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

Intraseasonal fluctuation with periods of similar to 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 similar to 69% of the subinertial variance. This fluctuation propagates westward along the mooring section with a phase speed of similar to 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.