Journal of Oceanography

, Volume 57, Issue 5, pp 549–563 | Cite as

Low Salinity, Cool-Core Cyclonic Eddy Detected Northwest of Luzon during the South China Sea Monsoon Experiment (SCSMEX) in July 1998

  • Peter C. Chu
  • Chenwu Fan


To detect eddies, intensive surveys of the northeast South China Sea (SCS) (114°30′–121°30′ E, 17°–22°N) were conducted in July 1998 during the international SCS Monsoon Experiment (SCSMEX), the U.S. Navy using Airborne Expendable Bathythermograph and Conductivity-Temperature-Depth sensors (AXBT/AXCTD), and the Chinese Academy of Sciences using Acoustic Doppler Current Profilers (ADCP). The hydrographic survey included 307 AXBT and 9 AXCTD stations, distributed uniformly throughout the survey area. The ADCP survey had two sections. The velocity field inverted from the AXBT/AXCTD data and analyzed from the ADCP data confirm the existence of a low salinity, cool-core cyclonic eddy located northwest of Luzon Island (i.e., the Northwest Luzon Eddy). The radius of this eddy is approximately 150 km. The horizontal temperature gradient of the eddy increases with depth from the surface to 100 m and then decreases with depth below 100 m. The cool core was evident from the surface to 300 m depth, being 1°–2°C cooler inside the eddy than outside. The tangential velocity of the eddy is around 30–40 cm/s above 50 m and decreases with depth. At 300 m depth, it becomes less than 5 cm/s.

Mesoscale eddies South China Sea Monsoon Experiment (SCSMEX) P-vector method airborne expendable bathythermograph (AXBT) airborne expendable CTD (AXCTD) 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Chao, S. Y., P. T. Shaw and J. Wang (1996): Deep water ventilation in the South China Sea. Deep-Sea Res., 43, 445–466.CrossRefGoogle Scholar
  2. Chu, P. C. (1995): P vector method for determining absolute velocity from hydrographic data. Mar. Technol. Soc. J., 29(3), 3–14.Google Scholar
  3. Chu, P. C. (2000): P-vector spirals and determination of absolute velocities. J. Oceanogr., 56, 591–599.CrossRefGoogle Scholar
  4. Chu, P. C. and C. P. Chang (1997): South China Sea warm pool in boreal spring. Adv. Atmos. Sci., 14, 195–206.Google Scholar
  5. Chu, P. C. and R. F. Li (2000): South China Sea isopycnal surface circulations. J. Phys. Oceanogr., 30, 2,419–2,438.CrossRefGoogle Scholar
  6. Chu, P. C., H. C. Tseng, C. P. Chang and J. M. Chen (1997a): South China Sea warm pool detected in spring from the Navy's Master Oceanographic Observational Data Set (MOODS). J. Geophys. Res., 102, 15,761–15,771.Google Scholar
  7. Chu, P. C., S. H. Lu and Y. C. Chen (1997b): Temporal and spatial variabilities of the South China Sea surface temperature anomaly. J. Geophys. Res., 102, 20,937–20,955.Google Scholar
  8. Chu, P. C., S. K. Wells, S. D. Haeger, C. Szczechowski and M. Carron (1997c): Temporal and spatial scales of the Yellow Sea thermal variability. J. Geophys. Res., 102, 5,655–5,667.Google Scholar
  9. Chu, P. C., C. W. Fan, C. J. Lozano and J. Kerling (1998a): An airborne expandable bathythermograph (AXBT) survey of the South China Sea, May 1995. J. Geophys. Res., 103, 21,637–21,652.Google Scholar
  10. Chu, P. C., C. W. Fan and W. J. Cai (1998b): P vector inverse method evaluated using the Modular Ocean Model (MOM). J. Oceanogr., 54, 185–198.Google Scholar
  11. Chu, P. C., N. L. Edmons and C. W. Fan (1999a): Dynamical mechanisms for the South China Sea seasonal circulation and thermohaline variabilities. J. Phys. Oceanogr., 29, 2,971–2,989.CrossRefGoogle Scholar
  12. Chu, P. C., S. H. Lu and W. T. Liu (1999b): Uncertainty of the South China Sea prediction using NSCAT and NCEP winds during tropical storm Ernie 1996. J. Geophys. Res., 104, 11,273–11,289.Google Scholar
  13. Chu, P. C., S. H. Lu and Y. C. Chen (1999c): A coastal airocean coupled system (CAOCS) evaluated using an airborne expandable bathythermograph (AXBT) data set. J. Oceanogr., 55, 543–558.CrossRefGoogle Scholar
  14. Chu, P. C., J. M. Veneziano and C. W. Fan (2000): Response of the South China Sea to tropical cyclone Ernie 1996. J. Geophys. Res., 105, 13,991–14,009.CrossRefGoogle Scholar
  15. Gandin, L. S. (1965): Objective Analysis of Meteorological Fields. Israel Program for Scientific Translation, Jerusalem, 242 pp.Google Scholar
  16. Li, L., W. D. Nowlin, Jr. and J. Su (1998): Anticyclonic rings from the Kuroshio in the South China Sea. Deep-Sea Res. I, 45, 1,469–1,482.Google Scholar
  17. Li, R., Q. Zeng, Z. Ji and D. Gun (1992): Numerical simulation for a northeastward flowing current from area off the eastern Hainan Island to Tsugaru/Soya Strait. La Mer, 30, 229–238.Google Scholar
  18. Lozano, C. J., A. R. Robinson, H. G. Arango, A. Gangopadhyay, Q. Sloan, P. J. Haley, L. Anderson and W. Leslie (1996): An interdisciplinary ocean prediction system: assimilation strategies and structure data model. p. 413–452. In Modern Approaches to Data Assimilation in Ocean Modeling, ed. by P. Malanotte-Rizzoli, Elsevier, Amsterdam.Google Scholar
  19. 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.CrossRefGoogle Scholar
  20. Nitani, H. (1970): Oceanographic conditions in the sea east of Philippines and Luzon Strait in summer of 1965 and 1966. p. 213–232. In The Kuroshio—A Symposium on Japan Current, ed. by J. D. Marr, East-West Press, Honolulu, Hawaii.Google Scholar
  21. Qiu, D. Z., Y. T. Huang, L. M. Chen and Z. X. Guo (1985): Circulation structures in the studied waters. Comprehensive Investigations and Studies of the South China Sea, Vol. 2, Science Press, Beijing, p. 204–230 (in Chinese).Google Scholar
  22. Shaw, P. T. (1989): The intrusion of water masses into the sea southwest of Taiwan. J. Geophys. Res., 94, 18,213–18,226.Google Scholar
  23. Shaw, P. T. (1991): The seasonal variation of the intrusion of the Philippine Sea water into the South China Sea. J. Geophys. Res., 96, 821–827.CrossRefGoogle Scholar
  24. Soong, Y. S., J. H. Hu, C. R. Ho and P. P. Niiler (1995): Coldcore eddy detected in South China Sea. Eos Trans. AGU, 76, 345–347.Google Scholar
  25. South China Sea Institute of Oceanology (1985): Integrated Investigation Report on Sea Area of the South China Sea, Vol. 2, p. 183–231, Science Press, Beijing (in Chinese).Google Scholar
  26. Teague, W. J., M. J. Carron and P. J. Hogan (1990): A comparison between the Generalized Digital Environmental Model and Levitus climatology. J. Geophys. Res., 95, 7,167–7,183.Google Scholar
  27. Wu, C. R., P. T. Shaw and S. Y. Chao (1999): Assimilating altimetric data into a South China Sea model. J. Geophys. Res., 104, 29,987–30,005.Google Scholar
  28. Wyrtki, K. (1961): Scientific results of marine investigations of the South China Sea and Gulf of Thailand 1959–1961, Naga Rep., 2, p. 164–169, Scripps Institute of Oceanography, University of California, San Diego.Google Scholar
  29. Xu, X. Z., Z. Qiu and H. C. Chen (1982): The general description of the horizontal circulation in the South China Sea. Proceedings of the Symposium of the Chinese Society of Marine Hydrology and Meteorology, Chinese Society of Oceanology and Limnology, Science Press, Beijing, p. 119–127 (in Chinese with English abstract).Google Scholar
  30. Zhou, F. X., J. J. Shen, A. L. Berestov and A. D. Marushkevich (1995): Seasonal features of large-scale geostrophic circulations in the South China Sea. Tropical Oceanol., 14(4), 9–14 (in Chinese with English abstract).Google Scholar

Copyright information

© The Oceanographic Society of Japan 2001

Authors and Affiliations

  • Peter C. Chu
    • 1
  • Chenwu Fan
    • 1
  1. 1.Department of OceanographyNaval Postgraduate SchoolMontereyU.S.A

Personalised recommendations