Title: Introduction to special section: Dynamics and Circulation of the Yellow, East, and South China Seas
Abstract: [1] The Yellow Sea (YS), East China Sea (ECS), and South China Sea (SCS) (YESS) are the marginal seas of the western Pacific located within 2°30′N–39°50′N latitudes and 99°10′E–131°03′E longitudes as shown in Figure 1. The total area is about 4.65 × 106 km2. The seas are surrounded by 12 countries: China, North Korea, South Korea, Japan, the Philippines, Indonesia, Brunei, Malaysia, Singapore, Thailand, Cambodia, and Vietnam, which account for over 2.0 billion of the human inhabitants (mid-2005 estimate), nearly one third of the world population. These populations are impacted by all coastal manifestations of global climate change, such as rising sea level and more frequent and severe storms [Anderson et al., 2001]. Since ancient times, the seas have served as a convenient navigation waterway for the East Asian and Southeast Asian nations to communicate with each other and with nations of the outside world [Guo et al., 2004; Su and Yuan, 2005]. Even today, the seas are among the busiest waterways in the world because of the size and the high growth rates of the region in the world economy and trade. [2] Figure 1 shows that the water bodies of YESS connect together, but they are named separately owing to different geographic locations and distinct hydrographical features. The efforts by previous investigators have provided a general understanding of the oceanographic features of these seas. The Yellow Sea, the northernmost of the three seas, is located between 31°40′N–39°50′N and 119°10′E–126°50′E. On the north side, it borders on the Bohai Sea with a line from the Penglai Foreland of Shandong Peninsula to the Laotieshan Headland of Liaoning Peninsula. On the south side, it borders on the ECS with a line from the Qidong Bill on the north bank of the Changjiang River mouth to the southwest tip of Cheju Island. The YS is a semienclosed shallow water on the continental shelf. The meridional extent is about 870 km, and the zonal width is about 556 km with an area of about 0.38 × 106 km2. The average depth is 44 m, while the maximum depth is 140 m. The main hydrographic features of YS include the Yellow Sea Cold Water Mass [Ho et al., 1959; Guo, 1993; Yuan and Li, 1993], the Yellow Sea Warm Current, and coastal currents [Uda, 1934; Zheng and Klemas, 1982; Hsueh et al., 1986; Beardsley et al., 1992; Yanagi and Takahashi, 1993; Tang et al., 2000; Qiao et al., 2001, 2004a; Xu et al., 2002]. [3] The ECS is located between 21°54′N–33°17′N and 117°05′E–131°03′E off east China, sandwiched between the YS in the north and the SCS in the south, and separated from the western Pacific in the east by the Ryukyu Islands. It borders on the SCS with a line from the Tielugang Harbor of Fujian to the Maobitou Foreland at the south tip of Taiwan Island. The south-north length is about 1300 km, and the east-west width is about 740 km. The area is about 0.77 × 106 km2. The average depth is 370 m, while the maximum depth is 2322 m. The continental shelf on the western side of the sea occupies 66% of the total area. The main hydrographic features of ECS include the Kuroshio and its branches, the Yangtze River Diluted Water, Taiwan Warm Current, Tsushima Warm Current, formation of shelf-break fronts, and mesoscale processes [Uda, 1934; Mao et al., 1963; Beardsley et al., 1985; Fang and Zhao, 1988; Zheng and Yuan, 1989; Qiu and Imasato, 1990; Fang et al., 1991; Chen et al., 1992; Chern and Wang, 1992; Hsueh et al., 1992; Guan, 1994; Lie and Cho, 1994; Michida et al., 1994; Katoh et al., 2000; Ichikawa and Beardsley, 2002; Chang and Isobe, 2003; Lie et al., 2003; Guan and Fang, 2006; Qiao et al., 2005; Chen et al., 2003; Chen, 2006; Ou and Chen, 2006]. [4] The SCS, the southernmost and the largest of the three seas, is located between 2°30′N–23°30′N and 99°10′E–121°50′E. The area is about 3.50 × 106 km2. In the central SCS, there is a deep basin with a maximum depth reaching 5000 m, occupying 16% of the total area. The continental and island shelf, with the depth less than 200 m extending from the coast, occupies 48% of the total area. In between is the continental and island slope, occupying 36% of the total area. The SCS is a nearly enclosed marginal sea, connected to the ECS, the Pacific, the Sulu Sea, the Java Sea, and the Indian Ocean through the Taiwan, Luzon, Balabac, Karimata, and Malacca Straits, respectively. The main circulation features in SCS include the South China Sea Warm Current, interocean circulation, Kuroshio Intrusion, multigyre structure, upwelling, mesoscale eddies, and strong internal waves [Wyrtki, 1961; Guan, 1978; Guo et al., 1985; Shaw and Chao, 1994; Liu et al., 1998; Fang et al., 1998; Li et al., 1998; Chu and Li, 2000; Ho et al., 2000; Hu et al., 2000; Qu, 2000; Kuo et al., 2000; Zheng et al., 2001; Fang et al., 2005]. [5] The dynamic processes and circulation system in YESS are highly characterized not only by their interconnectivity through narrow straits and passages, but also by their connectivity with the Pacific and Indian Oceans. The seasonally reversing monsoon winds also contribute to one of the most complicated current systems in the world oceans [Metzger and Hurlburt, 1996; Song and Tang, 2002]. As the most energetic western boundary current of the Pacific, the Kuroshio directly interacts with dynamical processes with the wide range of time and length scales in YESS [Hsueh et al., 1997; Su, 1998]. The circulation patterns and interbasin exchange of water masses in the region have been of great interest because of their effects on the El Nino-Southern Oscillation (ENSO) development and the global thermohaline circulation [Masumoto and Yamagata, 1996; Godfrey, 1996; Hu et al., 2000; Qu et al., 2004]. The seas serve as a major filter between the Asian continent and the Pacific with a significant amount of the terrestrial nutrients and biomass being trapped [Clift et al., 2003]. Thus, studies of YESS are of significance not only regionally, but also globally. [6] These important marginal seas, however, have traditionally been lacking of systematic fieldwork by advanced ocean survey technologies and detailed studies with advanced methodologies. The research work and results have seldom been reported in international journals since the high-resolution features of circulation systems and their variability trends were poorly understood. In particular, the exchange and interaction between YESS and surrounding waters, as well as the impact of freshwater forcing from river runoffs and precipitation in modulating the circulation systems have poorly been investigated and quantified. The responses of YESS to the large-scale processes such as ENSO events and monsoon circulation were lacking in in-depth studies too. [7] Fortunately, the situation is gradually being remedied. In recent years, a great deal of progresses has been made in the studies of the dynamic processes and ocean circulation in the YESS. A series of programs and field observations, including the China-Japan Joint Research Program on the Kuroshio (1986–1992), the China-Korea Joint Investigation of the Ocean Circulation in the Yellow Sea (1996–1999), and the Environment Investigation of the China Seas (1997–2002), have been carried out. More recently, a National Key Basic Research Program funded by the Ministry of Science and Technology of China, entitled "Research on the Formation and Variation Mechanism, Numerical Prediction Method of Coastal Circulation and the Effects on the Environment in China Seas," was conducted from October 1999 to September 2004. In order to exchange ideas and to share research results derived from those cruises and related projects, "2004 International Workshop on Dynamic Processes/Circulation in the Yellow, East, and South China Seas (YESS 2004)" was held on November 3–6, 2004, in Qingdao, China. More than 50 papers offering novel research contributions to coastal ocean dynamic processes and circulation, observations, data analyses, theories, numerical modeling, and remote sensing studies related to the YESS were presented. The majority of the papers solicited for this Journal of Geophysical Research–Oceans special section, "Dynamics and Circulation of the Yellow, East, and South China Seas," are developed from the research results presented in YESS 2004. [8] The major advances and new results gained by the papers in this comprehensive collection can be categorized into three main themes. (1) Revelation of fine structures of hydrographic features and enrichment of understanding of regional physical oceanography: The state-of-the-art ocean survey technologies, such as Conductivity-Temperature-Depth (CTD) profiler, Acoustic Doppler Current Profiler (ADCP), and satellite remote sensing, have been used to collect data for the regional oceanographic studies. These reveal numerous fine structures in circulation features, including seasonal and low-frequency variability and three-dimensional structures of circulation in the YS; dynamical parameter estimation of Changjiang River Diluted Water Plume, thin layer structure off Changjiang Estuary, upwelling structures on the ECS shelf, fronts in the Taiwan Strait, and the circulation in the SCS. (2) Development of numerical and theoretical models used to simulate the regional dynamical processes: A wave-tide-circulation coupled numerical model based on the POM [Blumberg and Mellor, 1987] has been developed. The model is characterized by adding a wave-induced mixing term into the modeling of the upper ocean dynamics [Yuan et al., 1991, 1992; Qiao et al., 2004b]. The 3-D hydrographic structures of YS and upwelling along the west coast of ECS generated by the model agree with observations. The flow instability theories are developed to verify the generation mechanisms of the Kuroshio-induced ocean internal wave in the Luzon Strait. (3) Explorations of long-term variability trends and interbasin exchange and interaction: Using satellite data the long-term variability trends of the sea surface winds, sea surface height, and SST in SCS are derived, and the interbasin transport is estimated. [9] The publication of these important results marks a new mile stone for the YESS regional oceanographic studies. We do hope that the progress will be continued, in particular, new research programs to enhance the understanding of responses of YESS to the large-scale processes such as ENSO events and monsoon variability, as well as the role of YESS played in interbasin (and interocean) exchange (and interaction) should be launched in the future. Additional new data and novel model-data synthesis efforts will be truly valued contributions to the global efforts of world oceanography community. [10] The authors of individual papers acknowledge the support of the appropriate funding agencies. The YESS 2004 Workshop and the projects, which yield the papers contributed by authors from FIO, were supported by the Ministry of Science and Technology of China through grant G1999043800. Zheng acknowledges the support of the ONR (N00014-05-1-0328 and N00014-05-1-0606). Fang was supported by NSFC under grant 40520140074 and the National Basic Research Program of China under grant G1999043808. Song's research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. His work was also funded by the ONR (N00014-03-IP-20059). We thank the dedicated work of all the reviewers, and appreciate the extensive and sustained efforts of Raghu Murtugudde, the JGR-Oceans editor and his editorial assistants without whose perseverance and guidance this special section would not be possible. We thank Xiaomin Hu for drawing the nice figure of YESS.