The surface circulation of the northern South China Sea (NSCS) for the period of 1986-2006 is studied using the data of more than 505 satellite-tracked drifters from NOAA/AOML database and the data from ten drifters which were released by our lab in the Penghu channel and in the Luzon Strait in 2006. In this study, the spatial structure and the temporal variability of the surface currents, at mesoscale to seasonal cycle, are described in terms of Eulerian and Lagrangian statistics from the drifter velocities that have been processed.
Maps of mean currents, velocity variance ellipses and mean kinetic energies were produced in domain of 0.5¢X¡Ñ0.5¢X. The mean flow map confirms that during the winter monsoon, there is a global cyclonic circulation in the NSCS and the southwestward current which passes Dongsha Island and is called the ¡§Dongsha Current¡¨. Its continuation is the southward coastal jet off Vietnam which is called the ¡§Vietnam Current¡¨. Maximum velocities in the Vietnam Current can exceed 100 cm/s. During the summer monsoon, the Dongsha Current became very weak and the drifters looped near Dongsha Island. The drifter data shows that part of Kuroshio water intrudes into South China Sea through Luzon Strait, Dongsha Current and Vietnam Current were coherent flows.
Values of 5.12¡Ñ107 cm2/s, 2.56 days and 64.43 km were obtained for the diffusivity, Lagrangian time scale and spatial scale in the meridional direction in the NSCS, respectively. In the zonal direction, the statistics are half of the above values which show that the characteristic time and space scale are anisotropic.
The mean velocity in the Dongsha Current is 0.33 m/s. The domain of Dongsha Current is subdivided into ten boxes of size 2¢X¡Ñ 2¢X in order to analyze the spatial structure of Lagrangian statistics. The result shows that the eddy kinetic energy is considerably higher than the mean kinetic energy in the region 113-121¢XE, indicating that the mesoscale motions are particularly frequent. The eddy kinetic energy gradually decreases toward the west and has a maximum value near the Luzon Strait.
The drifters that flow southward along the east coast of Vietnam shows that the width of the Vietnam Current varies between 80 and 100 km and has a mean core speed of 60-150 cm/s. In winter, Maximum southward velocities could reach 130 cm/s at 38 km off the coast. In spring, a weaker maximum speed (around 100 cm/s) exists at about 18 km off the Vietnam coast. There were not enough drifter data in summer and fall.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0812107-162523 |
| Date | 12 August 2007 |
| Creators | Tseng, Kuang-ming |
| Contributors | L. G. Leu, R. S. Tseng, W.-D. Liang, Y. H. Wang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0812107-162523 |
| Rights | unrestricted, Copyright information available at source archive |
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