Numerical modelling of Lagrangian residual current in the Bohai Strait

The Bohai Strait is the only passage-way of the semienclosed Bohai Sea into the outer ocean. The various dynamical processes have great effects on both sides of the strait, especially on the Bohai Sea. Tidal current dominates in the strait, and among the tidal components the M₂ component tide is prevailing.
The seawater in the strait is homogeneous vertically almost the whole year because of strong tidal mixing. The M₂ component tide was simulated numerically using two dimensional barotropical model, and the Eulerian tide-induced residual currents were also deduced. The results showed that the tidal currents were dominated by the coastal line and topography. There exist many eddies in the tide-induced residual current fields, particularly near the northern coast.
On the basis of the simulation of the tidal currents, the movements of the water particles in the strait were tracked by means of Lagrangian techniques. Consequently the Lagrangian residual currents were obtained. Somewhat similar to the Eulerian residual currents, the trend of magnitude appears also large in the north and small in the south.But the values of the Lagrangian residual currents and the Eulerian residual currents are not the same.For certain tidal current fields Eulerian residual currents are steady, but the Lagrangian residual currents are the functions of tide phase.