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不同PDO位相下El Niño发展年和La Niña年东亚夏季风的季节内变化
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国家自然科学基金项目41706028、41630530


Intraseasonal Variations of the East Asian Summer Monsoon in El Niño Developing Years and La Niña Years under Different Phases of the Pacific Decadal Oscillation
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    摘要:

    基于1957~2017年观测和再分析资料,合成分析了北太平洋年代际振荡(Pacific decadal oscillation,PDO)不同位相下El Niño发展年和La Niña年东亚夏季风的环流、降水特征及季节内变化。结果表明,PDO正、负位相作为背景场,分别对El Niño发展年、La Niña年东亚夏季风及夏季降水具有加强作用。PDO正位相一方面可增强El Niño发展年夏季热带中东太平洋暖海温异常信号,另一方面通过冷海温状态加强中高纬东亚大陆与西北太平洋的环流异常,从而在一定程度上增强了东亚夏季风环流的异常程度;反之,PDO负位相则增强了La Niña年热带海气相互作用以及中高纬环流(如东北亚反气旋)的异常。在季节内变化方面,El Niño发展年6月贝湖以东反气旋性环流为东亚地区带来稳定的北风异常,东北亚位势高度减弱;7月开始,环流形势发生调整,日本以东洋面出现气旋性异常,东亚大陆偏北风及位势高度负异常均得到加强;8月,随着东亚夏季风季节进程和El Niño发展,西太平洋出现气旋性环流异常,东亚副热带位势高度进一步降低,西北太平洋副热带高压(简称副高)明显东退。La Niña年6月异常较弱,主要环流差异自7月西北太平洋为大范围气旋性异常控制开始,东亚—太平洋遥相关型显著,副高于季节内始终偏弱偏东。上述两种情况下,均造成东亚地区夏季降水总体上偏少,尤其是中国北方降水显著偏少。

    Abstract:

    Based on observational and reanalysis datasets of 1957-2017, this study compares the impact of different phases of the Pacific Decadal Oscillation (PDO) on the seasonal and intraseasonal variation of the East Asian Summer Monsoon (EASM) in El Niño developing years and La Niña years. The results show that the PDO positive (negative) phase reinforces El Niño developing (La Niña) behaviors mainly by modifying the background EASM circulation, precipitation, and intraseasonal variation. When El Niño is in phase with the PDO (El Niño/high PDO), the PDO amplifies the warm SST (sea surface temperature) anomalies signal of the central and eastern Pacific during the summer; in addition, it strengthens the mid-high latitudes circulation anomalies of the East Asia continent and the Northwest Pacific through the cold SST state. In La Niña years, the negative PDO phase promotes the tropical air-sea interaction and also causes circulation anomalies in mid-high latitudes, such as an anti-cyclonic anomalies in Northeast Asia. Regarding intraseasonal variations, during June in El Niño developing years, there exists stable northerly anomalies from the anti-cyclonic circulation east of Lake Baikal, which induces negative geopotential height anomalies over East Asia. From July, the circulation is adjusted, a cyclonic anomalies appears in the eastern ocean of Japan, and the northerlies, and negative geopotential height anomalies are strengthened. In August, with the EASM seasonal march and the development of El Niño, a cyclonic anomalies occurs in the western Pacific Ocean, the subtropical geopotential height further reduces, and WPSH (western Pacific subtropical high) retreats eastward. In La Niña years, the circulation anomalies are weak in June. The main differences begin with July, characterized by a large-scale cyclonic anomalies control in the Northwest Pacific Ocean and a significant East Asia-Pacific teleconnection pattern, which eventually weakens the WPSH and retreats it eastward. As a result, during the period 1957-2017, less summer precipitation existed in both cases over East Asia, especially in northern China.

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张雯,董啸,薛峰.不同PDO位相下El Niño发展年和La Niña年东亚夏季风的季节内变化.大气科学,2020,44(2):390~406 ZHANG Wen, DONG Xiao,XUE Feng.Intraseasonal Variations of the East Asian Summer Monsoon in El Niño Developing Years and La Niña Years under Different Phases of the Pacific Decadal Oscillation.Chinese Journal of Atmospheric Sciences (in Chinese),2020,44(2):390~406

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  • 收稿日期:2018-12-12
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  • 在线发布日期: 2020-03-20
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