Baoshu Yin

Numerical study of the ocean circulation on the East China Sea shelf and a Kuroshio bottom branch northeast of Taiwan in summer

Using the Regional Ocean Model System, the ocean circulation on the East China Sea (ECS) shelf was examined by a fine-resolution model which was nested in a coarse-resolution Pacific Ocean model. The high-resolution simulation shows an accurate volume transport of 2.70 Sv (Sv = 10(6) m(3)s(-1)) through the Tsushima Strait, which is more consistent with the previous 5.5 year observation value (2.64 Sv) than former model results. For the Taiwan Strait it also shows a close volume transport (1.03 Sv) to a recent estimate (1.20 Sv). At the same time the model results reproduced almost all of the known circulation structure on the ECS shelf. In addition, the hindcast of 2009 shows a Kuroshio Bottom Branch Current to the northeast of Taiwan (KBBCNT). The KBBCNT is confirmed by the observational bottom high-salinity water (from 15 August to 2 September 2009) whose distribution is also reproduced by the model results. Tracer and particle experiments were carried out to elucidate the formation of the high-salinity water and the pathway of the KBBCNT. In light of the field observation and numerical experiments, a new pathway of the KBBCNT is proposed: bifurcated from the subsurface water of Kuroshio northeast of Taiwan, it upwells northwestward gradually from 300 to 60 m, then turns to northeast in the region around 27.5 degrees N, 122 degrees E, and finally reaches 31 degrees N off the mouth of the Changjiang River along similar to 60 m isobaths, forming the bottom saline water off the coast of Zhejiang province, China.

Numerical study on the pattern and origins of Kuroshio branches in the bottom water of southern East China Sea in summer

Pattern and origins of Kuroshio branches in the bottom water of southern East China Sea (ECS), were carefully examined by numerical simulations based on the Regional Ocean Modeling System (ROMS) together with observations. Model results show that in the bottom water of ECS, the intrusion pattern of Kuroshio is mainly composed of an Offshore Kuroshio Branch Current (OKBC) which, bifurcated from the Kuroshio northeast of Taiwan, flows nearly along the isobath of similar to 100 m, and a Nearshore Kuroshio Branch Current (NKBC) which, originated from the Kuroshio northeast of Taiwan, upwells northwestward gradually from similar to 250 m to similar to 60 m, then turns to northeast around 27.5 degrees N, 122 E, thereafter flows northeastward along the isobath of similar to 60 m, and finally reaches at 30.5 degrees N where it turns to east. Furthermore, we found that the NKBC mostly originated in the Kuroshio subsurface water (120-250 m) east of Taiwan, whereas the OKBC mainly stemmed from the Kuroshio water (60-120 m) east of Taiwan. This pattern and origins of OKBC and NKBC well addressed the observational phenomena that off the coast of Zhejiang province, China, there were colder, less saline, and more phosphate-rich bottom water near the isobath of similar to 60 m rather than near the isobath of similar to 100 m in August 2009. Finally, it is proposed that on southern ECS continental shelf, Kuroshio exhibits its intrusion branches by an anticyclonical stair structure: bottom stair NKBC, middle stair OKBC, and top stair Kuroshio surface branch (KBC).

Variability of internal tides and near-inertial waves on the continental slope of the northwestern South China Sea

Structure and variability of internal tides (IT) and near-inertial waves (NIW) on the continental slope of the northwestern South China Sea were investigated, based on 9-month moored current observations from autumn to early summer in 2008 and 2009. The diurnal IT kinetic energy, dominant over that of semidiurnal tides, is found to exhibit apparent seasonal variability-strongest in summer and weakest in winter-whereas the semidiurnal variance remained nearly uniform throughout the observation period. Moreover, the diurnal IT were more coherent (i.e., phase-locked to the astronomical forcing) than the semidiurnal constituents. Coherent diurnal variance accounts for about 40% of diurnal motions, but semidiurnal tides contain a much smaller fraction (10%) of coherent motions. Further analysis demonstrates that the diurnal IT are dominated by the first mode, whereas the semidiurnal tides show a variable multimodal structure: the second mode is dominant in summer and comparable to the first mode in spring and autumn, but the first mode predominates in winter. Multimodal semidiurnal IT are more influenced by varying stratification structures and background currents and thus exhibit highly incoherent and intermittent behavior, which may wash out seasonal variability during their long propagation from the generation source. The observed NIW are seasonally independent and comparable to the semidiurnal motions. During the passage of Typhoon Hagupit, however, the NIW became the most energetic component of the inertia-gravity waveband motions. NIW energy and shear were significantly enhanced and exceeded tidal counterparts by a factor of 2 to 3 in the upper layer.

Analysis of seasonal variation of water masses in East China Sea

Seasonal variations of water masses in the East China Sea (ECS) and adjacent areas are investigated, based on historical data of temperature and salinity (T-S). Dynamic and thermodynamic mechanisms that affect seasonal variations of some dominant water masses are discussed, with reference to meteorological data. In the ECS above depth 600 m, there are eight water masses in summer but only five in winter. Among these, Kuroshio Surface Water (KSW), Kuroshio Intermediate Water (KIW), ECS Surface Water (ECSSW), Continental Coastal Water (CCW), and Yellow Sea Surface Water (YSSW) exist throughout the year. Kuroshio Subsurface Water (KSSW), ECS Deep Water (ECSDW), and Yellow Sea Bottom Water (YSBW) are all seasonal water masses, occurring from May through October. The CCW, ECSSW and KSW all have significant seasonal variations, both in their horizontal and vertical extents and their T-S properties. Wind stress, the Kuroshio and its branch currents, and coastal currents are dynamic factors for seasonal variation in spatial extent of the CCW, KSW, and ECSSW, whereas sea surface heat and freshwater fluxes are thermodynamic factors for seasonal variations of T-S properties and thickness of these water masses. In addition, the CCW is affected by river runoff and ECSSW by the CCW and KSW.

Forced ILW-Burgers Equation as a Model for Rossby Solitary Waves Generated by Topography in Finite Depth Fluids

The paper presents an investigation of the generation, evolution of Rossby solitary waves generated by topography in finite depth fluids. The forced ILW- (Intermediate Long Waves-) Burgers equation as a model governing the amplitude of solitary waves is first derived and shown to reduce to the KdV- (Korteweg-de Vries-) Burgers equation in shallow fluids and BO- (Benjamin-Ono-) Burgers equation in deep fluids. By analysis and calculation, the perturbation solution and some conservation relations of the ILW-Burgers equation are obtained. Finally, with the help of pseudospectral method, the numerical solutions of the forced ILW-Burgers equation are given. The results demonstrate that the detuning parameter alpha holds important implications for the generation of the solitary waves. By comparing with the solitary waves governed by ILW-Burgers equation and BO-Burgers equation, we can conclude that the solitary waves generated by topography in finite depth fluids are different from that in deep fluids.

A New Integro-Differential Equation for Rossby Solitary Waves with Topography Effect in Deep Rotational Fluids

From rotational potential vorticity-conserved equation with topography effect and dissipation effect, with the help of the multiple-scale method, a new integro-differential equation is constructed to describe the Rossby solitary waves in deep rotational fluids. By analyzing the equation, some conservation laws associated with Rossby solitary waves are derived. Finally, by seeking the numerical solutions of the equation with the pseudospectral method, by virtue of waterfall plots, the effect of detuning parameter and dissipation on Rossby solitary waves generated by topography are discussed, and the equation is compared with KdV equation and BO equation. The results show that the detuning parameter.. plays an important role for the evolution features of solitary waves generated by topography, especially in the resonant case; alpha large amplitude nonstationary disturbance is generated in the forcing region. This condition may explain the blocking phenomenon which exists in the atmosphere and ocean and generated by topographic forcing.

Dissipative Nonlinear Schrodinger Equation for Envelope Solitary Rossby Waves with Dissipation Effect in Stratified Fluids and Its Solution

We solve the so-called dissipative nonlinear Schrodinger equation by means of multiple scales analysis and perturbation method to describe envelope solitary Rossby waves with dissipation effect in stratified fluids. By analyzing the evolution of amplitude of envelope solitary Rossby waves, it is found that the shear of basic flow, Brunt-Vaisala frequency, and beta effect are important factors to form the envelope solitary Rossby waves. By employing trial function method, the asymptotic solution of dissipative nonlinear Schrodinger equation is derived. Based on the solution, the effect of dissipation on the evolution of envelope solitary Rossby wave is also discussed. The results show that the dissipation causes a slow decrease of amplitude of envelope solitary Rossby waves and a slow increase of width, while it has no effect on the propagation velocity. That is quite different from the KdV-type solitary waves. It is notable that dissipation has certain influence on the carrier frequency.

Long-range propagation and associated variability of internal tides in the South China Sea

The variability of internal tides during their generation and long-range propagation in the South China Sea (SCS) is investigated by driving a high-resolution numerical model. The present study clarifies the notably different processes of generation, propagation and dissipation between diurnal and semidiurnal internal tides. Internal tides in the SCS originate from multiple source sites, among which the Luzon Strait is dominant, and contributes approximately 90% and 74% of the baroclinic energy for M2 and K1, respectively. To the west of the Luzon Strait, local generation of K1 internal tides inside the SCS is more energetic than the M2 tides. Diurnal and semidiurnal internal tides from the Luzon Strait radiate into the SCS in a north-south asymmetry but with different patterns because of the complex two-ridge system. The tidal beams can travel across the deep basin and finally arrive at the Vietnam coast and Nansha Island more than 1000-1500 km away. During propagation, M2 internal tides maintain a southwestward direction, whereas K1 exhibit complicated wave fields because of the superposition of waves from local sources and island scattering effects. After significant dissipation within the Luzon Strait, the remaining energy travels into the SCS and reduces by more than 90% over a distance of ∼1000 km. Inside the SCS, the K1 internal tides with long crests and flat beam angles are more influenced by seafloor topographical features and thus undergo apparent dissipation along the entire path, whereas the prominent dissipation of M2 internal tides only occurs after their arrival at Zhongsha Island. This article is protected by copyright. All rights reserved.

Depression and elevation internal solitary waves in a two-layer fluid and their forces on cylindrical piles

Both large amplitude depression and elevation internal solitary waves (ISWs) were observed on the continental shelf of the northwest South China Sea (SCS) during the Wenchang Internal Wave Experiment. In this study, we investigate the characteristics of depression and elevation ISWs based on comparisons between observational results and internal wave theories. It is suggested that the large amplitude depression wave is better represented by the extended Korteweg-de Vries (EKdV) theory than by the KdV model, whereas the large amplitude elevation wave is in better agreement with the KdV equation than with the EKdV theory. Wave-induced forces on a supposed small-diameter cylindrical pile by depression and elevation waves are also estimated using the internal wave theory and Morison formula. The wave-induced force by elevation ISWs is rarely reported in the literature. It is found that the force induced by the elevation wave differs significantly from that by the depression wave, and the elevation wave generally produces greater force on the pile in the lower water column than the depression wave. These results show that ISWs in the study area can present a serious threat to ocean engineering structures, and should not be ignored in the design of oil platforms and ocean operations.

Nutrient-controlled growth of Skeletonema costatum : an applied model

To model Skeletonema costatum blooms and their relationship with environmental parameters in situ, a S. costatum-specific zero-dimensional box model based on the mechanistic model Eco3M was established using physiological features. The parameters were calibrated using experimental counterparts, and simulations were compared with published laboratory findings. The resulting normalized objective function (NOF) values are less than 1.0 (and in most cases less than 0.58) and the values for the slope γ (between 0.656 7–1.127 4) and R2 (between 0.806 8–0.971) are close to 1.0 for most of the sub-figures. This indicates good agreement between simulated and measured data and suggests that the model reproduces the general characteristics of S. costatum growth and use of nutrients under different N- or P-limiting conditions. The model is appropriate for further applications and can be used to test more scenarios using other nutrients.