El Niño事件发展期对中国东部夏季极端降水的影响

Influence of developing phase of El Niño events on summer extreme precipitations in eastern China

  • 摘要: 利用1961—2020年的再分析资料和中国台站观测降水数据集,研究了东部型El Niño事件发展期夏季对中国夏季极端降水的影响.结果表明,东部型El Niño在发展期夏季对中国极端降水的影响主要表现在中国东部地区,造成华北和江南地区极端降水减少,江淮地区极端降水显著增多.进一步分析其中的物理过程发现,当东部型El Niño事件处于发展期夏季时,赤道东太平洋出现显著的海表面温度(sea surface temperature,SST)暖异常,西太平洋区域表现为冷异常,导致反气旋性环流异常.同时,西北太平洋区域存在SST暖异常,对应气旋性环流异常.异常的SST分布激发了“正-负-正(+ − +)”的东亚-太平洋型(East Asia-Pacific,EAP)波列异常,对应着“负-正-负(− + −)”的降水配置.在2个异常环流的交汇处有显著的辐合上升运动,为江淮地区带去了充足的水汽.而华北地区主要受到反气旋性环流和蒙古高压的共同控制,并受到来自高纬度地区的异常西北风影响,存在显著的辐散下沉运动,降水的动力条件不足.并且,在东部型El Niño事件发展期夏季,西太平洋副热带高压位置异常偏东,不利于江南地区降水的发生及水汽的输送,进一步造成江南地区极端降水减少.以上结果显示东部型El Niño事件在其发展期夏季对中国极端降水存在重要的影响,为区域极端气候预测提供了理论依据.

     

    Abstract: Re-analysis data and precipitation dataset from 1961 to 2020 were used in this paper to analyze the influence of developing phase of Eastern Pacific El Niño events on summer extreme precipitations in China. It was found that during the developing summer, El Niño mainly affected eastern China, resulting in extreme precipitations in Northern China. Extreme precipitations decreased in the Jiangnan region, but increased significantly in the Jianghuai region. Physical process analysis revealed that when Eastern Pacific El Niño event is in the developing summer, significant positive SST anomalies were observed in the equatorial Eastern Pacific and negative SST anomalies were observed in the Western Pacific, which are associated with anticyclonic circulation anomalies. There were positive SST anomalies in the Northwest Pacific, corresponding to cyclonic circulation anomalies. Anomalous SST stimulated “+ - +” EAP wave train anomalies and caused “- + -” precipitation configuration. At the intersection of anomalous circulations, it showed a significant anomalous convergence and ascent, which brought sufficient water vapor to the Jianghuai region. Northern China was mainly controlled by anticyclonic circulation and Mongolian high, however, affected by anomalous northwest wind at high latitudes. There was significant anomalous divergence and sinking, the dynamic conditions of precipitation were insufficient. During the developing phase of Eastern Pacific El Niño events, the Western Pacific subtropical high shifted eastward, which weakened the occurrence of precipitation and water vapor transport in Jiangnan region, resulting in decreased extreme precipitations in Jiangnan region. These results highlight the important impact of Eastern Pacific El Niño events on extreme precipitations in China during the developing summer, and provide a theoretical basis for regional extreme climate prediction.

     

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