Effect of Horizontal Resolution on the Representation of the Global Monsoon Annual Cycle in AGCMs
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The sensitivity of the representation of the global monsoon annual cycle to horizontal resolution is compared in three AGCMs: the Met Office Unified Model-Global Atmosphere 3.0; the Meteorological Research Institute AGCM3; and the Global High Resolution AGCM from the Geophysical Fluid Dynamics Laboratory. For each model, we use two horizontal resolution configurations for the period 1998–2008. Increasing resolution consistently improves simulated precipitation and low-level circulation of the annual mean and the first two annual cycle modes, as measured by the pattern correlation coefficient and equitable threat score. Improvements in simulating the summer monsoon onset and withdrawal are region-dependent. No consistent response to resolution is found in simulating summer monsoon retreat. Regionally, increased resolution reduces the positive bias in simulated annual mean precipitation, the two annual-cycle modes over the West African monsoon and Northwestern Pacific monsoon. An overestimation of the solstitial mode and an underestimation of the equinoctial asymmetric mode of the East Asian monsoon are reduced in all high-resolution configurations. Systematic errors exist in lower-resolution models for simulating the onset and withdrawal of the summer monsoon. Higher resolution models consistently improve the early summer monsoon onset over East Asia and West Africa, but substantial differences exist in the responses over the Indian monsoon region, where biases differ across the three low-resolution AGCMs. This study demonstrates the importance of a multi-model comparison when examining the added value of resolution and the importance of model physical parameterizations for simulation of the Indian monsoon.
Key wordsglobal monsoon high resolution modeling monsoon annual cycle AMIP
利用分别来自英国, 日本和美国的三个大气环流模式(AGCM): MetUM-GA3, MRI-AGCM和GFDL-HiRAM, 对比了水平分辨率提高对全球降水年循环模拟的影响. 通过对比分析1998-2008年3个AGCM不同分辨率模式模拟结果, 研究发现较之低分辨率版本, 高分辨率一致提高了低分辨率模式对年平均降水, 全球季风前两个年循环模态的降水和低层环流的模拟能力. 高分辨率对夏季风爆发和撤退时间的模拟的影响却具有区域依赖性, 高分辨率在三个AGCM对季风撤退时间模拟中的作用亦各不相同. 区域而言, 高分辨率一致减小了低分辨率模式中西非, 西北太平洋季风区年平均降水和前两个季风模态降水偏多的误差, 降低了东亚季风区的季风模态偏强, 春秋非对称模态偏弱的模拟偏差, 改善了三个AGCM中东亚和西非夏季风爆发偏早的误差. 然而在印度季风区, 不同低分辨率模式模拟的爆发时间偏差及其对高分辨率的响应均不相同. 因此, 本文表明有必要采用多模式比较的方法以明确高分辨率对模拟结果影响, 物理参数化过程对提升印度季风模拟能力至关重要.
关键词全球季风 高分辨率模拟 季风年循环 AMIP
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This work was jointly supported by the National Natural Science Foundation of China (Grant Nos. 41420104006, 41330423), Program of International S&T Cooperation under grant 2016YFE0102400, and the UK–China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund. Nicholas P. KLINGAMAN was funded by an Independent Research Fellowship from the Natural Environment Research Council (Grant No. NE/L010976/1).
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