Numerical Simulation Of Tide And Tidal Currents In The Qiongzhou Strait Based On FVCOM

The high-resolution, unstructured grid Finite-Volume Community Ocean Model (FVCOM) was used to examine the characteristics of tidal and tidal residual current in Beibu Gulf, Qiongzhou Strait and Leizhou Penisula in northwestern South China Sea.The model agrees well with observations and some conclusions can be obtained as follows:1. The co-tidal chart shows that the propagation directions of the semidiurnal and diurnal tidal waves are different in the Qiongzhou Strait. Semidiurnal tidal wave spread from Beibu Gulf to the strait, while diurnal tidal waves are opposite.2. The type of tidal current in the Qiongzhou Strait is different from west to east, the western part is diurnal tide, the middle part is irregular diurnal tide and the eastern part is irregular semidiurnal tide, respectively. The tidal current in the Qiongzhou Stait is diurnal and irregular diurnal.3. The tidal ellipses distribution suggests that in the strait is alternating current and the strait two sides is rotary current.4. The distribution of the tidal residual current suggests a near westward current in the strait, and the water flux through a profile is about 0.031*106 m3/s. The distribution of velocity in the strait from maximum to minimum is northern, southern and middle, respectively. We performed numerical experiments by forcing the model with individual M2, O1 and K1 tides. The results show that the residual flow in the strait is dominated by diurnal (O1, K1) tidally rectified currents:either O1 or K1 residual current is larger than M2 tidally rectified current. The magnitude and spatial distribution of sum of the M2, O1 and K1 tide-induced residual current is almost identical to the Control experiment.5. A momentum balance analysis for the along-strait and cross-strait components of the equations of motion was conducted to examine the physical processes that cause the formation of the westward current. We found that the westward residual current in the strait is driven by a strong nonlinear process in which the horizontal advection terms, the Coriolis force, and cross-strait surface pressure gradient force must all be taken into account. The distribution of these factors is corresponding to depth, so this residual current is driven by tidal rectification associated with the complex nonlinear interaction of tidal currents over variable bottom topography.6. When closing the east side of strait, the co-tidal charts change a lot. The tides from Beibu Gulf propagate into strait, so the energy in the gulf is decreased. In the strait, the amplitude and degree of semidiurnal is increase and decrease, respectively. And the harmonic constants of diurnal tide are both increase. So the tides from west side of strait mainly are semidiurnal tides. The direction of residual current in strait is eastward, as the main tides is semidiurnal tides.If the west side of strait is closed, the semidiurnal tides can not propagate through the strait, and the direction turn to be northward. As a result, the energy in the gulf is increased. The semidiurnal tide change a lot, while diurnal tides in the northeastern area change little. In the strait, the amplitude of diurnal change little, and it’s degree is decrease. The harmonic constants of semidiurnal tide are both increase. The residual current is similar to the control experiment, and its magnitude is smaller than Exp_ctrl. No matter which side be closed, a complete tidal wave system was shown in the gulf.