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CN 11-1768/O4

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2019年4-6月云南持续性高温天气的大气环流异常成因
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中国气象科学研究院气候系统研究所

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国家自然科学基金(批准号: 41705052, 41775052)


Possible causes of persistently extreme hot days related circulation anomalies in Yunnan during April to June in 2019
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Institute of Climate System,Chinese Academy of Meteorological Sciences

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    摘要:

    2019年4-6月,云南省发生了历史罕见的持续性极端高温天气,并引发了严重气象干旱。本文利用1961-2019年逐日温度和大气再分析等资料以及CESM-LE计划(Community Earth System Model Large Ensemble Project)模式模拟结果,分析了历史同期云南极端高温天气发生的环流特征,探讨了2019年云南破纪录持续性高温的成因。历史极端高温天的合成分析表明,云南地区对流层上层显著异常反气旋伴随的强下沉异常和到达地表太阳辐射增加,是引发该区域极端高温天气的主要成因。该异常反气旋的形成主要源自北大西洋经东欧平原、西西伯利亚平原向东亚传播的高纬度罗斯贝波和经北非、黑海、伊朗高原向东亚传播的中纬度罗斯贝波之间的相互作用。2019年极端高温的强度和与之相应异常反气旋出现自1961年以来的最强。外强迫导致的增暖对2019年极端暖异常强度和发生概率的贡献分别约为37.51%和56.32%,内部变率对该事件也具有重要贡献。2019年4-6月,北极涛动(Arctic Oscillation,AO)和ENSO事件分别处于历史极端负位相和暖位相。一方面,在AO强负位相影响下,极地上空深厚的位势高度正异常向南伸至东欧平原,有利于高纬度波列和云南上空的反气旋异常增强。另一方面,ENSO事件暖位相加强了西北太平洋异常反气旋环流,令西北太平洋副热带高压增强西伸至我国内陆地区,维持了云南上空反气旋异常。两者的共同作用,造成了2019年4-6月云南上空持续的深厚异常反气旋,云南地区继而出现持续性极端高温事件。

    Abstract:

    Persistently extreme hot days broke the historical length record, which attacked Yunnan province and induced the local serve drought during April to June in 2019. Based on daily in-suit surface air temperature in China, JRA-55 reanalysis datasets and outputs of the Community Earth System Model Large Ensemble (CESM-LE) Project, we investigated the general circulation regime related to the hot weathers in Yunnan, and discuss the possible causes of the persisting hot days in 2019. Our results show the lower- and upper-level strong anticyclonic circulation anomalies directly results in the local hot weather, it induces adiabatic warming by descending motion and enhances the solar radiation heating at surface. The anti-cyclonic anomaly is one node of high and mid-latitude eastward propagating wave trains, originated from North Atlantic. The 2019 April-June mean temperature and associated anticyclonic anomalies was the highest since 1961. The anthropogenic contribution to the magnitude and occurrence probability of the temperature anomaly in 2019 is approximately 37.51% and 56.32%, with an important impact of internal variability. The negative phase of Arctic Oscillation (AO) and warm phase of El Nino and Southern Oscillation (ENSO) are important external forcing factors responsible for the persistent anticyclonic anomalies over Yunnan during April to June in 2019. The negative phase of AO causes the southward shift of the positive geopotential height anomalies over Arctic at the longitudes of Eastern Europe, favors the high-latitude wave train and anti-cyclonic anomaly over Yunnan. The warm phase of ENSO enhances the western North Pacific anticyclone and favors its westward shift, leading to the persistence of the anticyclonic anomalous circulation over Yunnan. The negative phase of AO and warm phase of ENSO jointly reinforce the intensity, duration of the anticyclonic anomalous circulation over Yunnan, and result in frequent and persistent occurrences of the record-breaking extremely high temperatures and serve drought event in 2019 under recent global warming.

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  • 收稿日期:2019-10-14
  • 最后修改日期:2020-01-13
  • 录用日期:2020-05-12
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