125 / 2023-08-05 00:30:17

Vertical circulation of coastal front observed in the northwestern South China Sea

vertical velocity, ocean front, northwestern south China Sea, tide

The ocean front plays a crucial role in the air-sea interaction and biogeochemical processes due to active vertical transports within the fronts. Using mooring observations in winter 2021, this study investigates the vertical circulation in the front occurred in the northwestern South China Sea. The satellite observations show an SST front of 0.05^OC/km extends along the shelf at a depth of about 40 m with a width of about 20 km. The temperature gradient derived from the cross-shelf mooring observations reaches above 0.15^OC/km in the whole water column with a maximum value of 0.35^OC/km near the surface. The front intensity varies with the tidal current, and shows strong symmetric instability (SI) as a strong front appears. The diagnosed vertical velocity shows intensified downwelling in the front, which is above -2×10^-5 m/s derived from the quasi-geostrophic omega equation, and reaches O(10^-3) m/s derived from the single-mooring diagnosis method with the total velocity. The variation of the vertical circulation corresponds well to the front intensity, indicating the effects of tides on the variation of the frontal circulation.