IOD Modoki事件对华南后汛期降水异常的影响及可能机理
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国家自然科学基金资助项目(42088101;42030605;41905061);江苏省高等学校自然科学研究面上项目(19KJB170024);安徽省自然科学基金青年项目(2008085QD190)


Influence of SSTA in the Indian Ocean on rainfall anomalies during the second rainy season in South China and its mechanism
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    摘要:

    利用1979—2019年CN05.1中国区域高分辨率降水格点数据、英国Hadley中心观测海温数据、ERA5逐月大气再分析资料及大气环流模式,研究了华南后汛期期间(7—9月)IOD Modoki事件与华南后汛期降水异常的关系及可能机理。观测资料结果表明,华南后汛期降水异常与热带印度洋中部(东和西部)海温异常呈显著正(负)相关关系,表现为印度洋IOD Modoki或印度洋三极子事件的空间分布型。滤除ENSO信号影响后,华南后汛期降水异常仍和IOD Modoki存在较为密切的联系。IOD Modoki正异常对华南后汛期降水异常的影响有以下途径,一方面,异常水汽从热带印度洋东部向西输送至热带中印度洋后,在北半球受科氏力作用向东输送至华南地区,为华南地区提供了充足的水汽条件,并且对华南地区降水正异常的主要水汽辐合贡献为平均水汽的水平扰动散度项和扰动引起的平均水汽垂直平流项。另一方面,热带东南印度洋海温负异常,通过Mastuno-Gill响应引起对流层低层自热带东南印度洋至热带中印度洋有东南风异常,增强了70°E附近的越赤道气流,在北半球向东输送至西北太平洋,这引起了华南地区对流层低层气旋式环流异常。另外,热带东印度洋对流层低(高)层异常辐散(辐合),华南地区低(高)层异常辐合(辐散)增强了东亚地区的局地Hadley环流,有利于华南地区降水的产生。再者,IOD Modoki引起南亚季风区受异常下沉运动控制,并通过季风-荒漠机制引起副热带北大西洋东部、北非荒漠区及地中海西部周围正涡度异常,激发了沿急流向下游传播的准静止Rossby波,增强了日本海高压异常和华南及邻近地区对流层低层气旋式环流异常。上述原因均有利于华南地区降水的产生,反之亦然。上述结果在数值模式中亦得到了验证。

    Abstract:

    South China has an important position and influence in economic,cultural and social development,and the SST anomalies in the Indian Ocean have a non-negligible impact on the weather and climate of South China.This paper explores the mechanism of precipitation anomalies during the second rainy season in South China to improve the theoretical system of precipitation anomalies in South China,and to provide a scientific basis for a deep understanding of drought and flooding anomalies,and work on prevention and mitigation of disasters in South China.In this paper,the relationship between IOD Modoki and precipitation anomalies during the second rainy season (July to September) in South China and possible mechanisms were investigated using CN05.1 Chinese regional high-resolution precipitation grid data for 1979—2019,SST data from Hadley Centre observations made in the UK,and ERA5 month-by-month atmospheric reanalysis data.The results show that the precipitation anomalies during the second rainy season in South China are significantly positively (negatively) correlated with the SST anomalies in the central (eastern and western) tropical Indian Ocean,manifesting as the spatial distribution of Indian Ocean IOD Modoki or Indian Ocean triple polariton events.After filtering out the influence of the ENSO signal,the precipitation anomalies during the second rainy season in South China are still more closely related to the IOD Modoki.The influences of positive IOD Modoki anomalies on the precipitation anomalies during the second rainy season in South China are as follows:1.The anomalous water vapour is transported westward from the eastern tropical Indian Ocean to the tropical Central Indian Ocean,then transported eastward to South China by the Koch force in the northern hemisphere,thus providing sufficient water vapour conditions in South China.The main water vapour convergence contributions to the positive precipitation anomaly in South China are the horizontal disturbance divergence term of the mean water vapour and the mean water vapour vertical advection term caused by the disturbance.2.Negative SST anomalies in the tropical southeast Indian Ocean cause southeasterly wind anomalies in the lower troposphere from the tropical southeast Indian Ocean to the tropical central Indian Ocean through the Mastuno—Gill response,enhancing the trans-equatorial flow near 70°E,which is then transported eastward to the northwest Pacific in the northern hemisphere,where it causes lower tropospheric cyclonic circulation anomalies.3.The anomalous low (high) tropospheric divergence (convergence) in the tropical East Indian Ocean and anomalous low (high) tropospheric convergence (divergence) anomalous convergence in South China enhance the local Hadley circulation in East Asia and favour precipitation generation in South China.4.The IOD Modoki causes the South Asian monsoon region to be controlled by anomalous downwelling motion,and causes positive vorticity anomalies around the eastern subtropical North Atlantic,North African desert region and western Mediterranean through the monsoon—desert mechanism.This in turn excites quasi-stationary Rossby waves propagating downstream along the rapids,and enhances the Japan Sea high pressure anomaly and lower tropospheric cyclonic circulation anomaly in South China and adjacent areas.All of these factors favour the production of precipitation in South China,while the absence of these factors is detrimental to the production of precipitation in South China.The above results are also verified in the numerical model.

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陈业雁,金大超,史瀛龙,张茜,柳春,2024. IOD Modoki事件对华南后汛期降水异常的影响及可能机理[J].大气科学学报,47(3):425-437. CHEN Yeyan, JIN Dachao, SHI Yinglong, ZHANG Qian, LIU Chun,2024. Influence of SSTA in the Indian Ocean on rainfall anomalies during the second rainy season in South China and its mechanism[J]. Trans Atmos Sci,47(3):425-437. DOI:10.13878/j. cnki. dqkxxb.20220817001

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  • 收稿日期:2022-08-17
  • 最后修改日期:2023-12-05
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  • 在线发布日期: 2024-06-15
  • 出版日期: 2024-05-28

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