青藏高原夏季热力状态和南半球大气环流的可能联系

本文通过对观测和再分析数据采用最大协方差分析以及回归、合成等分析方法,研究了青藏高原夏季地表气温与南半球大气环流之间的遥相关关系。结果表明,前期(4月)南半球极地—中高纬度大气环流呈现负位势高度异常、较低纬度印度洋—西太平洋区域呈现正位势高度异常时,高原中部和东部大部分区域夏季出现暖异常。在上述遥相关中,印度洋—西太平洋海温异常可能起到了重要的中间桥梁作用。在高原夏季温度偏高的年份,前期跨赤道的印度洋—西太平洋海温也持续偏暖,带来的海陆热力对比减小、经向跨赤道气流减弱有利于削弱夏季的季风环流,使得高原夏季降水偏少,有利于形成高原夏季的暖异常。在这一高原气温—南半球大气环流的遥相关关系中,4月南半球的大气位势高度场异常和与印度洋—西太平洋海温异常相关的异常高度场分布也十分相似。这一前期的跨赤道区域海温异常与南半球中高纬度位势高度场异常的因果关系仍有待进一步揭示。

Possible relationship between the summer thermal state of the Tibetan Plateau and the atmospheric circulation in the Southern Hemisphere

In this paper, the teleconnection between the summer surface air temperature on the Tibetan Plateau and the Southern Hemisphere atmospheric circulation were investigated by using Maximum Covariance Analysis (MCA) as well as regression and composite analysis with the observation and reanalysis data. Results show that warm anomalies occur in most of the central and eastern plateau in summer when the Southern Hemisphere atmospheric circulation shows negative geopotential height anomalies in the polar-and-mid latitude and positive height anomalies in the lower latitude Indian Ocean-West Pacific regions in April. In the above connection, the Indian Ocean-West Pacific SST anomaly may play an important role in bridging the two fields. When the plateau summer temperature is high, the equatorial Indian Ocean-West Pacific SST exhibits warm anomalies lasting from earlier spring to summer, resulting in reduced sea-land thermal contrast and weakened cross-equatorial flow, which is conducive to the weakened summer monsoon circulation and reduced summer precipitation in Tibetan Plateau. The latter is conducive to the formation of the summer warm temperature anomaly in the plateau. In such teleconnection, the atmospheric geopotential height anomaly in the Southern Hemisphere in April is very similar to the distribution of anomalous geopotential height associated with the Indian Ocean-West Pacific SST anomaly. The causal relationship between this pre-existing Indian Ocean-West Pacific SST anomaly and the Southern Hemispheric mid-high latitude atmospheric circulation needs further investigations.