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ISSN 1006-9895

CN 11-1768/O4

2020年江淮流域超强梅雨年际异常的驱动因子分析
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作者单位:

1.国家气候中心;2.武汉区域气候中心

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基金项目:

国家自然科学基金


What drives the super strong precipitation over the Yangtze-Huaihe Valley in Meiyu periods of 2020?
Author:
Affiliation:

Laboratory for Climate Studies, CMA-NJU Joint Laboratory for Climate Prediction Studies, National Climate Center, China Meteorological Administration

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    摘要:

    利用观测诊断和数值模拟相结合的方法,研究了2020年江淮流域6~7月超强梅雨年际异常的环流特征和驱动因子。结果表明:(1)2020年梅雨期长度和江淮流域总降水量均为1961年以来第一位,超强梅雨主要与西北太平洋异常反气旋(WNPAC)的异常偏强和异常西伸有关,WNPAC为江淮流域梅雨期持续的强降水提供了充沛的水汽来源;(2)2019年11月~2020年3月,赤道中东太平洋发生一次弱的中部型El Ni?o事件,本次事件持续时间短、强度偏弱,不足以激发和维持2020年梅雨期异常偏强的WNPAC,而春、夏季热带印度洋和热带北大西洋海温异常持续偏暖是WNPAC异常偏强和西伸的主要驱动因子;(3)热带印度洋暖海温在其东部的西太平洋激发出大气Kelvin波响应,造成了纬向风变化的不均匀分布,通过埃克曼抽吸,抑制了局地对流活动,驱动了WNPAC的生成;而热带北大西洋暖海温则引起局地对流活动增强,导致热带北大西洋上空上升运动和热带中部太平洋下沉运动增强,在西北太平洋上空激发异常的低空反气旋;热带印度洋和热带北大西洋暖海温对2020年6~7月WNPAC异常偏强均有显著的正贡献。

    Abstract:

    Record–breaking rainfalls occurred over Yangtze–Huaihe River Basin (YHRB) in China during Meiyu Period (June–July, JJ) of 2020, causing severe floods and disasters. These rainfall anomalies were closely linked to the extremely strong anomalous anticyclone over the western North Pacific (WNPAC), which favored convergence of water vapor over YHRB. This study argued what have drived the record–breaking rainfalls and WNPAC in Meiyu periods of 2020. A weak Central–Pacific El Ni?o rapidly decayed in spring and developed to a La Ni?a in late summer, while sea surface temperature (SST) in the tropical Indian Ocean (TIO) and tropical northern Atlantic (TNA) was considerably high from previous winter to summer. We revealed that the weak decaying El Ni?o alone was not sufficient to maintain the strong WNPAC in JJ of 2020, whereas the long-lasted warm SST anomalies in the TIO and TNA prominently contributed to the enhancement and westward shift of the WNPAC. The TIO warming intensifies the WNPAC through the eastward propagation of Kelvin waves and/or modulating the Hadley circulation. The TNA warming can force a westward–extending overturning circulation over the Pacific–Atlantic Oceans, with a sinking branch over the central tropical Pacific, which suppresses the convection activity over there and in turn gives rise to the WNPAC. The TIO and TNA warming contributed significantly to the extremely strong WNPAC in JJ of 2020.

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  • 收稿日期:2021-01-24
  • 最后修改日期:2021-04-08
  • 录用日期:2021-04-19
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