Water transports through the four main straits around ... - Springer Link

Chinese Journal of Oceanology and Limnology Vol. 27 No. 2, P. 229-236, 2009 DOI: 10.1007/s00343-009-9142-y

Water transports through the four main straits around the South China Sea* WANG Qingye (王庆业) †,** , CUI Hong (崔红) ††, ZHANG Shuwen (张书文) †, HU Dunxin (胡敦欣) †† †

South China Sea Environmental Institute, Guangdong Ocean University, Zhanjiang 524088, China

††

Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China

Received June 25, 2008; revision accepted Nov. 26, 2008 Abstract A quasi-global high-resolution HYbrid Coordinate Ocean Model (HYCOM) is used to investigate seasonal variations of water transports through the four main straits in the South China Sea. The results show that the annual transports through the four straits Luzon Strait, Taiwan Strait, Sunda Shelf and Mindoro Strait are -4.5, 2.3, 0.5 and 1.7 Sv (1 Sv=106 m3s-1), respectively. The Mindoro Strait has an important outflow that accounts for over one third of the total inflow through the Luzon Strait. Furthermore, it indicates that there are strong seasonal variations of water transport in the four straits. The water transport through the Luzon Strait (Taiwan Strait, Sunda Shelf, Mindoro Strait) has a maximum value of -7.6 Sv in December (3.1 Sv in July, 2.1S v in January, 4.5Sv in November), a minimum value of -2.1 Sv in June (1.5 Sv in October, -1.0 Sv in June, -0.2 Sv in May), respectively. Keyword: circulation; volume transport; numerical model; South China Sea

1 INTRODUCTION The South China Sea (SCS) is a region with highly complex geometry of continental shelf, slope and deep sea basin, and is connected with its adjacent oceans through several narrow straits and passages. In the northeast, it connects the Pacific Ocean via the wide and deep Luzon Strait, and the East China Sea through the Taiwan Strait. In the south, it connects Java Sea and Andaman Sea through the Sunda Shelf, and Sulu Sea through the Mindoro and Balabac Straits. Therefore, it is important for water exchange through these straits. In addition, both seasonally reversing monsoon winds and intrusion of the Kuroshio current via the Luzon Strait play important roles in determining ocean circulation in the SCS (Shaw and Chao, 1994; Su, 2005). There have been many studies on Luzon Strait transport (LST) using historical observational data (Huang, 1983; Guo and Fang, 1988, Liu et al., 2000; Qu, 2000; Liang et al., 2002; Tian et al., 2006). In an early study, Huang (1983) showed that the maximum transport from the Pacific Ocean to the SCS through the Luzon Strait appeared in winter (31Sv) based on 13 cruises of hydrographic data. According to temperature and salinity survey data collected in

1985, Guo and Fang (1988) displayed that the westward transport through 120°E section was 11~12 Sv. Based on PR21 section, Liu et al. (2000) indicated that the west and east transports in winter were 10–12 Sv and 5–8 Sv, respectively. Qu (2000) reported that the LST (relative 400 m) was 3.0Sv, with the maximum (5.3 Sv) in winter and the minimum (0.2 Sv) in summer. As for observation of the Taiwan Strait transport (TST), Fang et al. (1991) estimated the annual mean transport could be about 2 Sv, with 3.1 Sv in summer and 1.0 Sv in winter. Teague et al. (2003) used ADCP data and found that the TST between October and December in 1999 was 0.14 Sv. Wang et al. (2003) estimated the TST in 1999–2001 was 1.8 Sv by using ADCP data. In a recent study, Guo et al. (2005) estimated that the TST could be 1.27 Sv per year, with 2.27 Sv in summer and 0.46 Sv in winter. At the same time, a number of numerical studies have focused on this topic in this decade (Metzger and Hurlburt, 1996; Chu and Li, 2000; Lebedev and * Supported by National Natural Science Foundation of China (No. 40806012, 40876013), Open Fund of the Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences (No. KLOCAW0803) and Scientific Research Foundation for talent, Guangdong Ocean University (No. E06118) ** Corresponding author: [email protected]

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Yaremchuk, 2000; Bao et al., 2002; Cai et al., 2002, 2005; Fang et al., 2002, 2005;). Metzger and Hurlburt (1996) suggested that the annual mean LST into the SCS could be about 2.4–4.4 Sv with large monthly variations. Chu and Li (2000) computed the LST using U. S. Navy’s climatological temperature and salinity dataset by P-vector method, and reported that “The computed monthly volume transport through the Luzon Strait is negative (inflow) all year round with a minimum value of -13.7 Sv in February (strongest intrusion) and a maximum value of -1.4 Sv in September (weakest intrusion). The annual mean transport is -6.5 Sv (intrusion)”. Cai et al. (2002) used global circulation model of LICOM (LASG/IAP Climate Ocean Model) with horizontal resolution 0.5° to simulate the transports through the main straits and their results showed that the magnitude of transport was small. Fang et al. (2002) employed a variable-grid resolution of 1/6° in the China seas, and showed that about 5.3 Sv water flowed out of the SCS and joined to the Indonesian Throughflow. Using 900-year integration of a global ocean circulation model LICOM with uniform 0.5° grid, Cai et al. (2005) demonstrated that the transports through the Luzon Strait, Taiwan Strait, Sunda Shelf, Mindoro Strait and Balabac Strait is -4.06, 2.01, 2.26, -0.12 and -0.08 Sv, respectively. Up to now, the observation results of the transports through the main straits in the SCS are still limited, especially for the Sunda Shelf transport (ST) and Mindoro Strait transport (MT) because of the funding limitation. A good alternative way to study this topic is to use numerical model. However, there are rather large differences among the different numerical results. It is mainly caused by the different configurations of numerical experiments and the different numerical schemes used in different models. A model with higher horizontal resolution would give a better representation of bathymetry, especially in the region with complex geometry, and would be more likely to give reasonable results. Also, many studies have noted that the choice of vertical coordinate system is the single most important factor for an ocean model (Chassignet and MalanotteRizzoli, 2000). Therefore, it is necessary to reassess the transports through the main straits by superior model and configuration. In this paper, a quasi-global high-resolution HYbrid Coordinate Ocean Model (HYCOM) with three kinds of different vertical coordinates configured high-resolution (1/6°) in the western tropical Pacific is used to compute the seasonality of

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the transport through the four main straits. Section 2 describes the numerical experiments. Results and Discussion are presented in Section 3 and 4, respectively. Summary and conclusions are drawn in Section 5.

2 MODEL DESCRIPTIONS The ocean circulation model used in this study is HYCOM 2.1.20 (Bleck, 2002). Its horizontal grid is a staggered “C” grid and three kinds of coordinates (z, sigma and isopycnal coordinate) are all used in the discretization of vertical direction. Meanwhile, several mixing themes are provided in HYCOM as well. Therefore, it may be reasonable to assume that HYCOM will be more competent in the simulation of ocean-basin scale than others with only one kind of vertical coordinate. The domain of the simulation is nearly the whole of globe, from 76°S to 70°N. The model has a horizontal resolution of 1/6° both in longitude and latitude in the region from 15°S to 31°N and from 101°E to 165°E, around which the resolution decreases from 1/6° until 2° with the transition belt of 37° width. The model is configured with 20 levels, corresponding potential density ( σ θ ) values of 19.50, 20.25, 21.00, 21.75, 22.50, 23.25, 24.0, 24.70, 25.28, 25.77, 26.18, 26.52, 26.80, 27.03, 27.22, 27.38, 27.52, 27.64, 27.74 and 27.82. The bottom topography is from ETOPO5 dataset and the coastline is set to the isodepth line of 10 m (Fig.1). The K-Profile Parameterization (KPP) vertical mixing model is used in our experiments.

Fig.1 The real coastline and coastline (solid line) of model in the SCS Four main straits are also shown (heavy solid line)

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WANG et al.: Water transports through the four main straits around the South China Sea

The model is initialized with summer temperature and salinity data from the Levitus monthly climatology (Levitus and Boyer, 1994). It is forced by the European Center for Medium range Weather Forecasting (ECMWF) wind stress and thermal climatology, and both the sea surface temperature (SST) and sea surface salinity (SSS) are relaxed to climatology of Levitus data. The boundary condition is set at 76°S and 70°N by buffer zones that are 5 grid points wide where temperature, salinity and interface depth are relaxed to Levitus climatological values. The relaxation time scale increases from 20 to 120 days with distance away from the boundaries. The model is integrated for 30 years, and the tropical ocean has adjusted to climatological equilibrium. The averaged model data of the last 5 years (26–30 year) is used for analysis in this paper.

3 RESULTS In order to clarify the validation of model results, we compare simulated sea surface height (SSH) in the SCS and the mean dynamic ocean topography from 1992–2002 calculated using jointly data of satellite altimetry, near-surface drifters, NCEP wind and GRACE (Gravity Recovery and Climate Experiment Mission) (Maximenko and Niiler, 2005,

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Fig.2a, b). The pattern of simulated sea surface height is similar to that of observation. A low center is near 118°E, 19°N. The sea surface height increases southward from 15°N (Fig.2a, b). Note that there is a large difference in the Gulf of Beibu due to the complex physical processes, such as tide and wave. In addition, seasonal variation of the simulated SSH (Fig.2c–f) is compared with monthly absolute dynamic topography (not shown) from AVISO altimetry data, which shows good consistence with observation. Therefore, the simulated results are generally thought to be valid. In February, the main characteristics of SSH field are the basin scale cyclonic gyre, and two small scale cold eddies lie south of 13°N (Fig.2c). The surface current is southwestward due to the prevailing winter monsoon (Fig.3a). In May, the west Luzon eddy becomes weaker, and the SSH field is generally two gyres along about 15°N (Fig.2d). The northward flow appears in southern SCS (Fig.3b). In August, the west Luzon eddy becomes weaker further, but the anticyclonic gyre becomes strongest, especially in the southern SCS (Fig.2e). Also, the dipole structure off the central Vietnam is protruding, which has been presented using the altimetry data through Empirical Orthogonal Function analysis for the first time (Fang

Fig.2 a. Simulated sea surface height (cm); b. 1992–2002 mean ocean dynamic topography (cm); c. simulated sea surface height (cm) in February; d. May; e. August; f. November

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et al., 2006). And the surface flow in the whole SCS is generally northward due to summer monsoon (Fig.3c). In November, the winter monsoon is reconstructed, and the basin scale cyclonic gyre appears again and the west Luzon eddy become stronger gradually (Fig.2f). Correspondingly, the circulation pattern in Fig.3d changes greatly, comparing with that in August. There five straits exist around the SCS in our model. They are the Luzon Strait, Taiwan Strait, Sunda Shelf, Mindoro Strait and Balabac Strait, but the Balabac Strait is not considered in this paper due to the shallow water depth there. The specific sections used to compute the transports of the Luzon Strait, Taiwan Strait, Sunda Shelf and Mindoro Strait are set at 120.67°E from 18.67°N to 22.00°N, 24°N from 118.00°E to 120.17°E, 1.5°N from 104.33°E to

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108.83°E, and 12.33°N from 120.00°E to 121.00°E, respectively (Fig.1). The annual mean LST, TST, ST and MT computed by HYCOM results are -4.5, 2.3, 0.5 and 1.7 Sv (The positive means flowing out of the SCS), respectively, and their seasonal variations are shown in Fig.4. Also, our results are compared with previous results (Table 1). The net transport through the Luzon Strait is westward during the whole years. The annual mean value is -4.5 Sv, and the maximum value (-7.6 Sv) appears in December and the minimum value (-2.1 Sv) in June. The TST (Fig.4) has an obvious seasonal cycle, with the maximum value (3.1 Sv) in July, the minimum (1.5 Sv) in October, and its mean transport is 2.3 Sv.

Fig.3 Simulated horizontal velocity (cm/s) at the surface a. February; b. May; c. August; d. November

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4 DISCUSSIONS 4.1 The LST and the TST

Fig.4 Seasonal variation of the transport (Sv) through Luzon Strait (“circle” symbol), Taiwan Strait (“star” symbol), Sunda Shelf (“square” symbol) and Mindoro Strait (“point” symbol). Positive transport is defined as the flowing out of the SCS Table 1 Some observation transports (Sv) through Luzon and Taiwan Straits. The number in bracket is the month Mean(Seasonal) Transport Luzon St. Luzon St. Luzon St. Taiwan St. Taiwan St. Taiwan St.

Qu (2000) Liang et al. (2002) Tian et al. (2006) Fang et al. (1991) Wang et al. (2003) Guo et al. (2005)

-3.0 (-0.2[6-7] ~-5.3[1-2]), (0-400 m) -3.3, (0-300 m) 6±3 (in Oct., 2005) 2 (1.0[winter] ~3.1[summer]) 1.8 (0.9[1] ~2.7[7]) 1.27 (0.46[winter] ~2.27[summer])

The ST (Fig.4) has positive maximum value of 2.1 Sv in January (outflow), and negative maximum value of -1.0 Sv in June (inflow). The annual mean transport is 0.5 Sv. The MT (Fig.4) has a positive maximum value of 4.5 Sv in November (outflow), and a negative maximum value of -0.2 Sv in May (inflow). The annual mean transport is 1.7 Sv. The annual mean transport calculated via the Balabac Strait is only -0.01 Sv, which is thus not considered in detail in this paper.

The LST seems to be consistent with observations (Qu, 2000; Liang et al., 2002; Tian et al., 2006). From Table 1, it is a slightly larger than the results of Qu (2000) and Liang et al. (2002), which could be resulted from the fact that only upper layers are considered in their studies, and the transport value in October (-5.5 Sv) is reasonable by comparison with observation 6 ± 3 Sv (Tian et al., 2006). According to Table 2, our result is consistent with other model results (Bao et al., 2002; Fang et al., 2005; Cai et al., 2005), but the LST in this paper is not different from that of Fang et al. (2002). The reason could be that the models used in Fang et al. (2002) were respectively integrated for 6 years, and the ocean circulation was possible unstable. In fact, we also find that the LST is -5.4 Sv when the model is integrated for 11 years, which is 25% larger than that mentioned above. Generally, all simulations listed in Table 2 show similar seasonality of LST with larger value in winter and the lower value in summer. The seasonality may be associated with the reversing monsoon and the bifurcation point of the North Equatorial Current (NEC) at the east Philippine coast. Wang and Hu (2006) showed that the bifurcation latitude of the NEC at surface happens at northernmost position (14.1°N) in December and at southernmost position (12.9°N) in June. Local wind force and remote Rossby wave are two factors of dominating bifurcation latitude. Kim et al. (2004) thought that the bifurcation latitude of the NEC is highly correlated with the transport of Kuroshio.

Table 2 Some model results of annual mean and seasonal transport (Sv) through main straits in the SCS The number in bracket is the month References Bao et al. (2002) Fang et al. (2002) Cai et al. (2005) Fang et al. (2005) This paper

Luzon St.

Taiwan St.

Sunda Shelf

Mindoro St.

-4.8 (-1.8[6]~-8.3[12]) -6.40 (-1.2[6]~-13.3[12]) -4.27 (-2.67[6]~-6.16[12]) -4.37 (-1.68[9]~-7.80[1]) -4.5 (-2.1[6]~-7.6[12])

2.0 (0.9[11]~3.1[7]) 1.15 (-0.4[11]~2.9[7]) 2.56 (2.31[3]~2.86[7]) 0.45 (-0.98[11]~2.11[7]) 2.3 (1.5[10]~3.1[7])

1.35 (-0.8[6]~3.9[1]) 3.65 (-2.1[7]~9.5[12]) 1.86 (0.23[6]~3.44[12]) 1.32 (-1.54[7]~4.22[1]) 0.5 (-1.0[6]~2.1[1])

2.3 (0.1[6]~2.9[12]) 0.25 (-0.6[4,5]~1.3[11])

Balabac St. --1.35 (0[5]~3.1[11])

-0.07

-0.08

1.77 (0.68[6]~3.24[12]) 1.7 (-0.2[5]~4.5[11])

0.61 (0.37[5]~0.98[11]) -0.01

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The mean zonal velocity along the Luzon Strait and its seasonal variations are shown in Fig.5. In the mean state, the eastward, westward and stronger eastward flows are respectively distributed in the southern, central and northern Luzon Strait (Fig.5a), and water exchange between the SCS and Pacific Ocean mainly happens at 0–500 m. The maximum velocity of the eastward flow is 15 cm/s, with its core 37 m depth. The maximum velocity of the westward flow is 38 cm/s, with its core 50 m depth, and the maximum velocity of the stronger eastward flow is 60 cm/s, with its core 50 m depth locating just south tip of Taiwan Strait. Generally, the characteristics of the velocity structure near the Luzon Strait agrees with many previous observations (Huang, 1984; Xu and Su, 1997; Liu et al., 2000). Fig.5b–e suggested that the structure of zonal velocity is relative stable with no obvious seasonal variations. The difference among them is mainly the magnitude and position of the velocity core. For example, the westward

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Kuroshio intrusion in February and November is stronger and the maximum velocity happens at the surface, but weaker in May and August with the maximum velocity core lies near about 46–64 m, 20.5°N. For the TST, our value (2.3 Sv) is higher than the observational results (Table 1), and it is nearly twice than the value of recent result of Guo et al. (2005). Fang et al. (1991) estimated it’s about 2 Sv, with 3.1 Sv in summer and 1.0 Sv in winter, and Guo et al. (2005) estimated that it’s 1.27 Sv, with 2.27 Sv in summer and 0.46 Sv in winter. Wang et al. (2003) showed that the Taiwan Strait transport in 1999–2001 was 1.8 Sv by ADCP data, with 2.7 Sv in summer and 0.9 Sv in winter. The specific reason for the difference is not clear, and needs to be studied further. However, comparing with other model results (Table 2), our result seems reasonable between the reported values of Fang et al. (2002) and Cai et al. (2005).

Fig.5 Simulated zonal velocity (cm/s) along Luzon Strait (a) annual mean, (b) February, (c) May, (d) August and (e) November Positive velocity is in eastward direction

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Both the TST values in this paper and in Fang et al. (2002) show obvious seasonal variation, which is clear from the simulated meridional velocity along Taiwan Strait (not shown). In February and November, the weak southward flow exists in the west part of the strait where the water depth is less than 40m, and the strong northward flow exists in the east of 119.6°E. In May and August, the southward flow disappears due to summer monsoon, and the flow in the east of 119.6°E becomes stronger. However, the seasonality of the TST reported by Cai et al. (2005) was not significant, which could be due to the relative coarse horizontal resolution. 4.2 The ST and MT We compare the ST and MT with other model results due to limited field observations obtained. The estimated annual mean ST is 0.5 Sv, which is much smaller than the value calculated in Fang et al. (2002) and Cai et al. (2005). The possible reason is discussed in this section. The seasonal variation is significant, which is consistent with the finding reported by Fang et al. (2002) and Cai et al. (2005). The protruding difference from other model results is the MT (Table 2). The annual mean MT is 1.7 Sv which accounts for over one third of the total inflow through the Luzon Strait. This result supports to some extent the viewpoints of Yamada et al. (2006) and Lebedev and Yaremchuk (2000) suggesting that the Mindoro Strait is an important outflow of the SCS. Yamada et al. (2006) showed that the outflow of the SCS through Mindoro played an important role for water characteristics of the Sulu Sea, which transports tropical and intermediate water origin from the North Pacific (NPTW and NPIW). Based on a variable grid global general circulation model with 1/6° resolution, Lebedev and Yaremchuk (2000) reported that the major part (3.9 Sv) of the inflow via the Luzon Strait (6.2 Sv) followed the route through the Mindoro Strait at 120°E, 13°N. A proper interpret is that the flows via the Mindoro Strait can be viewed as an extension of the Mindanao Current which is a western boundary current of subtropical gyre in the North Pacific. However, Fang et al. (2002) and Cai et al. (2005) showed that the MT value accounted for less than 4% of the net inflow in the Luzon Strait. The possible reason for the low value of Cai et al. (2005) is that their model had relative coarse horizontal resolution and the Mindoro Strait (about0.8° width over 20 m depth) could not be well represented. For Fang et al. (2002), their model used z vertical coordinate, which

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could have relative large error in describing the topography, especially in very shallow or steep regions. According to atlas, the maximum water depths through the Sunda Shelf, Mindoro Strait and Balabac Strait are about 58 m, 420 m, and 10m, respectively. Fang et al. (2002) used the thickness of 25 m as the first layer in their model, which could result in relative large errors in topography and transports through the three straits mentioned above. As for the Balabac Strait with 10 m maximum depth, the transport thus is rather small and can be neglected. Note that the transport (1.77 Sv) via the Mindoro Strait calculated in Fang et al. (2002) seems to be consistent with our results. Using the same model but configured with higher vertical resolution to describe topography, Fang et al. (2005) obviously showed the significant outflow through the Mindoro Strait (Table 2). However, there was large different in the Balabac Strait, which could result from the limit of z coordinate to represent the shallow strait. For the seasonality (Fig.4), the strongest outflow (4.5 Sv) happens in November, and the strongest inflow (-0.2 Sv) occurs in May, which suggests the important role of the seasonal reversing monsoon on controlling the MT. However, some other model results (Bao et al., 2002; Fang et al., 2005) show that there exists outflow all year around. For the different viewpoints, more observations are needed to clarify these uncertainties.

5 SUMMARY AND CONCLUSIONS A quasi-global high-resolution model HYCOM configured with ECMWF wind and heat forces is used to study the seasonality of water transport through the four main straits in the South China Sea. Due to high resolution and finer vertical coordinate, the HYCOM model is superior to many previous models. In the mean state, the LST, TST, ST and MT are -4.5, 2.3, 0.5 and 1.7 Sv, respectively. The Mindoro Strait plays an important role in water exchange. It has a vital outflow that accounts for over one third of the total inflow through the Luzon Strait. Compared our model results with the observational data, the LST and TST derived from the model are generally consistent with the observations further suggesting the validity of our model results. In the seasonal timescale, our model indicates that the transports via the four straits all exhibit an obvious seasonal cycle. The LST and TST all have a maximum value of -7.6 Sv in December and 3.1 Sv in

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July, and a minimum value of -2.1 Sv in June and 1.5 Sv in October, respectively. There are obvious outflows through both the Sunda Shelf and Mindoro Strait during winter and inflows during summer, which suggests the important role of the seasonal reversing monsoon. The ST and MT have a maximum value of 2.1 Sv in January and 4.5 Sv in November, and a minimum value of -1.0 Sv in June and -0.2 Sv in May.

6 ACKNOWLEDGMENTS Comments and suggestions from two anonymous reviewers are greatly appreciated. The 1992–2002 mean ocean dynamic topography data (http:/ apdrc.soest.hawaii.edu/projects/DOT/index.html) is obtained from Nikolai Maximenko (IPRC) and Peter Niiler (SIO). References Bao, X. W., G. P. Gao and D. X. Wu, 2002. Study of water-transport through some main straits in the East China Sea and South China Sea. Chin. J. Oceanol. Limnol. 20(4): 293-302. Bleck, R., 2002. An oceanic general circulation model framed in hybrid isopycnic-cartesian coordinates. Ocean Modelling 4: 55-88. Cai, S. Q., H. L. Liu and W. Li, 2002. Water transport exchange between the South China Sea and its adjacent seas. Advances in Marine Science 20(3): 29-34. (in Chinese with English abstract) Cai, S. Q., H. L. Liu, W. Li et al., 2005. Application of LICOM to the numerical study of water exchange between the South China Sea and its adjacent oceans. Acta Oceanol. Sin. 24(4): 10-19. Chassignet, E. P. and P. Malanotte-Rizzoli (eds.), 2000. Ocean circulation model evaluation experiments for the North Atlantic Basin. Elsevier Science, Amsterdam. Dyn. Atmos. Oceans. (Special Issue) 32: 155-432. Chu, P. C. and R. F. Li, 2000. South China Sea isopycnal surface circulation. J. Phys. Oceanogr. 30: 2 419-2 438. Fang, G. H., B. Zhao and Y. Zhu, 1991. Water volume transports through the Taiwan Strait and the continental shelf of the East China Sea measured with current meters. In: Takano K. ed. Oceanography of Asian Marginal Seas. Elsevier, Amsterdam. p. 345-348. Fang, G. H., Z. X. Wei, B. Cui et al., 2002. Transportation of water, heat and salt in Chinese offshore sea area: Results of global variable grid model. Science in China (Ser. D) 32(12): 969-977. (in Chinese) Fang, G., D. Susanto, I. Soesilo et al., 2005. A note on the South China Sea shallow interocean circulation. Adv. Atmos. Sci. 22(6): 946-954. Fang, W. D., J. J. Guo, P. Shi et al., 2006. Low frequency variability of South China Sea surface circulation from 11 years of satellite altimeter data. Geophys. Res. Lett. 33, L22612, doi:10.1029/2006GL027431. Guo, Z. X. and W. D. Fang, 1988. The Kuroshio in Luzon

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Strait and its transport during September 1985. Journal of Tropical Oceanography 7(2): 13-19. (in Chinese) Guo, J. S., X. M. Hu and Y. L. Yuan, 2005. A Diagnostic analysis of variations in volume transport through the Taiwan Strait using Satellite altimeter data. Advances in Marine Science 23(1): 20-26. (in Chinese) Huang, Q. Z., 1983. Variability of current speed and flux of Kuroshio in the Bashi Channel. Journal of Tropical Oceanography 2(1): 35-40. (in Chinese) Huang, Q. Z., 1984. The oceanographic conditions in the Bashi Channel. Proceedings of Oceanography of South China Sea 6: 54-66. (in Chinese) Kim, Y. Y., T. Qu, T. Jensen et al., 2004. Seasonal and interannual variations of the North Equatorial Current bifurcation in a high-resolution OGCM, J. Geophy. Res. 109, C03040, doi:10.1029/2003JC002013. Lebedev, K. V. and M. I. Yaremchuk, 2000. A diagnostic study of the Indonesian Throughflow. J. Geophys. Res. 105(C5): 11 243-11 258. Levitus, S. and T. Boyer, 1994. World Ocean Atlas 1994, Volume 4: Temperature. NOAA Atlas NESDIS 4. US Dept. of Commerce, Washington, DC. Liang, W. D., T. Y. Tang, Y. J. Yang et al., 2002. Upper ocean current around Taiwan. Deep-Sea Res., Part II, 50: 1 085-1 150. Liu, Q. Y., H. J. Yang, W. Li et al., 2000. Velocity and transport of the zonal current in the Luzon Strait. Acta Oceanol. Sin. 22(2): 1-8. (in Chinese) Maximenko, N. A. and P. P. Niiler, 2005. Hybrid decade-mean global sea level with mesoscale resolution. In: Saxena N. ed. Recent Advances in Marine Science and Technology, 2004, PACON International, Honolulu. p. 55-59. Metzger, E. J. and H. E. Hurlburt, 1996. Coupled dynamics of the South China Sea, the Sulu Sea, and the Pacific Ocean. J. Geophys. Res. 101: 12 331-12 352. Qu, T., 2000. Upper layer circulation in the South China Sea. J. Phys. Oceanogr. 30: 1 450-1 460. Shaw, P. T. and S. Y. Chao, 1994. Surface circulation in the South China Sea. Deep Sea Res. 41: 1 663-1 683. Su, J. L., 2005. Overview of the South China Sea circulation and its dynamics. Acta Oceanol. Sin. 27(6): 1-8. (in Chinese with English abstract) Teague, W. J., G. A. Jacobs, D. S. Ko et al., 2003. Connectivity of Taiwan, Cheju and Korea Strait. Cont. Shelf Res. 23(15): 63-77. Tian, J. W., Q. X. Yang, X. F. Liang et al., 2006. Observation of Luzon Strait transport. Geophys. Res. Lett. 33: L19607, doi:10.1029/2006GL026272. Xu, J. P. and J. L. Su, 1997. Hydrographic analysis on the intrusion of the Kuroshio into the SCS, II. Observation results during the cruise from August to September in 1994. Tropic Oceanography 16(2): 1-23. (in Chinese) Wang, Q. Y. and D. X. Hu, 2006. Bifurcation of the North Equatorial Current derived from altimetry in the Pacific Ocean. J. Hydrodyn. Ser. B 18(5): 620-626. Wang, Y., S. Jan and D. P. Wang, 2003. Transports and tidal current estimates in the Taiwan Strait from shipboard ADCP observations (1999-2001). Estuarine Coastal Shelf Sci. 57: 193-199.