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CN 11-1768/O4

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不同PDO位相下El Ni?o发展年和La Ni?a年东亚夏季风的季节内变化
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1.中国气象局旱区特色农业气象灾害监测预警与风险管理重点实验室;2.宁夏回族自治区气候中心;3.中国科学院大气物理研究所国际气候与环境科学中心

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国家自然科学基金


Intraseasonal Variations of the East Asian Summer Monsoon in El Ni?o Developing Years and La Ni?a Years under Different Phases of the Pacific Decadal Oscillation
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International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences

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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 Ni?o发展年和La Ni?a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 Ni?o发展年、La Ni?a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 Ni?o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 Ni?a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 Ni?o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 Ni?o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,副高明显东退。La Ni?a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 during 1957-2017, this study compares the impact of different phases of the Pacific Decadal Oscillation (PDO) on seasonal and intraseasonal variation of the East Asian summer monsoon (EASM) in El Ni?o developing years and La Ni?a years. Results show that PDO positive (negative) phase reinforces El Ni?o developing (La Ni?a) behaviors mainly via modifying the background EASM circulation, precipitation and intraseasonal variation. When El Ni?o is in phase with PDO (El Ni?o/ high PDO), PDO amplifies the warm sea surface temperature (SST) anomaly signal of the central and eastern Pacific during the summer, besides it strengthens the mid-high latitudes circulation anomaly of the East Asia continent and the Northwest Pacific through the cold SST state. In La Ni?a years, the negative PDO phase promotes the tropical air-sea interaction and also causes the circulation anomalies in mid-high latitudes, such as an anti-cyclonic anomaly in northeast Asia. With respect to intraseasonal variations, during the June of El Ni?o developing years, there exist stable northerly anomalies from anti-cyclonic circulation east of Lake Baikal, which induces negative geopotential height anomalies over East Asian. Since July, the circulation has been adjusted, cyclonic anomaly has appeared in the eastern ocean of Japan, besides the northerlies and negative geopotential height anomalies have been strengthened. In August, with the seasonal march of EASM seasonal and the development of El Ni?o, cyclonic anomaly occurs in the Western Pacific Ocean, the subtropical geopotential height further reduces and the western Pacific subtropical high (WPSH) retreats eastward clearly. In La Ni?a years, the circulation anomalies are weak in June. The main differences begin with July, characterized by the large-scale cyclonic anomaly control in the Northwest Pacific Ocean and the significant East Asia-Pacific teleconnection pattern, which eventually weakened the WPSH and retreated it eastward. As a result, there was less summer precipitation in both cases over East Asia especially in northern China.

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  • 收稿日期:2018-12-12
  • 最后修改日期:2019-09-27
  • 录用日期:2019-09-29
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