Quantifying the radiative forcing due to aerosol-cloud interactions especially through cirrus clouds remains chal- lenging because of our limited understanding of aerosol and cloud processes. In this study, we investi...Quantifying the radiative forcing due to aerosol-cloud interactions especially through cirrus clouds remains chal- lenging because of our limited understanding of aerosol and cloud processes. In this study, we investigate the anthro-pogenic aerosol indirect forcing （AIF） through cirrus clouds using the Community Atmosphere Model version 5 （CAM5） with a state-of-the-art treatment of ice nucleation. We adopt a new approach to isolate anthropogenic AIF through cirrus clouds in which ice nucleation parameterization is driven by prescribed pre-industrial （PI） and present- day （PD） aerosols, respectively. Sensitivities of anthropogenic ice AIF （i.e., anthropogenic AIF through cirrus clouds） to different ice nucleation parameterizations, homogeneous freezing occurrence, and uncertainties in the cloud micro- physics scheme are investigated. Results of sensitivity experiments show that the change （PD minus PI） in global an-nual mean longwave cloud forcing （i.e., longwave anthropogenic ice AIF） ranges from 0.14 to 0.35 W m^-2, the change in global annual mean shortwave cloud forcing （i.e., shortwave anthropogenic ice AIF） from -0.47 to -0.20 W m^-2, and the change in net cloud forcing from -0.12 to 0.05 W m^-2. Our results suggest that different ice nucle-ation parameterizations are an important factor for the large uncertainty of anthropogenic ice AIF. Furthermore, im-proved understanding of the spatial and temporal occurrence characteristics of homogeneous freezing events and the mean states of cirrus cloud properties are also important for constraining anthropogenic ice AIF.展开更多
基金Supported by the National Science Foundation of US(ATM-1642289)National Natural Science Foundation of China(41775095)
文摘Quantifying the radiative forcing due to aerosol-cloud interactions especially through cirrus clouds remains chal- lenging because of our limited understanding of aerosol and cloud processes. In this study, we investigate the anthro-pogenic aerosol indirect forcing （AIF） through cirrus clouds using the Community Atmosphere Model version 5 （CAM5） with a state-of-the-art treatment of ice nucleation. We adopt a new approach to isolate anthropogenic AIF through cirrus clouds in which ice nucleation parameterization is driven by prescribed pre-industrial （PI） and present- day （PD） aerosols, respectively. Sensitivities of anthropogenic ice AIF （i.e., anthropogenic AIF through cirrus clouds） to different ice nucleation parameterizations, homogeneous freezing occurrence, and uncertainties in the cloud micro- physics scheme are investigated. Results of sensitivity experiments show that the change （PD minus PI） in global an-nual mean longwave cloud forcing （i.e., longwave anthropogenic ice AIF） ranges from 0.14 to 0.35 W m^-2, the change in global annual mean shortwave cloud forcing （i.e., shortwave anthropogenic ice AIF） from -0.47 to -0.20 W m^-2, and the change in net cloud forcing from -0.12 to 0.05 W m^-2. Our results suggest that different ice nucle-ation parameterizations are an important factor for the large uncertainty of anthropogenic ice AIF. Furthermore, im-proved understanding of the spatial and temporal occurrence characteristics of homogeneous freezing events and the mean states of cirrus cloud properties are also important for constraining anthropogenic ice AIF.
