as real-time air quality/climate forecasting, environmental management and industrial management, regional/global weather, Earth system, and ecosystem modeling. The interdisciplinary nature of the proposed work will provide a significant opportunity to train the next generation of scientists at the interface of atmospheric chemistry, physics, meteorology, and climate.