Abstract
Based on the EOF analyses of Absolute Dynamic Topography satellite data, it is found that, in summer, the northern South China Sea (SCS) is dominated by an anticyclonic gyre whilst by a cyclonic one in winter. A connected single-layer and two-layer model is employed here to investigate the dynamic mechanism of the circulation in the northern SCS. Numerical experiments show that the nonlinear term, the pressure torque and the planetary vorticity advection play important roles in the circulation of the northern SCS, whilst the contribution by seasonal wind stress curl is local and limited. Only a small part of the Kuroshio water intrudes into the SCS, it then induces a positive vorticity band extending southwestward from the west of the Luzon Strait (LS) and a negative vorticity band along the 200 m isobath of the northern basin. The positive vorticity field induced by the local summer wind stress curl is weaker than that induced in winter in the northern SCS. Besides the Kuroshio intrusion and monsoon, the water transports via the Sunda Shelf and the Sibutu Passage are also important to the circulation in the northern SCS, and the induced vorticity field in summer is almost contrary to that in winter. The strength variations of these three key factors (Kuroshio, monsoon and the water transports via the Sunda Shelf and the Sibutu Passage) determine the seasonal variations of the vorticity and eddy fields in the northern SCS. As for the water exchange via the LS, the Kuroshio intrusion brings about a net inflow into the SCS, and the monsoon has a less effect, whilst the water transports via the Sunda Shelf and the Sibutu Passage are the most important influencing factors, thus, the water exchange of the SCS with the Pacific via the LS changes dramatically from an outflow of the SCS in summer to an inflow into the SCS in winter.
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References
Cai, S., Liu, H., Li, W., and Long, X., 2005. Application of LICOM model to the numerical study of the water exchange between the South China Sea and its adjacent oceans. Acta Oceanologica Sinica, 24(4): 10–19.
Cai, S., Long, X., and Wang, S., 2007. A model study of the summer Southeast Vietnam Offshore Current in the southern South China Sea. Continental Shelf Research, 27(18): 2357–2372.
Cai, S., Su, J., Gan, Z., and Liu, Q., 2002. The numerical study of the South China Sea upper circulation characteritics and its dynamic mechanism, in winter. Continental Shelf Research, 22(15): 2247–2264.
Caruso, M. J., Gawarkiewicz, G. G., and Beardsley, R. C., 2006. Interannual variability of the Kuroshio intrusion in the South China Sea. Journal of Oceanography, 62: 559–575.
Chow, C. H, and Liu, Q., 2012. Eddy effects on sea surface temperature and sea surface wind in the continental slope region of the northern South China Sea. Geophysical Research Letters, 39, L02601, DOI: 10.1029/2011GL050230.
Fang, W., Guo, J., Shi, P., and Mao, Q., 2006. Low frequency variability of South China Sea surface circulation from 11 years of satellite altimeter data. Geophysical Research Letters, 33, L22612, DOI: 10.1029/2006GL027431.
Gill, A. E., 1982. Atmosphere-Ocean Dynamics. Academic Press, New York, 662pp.
Hu, J., Kawamura, H., Hong, H., Kobashi, F., and Wang, D., 2001. 3–6 months variation of sea surface height in the South China Sea and its adjacent ocean. Journal of Oceanography, 57: 69–78.
Jia, Y., and Chassignet, E. P., 2011. Seasonal variation of eddy shedding from the Kuroshio intrusion in the Luzon Strait. Journal of Oceanography, 67(5): 601–611.
Liu, Y., Wang, Q., Song, J., Zhu, X., Gong, X., and Wu, F., 2011. Numerical study on the bifurcation of the North Equatorial Current. Journal of Ocean University of China, 10(4): 305–313.
Liu, Z., Yang, H., and Liu, Q., 2001. Regional dynamics of seasonal variability in the South China Sea. Journal of Physical Oceanography, 31(1): 272–284.
Metzger, E. J., and Hurlburt, H. E., 2001. The nondeterministic nature of Kuroshio penetration and eddy shedding in the South China Sea. Journal of Physical Oceanography, 31(7): 1712–1732.
Nan, F., Xue, H., Xiu, P., Chai, F., Shi, M., and Guo, P., 2011. Oceanic eddy formation and propagation southwest of Taiwan. Journal of Geophysical Research, 116, C12045, DOI: 10.1029/2011JC007386.
Qu, T., Kim, Y. Y., Yaremchuk, M., Tozuka, T., and Yamagata, T., 2004. Can Luzon Strait play a role in conveying the impact of ENSO to the South China Sea. Journal of Climate, 17: 3644–3657.
Yuan, D., Han, W., and Hu, D., 2006. Surface Kuroshio path in the Luzon Strait area derived from satellite remote sensing data. Journal of Geophysical Research, 111, C11007, DOI: 10.1029/2005JC003412.
Yuan, Y., Liao, G., Guan, W., Wang, H., Lou, R., and Chen, H., 2008. The circulation in the upper and middle layers of the Luzon Strait during spring 2002. Journal of Geophysical Research, 113, C06004, DOI: 10.1029/2007JC004546.
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Cai, S., Zheng, S. & He, Y. Vorticity budget study on the seasonal upper circulation in the northern South China Sea from altimetry data and a numerical model. J. Ocean Univ. China 11, 455–464 (2012). https://doi.org/10.1007/s11802-012-2008-5
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DOI: https://doi.org/10.1007/s11802-012-2008-5