On the Taiwan Warm Current Water

With the use of historical data from their 1982-1985 special observation at the source area of the Taiwan Warm Current 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 are given below.(1)The Taiwan Warm Current Water can be divided into the "Surface Water of the Taiwan Warm Current" formed due to the mixing of the Kuroshio Surface Water flowing northward along the east coast of Taiwan with the Taiwan Strait Water, and the "Deep Water of the Taiwan Warm Current" originated from Kuroshio Subsurface Water to the east of Taiwan. It is characterized by stable low temperature and stable high salinity in summer. The maximum seasonal variation and maximum secular variation of temperature and salinity are 1.87℃, 0.26‰ and 2.96℃, 0.37‰, respectively.(2)The variation in strength of the Taiwan Warm Current is the main influe     

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.     

Seasonal and intraseasonal variations of the surface Taiwan Warm Current

To study seasonal and intraseasonal variations of the Taiwan Warm Current (TWC) in detail Rotated Empirical Orthogonal Function (REOF) and Extended Associate Pattern Analysis (EAPA) are jointly adopted with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in the present paper. Results show that the first and second REOFs of SST in the southern East China Sea (SECS) account for 50.8% and 39.8% of the total variance. The surface TWC contains persistent (multi-year mean), seasonal and intraseasonal components. The persistent one mainly inosculates with the Kuroshio but the seasonal and intraseasonal ones are usually active only on the continental shelf. Its persistent component is produced by inertial flow of the Kuroshio, however its seasonal and intraseasonal ones seems coming from seasonal and intraseasonal oscillations of monsoon force. The seasonal one reaches its maximum in late summer,lasting about four months and the intraseasonal one takes place at any seasons, lasting more than 40 days.     

A numerical study on seasonal variations of the Taiwan Warm Current

Princeton Ocean Model (POM) is employed to investigate the Taiwan Warm Current (TWC) and its seasonal variations. Results show that the TWC exhibits pronounced seasonal variations in its sources, strength and flow patterns. In summer, the TWC flows northeast in straight way and reaches around 32°N; it comes mainly from the Taiwan Strait, while its lower part is from the shelf-intrusion of the Kuroshio subsurface water (KSSW). In winter, coming mainly from the shelf-intrusion of the Kuroshio northeast of Taiwan, the TWC flows northward in a winding way and reaches up around 30°N. The Kuroshio intrusion also has distinct seasonal patterns. The shelf-intrusion of KSSW by upwelling is almost the same in four seasons with a little difference in strength; it is a persistent source of the TWC. However, Kuroshio surface water (KSW) can not intrude onto the shelf in summer, while in winter the intrusion of KSW always occurs. Additional experiments were conducted to examine effects of winds and transport through     

On the sources of the Taiwan Warm Current from the South China Sea

Historical hydrographic data across several sections in the South China Sea (SCS) and Taiwan Strait have been reconsidered. The year-around existence of the South China Sea Warm Current (SCSWC) along the shelf break off the Guangdong coast and the seemingly year-around southwestward current to the east of SCSWC are both evident in the data. The data also showed that the northward current in the Taiwan Strait seemed to be the extension of SCSWC. A barotropic numerical model is employed to explain some of the observed features. Reasonable simulation of the circulation in the northeast part of SCS has been found.     

Seasonality and causes of the Yellow Sea Warm Current

To study the seasonality and causes of the Yellow Sea Warm Current (YSWC) in detail, rotated empirical orthogonal function (REOF) and extended associate pattern analysis are adopted with daily sea surface salinity (SSS), sea surface temperature (SST) and sea surface height (SSH) datasets covering 1126 days from American Navy Experimental Real-Time East Asian Seas Ocean Nowcast System in the present paper. Results show that in the Yellow and East China Seas, the YSWC is a mean barotropic flow as compensation of winter-monsoon-driven surface currents, which has been directly observed. When East Asia winter monsoon weakens, so do the meridional pressure gradient of the surface seawater and the YSWC, while the transversal pressure gradient changes rather slowly that results in the YSWC left turning. In addition, there is southward mean flow compensation of summer-monsoon-driven surface currents, which actually was also directly ob-served.     

Nutrient structure of the Taiwan Warm Current and estimation of vertical nutrient fluxes in upwelling areas in the East China Sea in summer

Based on field data for nutrients collected on the continental shelf of the East China Sea (ECS) during summer 2006, the structure and variations of nutrients in every water mass related to the Taiwan Warm Current (TWC) were analyzed. The supplementary effect of nutrient of upwelling on harmful algal blooms (HABs) in the ECS was also estimated, based on upwelling data. Then the maintenance contribution of nutrient of upwelling to HABs was assessed. The results showed that N/P ratio is fairly low in both surface and deep layers of the TWC, which possibly controls nutrient structure of the HABs-frequently-occuring areas. In upwelling areas, the rate of phosphate (PO₄-P) uptake exceeds that of nitrate (NO₃-N) of the TWC. The TWC may relieve PO₄-P limitation during the process of HABs. Furthermore, upwelling plays an important role in providing nutrients to HABs. After estimating nutrient fluxes (NO₃-N, PO₄-P, SiO₃-Si) in the upwelling areas along a typical section (S07), the results showed that the nutrient uptake rate is the greatest at 10–20 m below euphotic zone, sustaining the ongoing presence of HABs. The uptake rate of PO₄-P is the highest among dissolved inorganic nutrients. Therefore, upwelling is most likely the main source of PO₄-P supply to HABs.     

REGIONAL FEATURES OF LONG-TERM SST VARIATION IN THE WESTERN PACIFIC WARM POOL AREA

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A numerical study of the South China Sea Warm Current during winter monsoon relaxation

Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current(SCSWC) in the northern South China Sea(NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea(SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.     

Fuzzy set study of water mass mixing in the source region of the Tsushima Warm Current

PFS-Fuzzy classification (Lu, 1989) was used on observational data obtained during a cruise (July–August, 1987) to classify the water masses in the source area of the Tsushima Warm Current. Their mixing features were studied by using numerical index analysis of fuzzy sets. The calculated results showed there are nine water masses belonging to three basic types. The analyses suggest that, though, in summer, the Surface Water of the Tsushima Warm Current located in a strongly mixed area is a mixture of the East China Sea Mixed Water, the Kuroshio Surface Water and the Kyushu Westerm Coastal Water, it originates mainly from the Kuroshio Surface Water and its deep water comes from the Kuroshio Subsurface Water. This study reveals that 1) regions such as the intensely mixed region, the frontal zone and the transition zone, Water, it originates deep water comes from water, usually have a higher fuzzy degree; 2) water masses with higher stability and little modification have a lower fuzzy degree; and 3) mixed water has a medium fuzzy degree. The differences and similarities in the size and density of these water masses and other waters are discussed.     

Summer temperature-salinity distributions and circulation characteristics of the source water of the Tsushima Warm current

Based on the data obtained in the area southwest of Kyushu in the summer of 1987, the temperature-salinity distribtutions and circulation characteristics are described and the origin of the Tsushima Warm Current is analysed.     

The inter-annual variability of the Yellow Sea Warm Current surface axis and its influencing factors

Based on the Pathfinder sea surface temperature(PFSST),the surface axis and its pattern of the Yellow Sea Warm Current(YSWC) are discussed.A structure of double-warm-tongue is found in February and it varies in different years.Two indexes are calculated to represent the westward shift(WSI) and northward extension(NEI) of the warm water in the Yellow Sea(YS).Wavelet analysis illustrates that the WSI and NEI have prominent periods of 3-6 years and 3-4 years,respectively.The Empirical Orthogonal Function(EOF) ...     

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT Ⅰ.BAROTROPIC CASE

In this work, Princeton Ocean Model (POM) was used to study the formation of the South China Sea Warm Current (SCSWC) in the barotropic case. Monthly averaged wind stress and the inflow/outflow transports in January were used in the numerical simulation which reproduced the SCSWC. The effects of wind stress and inflow/outflow were studied separately. Numerical experiments showed thatthe Kuroshio intrusion through the Luzon Strait and the slope shelf in the northern SCS are necessary conditions for the founation of the SCSWC. In a flat bottom topography experiment, the wind stress drivennortheast current in the northern SCS is a compensatory current.     

关中盆地深部地下热水残存沉积水的同位素证据

应用环境同位素水文地球化学方法,结合区域沉积演化史,对关中盆地固市凹陷、咸阳-礼泉断阶和西安凹陷深部地下热水成因类型进行了探讨,并就残存沉积水存在的可能性,寻找氢氧同位素关系、硫氧同位素关系、碳氧同位素关系、N(87Sr)/N(86Sr)与古盐度的关系等环境同位素证据,rNa/rCl值、ρ(Cl-)/ρ(Br-)、rBr/rI值与ρ(Cl-)的关系等水文地球化学证据以及沉积演化史证据。结果表明:固市凹陷华阴地下热水的同位素、水文地球化学特征已基本符合沉积水的特征,推测其为混有古入渗水的残存沉积水;固市凹陷华阴之外的其他构造单元、咸阳—礼泉断阶和西安凹陷地下热水的同位素和水文地球化学特征部分接近沉积水的特征,部分介于古入渗水和沉积水之间;咸阳—礼泉断阶东部地下热水可能为古入渗水或残存沉积水与后期入渗水的混合;西安凹陷及咸阳—礼泉断阶西部地下热水属于现代入渗水与古入渗水的混合水。     

Counter-Wind Deep Current in the Northern Beibu Gulf in Boreal Winter

The Beibu Gulf is at an important geographical location and rich in gas, oil and biological resources. The observed currents showed that the current in the upper layer was opposite to that in the lower layer in boreal winter in the northern Beibu Gulf and it was northeastward in the lower layer. This northeastward current was reproduced by a 3 D baroclinic model in this study. It's found that the counter-wind deep current(referred to as ‘CWDC' hereinafter) strengthened from September to November but weakened from December to the following February. A closed meridional circulation in vertical direction was found in the northern Beibu Gulf, including CWDC, surface southwestward current, an upwelling, and a downwelling. The temporal variation process of the meridional circulation was similar to that of CWDC, with strength and range stronger in November and December than in other four months. Similar to the variation process of CWDC, the monsoon wind changed from weak easterly wind in September to strong northeasterly wind in November and December, and it was transformed into weak southeasterly wind in February again. The sensitive experiments showed that CWDC and the meridional circulation were controlled by the monsoon wind and were adjusted by heat flux-and tide-induced mixing, respectively. According to the momentum balance equation, it can be revealed the counter-wind deep current is a compensation current which is induced by the surface elevation gradient balanced by the Coriolis force, vertical diffusion and baroclinic pressure gradient.     

Spatial distribution characteristics of surface tidal currents in the southwest of Taiwan Strait

This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar (HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M₂ is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M₂ tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity (PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity (MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.     

AN ANALYSIS OF WATER RESOURCE CHARACTERISTICS OF THE RIVERS IN THE NORTHERN SLOPE OF THE KUNLUN MOUNTAINS

ＡＮＡＮＡＬＹＳＩＳＯＦＷＡＴＥＲＲＥＳＯＵＲＣＥＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＴＨＥＲＩＶＥＲＳＩＮＴＨＥＮＯＲＴＨＥＲＮＳＬＯＰＥＯＦＴＨＥＫＵＮＬＵＮＭＯＵＮＴＡＩＮＳＸｕＹｏｕｐｅｎｇ（许有鹏）；ＧａｏＹｕｎｊｕｅ（高蕴珏）（Ｄｅｐａｒｔ...     

Numerical study on interaction between eddies and the Kuroshio Current east of Taiwan,China

We investigated the interaction between mesoscale eddies and the Kuroshio Current east of Taiwan,China,using a fine-resolution regional general circulation model.Mesoscale eddies are injected into a region east of Taiwan,China,according to the quasi-geostrophic theory of stratified fluids.Modeled eddies propagated westward at the velocity of the first baroclinic mode Rossby wave.When eddies collide with the Kuroshio Current east of Taiwan,China,the spatial structure and volume transport of the Kuroshio Current shows a significant variation.The upper 600 m of the anticyclonic eddy cannot cross the Kuroshio Current to reach the region west of the Kuroshio Current;rather,these waters flow northward along the eastern side of the Kuroshio Current.The upper water carried by the anticyclonic eddies cannot reach the shelf of the East China Sea(ECS).In contrast,the waters in the upper layer of the cyclonic eddy reach the western side of the Kuroshio Current and then flow northward.The dynamic mechanism analysis shows that the interaction between the Kuroshio Current and the cyclonic(anticyclonic) eddy decrease(increase)the horizontal potential vorticity(PV) gradient,or PV barrier,whereby the cyclonic(anticyclonic) eddy can(cannot) cross the Kuroshio Current.This study implies that the continental shelf could potentially be influenced by cyclonic eddies in the open ocean,which can transport heat and material from the upper open ocean acro s s the Kuroshio Current to the shelf waters.     

Near-surface structure and energy characteristics of the Antarctic Circumpolar Current

Historical surface drifter observations collected from the Southern Ocean are used to study the near-surface structure, variability, and energy characteristics of the Antarctic Circumpolar Current （ACC）. A strong, nearly zonal ACC combined with complex fronts dominates the circulation system in the Southern Ocean. Standard variance ellipses indicate that both the Agulhas Return Current and the East Australian Warm Current are stable supplements of the near-surface ACC, and that the anticyclonic gyre formed by the Brazil warm current and the Malvinas cold current is stable throughout the year. During austral winter, the current velocity increases because of the enhanced westerly wind. Aroused by the meridional motion of the ACC, the meridional velocity shows greater instability characteristics than the zonal velocity does over the core current. Additionally, the ACC exhibits an eastward declining trend in the core current velocity from southern Africa. The characteristics of the ACC are also argued from the perspective of energy. The energy distribution suggests that the mean kinetic energy （MKE）, eddy kinetic energy （EKE）, and are strong over the core currents of the ACC. However, in contrast, EKE/MKE suggests there is much less （more） eddy dissipation in regions with strong （weak） energy distribution. Both meridional and zonal energy variations are studied to illustrate additional details of the ACC energy characteristics. Generally, all the energy forms except EKE/MKE present west-east reducing trends, which coincide with the velocity statistics. Eddy dissipation has a much greater effect on MKE in the northern part of the Southern Ocean.     

TECTONIC CHARACTERISTICS OF TAIWAN CHANNEL AND ITS ENVIRONS IN LATE MESOZOIC

Taiwan Channel and environs developed typical collision structural zones in the Zhejiang-Fujian coast and Taiwan central mountain, analysis of which revealed their Late Mesozoic collision orogenesis.