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Mainly driven by wind stress, the upper ocean dynamic processes in the North Pacific Ocean serve as important pathways for mass and energy exchanges of the global ocean and thus play an essential role in modulating the global climate. In this study, eight commonly used surface wind datasets are compared on mean state, seasonal and interannual time scales over the North Pacific Ocean. The dataset-derived wind stress, wind stress curl, and Sverdrup stream function and their effects on the current structure, which are illustrated by a set of 1.5-layer linear reduced gravity ocean model experiments, are thoroughly compared. The results show that for each time scale, the spreads among the tested products for the wind stress curl, Sverdrup stream function, thermocline displacement, and North Equatorial Current (NEC)/North Equatorial Countercurrent (NECC) transport are relatively large, caused by the small spread among the tested products for zonal/meridional wind stress occurring in the open ocean/nearshore water. MERRA2 and NCEP/DOE are the dominant contributors to the spread in the zonal and meridional wind stress and thus in the other variables, respectively, indicating that they could force a more fluctuating current field. On the interannual scale, the simulated latitudinal positions of the NEC/NECC are sensitive to the choice of wind forcing. NCEP/NCAR and ASCAT deviate most from the ensemble mean. Generally, ERA5 shows the most resemblance with the ensemble mean over the tested products. [ABSTRACT FROM AUTHOR]

In shallow waters, tidal friction at seabed is proportional to the square of tidal current velocity, and can induce shallow water tides. M 2 , S 2 and N 2 are the most important semi-diurnal constituents in the Bohai and Yellow Seas, and their interaction through the frictional nonlinearity can induce shallow water tides, with 2MS 2 and 2MN 2 being the most representative constituents. In this paper, we analyze the observed hourly records at 27 tidal stations along the coast of the Bohai and Yellow Seas and obtain harmonic constants of μ 2 and L 2 constituents, which can be separated into astronomical parts μ 2 ′ and L 2 ′ , and frictional nonlinearity-induced parts, 2MS 2 and 2MN 2 , respectively. A numerical model is also performed to simulate the constituents 2MS 2 and 2MN 2. It shows a fairly good agreement between the model and observations in the harmonic constants of constituents 2MS 2 and 2MN 2. The cotidal charts of 2MS 2 and 2MN 2 are presented. It is found that the frictional nonlinearity-induced shallow water tides can significantly reduce the main fortnightly and monthly modulations. • Harmonic constants of μ 2 and L 2 constituents are obtained from 27 tide gauges. • The nonlinear interplay between M 2 , S 2 and N 2 tides can induce 2MS 2 and 2MN 2 tides. • Nonlinearity-induced shallow water tides reduce main fortnightly and monthly modulations. [ABSTRACT FROM AUTHOR]

A parameterized internal tide dissipation term and self-attraction and loading (SAL) tide term are introduced in a barotropic numerical model to investigate the dynamics of semidiurnal tidal constituents M 2 and S 2 in the Bohai Sea, Yellow Sea and East China Sea (BYECS). The optimal parameters for bottom friction and internal dissipation are obtained through a series of numerical computations. Numerical simulation shows that the tide-generating force contributes 1.2% of M 2 power for the entire BYECS and up to 2.8% for the East China Sea deep basin. SAL tide contributes 4.4% of M 2 power for the BYECS and up to 9.3% for the East China Sea deep basin. Bottom friction plays a major role in dissipating tidal energy in the shelf regions, and the internal tide effect is important in the deep water regions. Numerical experiments show that artificial removal of tide-generating force in the BYECS can cause a significant difference (as much as 30 cm) in model output. Artificial removal of SAL tide in the BYECS can cause even greater difference, up to 40 cm. This indicates that SAL tide should be taken into account in numerical simulations, especially if the tide-generating force is considered. [ABSTRACT FROM AUTHOR]

The wind stresses and their derived wind stress curls, and Sverdrup stream functions over the South China Sea (SCS) in typical winter and summer months from nine datasets are compared. The datasets include CCMP, CERSAT, ASCAT, QSCAT, NCEP, QSCAT-NCEP, HR, ERA-40, and ERA-Interim. Results show that the overall patterns of the wind stresses, wind stress curls, and Sverdrup stream functions from different datasets are similar. However, their magnitudes are remarkably different. Among them, ERA-40 is the smallest while HR is the largest. The former is about 40 % smaller than the mean value, while the latter is about 50 % greater than the mean value. The spatial resolution is important for the presentation of the wind stress features in the SCS. It can be expected that the same numerical ocean model driven by different wind stress would yield remarkably different results. [ABSTRACT FROM AUTHOR]

Abstract: The South China Sea (SCS) interocean circulation and its associated heat and freshwater budgets are examined using the results of a variable-grid global ocean model. The ocean model has a 1/6° resolution in the SCS and its adjacent oceans. The model results from 1982 to 2003 show that the western Pacific waters enter the SCS through the Luzon Strait with an annual mean volume transport of 4.80Sv, of which 1.71Sv returns to the western Pacific through the Taiwan Strait and East China Sea and 3.09Sv flows toward the Indian Ocean. The heat in the western Pacific is transported to the SCS with a rate of 0.373PW (relative to a reference temperature 3.72°C), while the total heat transport through the outflow straits is 0.432PW. The net heat transport out of the SCS is thus 0.059PW, which is balanced by a mean net downward heat flux of 17W/m2 across the SCS air–sea interface. Therefore, the interocean circulation acts as an “air conditioner”, cooling the SCS and its overlaying atmosphere. The SCS contributes a heat transport of 0.279PW to the Indian Ocean, of which 0.240PW is from the Pacific Ocean through the Luzon Strait and 0.039PW is from the SCS interior gained from the air–sea exchange. The Luzon Strait salt transport is greater than the total salt transport leaving the SCS by 3.97Gg/s, implying a mean freshwater flux of 0.112Sv (or 3.54×1012 m3/year) from the land discharge and P−E (precipitation minus evaporation). The total annual land discharge to the SCS is estimated to be 1.60×1012 m3/year, the total annual P−E over the SCS is thus 1.94×1012 m3/year, equivalent to a mean P−E of 0.55m/year. The SCS freshwater contribution to the Indian Ocean is 0.096Sv. The pattern of the SCS interocean circulation in winter differs greatly from that in summer. The SCS branch of the Pacific-to-Indian Ocean throughflow exists in winter, but not in summer. In winter this branching flow starts at the Luzon Strait and extends to the Karimata Strait. In summer the interocean circulation is featured by a north-northeastward current starting at the Karimata Strait and extending to the Taiwan and Luzon Straits, and a subsurface inflow from the Luzon Strait that upwells into the surface layer in the SCS interior to supply the outward transports. [Copyright &y& Elsevier]

Assesses the mean sea surface heights of the South and East China Seas from ocean circulation model and geodetic leveling. Intercomparison of model results from geodetic level measurements; Reduction of standard deviation by 4½ centimeter; Applications of satellite altimetry to ocean monitoring.

Marine heatwaves (MHWs) are prolonged discrete events of anomalously warm seawater observed around the world. The occurrence of MHWs in the Japan/East Sea (JES), a middle latitude marginal sea with abundant aquatic resources, has severe impacts on marine ecosystems and human society. We used satellite remote sensing products spanning 1982–2020 to investigate the mean states and variations of JES MHWs. The results show that the JES MHWs occurred twice per year. More than 40% of the MHWs were shorter than the mean duration of 12.6 days and weaker than the mean intensity of 2.4 °C. Frequent MHWs were observed in August, while high mean intensities were observed in winter and spring in the western JES. In recent years, the area's averaged yearly sum of MHW intensity in the JES has increased dramatically, with a positive trend of 29.62 °C days per decade—over twice the average global trend (12.37 °C days per decade), which is further confirmed by its first empirical orthogonal function mode. The strengthening trend in MHWs may be explained by oceanic dynamics rather than atmospheric forcing, and may result in increased surface latent heat flux from the ocean to the atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: A global sensitivity analysis (GSA) is performed on a marine ecosystem dynamic model by using Morris’ method with testing 10,000 times in this paper. This statistical sampling method allows to display nonlinear characteristics of interactions among various parameters and rank the most relevant parameters of the model. With this method, we proposed the model''s parameter optimization strategy and applied this to the Sanggou Bay. The results showed that the method not only can safeguard the objectivity of parameter set initial values, but also can avoid stochasticity of analytical results. Compared with the local one, the GSA is found to have a series of advantages, which supports necessity of developing it. [Copyright &y& Elsevier]

Models of marine ecosystem dynamics play an important role in revealing the evolution mechanisms of marine ecosystems and in forecasting their future changes. Most traditional ecological dynamics models are established based on basic physical and biological laws, and have obvious dynamic characteristics and ecological significance. However, they are not flexible enough for the variability of environment conditions and ecological processes found in offshore marine areas, where it is often difficult to obtain parameters for the model, and the precision of the model is often low. In this paper, a new modeling method is introduced, which aims to establish an evolution model of marine ecosystems by coupling statistics with differential dynamics. Firstly, we outline the basic concept and method of inverse modeling of marine ecosystems. Then we set up a statistical dynamics model of marine ecosystems evolution according to annual ecological observation data from Jiaozhou Bay. This was done under the forcing conditions of sea surface temperature and surface irradiance and considering the state variables of phytoplankton, zooplankton and nutrients. This model is dynamic, makes the best of field observation data, and the average predicted precision can reach 90% or higher. A simpler model can be easily obtained through eliminating the terms with smaller contributions according to the weight coefficients of model differential items. The method proposed in this paper avoids the difficulties of obtaining and optimizing parameters, which exist in traditional research, and it provides a new path for research of marine ecological dynamics. [ABSTRACT FROM AUTHOR]

Using 10-year (January 1998-October 2007) dataset of Sea-viewing Wide Field-of-view Sensor (SeaWiFS), we extracted the dominant spatial patterns and temporal variations of the chlorophyll distribution in the central western South China Sea (SCS) through Empirical Orthogonal Function (EOF) analysis. The results show that the first EOF mode is characterized by a high chlorophyll concentration zone along the Vietnam coast. We found two peaks in summer (July-August) and in winter (December), respectively, in normal years. The second EOF mode is characterized by a jet-shaped tongue of high chlorophyll concentration extending seaward to the northeast in summer (July-August). To investigate the interannual variability of the chlorophyll concentration, we extracted the first non-seasonal (annual cycle removed) EOF mode, which shows high spatial variability off the southeast Vietnam coast. Both spatial pattern and time coefficients correspond well with those of sea surface temperature mode, and are closely correlated to ENSO events, with a lag of 7 months. [ABSTRACT FROM AUTHOR]

11-year satellite altimeter sea surface height (SSH) anomaly data from January 1993 to December 2003 are used to present the dominant spatial patterns and temporal variations of the South China Sea (SCS) surface circulation through Empirical Orthogonal Function (EOF) analysis. The first three EOF modes show the obvious seasonal variations of SSH in the SCS. EOF mode one is generally characterized by a basin-wide circulation. Mode two describes the double-cell basin scale circulation structure. The two cells were located off west of the Luzon Island and southeast of Vietnam, respectively. EOF mode three presents the mesoscale eddy structure in the western SCS, which develops into a strong cyclonic eddy rapidly from July to September. EOF mode one and mode three are also embedded with interannual signals, indicating that the SCS surface circulation variation is influenced by El Niño events prominently. The strong El Niño of 1997/98 obviously changed the SCS circulation structure. This study also shows that there existed a series of mesoscale eddies in the western SCS, and their temporal variation indicates intra-seasonal and interannual signals. [ABSTRACT FROM AUTHOR]

We adopt a parameterized internal tide dissipation term to the two-dimensional (2-D) shallow water equations, and develop the corresponding adjoint model to investigate tidal dynamics in the South China Sea (SCS). The harmonic constants derived from 63 tidal gauge stations and 24 TOPEX/Poseidon (T/P) satellite altimeter crossover points are assimilated into the adjoint model to minimize the deviations of the simulated results and observations by optimizing the bottom friction coefficient and the internal tide dissipation coefficient. Tidal constituents M 2 , S 2 , K 1 and O 1 are simulated simultaneously. The numerical results (assimilating only tidal gauge data) agree well with T/P data showing that the model results are reliable. The co-tidal charts of M 2 , S 2 , K 1 and O 1 are obtained, which reflect the characteristics of tides in the SCS. The tidal energy flux is analyzed based on numerical results. The strongest tidal energy flux appears in the Luzon Strait (LS) for both semi-diurnal and diurnal tidal constituents. The analysis of tidal energy dissipation indicates that the bottom friction dissipation occurs mainly in shallow water area, meanwhile the internal tide dissipation is mainly concentrated in the LS and the deep basin of the SCS. The tidal energetics in the LS is examined showing that the tidal energy input closely balances the tidal energy dissipation. [ABSTRACT FROM AUTHOR]

Sub-inertial currents (SICs) over the continental shelf of the northern South China Sea (NSCS) are investigated using the in-situ current observations of acoustic Doppler current profiler (ADCP) mooring arrays off the Pearl River Estuary in 2006 and 2007. The survey was carried out in four separate time periods: summer, winter, spring (before the onset of the southwesterly monsoon), and fall (after the establishment of the northeasterly monsoon). The observations showed that the current directions were generally along the shelf, consistent with the directions of monsoonal winds. The currents were also affected by a few of mesoscale eddy events. In summer 2006, the volume transport was northeastward with a mean magnitude of 1.4 Sv through a cross-shelf section from the site of the depth of 135 m to the coast; in winter 2006/2007, spring 2007 and fall 2007, the volume transports were all southwestward with magnitudes of 2.0, 2.1, and 0.9 Sv, respectively, through a cross-shelf section from the site of the depth of 290 m to the coast. The standard deviations of the SICs were generally smaller than the velocities of the mean currents, and the variability of SICs showed significant correlation with the local sea surface winds. No persistent counter-wind currents were observed in the study area during the fall and winter observational periods. [ABSTRACT FROM AUTHOR]