摘要:中国江南地区是高温热浪灾害的高影响区。以往的一些研究发现了不同海域海温异常在年际或年代际尺度上的变化对中国南方夏季平均温度异常的影响效应。但是，关于这些关键海域海温季节内尺度变化对江南地区高温事件发生和维持影响的研究尚不多见。为此，本文利用中国站点观测、美国气象环境预报中心和美国国家大气研究中心（NCEP/NCAR）再分析以及美国国家海洋大气管理局（NOAA）海温等资料，首先以2016年江南地区夏季2次高温事件为例（分别发生在7月21日至31日和8月15日至25日），重点探讨了热带大西洋海温季节内变化的可能贡献。在此基础上，基于1981～2016年多高温事件合成结果，进一步分析了热带大西洋海温季节内变化影响江南高温事件的可能链接过程。研究发现，热带西大西洋暖海温异常在季节内尺度上的发展与维持有利于在欧亚大陆激发出较为稳定的Rossby波列结构，使东亚及其沿海地区为深厚的高压系统控制，进而引发江南地区持续性高温事件。这种热带大西洋暖海温的阶段性增强与维持及其相应的稳定Rossby波列结构超前于持续性高温事件：在热带大西洋海温显著升高1个月之内，江南地区可能出现持续性高温事件。在季节内尺度上，热带大西洋显著暖海温异常出现明显的阶段性增强之后10天左右，北印度洋暖海温也出现了阶段性增强。这暗示热带大西洋热力异常除通过直接激发欧亚大陆Rossby波列之外，还有可能通过影响热带印度洋海温的阶段性异常，进而对江南地区高温事件的发生和维持产生一定影响。另外，在厄尔尼诺衰减并向拉尼娜转变阶段，热带中东太平洋冷海温异常和北印度洋暖海温异常在季节内的协同阶段性变化可能也对持续性高温事件有贡献。上述关键区海温的季节内变化对中国江南地区高温事件具有一定的前期指示意义，但它们的具体影响过程，特别是在季节内尺度上的协同影响效应和物理过程，尚需未来进一步研究。
关键词:江南地区/
持续性高温事件/
季节内/
大西洋/
印度洋/
太平洋
Abstract:The area south of the Yangtze River is highly impacted by heatwave disasters. Previous studies have shown the effects of sea surface temperature anomalies (SSTAs) in several crucial sea regions (e.g., the tropical Atlantic, the North Indian Ocean, and the tropical central eastern Pacific) on summer mean air temperature anomalies over southern China on interannual or interdecadal time scales. However, little research exists focusing on the impacts of SSTAs in these key sea regions on the occurrences and maintenances of heatwave events over the area south of the Yangtze River on the intraseasonal time scale. For this reason, using observational data in gauge stations in China, the National Centers for Environmental Prediction–National Center for Atmosphere Research (NCEP/NCAR) reanalysis, and the National Oceanic and Atmospheric Administration (NOAA) SSTs, the present study focuses on the potential contribution of SSTAs in the tropical Atlantic to heatwave events over the area south of the Yangtze River by analyzing two summer heatwave events (occurred during July 21 to 31 and August 15 to 25) in 2016. In addition, based on the composites of multiple heatwave events during 1981–2016, the present study further explores a possible physical link explaining the effect of the intraseasonal evolution of SSTAs in the tropical Atlantic on heatwave events over the area south of the Yangtze River. The results indicate that the development and maintenance of warmer SSTAs in the tropical western Atlantic are conducive in stimulating a relatively stable Rossby wave train over Eurasia on the intraseasonal time scale. As a result, a deep high-pressure anomaly governs East Asia and its coastal areas, resulting in long-term persistent (≥8 days) heatwave events over the area south of the Yangtze River. This phased increase and maintenance of SSTAs in the tropical Atlantic and associated steady Rossby wave train are prior to the long-term persistent heatwave events, and the latter might occur in a month since the SSTs in the tropical Atlantic are significantly enhanced. On the intraseasonal time scale, there is a clearly phased increase in the SSTs in the North Indian Ocean, around 10 days after the significant increase in the SSTs in the tropical Atlantic Ocean. This implies that in addition to directly exciting the Rossby wave train across Eurasia, it is probable that SSTAs in the tropical Atlantic may affect the occurrence and maintenance of the heatwave events through modulating the phased variation of SSTAs in the North Indian Ocean on the intraseasonal time scale. Furthermore, during the period of El Ni?o decay and transition to La Ni?a, the synergistic intraseasonal variations accompanied with cooler SSTAs in the tropical central eastern Pacific and warmer SSTAs in the North Indian Ocean may also contribute to the long-term persistent heatwave events. The intraseasonal variations in SSTAs in the three key sea regions seem to be able to be used as precursory signals for the heatwave events. Nevertheless, the specific process explaining the intraseasonal effects of SSTAs in the three key regions, especially the joint effect of SSTAs in these regions and related physical process, requires further investigation in the future.
Key words:South of the Yangtze River/
Persistent heatwave events/
Intraseasonal/
the Atlantic/
the Indian Ocean/
the Pacific
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