Aerosol Direct Radiative and Cloud Adjustment Effects on Surface Climate over Eastern China: Analyses of WRF Model Simulations

Abstract

The WRF-simulated changes in clouds and climate due to the increased anthropogenic aerosols for the summers of 2002?08 (vs the 1970s) over eastern China were used to offline calculate the radiative forcings associated with aerosol?radiation (AR) and aerosol?cloud?radiation (ACR) interactions, which subsequently facilitated the interpretation of surface temperature changes. During this period, the increases of aerosol optical depth (?AOD) averaged over eastern China range from 0.18 in 2004 to 0.26 in 2007 as compared to corresponding cases in the 1970s, and the multiyear means (standard deviations) of AR and ACR forcings at the surface are ?6.7 (0.58) and ?3.5 (0.63) W m?2, respectively, indicating the importance of cloud changes in affecting both the aerosol climate forcing and its interannual variation. The simulated mean surface cooling is 0.35°C, dominated by AR and ACR with a positive (cooling) feedback associated with changes in meteorology (~10%), and two negative (warming) feedbacks associated with decreases in latent (~70%) and sensible (~20%) heat fluxes. More detailed spatial characteristics were analyzed using ensemble simulations for the year 2008. Three regions?Jing-Jin-Ji (?AOD ~ 0.63), Sichuan basin (?AOD ~ 0.31), and middle Yangtze River valley (?AOD ~ 0.26)?at different climate regimes were selected to investigate the relative roles of AR and ACR. While the AR forcing is closely related to ?AOD values, the ACR forcing presents different regional characteristics owing to cloud changes. In addition, the surface heat flux feedbacks are also different between regions. The study thus illustrates that ACR forcing is useful as a diagnostic parameter to unravel the complexity of climate change to aerosol forcing over eastern China.