Vertical structure and seasonal variation of tidal and residual currents in the northern Huanghai Sea

Analysis of tidal current and sea level has been made based on the observations from the summer of 2006 to the winter of 2007, respectively. The result indicates that a two-layer structure of residual current exists in summer, with its upper layer going northwestward and the lower layer southeastward. In addition, some strong residuals exist in the neighboring depth of the pycnocline during the current period of astronomical tide. In winter, except some individual layersthe residual currents mostly direct to the northwest, from which we can see the fluctuation of abnormal sea-level and the appearance of associated current because of the changes of the wind field. The analysis of tidal ellipse indicates that the direction of the maximum semidiurnal component is clockwise from summer to winter, with an angle of 16fl-18fl. Moreover, in summer the semidiurnal component rotates with depth clockwise while the diurnal component counterclockwise. However, the vertical structure is almost homogeneous in winter.