Seasonal variation of the Taiwan Warm Current Water and its underlying mechanism

Based on the historical observed data and the modeling results,this paper investigated the seasonal variations in the Taiwan Warm Current Water(TWCW)using a cluster analysis method and examined the contributions of the Kuroshio onshore intrusion and the Taiwan Strait Warm Current(TSWC)to the TWCW on seasonal time scales.The TWCW has obviously seasonal variation in its horizontal distribution,T-S characteristics and volume.The volume of TWCW is maximum(13746 km^3)in winter and minimum(11397 km^3)in autumn.As to the contributions to the TWCW,the TSWC is greatest in summer and smallest in winter,while the Kuroshio onshore intrusion northeast of Taiwan Island is strongest in winter and weakest in summer.By comparison,the Kuroshio onshore intrusion make greater contributions to the Taiwan Warm Current Surface Water(TWCSW)than the TSWC for most of the year,except for in the summertime(from June to August),while the Kuroshio Subsurface Water(KSSW)dominate the Taiwan Warm Current Deep Water(TWCDW).The analysis results demonstrate that the local monsoon winds is the dominant factor controlling the seasonal variation in the TWCW volume via Ekman dynamics,while the surface heat fl ux can play a secondary role via the joint ef fect of baroclinicity and relief.

On the origin of the Tsushima Warm Current Water

The origin of the Tsushima Warm Current Water(TWCW) in summer is studied mainly on the basis of the CTD data and the observations of satellite-traced surface drifters of Coastal Ocean Process Experiment of the East China Sea(COPEX-ECS) conducted by Korea Ocean Research and Development Institute. The main results are as follows: (1) The structures of the TWCW show obvious regional varitaions. The TWCW can be divided into three layers in the northern Okinawa Trough west of Kyushu and into two layers on the continental shelf and in the Tsushima/Korea Strait. (2) The surface TWCW, charactered by a sub-high salinity (33. 5～ 34. 10), comes mainly from the coastal water composed largely of the Changjiang Diluted Water, the surface Kuroshio water and the shelf water in the area south of the East China Sea (ECS). (3) The middle TWCW is sub-grouped into two parts: the water of salinity (S) larger than 34. 50 located below the thermocline originates from the climbed sub-surface Kuroshio water;the TWCW lying in the thermocline is a mixture of the Kuroshio water and the shelf water with low salinity. (4) In the strait, the water from the source area is denatured obviously due to mixing unceasingly wth the shelf water and coastal water. The high salinity water of S >34. 5 appears only in the bottom layer with depths>50m.

Kuroshio warm filament and the source of the warm water of the Tsushima Current

Characteristics and evolution of the Kuroshio frontal eddies and warm filaments are analyzed according to two series of satellite images (March 5 to 7, 1986 and April 14 to 16, 1988). The results show that the frontal eddies in the East China Sea are generated at the shelf break and move along the continental slope at a speed of 15 cm/s with the Kuroshio. The frontal eddies occur about every 10 d and evolve to be warm filaments a few hundred km in length and 30-40 km in width in the area west of the Yaku-shima. Meanwhile, the existence of the warm filament was also found in the area by analysing the hydrographic data in the area west of Kyushu during May 24-June 5, 1988.The Kuroshio warm filaments move westward opposite to the Kuroshio and then turn northward at the shelf break and become the main source of the warm water of the Tsushima Warm Current. A simple dynamic explanation for the process is presented in this paper.

Assimilation of surface currents into a regional model over Qingdao coastal waters of China

Surface currents measured by high frequency （HF） radar arrays are assimilated into a regional ocean model over Qingdao coastal waters based on Kalman filter method. A series of numerical experiments are per- formed to evaluate the performance of the data assimilation schemes. In order to optimize the analysis pro- cedure in the traditional ensemble Kalman filter （ENKF）, a different analysis scheme called quasiensemble Kaman filter （QENKF） is proposed. The comparisons between the ENKF and the QENKF suggest that both them can improve the simulated error and the spatial structure. The estimations of the background error covariance （BEC） are also assessed by comparing three different methods： Monte Carlo method; Canadian quick covariance （CQC） method and data uncertainty engine （DUE） method. A significant reduction of the root-mean-square （RMS） errors between model results and the observations shows that the CQC method is able to better reproduce the error statistics for this coastal ocean model and the corresponding external forcing. In addition, the sensibility of the data assimilation system to the ensemble size is also analyzed by means of different scales of the ensemble size used in the experiments. It is found that given the balance of the computational cost and the forecasting accuracy, the ensemble size of 50 will be an appropriate choice in the Qingdao coastal waters.

Analysis of thermohaline and current distribution characteristics of Zhejiang and Fujian waters in summer

This paper analyzed the distribution of thermohaline and circulation characteristics of Zhejiang and Fujian waters,based on the cross-sectional thermohaline data and on current data （up to 30 d duration） at fixed-point moorings,collected in the summer of 2006.We also performed low-pass filtering and spectrum analysis on the mooring submersible buoy data.Based on that analysis,we discussed the characteristics of low frequency currents and time-variations in these waters.The main conclusions are as follows.（1） There is a low salinity pinnate area near the Hangzhou Bay in summer,and outside the low salinity area,an obvious salinity front is present from surface to bottom near 123 E.There is also a temperature front below the surface at a corresponding position.（2） Bottom water of the Taiwan Warm Current comes from the subsurface of Kuroshio.（3） The direction of low frequency current at fixed anchor stations is N-NE or S,which mainly depends on the interaction of control currents in this waters.（4） Significant spectral peaks at all mooring stations are typically semidiurnal and diurnal tides.Semidiurnal tidal waves are the main ones in these waters,and have more energy closer to the shore.（5） Significant energy spectral peaks of middle period （3 to 8 d） of currents are responses to weather frequency.（6） Significant energy spectral peaks of long periods at the surface or bottom are probably responses to seasonal wind or bottom friction,while,the long period peaks of other depths can reflect cyclical changes of interactions between currents.We conclude that the pulsation period of the Taiwan Warm Current in these waters is 10-17 d.

Current Situation and Comprehensive Control Measures of Water Environment in the Chaohu Lake

Based on the analysis of current situation of water environment in the Chaohu Lake,general ideas and measures of controlling the water environment were proposed. In respect of control ideas,controlling outbreaks of blue-green algae should be as one of control goals; it is needed to combine reducing the quantity of blue-green algae with decreasing eutrophication level to make the decrease in the quantity of blue-green algae larger than their natural increase until outbreaks of blue-green algae are eliminated; all kinds of techniques should be combined closely,integrated and innovated,and corresponding safeguard measures should be adopted. In respect of control measures,controlling sources of pollution and intercepting pollutants are basic measures,of which improving sewage treatment capacity and standard greatly is a key measure,and actively controlling pollution from large-scale livestock and poultry breeding is one of main measures; rivers polluted heavily should be controlled,and using microorganisms to purify small and moderate rivers can be as one of preferred techniques; blue-green algae should be dredged deeply to reducing their quantity; water should be transferred from the Yangtze River to the Chaohu Lake or the Hauihe River to purify water bodies and increase environmental capacity; reed wetland should be restored on a large scale to increase vegetation coverage from 5% to 20%; dredging should be combined with the elevation of basement of restored reed wetland.

On the Taiwan Warm Current Water

Using our data from special observation in the source area of the Taiwan Warm Current from 19S2 to 1985) and historical data, the authors conducted studies to clarify the temperature and salinity characteristics, variability, and origin of the Taiwan Warm Current Water, and its influence on the expanding direction of the Changjiang Diluted Water.The main results of these studies are briefly given below. (1) The Taiwan Warm Current Water can be divided into two parts:the Surface Water of the Taiwan Warm Current and the Deep Water of the Taiwan Warm Current; the former is formed due to the mixing of the Kuroshio Surface Water flowing northward along the east coast of Taiwan with the Taiwan Strait Water; the latter completed originates from Kuroshio Subsurface Water to the east of Taiwan. It is characterized by lower temperature and higher salinity in summer and the characteristics of temperature and salinity are more stable. The maximum seasonal variational range and maximum secular variational range of

Water Dissociation Phenomena on a Bipolar Membrane──Current-voltage Curve in Relation with IonicTransport and Limiting Current Density

The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage; while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ-Ⅴ in the two directions were com

A study on the source of the Tsushima Warm Current water

On the basis of the hydrographic data in the area west of Kyushu from four cruises of R/V Xiangyanghong No. 9 from 1987 to 1988 , the circulation features in the investigation area are described and the source of the Tsushima Warm Current water (TWCW) is explored by using the observed and geostrophic current results and tracking the Kuroshio Subsurface High Salinity Core (KSHSC).

Combined refraction and diffraction models for sea waves over complicated topography and with currents in shallow water

-Combined refraction and diffraction models in the form of linear parabolic approximation are derived through smallparameter method. More strictly theoretical basis and more accuracy in the models than Lozano's (1980) are obtained. Some theoretical defects in Liu's model (1985) with consideration of current are not only found but also eliminated. More strict and accurate models are, therefore, presented in this paper.The calculation results and analysis in applying the models to actual wave field with consideration of bottom friction will be given in the following paper.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTA-TION (Ⅰ)-THE CONTINUOUS-TIME CASE

An initial-boundary value problem for shallow equation system consisting of water dynamics equations,silt transport equation, the equation of bottom topography change,and of some boundary and initial conditions is studied, the existence of its generalized solution and semidiscrete mixed finite element(MFE) solution was discussed, and the error estimates of the semidiscrete MFE solution was derived.The error estimates are optimal.

Numerical study on water waves and wave-induced longshore currents in Obaky coastal water

In this paper, the water waves and wave-induced longshore currents in Obak6y coastal water which is located at the Mediterranean coast of Turkey were numerically studied. The numerical model is based on the parabolic mild-slope equation for coastal water waves and the nonlinear shallow water equation for the wave-induced currents. The wave transformation under the effects of shoaling, refraction, diffraction and breaking is considered, and the wave provides radiation stresses for driving currents in the model. The numerical results for the water wave-induced longshore currents were validated by the measured data to demonstrate the efficiency of the numerical model. Then the water waves and longshore currents induced by the waves from main directions were numerically simulated and analyzed based on the numerical results. The numerical results show that the movement of the longshore currents was different while the wave proDaRated to a coastal zone from different directions.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTATION (Ⅱ)——THE DISCRETE-TIME CASE ALONG CHARACTERISTICS

The mixed finite element(MFE) methods for a shallow water equation system consisting of water dynamics equations,silt transport equation,and the equation of bottom topography change were derived.A fully discrete MFE scheme for the discrete_time along characteristics is presented and error estimates are established.The existence and convergence of MFE solution of the discrete current velocity,elevation of the bottom topography,thickness of fluid column,and mass rate of sediment is demonstrated.

Effects of wave-current interaction on the waves, cold-water mass and transport of diluted water in the Beibu Gulf

Wave-current interaction and its effects on the hydrodynamic environment in the Beibu Gulf(BG) have been investigated via employing the Coupled Ocean–Atmosphere–Wave–Sediment Transport(COAWST) modeling system. The model could simulate reasonable hydrodynamics in the BG when validated by various observations.Vigorous tidal currents refract the waves efficiently and make the seas off the west coast of Hainan Island be the hot spot where currents modulate the significant wave height dramatically. During summer, wave-enhanced bottom stress could weaken the near-shore component of the gulf-scale cyclonic-circulation in the BG remarkably, inducing two major corresponding adjustments: Model results reveal that the deep-layer cold water from the southern BG makes critical contribution to maintaining the cold-water mass in the northern BG Basin.However, the weakened background circulation leads to less cold water transported from the southern gulf to the northern gulf, which finally triggers a 0.2℃ warming in the cold-water mass area;In the top areas of the BG, the suppressed background circulation reduces the transport of the diluted water to the central gulf. Therefore, more freshwater could be trapped locally, which then triggers lower sea surface salinity(SSS) in the near-field and higher SSS in the far-field.

Evaluation of flow regime of turbidity currents entering Dez Reservoir using extended shallow water model

In this study, the performance of the extended shallow water model （ESWM） in evaluation of the flow regime of turbidity currents entering the Dez Reservoir was investigated. The continuity equations for fluid and particles and the Navier-Stokes equations govern the entire flow of turbidity currents. The shallow water equations governing the flow of the depositing phase of turbidity currents are derived from these equations. A case study was conducted on the flow regime of turbidity currents entering the Dez Reservoir in Iran from January 2002 to July 2003. Facing a serious sedimentation problem, the dead storage of the Dez Reservoir will be full in the coming 10 years, and the inflowing water in the hydropower conduit system is now becoming turbid. Based on the values of the dimensionless friction number （ Nf ≤1 ） and dimensionless entrainment number （ NE≤ 1 ） of turbidity currents, and the coefficient of determination between the observed and predicted deposit depths （R2 = 0.86） for the flow regime of negligible friction and negligible entrainment （NFNE）, the flow regime of turbidity currents coming into the Dez Reservoir is considered to be NFNE. The results suggest that the ESWM is an appropriate approach for evaluation of the flow regime of turbidity currents in dam reservoirs where the characteristics of turbidity currents, such as the deposit depth, must be evaluated.

NONLINEAR DYNAMICS RESPONSE OF CASING PIPE UNDER COMBINED WAVE-CURRENT

The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison’s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin’s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.

Mechanical Behaviors of Submerged Floating Tunnel under Current Effect

In order to provide a technical reference and guidance for the safety and stability analysis of the submerged floating tunnel （SFT） in the future, the mechanical behaviors of SFT under the action of water current with different velocities were studied by experiments on an SFT tube model made of rubber. Then, a numerical simulation on the coupling interaction between SFT and water current was conducted by finite element method （FEM）. The comparison .between the results obtained from experiment and those derived from the numerical simulation shows that the experimental results approximately tally with the simulational ones. As a result, the relationships between water current velocities and the mechanical behaviors of tube, such as the annular and axial strains, internal forces （ axial force and bending moment）, and deformations of the tube structure and the forces borne by the tension cables, were concluded.

The study on seasonal characteristics of water masses in the western East China Sea shelf area

On the basis of the CTD data and the modeling results in the winter and summer of 2009, the seasonal characteristics of the water masses in the western East China Sea shelf area were analyzed using a cluster analysis method. The results show that the distributions and temperature-salinity characteristics of the water masses in the study area are of distinct seasonal difference. In the western East China Sea shelf area, there are three water masses during winter, i.e., continental coastal water（CCW）, Taiwan Warm Current surface water（TWCSW） and Yellow Sea mixing water（YSMW）, but four ones during summer, i.e., the CCW, the TWCSW, Taiwan Warm Current deep water（TWCDW） and the YSMW. Of all, the CCW, the TWCSW and the TWCDW are all dominant water masses. The CCW, primarily characterized by a low salinity, has lower temperature, higher salinity and smaller spatial extent in winter than in summer. The TWCSW is warmer, fresher and smaller in summer than in winter, and it originates mostly from the Kuroshio surface water（KSW） northeast of Taiwan, China and less from the Taiwan Strait water during winter, but it consists of the strait water and the KSW during summer. The TWCDW is characterized by a low temperature and a high salinity, and originates completely in the Kuroshio subsurface water northeast of Taiwan.

Study on the Water Quality and Protection Measures of Dongting Lake

From nitrogen and phosphorus,chemical oxygen demand,phytoplankton,and eutrophication,this article analyzes the current situation of water quality in the Dongting Lake area,and discusses the factors influencing the water quality of Dongting Lake. Based on the actual production,geographic characteristics and outstanding problem of grim water pollution situation in the Dongting Lake area,some specific proposed measures are put forward in order to provide the basis and reference for the future pollution control in the Dongting Lake area,such as strengthening the industrial pollution control,developing ecological agriculture,and enhancing ecological restoration and water quality early warning.

Progress in Chinese research on water masses and circulation in the Arctic and subarctic ocean

The Arctic Ocean and Arctic sea ice have undergone a series of rapid changes. Oceanographic surveying has become one of the key missions of the Chinese National Arctic Research Expeditions since 1999. Using the data obtained in these surveys and from other sources, Chinese researchers have carried out a series of studies in the field of Arctic physical oceanography. The Near Sea-surface Temperature Maximum, freshwater content and heat flux in different regions of the Arctic have drawn wide attention from Chinese researchers. Arctic circulation is changing with the decline of sea ice, which is also influencing the structure and distribution of water masses. Studies have also focused on these issues. In this paper, the main results of research on water masses, currents, the structure of the upper ocean and other major hydrological phenomena over the past two decades are summarized.