In the numerical studies of a real tide M₄ resonance system, the Xiangshan Port which is a partially-closed bay, Dong et al.[1999.Acta Oceanologica Sinica, 21 (3):1~6] found the interesting phenomenon that the advection plays an important role in inhibiting the growth of the amplitude of the tidal second-order resonance response (M₄).This result is contrary to the general traditional ideas for a non-resonance system.How this phenomenon is interpreted and what internal mechanism is behind the phenomenon are the main focuses of this study.The followings are examined:(1) the dynamic features of a second-order resonance system of tide; (2) the dominating factors on the second-order resonance responses; (3) the effects of both the friction and the advection on the second-order resonance responses; and (4) their roles in dominating the second-order resonance response and internal mechanisms by using the analytical methods.The respective results show that:(1) Both the bottom friction and the advection play significant roles in dominating the magnitude of the amplitude of the second-order resonance responses; (2) the effect of the friction on the second-order resonance response depends on the distribution ratio of the work-done of the system to friction force exhausted into between the damping of the first-order system and the inner excitation of the second-order system; (3) the advection plays a positive role in increasing the amplitude of the second-order non-resonance response in the second order non-resonance of tide; (4) in a second-order resonance system of tide, the effect of the advection may be either to increase or to decrease the amplitudes of the second-order resonance responses of tide, which depends on the distribution ratio mentioned above

Mooring observations aimed at understanding the vertical mixing were carried ont on the outer shelf of the South China Sea from April to May in 2002. Temporal and vertical distributions of horizontal velocity shear and Brunt-Vaisala frequencies are calculated with these observations. Dissipation rate and diapycnal diffusivity are then inferred from the fine-scale parameterization. The temporally and vertically averaged dissipation is 15 nW/kg and the associated diapycnal diffusivity is 2×10^-5 m²/s. Daily-averaged diapycnal diffusivity is well related to the tides, larger during the spring tide, and smaller during the neap tide. Depth-averaged diapycnal diffusivity, which is as larger as 5×l0^-5 m²/s during the spring tide, is 8.3 times that of the neap tide, which is only 6×l0^-5 m²/s. This is in proportion to the vertical energy flux from barotropic tide to baroclinic tide. During the spring tide, the energy flux from the semi-diurnal and diurnal barotropic tide to the internal tide is 160 mW/m, while it is only 35 mW/m during the neap tide. Vertically, monthly-averaged dissipation rate and associated diapycnal diffusivity are large near the upper mixing layer and the bottom boundary. Dissipation rate is about 30~100 nW/kg, diapycnal diffusivity is about 4×10^-5~10×l0^-5 m²/s. However, both of them are quite small in the mid column, where dissipation rate is 3~10 nW/kg and diapycnal diffusivity is 4×10^-6~40×10^-6 m²/s.

Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan.They are also modulated by tides and storm surges.The effects of the variability in surface wind forcing,tides and storm surges on the waves are investigated using a wave model,a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model.Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields,tides and storm surges during January 1997.Compared with observed mean wave parameters,results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation.Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyō,but not for other regions in the Sea of Japan.High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas,especially near the coastal regions.

The computer model for near shore wave propagation, SWAN, was used to study wave climates in Liverpool Bay, northwest England with various input parameters, including bottom friction factor, white capping, wind drag formulation and effects of tidal modulations. Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions. In particular, the model results were found very sensitive to different input formulations, and tend to underestimate the wave parameters under storm conditions in comparison with the observations. It is therefore important to further validate the model against detailed field measurements, particularly under large storms that are often of the primary concern.

The daily and monthly-mean characteristics of cold water patches (CWPs) off the Jiangsu coast in 35 a of 1982-2016 are examined based on advanced very high resolution radiometer (AVHRR) data. Most of the CWPs are found to occur in the warm and hot months (May-September), with some CWPs in the cool and cold months (October-April). The average radius and intensity of the monthly-mean CWPs are about 81 km and 0.6℃, respectively. The average difference in the sea surface temperature (SST) between the centers of the CWPs and the nearshore is about 2.0℃. The correlation analysis between the CWPs, winds and tides indicates that most of the CWPs occurred during the southerly winds, with some CWPs occurring during the northerly winds. The average intensity of the CWPs during spring tides is slightly stronger than that during neap tides in the warm and hot months, and the difference is very small in the cool and cold months.

The systems of diurnal tidal wave (K₁) and semi-diurnal tidal wave (M₂) in the Beibu Gulf are studied with numerical method. Also discussed in this paper are the influences of the Qiongzhou Strait, the bottom friction term, the horizontal turbulent friction term and the inertial (acceleration) term in dynamic equations on the tidal system. The calculated results show that there is an independent left-handed tidal system in the diurnal tidal wave of the gulf, the amphidromic point being roughly located at Taigeli Island; that the semi-diurnal wave constitutes no tidal system, generating a small tidal range in the region near Feizhulong Islands; and that the influence of the tidal wave from the strait on the tidal system of the K₁ is not evident, but its effect on the system of the M₂ component tide is quite obvious. The bottom friction term, the horizontal turbulent friction term, and the inertial term have effects upon the tidal system in the gulf.

The Shacheng Bay (SCB) is one of the most complex coastal bays in southeast China and due to the fact of complicated geometry and dynamic coastal processes, it is considered as a challenging area for the numerical simulation of its hydrodynamic characteristics. The most advanced finite volume ocean model, finite- volume coastal ocean model (FVCOM), has adopted to simulate this hydrodynamic system, where tidal currents, tidal residual current and dye diffusion processes were studied and analyzed quantitatively. The validation of this numerical model matches well with various observation data, including elevation and current data. The misfit of a tidal elevation has a relative standard error of 3.66% and 4.67% for M₂ and S₂ tide components. The current validation shows a good match with an average error of 10 cm/s and 8° in the speed major axis and its direction respectively between the simulation and the measurement. This proves the robustness and reliability of this model. It is also found that the cape effect is significant and important in this system. The dye diffusion simulations show a 53 d flushing period for the whole inner bay waterbody. The results are of its first kind for understanding the hydrodynamic system in the SCB and they can provide helpful and trustful scientific information for others.

In this study, to meet the need for accurate tidal prediction, the accuracy of global ocean tide models was assessed in the South China Sea (0°–26°N, 99°–121°E). Seven tide models, namely, DTU10, EOT11a, FES2014, GOT4.8, HAMTIDE12, OSU12 and TPXO8, were considered. The accuracy of eight major tidal constituents (i.e., Q₁, O₁, P₁, K₁, N₂, M₂, S₂ and K₂) were assessed for the shallow water and coastal areas based on the tidal constants derived from multi-mission satellite altimetry (TOPEX and Jason series) and tide gauge observations. The root mean square values of each constituent between satellite-derived tidal constants and tide models were found in the range of 0.72–1.90 cm in the deep ocean (depth>200 m) and 1.18–5.63 cm in shallow water area (depth<200 m). Large inter-model discrepancies were noted in the Strait of Malacca and the Taiwan Strait, which could be attributable to the complicated hydrodynamic systems and the paucity of high-quality satellite altimetry data. In coastal regions, an accuracy performance was investigated using tidal results from 37 tide gauge stations. The root sum square values were in the range of 9.35–19.11 cm, with the FES2014 model exhibiting slightly superior performance.

This paper is devoted to the study of the propagation of tide wave in a basin with variable cross-sectional area. With the W.K.B. method an analytic solution of amplitude is obtained. It is found that the motion of co-oscillating tide wave in a basin with variable cross-section is a progressive one, depending on the cross-section as well as the frictional force. The effects of friction on the motion of tide wave is discussed in detail.

An attempt is made to infer the global mean sea level (GMSL) from a global tide gauge network and frame the problem in terms of the limitations of the network. The network, owing to its limited number of gauges and poor geographical distribution complicated further by unknown vertical land movements, is ill suited for measuring the GMSL. Yet it remains the only available source for deciphering the sea level rise over the last 100 a. The poor sampling characteristics of the tide gauge network have necessitated the usage of statistical inference. A linear optimal estimator based on the Gauss-Markov theorem seems well suited for the job. This still leaves a great deal of freedom in choosing the estimator. GMSL is poorly correlated with tide gauge measurements because the small uniform rise and fall of sea level are masked by the far larger regional signals. On the other hand, a regional mean sea level (RMSL) is much better correlated with the corresponding regional tide gauge measurements. Since the GMSL is simply the sum of RMSLs, the problem is transformed to one of estimating the RMSLs from regional tide gauge measurements. Specifically for the annual heating and cooling cycle, we separate the global ocean into 10°-latitude bands and compute for each 10°-latitude band the estimator that predicts its RMSL from tide gauges within. In the future, the statistical correlations are to be computed using satellite altimetry. However, as a first attempt, we have used numerical model outputs instead to isolate the problem so as not to get distracted by altimetry or tide gauge errors. That is, model outputs for sea level at tide gauge locations of the GLOSS network are taken as tide gauge measurements, and the RMSLs are computed from the model outputs. The results show an estimation error of approximately 2 mm versus an error of 2.7 cm if we simply average the tide gauge measurements to estimate the GMSL, caused by the much larger regional seasonal cycle and mesoscale variation plaguing the individual tide gauges. The numerical model, Los Alamos POP model Run 11 lasting 3 1/4 a, is one of the best eddy-resolving models and does a good job simulating the annual heating and cooling cycle, but it has no global or regional trend. Thus it has basically succeeded in estimating the seasonal cycle of the GMSL. This is still going to be the case even if we use the altimetry data because the RMSLs are dominated by the seasonal cycle in relatively short periods. For estimating the GMSL trend, longer records and low-pass filtering to isolate the statistical relations that are of interest. Here we have managed to avoid the much larger regional seasonal cycle plaguing individual tide gauges to get a fairly accurate estimate of the much smaller seasonal cycle in the GMSL so as to enhance the prospect of an accurate estimate of GMSL trend in short periods. One should reasonably expect to be able to do the same for longer periods during which tide gauges are plagued by much larger regional interannual (e. g., ENSO events) and decadal sea level variations. In the future, with the availability of the satellite altimeter data, we could use the same approach adopted here to estimate the seasonal variations of GMSL and RMSL accurately and remove these seasonal variations accordingly so as to get a more accurate statistical inference between the tide gauge data and the RMSLs (therefore the GMSL) at periods longer than 1 a, i. e., the long-term trend.