Using the generalized omega equation and cruise observations in July 2012, this study analyzes the 3D vertical circulation in the upwelling region and frontal zone east of Hainan Island, China. The results show that there is a strong frontal zone in subsurface layer along the 100-m isobath, which is characterized by density gradient of O(10−4) kg m−4 and vertical eddy diffusivity of O(10−5–10−4) m2 s−1. The kinematic deformation term SDEF, ageostrophic advection term SADV, and vertical mixing forcing term SMIX are calculated from the observations. Their distribution patterns are featured by banded structure, that is, alternating positive–negative alongshore bands distributed in the cross-shelf direction. Correspondingly, alternating upwelling and downwelling bands appear from the coast to the deep waters. The maximum downward velocity reaches −5 × 10−5 m s−1 within the frontal zone, accompanied by the maximum upward velocity of 7 × 10−5 m s−1 on two sides. The dynamic diagnosis indicates that SADV contributes most to the coastal upwelling, while term SDEF, which is dominated by the ageostrophic component SDEFa, plays a dominant role in the frontal zone. The vertical mixing forcing term SMIX, which includes the momentum and buoyancy flux terms SMOM and SBUO, is comparable to SDEF and SADV in the upper ocean, but negligible below the thermocline. The effect of the vertical mixing on the vertical velocity is mainly concentrated at depths with relatively large eddy diffusivity and eddy diffusivity gradient in the frontal zone.

The independent point scheme (IPS) is applied to inverting initial condition with the adjoint method for the ocean pollutant transport model in this work. As an improvement, the linear Cressman interpolation is removed and the surface spline interpolation is implemented in the IPS. A series of numerical experiments are carried out to test and compare the improved IPS. And experiment results show that through applying the improved IPS, what is further reduced is mean absolute errors between simulation results and observations. Moreover, the inverted distributions are more smooth, accurate and reasonable. In addition, the application of improved IPS also reduces the variables that need to be inverted and promotes the computational efficiency. By these numerical experiment results, it is demonstrated that the combination of improved IPS and adjoint method can be used for the inversion of initial conditions and parameters estimation more effectively and reliably.

The spline interpolation method is applied to the inversion of the time-varying pollutant emission rate based on an ocean pollutant diffusion model with the adjoint method. A series of numerical experiments are performed to compare the spline interpolation with the Cressman interpolation. Experimental results show that the spline interpolation improves the inversion results in terms of the smoothness and accuracy. Furthermore, it is the advantages of spline interpolation—better resistance to the impact of errors and demand for fewer observations—that give rise to a better performance in practice.

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In the background of global warming and climate change, nuisance flooding is only caused by astronomical tides, which could be modulated by the nodal cycle. Therefore, much attention should be paid to the variation in the amplitude of the nodal cycle. In this paper, we utilize the enhanced harmonic analysis method and the independent point scheme to obtain the time-dependent amplitudes of the 8.85-year cycle of N2 tide and the 4.42-year cycle of 2N2 tide based on water level records of four tide gauges in the Gulf of Maine. Results indicate that the long-term trends of N2 and 2N2 tides vary spatially, which may be affected by the sea-level rise, coastal defenses, and other possible climate-related mechanisms. The comparison between Halifax and Eastport reveals that the topography greatly influences the amplitudes of those cycles. Moreover, a quasi 20-year oscillation is obvious in the 8.85-year cycle of N2 tide. This oscillation probably relates to a 20-year mode in the North Atlantic Ocean.

An idealized three‐dimensional numerical model is used to investigate turbulent kinetic energy (TKE) production in a far‐field river plume under upwelling‐favorable winds. TKE production decreases over longer length scales as the river plume thickens. Maximum TKE production appears in the surface layer and is mainly generated by the alongshore component of the velocity shear. The large velocity shear and weak stratification in the surface layer result in a gradient Richardson number (Ri) of <0.25, which corresponds to the locally high TKE production. We find that asymmetrical TKE production occurs at the two edges of the river plume, due to the opposite nonlinear interaction of the Ekman and geostrophic effects at the shoreward and seaward edges of the river plume. This asymmetrical TKE production combines with secondary upwelling circulation in the river plume under upwelling‐favorable winds, which may generate more intense biological activity at the shoreward edge of the river plume than at the seaward edge. Numerical model experiments are performed to examine the effects of wind, river discharge, and stratified conditions on TKE production in the river plume. Finally, we propose a conceptual model in which the depth‐averaged TKE production in the river plume is proportional to the alongshore wind stress (τy2.5 ${{\tau }_{y}}^{2.5}$) and inversely proportional to the cube of the surface boundary layer thickness (D3), which is consistent with the results of numerical experiments.

Using the 25-h continuing hydrographic observations at three successive stations in February 2012 and the mooring time series of current observations from January to March 2015, the tidal currents and tidal energy fl uxes in the coastal waters east of Hainan Island in the northwestern South China Sea were analyzed. The diurnal and semidiurnal (using K 1 and M 2 as proxies, respectively) tidal currents and associated isopycnal undulations were derived with harmonic analysis. Results show that the velocities of the diurnal and semidiurnal tides derived from the 25-h observations are comparable to those from the mooring series. The semi-major axes of the tidal ellipses were O (4-7 cm/s) for barotropic tides and O (2-4 cm/s) for baroclinic tides. The directions were in NE-SW at deeper stations to N-S at the shallowest station for the diurnal tide and from NW-SE to NE-SW for the semidiurnal tide. Both the diurnal and semidiurnal isopycnal fl uctuations reached O (5 m), O (8 m), and O (10 m) at the cross-shelf stations (H03, H04, and H05) from 35 m, 45 m, to 55 m, respectively, showing insignifi cant vertical variation, and the barotropic signals were predominate. The baroclinic diurnal tide showed fi rst-mode structures at H03-05, as does the semidiurnal tide at H03. The semidiurnal tide at H04 and H05 exhibited higher-mode structures. The time series of both the alongshore and cross-shore components reveal the vertically propagation features of the baroclinic tidal phase and energy. The calculated horizontal energy fl uxes of the diurnal and semidiurnal internal tides decreased from O (0.1 W/m) at H05 to O (0.01 W/m) at H03, implying a propagation and dissipation of energy from off shore to inshore.