References

Ocean Science

Ocean Sci.

1812-0792

Copernicus Publications

Göttingen, Germany

10.5194/os-7-661-2011

Eddy characteristics in the northern South China Sea as inferred from Lagrangian drifter data

Jiaxun Li

¹ ² Ren Zhang

¹ Baogang Jin

Key Laboratory of Ocean Hydrology Environment, Institute of Meteorology, PLA University of Science and Technology, Nanjing, China

State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, SOA, Hangzhou, China

Beijing Applied Institute of Meteorology, Beijing, China

21 10 2011

7 5 661 669

2011

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://os.copernicus.org/articles/7/661/2011/os-7-661-2011.html

The full text article is available as a PDF file from https://os.copernicus.org/articles/7/661/2011/os-7-661-2011.pdf

Cyclonic and anticyclonic eddies from large scale to submesoscale in the northern South China Sea (NSCS) have been statistically characterized based on the satellite-tracked Lagrangian drifters using our developed geometric eddy identification method. There are in total 2208 eddies identified, 70% of which are anticyclonic eddies. If the submesoscale eddies are eliminated, the other eddies in the NSCS will show a 1.2:1 ratio of the number of anticyclones (210) to the number of cyclones (171). The spatial distribution of the eddies is regional: in southwest of Taiwan, the number of anticyclones dominates the number of cyclones, and most of them are the submesoscale anticyclones with small radii; in contrast, the large and medium cyclonic eddies are a little more than the same scale anticyclonic eddies in northwest of Luzon. The temporal distribution of eddy number in the NSCS has a close relation with the Asian monsoon. The number of the large and medium eddies peaks during the winter monsoon, while the submesoscale eddies are apt to generate in the summer monsoon. The spatial and temporal patterns have a good agreement with the results of the sea surface height anomaly (SSHA). The maximum and mean tangential velocities of anticyclones (cyclones) are 40 (30) cm s<sup>−1</sup> and 25 (15) cm s<sup>−1</sup>, respectively. The calculated normalized vorticities from drifters suggest that although the mesoscale eddies may be considered in geostrophic balance, ageostrophic dynamics and centrifugal effects may play an important role for the growth and decay of the mesoscale cores.

References 1

Boebel, O., Lutjeharms, J., Schmid, C., Zenk, W., Rossby, T., and Barron, C.: The cape cauldron: a regime of turbulent inter-ocean exchange, Deep-Sea Res. Pt. II, 50, 57–86, 2003.

Chaigneau, A. and Pizarro, O.: Eddy characteistics in the eastern South Pacific, J. Geophys. Res., 110, C06005, <a href="http://dx.doi.org/10.1029/2004JC002815">https://doi.org/10.1029/2004JC002815</a>, 2005.

Chelton, D. B., Deszoeke, R. A., and Schlax, M. G.: Geographical variability of the first baroclinic Rossby radius of deformation, J. Phys. Oceanogr., 28, 433–460, 1998.

Chow, C.-H., Hu, J.-H., Centurioni, L. R., and Niiler, P. P.: Mesoscale Dongsha cyclonic eddy in the northern South China Sea by drifter and satellite observations, J Geophys. Res., 113, C04018, <a href="http://dx.doi.org/10.1029/2007JC004542">https://doi.org/10.1029/2007JC004542</a>, 2008.

Chu, P. C., Fan, C. W., Lozano, C. J., and Kerling, J. L.: An airborne expendable bathythermograph survey of the South China Sea, May 1995, J. Geophys. Res., 103, 21637–21652, 1998.

Hamilton, P.: Eddy statistics from Lagrangian drifters and hydrography for the northern Gulf of Mexico slope, J. Geophys. Res., 112, C09002, <a href="http://dx.doi.org/10.1029/2006JC003988">https://doi.org/10.1029/2006JC003988</a>, 2007.

Hansen, D. V. and Poulain, P.-M.: Quality control and interpolations of WOCE-TOGA drifter data, J. Atmos. Oceanic. Tech., 13, 900–909, 1996.

Hwang, C. and Chen, S.-A.: Circulations and eddies over the South China Sea derived from TOPEX/Poseidon altimetry, J. Geophys. Res., 105, 23943–23965, <a href="http://dx.doi.org/10.1029/2000JC900092">https://doi.org/10.1029/2000JC900092</a>, 2000.

Jia, Y. L. and Liu, Q. Y.: Eddy shedding from the Kuroshio bend at Luzon Strait, J. Oceanogr., 60, 1063–1069, 2004.

Li, L., Nowlin Jr., W. D., and Su, J. L.: Anticyclonic rings from the Kuroshio in the South China Sea, Deep-Sea Res. Pt. I, 45, 1469–1482, 1998.

Nan, F., He, Z. G., Zhou, H., and Wang, D. X.: Three long-lived anticyclonic eddies in the northern South China Sea, J. Geophys. Res., 116, C05002, <a href="http://dx.doi.org/10.1029/2010JC006790">https://doi.org/10.1029/2010JC006790</a>, 2011.

Pingree, R. D. and Cann, B. Le.: Three anti-cyclonic slope water oceanic eDDIES (SWODDIES) in the Southern Bay of Biscay in 1990, Deep-Sea Res. Pt. I, 39, 1147–1175, 1992.

Qu, T. D.: Upper-layer circulation in the South China Sea, J. Phys. Oceanogr., 30, 1450–1460, 2000.

Qu, T. D., Du, Y., Gan, J. P., and Wang, D. X.: Mean seasonal cycle of isothermal depth in the South China Sea, J. Geophys. Res., 112, C02020, <a href="http://dx.doi.org/10.1029/2006JC003583">https://doi.org/10.1029/2006JC003583</a>, 2007.

Sadarjoen, I. A. and Post, F. H.: Detection, quantification, and tracking of vortices using streamline geometry, Comp. Graph, 24, 333–341, 2000.

Shaw, P. T., Chao, S. Y., and Fu, L.: Sea surface height variations in the South China Sea from satellite altimetry, Oceanol. Acta, 22, 1–17, 1999.

Shoosmith, D. R., Richardson, P. L., Bower, A. S., Rossby, H. T.: Discrete eddies in the northern North Atlantic as observed by looping RAFOS floats, Deep-Sea Res. Pt II, 52, 637–650, 2005.

Su, J. L.: Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary, Cont. Shelf. Res., 24, 1745–1760, 2004.

Su, J. L., Xu, J. P., Cai, S. Q., and Wang, O.: Gyres and eddies in the South China Sea, onset and evolution of the South China Sea monsoon and its interaction with the ocean, edited by: Yihui, D. and Chongyin, L., China Meteorological Press, Beijing, China, 272–279, 1999 (in Chinese).

Swenson, M. S. and Niiler, P. P.: Statistical analysis of the surface circulation of the California Current, J. Geophys. Res., 101, 22631–22645, 1996.

Thomas, L. N., Tandon, A., and Mahadevan, A.: Submesoscale processes and dynamics. Eddy Resolving Ocean Modeling, edited by: Hecht, M. W. and Hasumi, H., Amer. Geophys. Union, 17–38, 2008.

van Aken, H. M.: Surface currents in the Bay of Biscay as observed with drifters between 1995 and 1999, Deep-Sea Res. Pt. I, 49, 1071–1086, 2002.

Wang, D. X., Xu, H. Z., Lin, J., and Hu, J. Y.: Anticyclonic eddies in the northeastern South China Sea during winter 2003/2004, J. Oceanogr., 64, 925–935, 2008.

Wang, G. H., Su, J. L., and Chu, P. C.: Mesoscale eddies in the South China Sea observed with altimeter data, Geophys. Res. Lett., 30, 2121, <a href="http://dx.doi.org/10.1029/2003GL018532">https://doi.org/10.1029/2003GL018532</a>, 2003.

Wang, G. H., Su, J. L., and Li, R. F.: Mesoscale eddies in the South China Sea and their impact on temperature profiles, Acta Oceanol. Sinica, 24, 39–45, 2005.

Wang, G. H., Chen, D. K., and Su, J. L.: Generation and life cycle of the dipole in the South China Sea summer circulation, J. Geophys. Res., 111, C06002, <a href="http://dx.doi.org/10.1029/2005JC003314">https://doi.org/10.1029/2005JC003314</a>, 2006.

Wang, G. H., Chen, D. K., and Su, J. L.: Winter eddy genesis in the eastern South China Sea due to orographic wind jets, J. Phys. Oceanogr., 38, 726–732, 2008.

Yuan, D. L., Han, W. Q., and Hu, D. X.: Surface Kuroshio path in the Luzon Strait area derived from satellite remote sensing data, J. Geophys. Res., 111, C11007, <a href="http://dx.doi.org/10.1029/2005JC003412">https://doi.org/10.1029/2005JC003412</a>, 2006.

Yuan, D. L., Han, W. Q., and Hu, D. X.: Anti-cyclonic eddies northwest of Luzon in summer-fall observed by satellite altimeters, Geophys. Res. Lett., 34, L13610, <a href="http://dx.doi.org/10.1029/2007GL029401">https://doi.org/10.1029/2007GL029401</a>, 2007.