Three-dimensional (3D) basin circulation provides the basic and important dynamic environment for processes in the SCS. Previous investigators have revealed that the large-scale three-layer ocean circulation in the SCS is featured by cyclonic/anticyclonic circulation in the upper layer, anticyclonic in the middle layer, and cyclonic in the deep layer (
e.g., Gan et al., 2016;
Cai and Gan, 2021). The new findings further show the meridional overturning circulation in the upper layer (
Lan and Jiang, 2021) and the variability of the deep circulation in the SCS (
Zhu et al., 2021). Meanwhile, intra-seasonal variations of currents in the upper and deep layers of the northern SCS were observed and attributed to the topographic Rossby waves (
Zheng et al., 2021b;
Shu et al., 2021). Subseasonal variability in the SCS was revealed by numerical simulations (
Xie et al., 2020). In terms of energy and vorticity balances,
Huang (2021) diagnosed the roles played in regulating the SCS circulation by the SCS throughflow, the local wind stress, the deep overflow through the Luzon Strait, the local thermohaline forcing and the meso/submeso-scale eddies, and concluded that the contribution from the open ocean plays a dominant role.