夏季赤道中东太平洋海温异常对南海低空越赤道气流的影响

The Influence of Sea Surface Temperature Anomalies in the Middle Eastern Equatorial Pacific on the Low-Level Cross-Equatorial Flow over the South China Sea in Summer

利用1979~2020年NCEP/NCAR逐月的风场、海平面气压场以及HadISST逐月海表面温度(Sea Surface Temperature, SST)等再分析资料,采用相关分析及合成分析等方法探讨了夏季赤道中东太平洋海表面温度异常(Sea Surface Temperature Anomalies, SSTA)对南海(South China Sea, SCS)低空越赤道气流(Cross-Equatorial Flow, CEF)变化的可能影响,结果表明:夏季SCS CEF (SCEF)强度变化与同期赤道中东太平洋SSTA呈显著的正相关关系。当夏季赤道中东太平洋SSTA增暖时,Walker环流异常减弱,赤道西太平洋出现异常下沉运动,位于赤道西太平洋的海洋性大陆和澳大利亚北部海平面气压异常上升;与此同时,东亚Hadley环流异常减弱,使得西北太平洋海平面气压异常降低,有利于产生南北向的气压梯度,从而引导SCEF增强;反之亦然。

The monthly mean NCEP/NCAR reanalysis data of wind field, sea-level pressure field, and Sea Surface Temperature (SST) data of HadISST are used in 1979~2020 to explore the relationship of the Low-level Cross-Equatorial Flow (CEF) over the South China Sea (SCS) and eastern equatorial Pacific Sea Surface Temperature Anomaly (SSTA). The results showed that the SSTA in the eastern and central tropical Pacific has important influence on the change of the SCS low-level CEF (SCEF) in the summer, and there is a significantly positive correlation between them. When the SSTA of the east-ern and central tropical Pacific gets warmer in the summer, the Walker circulation anomaly weakens, and anomalous subsidence occurs in the western tropical Pacific. Sea level pressure in the western tropical Pacific and northern Australia rise abnormally. At the same time, the East Asian Hadley circulation anomaly weakens, the anomalous sea-level pressure gets lower in the northwest Pacific, which is conducive to generating a north-south pressure gradient and then guides SCEF enhancement, and vice versa.