Eddy-Induced Heat Transport in the South China Sea

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.