| 前冬印度洋海盆一致模对ENSO衰减期华南春季降水的影响 |
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| 引用本文： | 殷鑫,吴小飞.前冬印度洋海盆一致模对ENSO衰减期华南春季降水的影响[J].高原山地气象研究,2022,42(4):49-59. |
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| 作者姓名： | 殷鑫 吴小飞 |
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| 作者单位： | 成都信息工程大学大气科学学院/高原大气与环境四川省重点实验室, 成都 610225 |
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| 基金项目： | 国家自然科学基金项目（41705065）；四川省自然科学基金项目（2022NSFSC0229） |
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| 摘 要： | 利用逐月台站观测降水、HadISST1.1海温和ERA5大气再分析资料，研究了前冬印度洋海盆一致模（Indian Ocean Basin，IOB）对华南春季降水（SCSR）与ENSO关系的影响，并分析了IOB通过调控ENSO环流异常进而影响SCSR的可能机制。结果表明:当前冬El Ni?o（La Ni?a）与IOB暖（冷）位相同时发生时，SCSR显著增多（减少）；而当El Ni?o或La Ni?a单独发生而IOB处于中性时，SCSR并无明显多寡倾向。其原因在于，当El Ni?o与IOB暖相位并存时，前冬热带印度洋和赤道中东太平洋均为正海温异常（Sea-Surface Temperature Anomaly，SSTA），且印度洋SSTA强度可一直维持至春季。在对流层低层，春季赤道中东太平洋的正SSTA激发出异常西北太平洋反气旋（Western North Pacific Anticyclone，WNPAC）。而热带印度洋的正SSTA在副热带印度洋激发出赤道南北反对称环流，赤道以北的东风异常有利于异常WNPAC西伸；赤道以南的西风异常与来自赤道西太平洋的东风异常在东印度洋辐合上升，气流至西北太平洋下沉，形成经向垂直环流，有利于春季WNPAC维持。在对流层高层，印度洋的正SSTA在热带印度洋上空激发出位势高度正异常，随之形成的气压经向梯度加强了东亚高空副热带西风急流，进而在华南上空形成异常辐散环流。WNPAC的西伸和加强可为华南提供充足的水汽，同时高空辐散在华南引发水汽上升运动，共同导致SCSR正异常。而若El Ni?o发生时IOB处于中性状态，El Ni?o相关的SSTA衰减较快，春季WNPAC不显著，SCSR无明显多寡趋势。
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| 关 键 词： | 华南春季降水 年际变率 厄尔尼诺-南方涛动 印度洋海温异常 |
| 收稿时间： | 2022-03-25 |
Influence of Indian Ocean Basin on South China Spring Rainfall during the Decaying Phase of ENSO in Preceding Winter |
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| Institution: | School of Atmospheric Sciences/Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, Chengdu University of Information Technology, Chengdu 610225, China |
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| Abstract: | Based on the monthly station-observed rainfall, HadISST 1.1 sea surface temperature (SST) and ERA5 atmospheric reanalysis datasets, the influence of the Indian Ocean SST basin mode (IOB) on the relationship between South China spring rainfall (SCSR) and ENSO in preceding winter is studied, and the possible mechanism of IOB affecting SCSR by regulating ENSO circulation anomalies is analyzed. The results show that: In preceding winter, above-normal (below-normal) SCSR usually occurs following the El Ni?o (La Ni?a) events associated with warm (cold) IOB phases; while the SCMR anomaly is ambiguous during El Ni?o or La Ni?a years with neutral IOB. The reason is that when El Ni?o occurs accompanied by warm IOB phases, the tropical Indian Ocean and the equatorial central-eastern Pacific Ocean are characterized by Sea-Surface Temperature Anomaly (SSTA), and SSTA persists from preceding winter to last spring. In the lower troposphere, positive SSTA in the central and eastern equatorial Pacific Ocean during spring induces an anomalous Western North Pacific Anticyclone (WNPAC). The positive SSTA in the tropical Indian Ocean induces an equatorial north-south antisymmetric circulation in the subtropical Indian Ocean, and anomalous easterly in the north of the equator favors the westward extension of the anomalous WNPAC. The anomalous westerly in the south of the equator the anomalous easterly from the equatorial western Pacific Ocean converge and rise in the eastern Indian Ocean, and the airflow sinks to the northwest Pacific Ocean, forming a meridional vertical circulation, which is conducive to the maintenance of WNPAC in spring. In the upper troposphere, the positive SSTA over the tropical Indian Ocean induces positive geopotential height anomalies over the tropical Indian Ocean associated with a strong pressure meridional gradient, resulting in an enhanced East Asian subtropical westerly jet, thus leading to anomalous divergence over South China. The westward extending and strengthening of WNPAC transports enough moisture to South China, and the moisture moves upward caused by the upper-tropospheric divergence, leading to above-normal SCSR. In contrast, during the El Ni?o events with neutral IOB, the SSTA decreases quickly and the WNPAC is not significant in the spring, resulting in indeterminate SCSR. |
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