Different Asian Monsoon Rainfall Responses to Idealized Orography Sensitivity Experiments in the HadGEM3-GA6 and FGOALS-FAMIL Global Climate Models
Recent work has shown the dominance of the Himalaya in supporting the Indian summer monsoon (ISM), perhaps by surface sensible heating along its southern slope and by mechanical blocking acting to separate moist tropical flow from drier midlatitude air. Previous studies have also shown that Indian summer rainfall is largely unaffected in sensitivity experiments that remove only the Tibetan Plateau. However, given the large biases in simulating the monsoon in CMIP5 models, such results may be model dependent. This study investigates the impact of orographic forcing from the Tibetan Plateau, Himalaya and Iranian Plateau on the ISM and East Asian summer monsoon (EASM) in the UK Met Office’s HadGEM3-GA6 and China’s Institute of Atmospheric Physics FGOALS-FAMIL global climate models. The models chosen feature oppositesigned biases in their simulation of the ISM rainfall and circulation climatology.
The changes to ISM and EASM circulation across the sensitivity experiments are similar in both models and consistent with previous studies. However, considerable differences exist in the rainfall responses over India and China, and in the detailed aspects such as onset and retreat dates. In particular, the models show opposing changes in Indian monsoon rainfall when the Himalaya and Tibetan Plateau orography are removed. Our results show that a multi-model approach, as suggested in the forthcoming Global Monsoon Model Intercomparison Project (GMMIP) associated with CMIP6, is needed to clarify the impact of orographic forcing on the Asian monsoon and to fully understand the implications of model systematic error.
Key wordsTibetan Plateau East Asian summer monsoon Indian summer monsoon model bias Global Monsoon Model Intercomparison Project (GMMIP)
最近的研究工作已经表明喜马拉雅山在印度夏季风的主导作用, 也许是靠其南侧斜坡地表感热或者是靠其机械阻挡作用使来自中纬度的干空气和热带湿气流隔离开. 以往的研究也已经表明如果在敏感性实验中仅仅去除青藏高原, 印度夏季降水并不会受到太大影响. 然而, 考虑到CMIP5模式在季风的模拟存在较大的偏差, 这样的结果可能具有模式依赖性. 本文使用来自UK Met Office HadGEM3-GA6和中国大气物理研究所FGOALS-FAMIL两个大气环流模式研究了青藏高原、喜马拉雅山和伊朗高原的地形强迫对印度夏季风和东亚夏季风的影响. 选择的两个模式在印度夏季风降水和环流的气候平均态上存在相反符号的偏差. 印度夏季风和东亚夏季风环流的变化在两个模式中都比较相似, 与以往研究结果一致. 然而, 印度和中国的降水响应存在相当大的差异, 在细节方面比如爆发和回撤的日期. 特别的, 两个模式在剔除喜马拉雅山和青藏高原的地形实验中在印度季风降水方面表现出相反的变化. 我们的研究表明, 正如即将到来的CMIP6中全球季风模式比较计划(GMMIP)所建议的, 需要使用多模式方法来阐明地形强迫对亚洲季风的影响并充分理解模式系统性偏差的意义.
关键词青藏高原 东亚夏季风 印度夏季风 模式偏差 GMMIP
This study was supported jointly by the UK–China Research and Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China and the Major Research Plan of the National Natural Science Foundation of China (Grant Nos. 91637312 and 91437219).
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