我国南方盛夏气温主模态特征及其与海温异常的联系

Major Modes of Midsummer Air Temperature in Southern China and Their Relationship with Sea Surface Temperature Anomalies

利用NCEP/NCAR大气环流资料、HadISST海温数据以及中国160站气温数据等,通过EOF分解、线性相关等统计方法,分析了我国南方盛夏气温异常的主导模态及其所对应的关键环流系统和可能的海洋外强迫信号。结果表明:我国南方盛夏气温偏高有两种不同的分布模态,一是以江淮地区为中心的江淮型高温,二是以江南和华南为中心的江南型高温,导致这两种高温型发生的环流影响系统和海温外强迫因子均有显著差异。影响江淮型高温的关键环流系统是高低空正压结构的高度场正距平和偏弱的东亚副热带西风急流。而影响这两个关键环流系统的海洋外强迫因子包括热带印度洋至东太平洋的"-+-"海温异常分布型及北大西洋中纬度的暖海温异常。2016年盛夏江淮型高温的大气环流和海温异常均表现出典型江淮型高温年的特征,更好的证明了统计分析的结论。而江南型高温的关键环流系统主要是加强西伸的西太平洋副热带高压。其海洋外强迫因子包括前冬赤道中东太平洋的暖海温异常和春季—盛夏热带印度洋全区一致型暖海温异常,其中热带印度洋海温的影响更为持续和显著。

The empirical orthogonal function（EOF） and correlation analyses are applied to NCEP/NCAR atmospheric circulation data, Had ISST data, and air temperature data collected at 160 observational stations in China to study the major spatial distribution modes of air temperature anomaly in southern China during midsummer（July–August）. Critical circulation systems corresponding to higher than normal temperature and possible external forcing signals of the ocean are investigated in great detail. The results show that there are two major modes of high temperature anomaly in southern China in the midsummer, i.e., the Jianghuai type with the center of high temperature anomaly located in the middle and lower reaches of the Yangtze River valley and Huai River valley and the Jiangnan type with the center of hightemperature anomaly located to the south of the Yangtze River valley. Both the atmospheric circulation and external forcing signals are quite different between the two types. For the Jianghuai type, the critical circulation systems are positive anomalies of geopotential height at 500 hPa and 200 hPa and weakened East Asian subtropical westerly jet. Meanwhile, the oceanic forcing signals include the anomalous ＂-＋-＂ sea surface temperature（SST） pattern from tropical Indian Ocean to the eastern Pacific and anomalous warm SST in the mid-latitude of North Atlantic Ocean. In the midsummer of 2016, both the atmospheric circulation anomalies and the SST anomaly pattern were consistent with the characteristics of the Jianghuai type, further confirming the statistical results. For the Jiangnan type, the critical circulation system is the westward-extending and intensified western Pacific subtropical high（WPSH）. Both the anomalous warm SST in the equatorial central-eastern Pacific in the preceding winter and the basin-wide warming pattern in the tropical Indian Ocean from the spring to summer influence the strong WPSH in the midsummer. However, the effect of SST forcing in the tropical Indian Ocean has been proved to be more significant and more persistent compared to that in the equatorial central-eastern Pacific.