CFMIP大气环流模式模拟的东亚云辐射强迫特征

Characteristics of cloud radiative forcings over East Asia as simulated by the AGCMs in the CFMIP

  • 摘要: 通过与卫星观测云和辐射资料的比较,检验了10个大气环流模式对东亚地区云量、垂直结构、光学属性以及辐射特征的模拟能力。10个模式的模拟结果均来自“云反馈模式比较计划”(CFMIP),为便于与国际卫星云气候计划(ISCCP)资料的比较,所有模式都引入了ISCCP模拟器。结果表明,10个模式均能模拟出东亚地区冬、夏两季云量及其辐射特征的基本分布,但也存在偏差。在北半球冬季,10个CFMIP模式能够合理地再现东海沿岸的总云量大值中心,一半的模式能够较合理地模拟出四川盆地上空的大值中心,但在这两个区域模拟的总云量总体偏少且主要由中低云引起。北半球夏季,CFMIP模式能够模拟出孟加拉湾和中国西南一直延伸至日本的带状多云区和西北太平洋的少云区,但模拟的多云区内高(中低云)云偏多(少)。模拟的短波(长波)云辐射强迫的空间分布和总云量(高云量)基本一致,但模式对辐射强迫的模拟能力优于云量,原因是模式模拟的云光学厚度偏大,从而部分抵消了中低云量偏少对短波辐射强迫的影响。云辐射强迫综合了晴空和全天的辐射特征,一些模式中除云属性的偏差外,冬季陆地晴空反照率偏大亦是导致短波辐射强迫偏小的重要原因。CFMIP模式对高原东侧中低云的模拟能力,依赖于其对垂直环流场的模拟效果。

     

    Abstract: Based on observational evidences from the satellitebased cloud and radiation retrievals, the authors evaluate the performances of ten current stateoftheart Atmospheric General Circulation Models (AGCMs) in simulating the cloud amount, cloud vertical structure, and cloud optical properties as well as its radiative characteristics over the East Asia domain. The simulations of ten AGCMs involved in the Cloud Feedback Model Intercomparison Program (CFMIP) are analyzed. The ISCCP simulator was employed in all models to facilitate the comparison between model results and satellite products. The results show that both the boreal winter and summer mean spatial patterns of cloud amount as well as cloud radiative characteristics are reasonably simulated by most of models. However, there still exist some discrepancies. Many AGCMs fail in capturing the boreal wintertime cloud maxima center on the lee side of Tibetan Plateau, and underestimate the middle-and low-level cloud amount around the East China Sea. The underestimate in total cloud amounts on the lee side of Tibetan Plateau and over the East China Sea are due to the underestimate of low- and middle- cloud amount. Many models are able to reasonably reproduce the total cloud maxima center over the Bay of Bengal and the southwestern China as well as a high cloud amount belt from southwest China to Japan in summer, but the amount of high level cloud is overpredicted and the middle-and low-level clouds are underpredicted over the cloudabounding region. The spatial pattern of simulated shortwave cloud radiative forcing resembles that of total cloud amount, while the spatial pattern of simulated longwave cloud forcing is similar to that of the high level cloud amount. However, the simulated cloud radiative forcing is better than the cloud amount both in spatial pattern and magnitude. The better simulation of shortwave cloud radiative forcing is resulted from the compensation of overestimated cloud optical thickness and underestimated cloud amount. In most models, the cloud optical depths at most levels are overestimated. The cloud radiative forcing is composited by the effects in both the cloudy and clear sky conditions. Besides cloud properties, the clear sky albedo is another cause to the discrepancy in shortwave cloud radiative forcing in boreal winter over land. The overestimate of clear sky surface albedo leads to a underestimate of shortwave cloud radiative forcing. The authors also propose whether the middle- and low-level cloud amount on the lee side of Tibetan Plateau can be properly reproduced in models is closely related to the fidelity of the simulated large scale circulation.

     

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