Influence of stratification on residual tidal currents in the Yellow Sea

Abstract

The M 2 tide and residual current generation in the Yellow Sea are examined using the Blumberg and Mellor [1987] numerical coastal ocean circulation model. With no stratification the model tide and tidal currents show good agreement with the observed tide and tidal currents. Coherent residual currents are predicted around the southwest of Korea, flowing northward as a strong jet with a maximum speed of 8 cm s −1 , and around Yangtze Bank, flowing southeastward as a weak broad current. With initial stratification, tidal mixing occurs in the bottom boundary layer, which leads to surface tidal fronts around Yangtze Bank and the southwest of Korea, and our model experiments reproduce successfully the basic water property structure in these regions. The resulting stratified tidal rectification intensifies the residual currents at the front and at the top of the bottom boundary layer over the sloping bottom, so that the vertical structure of the residual currents is modified. The strong residual currents in the top of the bottom mixed layer around Yangtze Bank support the interpretation of Kim et al . [1991] for the southeastward movement of Yellow Sea Bottom Cold Water in summer. The residual currents in the surface layer reach ∼40% of the mean currents observed by Beardsley et al. [1992] using satellite‐tracked drifters deployed in the Yellow Sea in summer. These results suggest that stratified tidal rectification is an important process in driving the summertime subtidal flow in the Yellow Sea.