Dynamics of the Baroclinic Rossby Waves Regulating the Abyssal South China Sea

Abstract Intraseasonal fluctuation with periods of ∼90 days in the South China Sea (SCS) basin is investigated based on an array of seven subsurface moorings. In the deep layer, the 90-day fluctuation is revealed to contribute significantly to the variability in the current, accounting for ∼69% of the subinertial variance. This fluctuation propagates westward along the mooring section with a phase speed of ∼4.6 cm s−1. In the upper layer, the fluctuation also propagates westward with a similar phase speed, but with opposite phase to that of the deep layer. These results suggest that the 90-day fluctuation regulating the abyssal SCS should be the first mode baroclinic Rossby wave. A set of experiments based on a two-layer dynamic model reveal that both the local wind stress curl and the flow originating from the North Pacific through the Luzon Strait contribute to drive the 90-day fluctuation in the deep SCS, while the latter plays the dominant role.