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。历史极端高温日的合成分析表明，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年极端暖异常强度的贡献约为37.51%，同时对类似2019年以及更强极端暖事件发生概率的贡献为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。
关键词:极端高温/
反气旋异常/
罗斯贝波列/
北极涛动/
ENSO
Abstract:A series of persistently extreme hot days, which broke the historical record for length, was experienced by Yunnan province from April to June 2019 and induced a severe local drought. Based on the daily in-situ surface air temperature in China, JRA-55 reanalysis datasets, and outputs from the Community Earth System Model Large Ensemble (CESM-LE) Project, we investigate the general circulation regime related to the hot weather in Yunnan and discuss the possible causes of these persistently hot days in 2019. Our results indicate that lower- and upper-level strong anticyclonic circulation anomalies directly result in the local hot weather, which induces adiabatic warming in a descending motion and enhances solar radiation heating at the surface. The anticyclonic anomaly is a node of high and mid-latitude eastward-propagating wave trains originating from the North Atlantic. The 2019 April–June mean temperature and associated anticyclonic anomalies were the highest recorded since 1961. The anthropogenic contribution to the magnitude of this 2019 temperature anomaly was approximately 37.51% and the occurrence probability of extreme-high-temperature events analogous to or higher than those of 2019 is 56.32%, with an important impact of internal variability. The negative phase of the Arctic Oscillation (AO) and warm phase of El Ni?o and the Southern Oscillation (ENSO) are important external forcing factors responsible for the persistent anticyclonic anomalies over Yunnan from April to June 2019. The negative phase of the AO causes a southward shift of the positive geopotential height anomalies over the Arctic at the longitudes of Eastern Europe, and favors a high-latitude wave train and an anticyclonic anomaly over Yunnan. The warm phase of ENSO enhances the western North Pacific anticyclone and favors its westward shift, which leads to the persistence of the anomalous anticyclonic circulation over Yunnan. Under the recent global warming conditions, the negative phase of the AO and the warm phase of ENSO jointly reinforce the intensity and duration of the anomalous anticyclonic circulation over Yunnan, which result in frequent and persistent occurrences of the record-breaking extremely high temperatures and the severe drought event in 2019.
Key words:Extreme hot days/
Anticyclonic anomaly/
Rossby wave trains/
Arctic Oscillation/
ENSO
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