Seasonal variation of the coastal currents in the Northern Bohai Strait

The seasonal variation of the coastal currents in the northern Bohai Strait has been investigated using long time-series current observational data.The mean current velocities in winter and summer both showed the largest values in the surface layer and the lowest values in the middle layer.In the bottom layer, the current velocities increased slightly comparing to the middle layer.In both seasons, the currents in the bottom layer showed shoreward cross-isobathic components, which suggested the shoreward movement of the bottom water existed all the year round.The current data were then analyzed with vector Empirical Orthogonal Function.The spatial mode of EOF1 showed that in both summer and winter, the currents mainly fluctuated along the isobaths.In winter, currents of the whole vertical profile varied in phase, and in summer the currents in the surface layer varied out of phase with the currents in the other layers.Surface wind was one of the forces in generating the currents in the study area, but it was not a dominant one.In winter, the current fluctuations lagged the wind by 18 hours and the current was significantly correlated with the wind of 6 days fluctuation period.In summer, the current lagged the wind by 9 hours and current was significantly correlated with the wind of 0.8 days fluctuation period.