华南夏季极端高温天气对应的不同环流型及其可能成因

The occurrence of extreme heat (EH) weather greatly threatens the human health, and the social and economic developments. South China experiences EH frequently in summer, with top-rank climatological frequency and increasing trend. Therefore, detailed investigation on the causes of EH in South China is of great significance. Our primary analysis shows that the synoptic circulation anomalies associated with EH in South China are obviously different from the typical anticyclonic pattern for many other regions. The synoptic circulation anomalies associated with EH in South China could be classified into three categories, including the anticyclonic pattern, the cyclonic pattern and the anticyclonic-cyclonic pattern. However, the vertical structures and the causes of these three circulation patterns are still unclear. Therefore, based on the facts that various circulation patterns are associated with EH in South China, this project plans to comprehensively investigate the different circulation patterns. The daily data from the China observational stations and the China homogenized temperature series, and the various 6-hourly reanalysis data of atmosphere would be used, and the climate statistical analysis and dynamical diagnose would be employed. The three-dimensional features and the evolutions of each EH circulation pattern would be analyzed in detail. Meanwhile, the influences of different circulation patterns on the features of EH, including the EH strength, duration, spatial distribution and occurrence date during the summer season, would be analyzed and the related physical processes would be explored. Furthermore, the possible causes for the formations of different circulation patterns would be investigated in depth.

极端高温对人体健康和社会经济发展造成巨大威胁。华南是我国极端高温天气频发且明显增多的地区，因此，研究华南高温的发生原因具有重要意义。初步的分析表明华南高温的天气尺度环流异常与典型的反气旋型明显不同，它体现为反气旋型、气旋型、反气旋-气旋对三种环流型，目前这些环流型的垂直结构以及形成原因尚不明确。因此，本项目拟从华南高温环流具有多样性这一独特的现象入手，利用中国台站逐日观测资料、中国均一化站点温度资料和多种大气逐6小时再分析资料，采用气候统计和动力诊断方法，详细地分析华南高温对应的各类环流型的三维空间分布和演变特征，系统地揭示各类环流型对华南高温的强度、持续性、空间分布、发生时间的季节内分布等特征的具体影响并阐明其物理过程，深入地探讨华南高温不同环流型形成的可能原因。

与一般的反气旋型不同，华南高温环流型具有独特性，表现为异常的反气旋-气旋对，该反气旋-气旋对是多种环流型的平均体现。本项目从华南高温环流的多样性入手开展研究，全面分析了华南高温不同环流型的结构和演变特征，细化比较不同环流型对高温特征的具体影响及其物理过程，深入探讨不同环流型的可能成因，进而深入理解华南高温的发生原因。主要研究结果包括：（1）华南高温的反气旋-气旋对环流型与热带季节内振荡有关。季节内振荡波列从热带西太平洋往西北向传播至华南，在反气旋异常的控制下华南容易出现高温。另外，不同波段的季节内振荡影响高温事件的持续时间、在高温事件的不同阶段所起作用不同。（2）华南高温的反气旋式环流异常与西太副高的加强西伸有关。反气旋式环流异常受热带海温影响，对应热带太平洋从前冬El Niño到同期夏季La Niña的转变位相。夏季热带西太平洋暖海温通过激发异常的局地Hadley环流有利于华南产生异常下沉形成高压，热带中东太平洋冷海温则通过Walker环流，进一步加强热带西太平洋的对流活动，从而间接影响华南上空的环流异常。即使在ENSO信号很弱时，热带西太平洋暖海温可以单独对华南高温造成重要影响。（3）华南高温与大气环流和热带海温的关系在1990年代初发生年代际变化。1990年代初之前，华南盛夏高温主要受中纬度遥相关波列影响，热带海温影响弱，反气旋型环流中心位于华南北侧。1990年代初之后，华南高温对应的中纬度波列弱，主要受热带海温影响，反气旋型环流中心位于华南上空，热带海温型呈现从El Niño向La Niña的转变位相。这些结果为华南高温不同时间尺度的预报和预测提供了科学依据，包括高温天气的延伸期预报、年际和年代际预测，有利于提高华南极端灾害的防灾减灾科技水平。