Eddy-induced heat transport (EHT) in the South China Sea (SCS) is important for the heat budget. However, knowledge of its variability is limited owing to discrepancies arising from the limitation of the downgradient method and uncertainties arising from numerical models. Herein, we investigated the spatiotemporal variability and dynamics of EHT using a well-validated assimilated model. In particular, to the southeast of Vietnam (SEV) and west of Luzon Strait (WLS), significant values of annual mean EHT are observed and most EHT is confined in the upper 400 m. EHT also exhibits significant seasonality, and the largest EHT amplitude in autumn at SEV is mainly driven by the wind stress curl, while that in winter at WLS is mainly related to the Kuroshio intrusion. Energy budget analysis reveals that both the barotropic and baroclinic instabilities increase the eddy kinetic energy in autumn at SEV, whereas only the barotropic instability contributes to the eddy kinetic energy at WLS in winter. Specially, an upgradient EHT is observed at WLS in all four seasons, characterized by the same directions between EHT and mean temperature gradient. The upgradient EHT at WLS is induced by the baroclinic instability through an inverse energy transfer, which is generated by the interaction between the Kuroshio intrusion and topography below the surface layer. Moreover, the most significant upgradient EHT in winter shows a wave-like southwestward-propagating pattern in the subsurface layer.

南中国海涡旋引起的热量输运

中文摘要：南海 (SCS) 的涡旋热量输运 (EHT) 在热收支中起到重要作用。然而，由于下降梯度法的局限性和数值模型的不确定性导致的差异，对其变异性的了解尚且不足。本文利用经过充分验证的同化模型研究了 EHT 的时空变异性和动力特征。特别是在越南东南部（SEV）和吕宋海峡以西（WLS），观测到显著的年平均EHT值，大部分EHT被限制在上部400米。 EHT也表现出明显的季节性，SEV秋季EHT最大振幅主要受风应力旋度驱动，而WLS冬季主要与黑潮入侵有关。能量收支分析表明，正压不稳定和斜压不稳定都会增加秋季 SEV 处的涡动能，而只有正压不稳定对冬季 WLS 处的涡动能有贡献。特别的是，在所有四个季节的 WLS 都观察到上升梯度的 EHT，其特征是 EHT 与平均温度梯度之间的方向相同。 WLS 的上升梯度 EHT 是由斜压不稳定性通过能量逆向级串引起的，而逆向能量转移是由黑潮入侵和海面以下地形的相互作用产生的。此外，冬季最显著的上升梯度EHT在次表层呈现波浪状西南向传播的空间模态。