Evaluation of Summer Monsoon Clouds over the Tibetan Plateau Simulated in the ACCESS Model Using Satellite Products
Cloud distribution characteristics over the Tibetan Plateau in the summer monsoon period simulated by the Australian Community Climate and Earth System Simulator (ACCESS) model are evaluated using COSP [the CFMIP (Cloud Feedback Model Intercomparison Project) Observation Simulator Package]. The results show that the ACCESS model simulates less cumulus cloud at atmospheric middle levels when compared with observations from CALIPSO and CloudSat, but more ice cloud at high levels and drizzle drops at low levels. The model also has seasonal biases after the onset of the summer monsoon in May. While observations show that the prevalent high cloud at 9–10 km in spring shifts downward to 7–9 km, the modeled maximum cloud fractions move upward to 12–15 km. The reason for this model deficiency is investigated by comparing model dynamical and thermodynamical fields with those of ERA-Interim. It is found that the lifting effect of the Tibetan Plateau in the ACCESS model is stronger than in ERA-Interim, which means that the vertical velocity in the ACCESS model is stronger and more water vapor is transported to the upper levels of the atmosphere, resulting in more high-level ice clouds and less middle-level cumulus cloud over the Tibetan Plateau. The modeled radiation fields and precipitation are also evaluated against the relevant satellite observations.
Key wordsTibetan Plateau cloud fraction ACCESS model COSP
利用COSP 2006-2012年的卫星雷达观测资料,本文对ACCESS 模式在青藏高原地区夏季云垂直结构的表现进行了详细评估.结果表明,和观测相比,模式对青藏高原上空的典型积云模拟偏少,而对高云和低云模拟明显偏多.卫星观测结果显示,夏季风爆发后,春季高原上空的高云逐渐向中低云转变,而ACCESS模拟的高云则主要向更高的高空发展,和卫星观测存在很大偏差.和ERA interim资料进行对比发现,ACCESS模式对青藏高原南坡的地形抬升作用描述偏强,季风爆发后,偏强的地形坡面抬升作用造成高原东南侧强对流发展过多过强,使得夏季青藏高原地区高云明显偏多,对流降水也比观测明显偏多.
关键词青藏高原 云量 ACCESS模式 COSP
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Drs. Gary DIETACHMAYER, Hongyan ZHU, and Tony HIRST are thanked for internally reviewing this manuscript. This study was funded by the Third Scientific Experiment of the Tibetan Plateau (Grant No. GYHY201406001), the National Natural Science Foundation of China (Grant Nos. 41575045, 41205030, and 41175046), and the Basic Research Fund of the Chinese Academy of Meteorological Sciences (Grant No. 2017Z013). The authors would like to thank TRMM TSDIS for providing the TRMM 3B42 datasets (ftp://disc2.nascom.nasa.gov/ftp/data/s4pa/TRMM L3/TRMM 3B42/). The CMAP precipitation data were provided by NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, via their website at https://doi.org/www.esrl.noaa.gov/psd/.
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