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
利用耦合了陆面模式的大气环流模式,结合青藏高原植被退化的范围和程度,通过在模式中修改高原地区(27°—40°N,75°—100°E)的叶面积指数的方法,探讨了植被退化以后对高原及其附近地区上空大气环流的影响。结果表明,...利用耦合了陆面模式的大气环流模式,结合青藏高原植被退化的范围和程度,通过在模式中修改高原地区(27°—40°N,75°—100°E)的叶面积指数的方法,探讨了植被退化以后对高原及其附近地区上空大气环流的影响。结果表明,该模式对高原地表温度场具有很强的模拟能力,并且能够很好地模拟出青藏高原及附近地区夏季位势高度场的平均特征及南亚高压的位置和强度,但南亚高压中心强度偏大且略微西退。在青藏高原植被出现退化以后,高原整体地表土壤温度和地表2 m空气温度升高,感热通量增加、潜热通量减小,进而改变了高原地区的波文比。地表感热增加导致高原及附近地区500 h Pa高度场降低和200 h Pa高度场升高,并在200 h Pa上存在强大的反气旋性环流异常,导致南亚高压增强和北扩东伸。植被退化造成的青藏高原感热增加导致了高原南部上升运动增强和北部上升运动减弱,同时又引起高原以北地区下沉气流的影响范围扩大,而下沉气流的强度减弱,其结果有助于高原以北的干旱范围扩大,而干旱程度却得到缓解。展开更多
The recent decline in the Arctic sea ice has coincided with more cold winters in Eurasia. It has been hypothesized that the Arctic sea ice loss is causing more mid-latitude cold extremes and cold winters, yet there is...The recent decline in the Arctic sea ice has coincided with more cold winters in Eurasia. It has been hypothesized that the Arctic sea ice loss is causing more mid-latitude cold extremes and cold winters, yet there is lack of consensus in modeling studies on the impact of Arctic sea ice loss. Here we conducted modeling experiments with Community Atmosphere Model Version 5 （CAM5） to investigate the sensitivity and linearity of Eurasian winter temperature response to the Atlantic sector and Pacific sector of the Arctic sea ice loss. Our experiments indicate that the Arctic sea ice reduction can significantly affect the atmospheric circulation by strengthening the Siberian High, exciting the stationary Rossby wave train, and weakening the polar jet stream, which in turn induce the cooling in Eurasia. The temperature decreases by more than I^C in response to the ice loss in the Atlantic sector and the cooling is less and more shifts southward in response to the ice loss in the Pacific sector. More interestingly, sea ice loss in the Atlantic and Pacific sectors together barely induces cold temperatures in Eurasia, suggesting the nonlinearity of the atmospheric response to the Arctic sea ice loss.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.
文摘利用耦合了陆面模式的大气环流模式,结合青藏高原植被退化的范围和程度,通过在模式中修改高原地区(27°—40°N,75°—100°E)的叶面积指数的方法,探讨了植被退化以后对高原及其附近地区上空大气环流的影响。结果表明,该模式对高原地表温度场具有很强的模拟能力,并且能够很好地模拟出青藏高原及附近地区夏季位势高度场的平均特征及南亚高压的位置和强度,但南亚高压中心强度偏大且略微西退。在青藏高原植被出现退化以后,高原整体地表土壤温度和地表2 m空气温度升高,感热通量增加、潜热通量减小,进而改变了高原地区的波文比。地表感热增加导致高原及附近地区500 h Pa高度场降低和200 h Pa高度场升高,并在200 h Pa上存在强大的反气旋性环流异常,导致南亚高压增强和北扩东伸。植被退化造成的青藏高原感热增加导致了高原南部上升运动增强和北部上升运动减弱,同时又引起高原以北地区下沉气流的影响范围扩大,而下沉气流的强度减弱,其结果有助于高原以北的干旱范围扩大,而干旱程度却得到缓解。
基金The Chinese Polar Environment Comprehensive Investigation and Evaluation Programmes under contract No.CHINARE2016-04-04the Public Science and Technology Research Funds Projects of Ocean under contract No.201505013the National Natural Science Foundation of China(NSFC)under contract No.41576029
文摘The recent decline in the Arctic sea ice has coincided with more cold winters in Eurasia. It has been hypothesized that the Arctic sea ice loss is causing more mid-latitude cold extremes and cold winters, yet there is lack of consensus in modeling studies on the impact of Arctic sea ice loss. Here we conducted modeling experiments with Community Atmosphere Model Version 5 （CAM5） to investigate the sensitivity and linearity of Eurasian winter temperature response to the Atlantic sector and Pacific sector of the Arctic sea ice loss. Our experiments indicate that the Arctic sea ice reduction can significantly affect the atmospheric circulation by strengthening the Siberian High, exciting the stationary Rossby wave train, and weakening the polar jet stream, which in turn induce the cooling in Eurasia. The temperature decreases by more than I^C in response to the ice loss in the Atlantic sector and the cooling is less and more shifts southward in response to the ice loss in the Pacific sector. More interestingly, sea ice loss in the Atlantic and Pacific sectors together barely induces cold temperatures in Eurasia, suggesting the nonlinearity of the atmospheric response to the Arctic sea ice loss.
