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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.

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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.

A three-dimensional numerical model is used to quantitatively evaluate the contribution of ea5ch driving force to the Lagrangian residual velocity (LRV) in Xiangshan Bay under conditions of constant buoyancy gradient in time and multi-frequency tide. Each component of the LRV from various processes is derived by tracking each driving force in a tidal period along the particle trajectory. For a comparison of the results, the driving force in the momentum equations is averaged at the fixed points to obtain six components of the Eulerian residual velocity (ERV). A quantitative evaluation of the contribution of each component to the total ERV and total LRV is performed. The sum of the acceleration component, nonlinear advection component, and barotropic pressure gradient component of ERV determines the structure of the total ERV. The LRV is influenced by different dynamic mechanisms. The barotropic pressure gradient component of LRV determines the outflow pattern of the total longitudinal LRV at the surface of the inner Xiangshan Bay, and the density gradient component of LRV is the main determinant of the structure of the total longitudinal LRV at the bottom of the inner Xiangshan Bay. The eddy viscosity component causes the total longitudinal LRV to flow seaward in the Niubi Channel. The sum of the acceleration component and nonlinear advection component of LRV is the main contributor to the inward total longitudinal LRV in the Fodu Channel. The barotropic pressure gradient component leads to total lateral flow in the outer Xiangshan Bay. The collective effect of the components induced by all of the forces determines the structure of the lateral LRV in the inner Xiangshan Bay.

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