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青藏高原冬春雪深异常对云南夏季降水的影响及可能机制
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1.云南电力调度控制中心;2.中国科学院大气物理研究所

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Impacts of Tibetan Plateau winter and spring snow depth anomalies on summer precipitation in Yunnan and possible mechanism
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1.Yunnan Electric Dispatching and Control Center;2.Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences

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    摘要:

    基于中国区域长时间序列雪深资料和CN05中国区域格点降水资料,本文利用奇异向量分解(SVD)和相关分析方法考察了云南地区夏季降水与前期青藏高原雪深的联系。结果表明,冬、春季高原中西部雪深偏多对应云南大部夏季降水的偏多,特别是云南北部金沙江流域和西南部区域降水偏多显著;且这种影响关系独立于ENSO对云南夏季降水的影响。结合ERA5再分析资料进一步揭示了高原关键区雪深异常对云南夏季降水的影响机制,指出前期高原中西部关键区积雪偏多时,通过积雪的反照率效应可导致春季高原中西部及附近区域近地面气温偏低,有利于南亚夏季风爆发偏晚,南亚夏季风偏弱,对应南亚季风低压偏弱,高原南侧为异常西风,有利于云南大部地区降水偏多。此外,高原关键区前期积雪偏多还可激发高低空波列,影响到东亚及我国西南的大气环流异常,其中高层200 hPa 波列沿中高纬西风急流传播,自高原西部经蒙古到达东北亚呈现明显的“负—正—负”位势高度异常传播,东北亚为气旋性环流异常,气旋性环流西侧的偏北气流有利于中高纬冷空气南下;850hPa低层波列自高原西南侧往南海传播,南海为异常反气旋环流。高原南侧西风和南海反气旋西北侧的西南风在云南上空形成低空切变,有利于云南地区夏季降水;同时冷空气南下到云南地区,与暖湿气流汇合,也有利云南地区夏季降水偏多。

    Abstract:

    Based on snow depth dataset over China and CN05 gridded precipitation data over China, the relationship between Tibet Plateau (TP) snow depth and the summer precipitation in Yunnan are investigated by using Singular Vector Decomposition (SVD) and correlation analysis. The results show that the positive snow depth anomalies in the central and western TP during winter and spring can enhance summer precipitation in Yunnan, especially in the Jinsha River basin and the southwest of Yunnan, and the correlations between TP snow depth and Yunnan summer precipitation may be independent of the influence of ENSO on summer precipitation in Yunnan. The possible impact mechanism has been investigated through the diagnostic analyses using ERA5 reanalysis datasets, it is suggested that heavier snow depth in the key region of TP lead to the lower surface air temperature in the central and western parts of the TP and nearby areas in spring, which is conducive to the late onset of the South Asian summer monsoon, hence weaker South Asian summer monsoon and the associated monsoon depression, along with the abnormal westerly wind to the south of the TP. Furthermore, colder surface temperature associated with heavier snow depth in the TP can also initiate the wave train at 200 hPa, which will propagate from the western part of the plateau through Mongolia to Northeast Asia along the westerly jet stream, and an anomalous cyclonic circulation could be found in Northeast Asia, which was conducive to the southward movement of the cold air in the middle and high latitudes, leading to more rainfall in Yunnan province. Meanwhile, wave train at the 850 hPa can also be found, which spread from the southwest side of the plateau to the South China Sea, leading to an anomalous anticyclone circulation in South China Sea. The anomalous low level shear over Yunnan will then be developed from the westerly wind on the south side of the plateau and the southwesterly wind on the northwest side of the South China Sea anticyclone, which is favorable for more precipitation in Yunnan. Meanwhile, cold air flows southward to Yunnan and converges with warm and humid air, which also contributes to enhanced summer precipitation in Yunnan.

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  • 收稿日期:2023-05-22
  • 最后修改日期:2023-06-10
  • 录用日期:2023-06-13
  • 在线发布日期: 2023-09-28
  • 出版日期: