Abstract The ocean-atmosphere interaction over a summer upwelling system in the South China Sea (SCS) is investigated. A strong positive correlation between sea surface temperature (SST) and wind stress exists near the southeast coast of Vietnam, where strong SST fronts occur during summertime. This air-sea coupling relationship indicates that the ocean drives the atmosphere and receives feedback at the oceanic mesoscale, in contrast with the case for large scales. The coupling process off the southeast coast of Vietnam is initiated by coastal upwelling, which is driven by wind-induced offshore Ekman transport in early summer. Cold upwelled water reduces the wind stress aloft and results in a positive wind stress curl. The Ekman pumping induced by the wind stress curl is on average 18% stronger than that of the offshore Ekman transport and occupies a larger extent. As the upwelling season terminates by the end of summer, the air-sea coupling also diminishes. Our results reveal that the SST-induced wind stress curl anomalies have a positive feedback on SST change and that wind stress curl anomalies can further reduce the SST magnitude by as much as 0.5 °C. The factors influencing the strength and interannual variability in ocean-atmosphere interaction are also explored. The wind stress directional steadiness (WSDS) plays an important role in the air-sea coupling over the SCS SST frontal regions. The coupling between the wind stress and SST can fully develop under high WSDS. Furthermore, the interannual variabilities in air-sea coupling are largely impacted by the El Nino events by changing the regional wind. The influence of a strong El Nino event on the summer upwelling system is characterized by a warmer SST and declining winds, which are associated with weakened SST gradients and mesoscale air-sea coupling. The present study reveals that the interannual climate signals have a significant impact on the mesoscale ocean-atmosphere interaction in a typical upwelling system. It provides an example for investigation of seasonal and interannual variability of mesoscale air-sea coupling in other coastal regions.

中文翻译：

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南海夏季上升流系统的海洋-大气相互作用

摘要 研究了南海夏季上升流系统的海洋-大气相互作用。越南东南海岸附近的海面温度 (SST) 和风应力之间存在很强的正相关关系，那里夏季会出现强 SST 锋。这种海气耦合关系表明，与大尺度的情况相反，海洋在海洋中尺度上驱动大气并接收反馈。越南东南沿海的耦合过程是由沿海上升流引发的，这是由初夏的风引起的海上 Ekman 运输驱动的。冷的上升流水降低了高空的风应力并导致正的风应力卷曲。风应力旋涡引起的埃克曼抽运比近海埃克曼输运平均强18%，占有的范围更大。随着上升流季节在夏末结束，海气耦合也减弱。我们的结果表明，SST 引起的风应力旋度异常对 SST 变化具有正反馈，并且风应力旋度异常可以进一步将 SST 幅度​​降低 0.5 °C。还探讨了影响海洋-大气相互作用强度和年际变化的因素。风应力方向稳定性（WSDS）在南海海温锋区的海气耦合中起着重要作用。风应力和 SST 之间的耦合可以在高 WSDS 下充分发展。此外，海气耦合的年际变化主要受厄尔尼诺事件通过改变区域风向的影响。强厄尔尼诺事件对夏季上升流系统的影响特点是海温升高和风速下降，这与海温梯度减弱和中尺度海气耦合有关。目前的研究表明，年际气候信号对典型上升流系统中的中尺度海洋-大气相互作用具有显着影响。它为调查其他沿海地区中尺度海气耦合的季节和年际变化提供了一个例子。这与减弱的海温梯度和中尺度海气耦合有关。目前的研究表明，年际气候信号对典型上升流系统中的中尺度海洋-大气相互作用具有显着影响。它为调查其他沿海地区中尺度海气耦合的季节和年际变化提供了一个例子。这与减弱的海温梯度和中尺度海气耦合有关。目前的研究表明，年际气候信号对典型上升流系统中的中尺度海洋-大气相互作用具有显着影响。它为调查其他沿海地区中尺度海气耦合的季节和年际变化提供了一个例子。