In order to better understand the flow dynamics in the Taiwan Strait (TS) and the adjacent seas, a series of field experiments were conducted to monitor the currents by deploying 30 SVP drifters, using shipboard ADCP measurements and analyzing historical drifter data in the TS. Examinations of historical drifter data reveal that the surface waters in the TS originate from the shelf of the South China Sea (SCS) in the summer. In wintertime, the mean surface current flows toward the south in the northern TS with a mean speed of approximately 0.3~0.4 m/s. The surface current in the eastern TS mainly flows northward, and it flows southward in the western TS in the fall. The surface waters of the Kuroshio do not intrude into the SCS in summer. Instead, a northeastward current of 0.5~0.7 m/s west of Luzon Island impinges on the Kuroshio across the Luzon Strait. Drifter tracks in the TS are classified according to the wind condition. The first type of drifter tracks is that the drifters move northward in the TS with an intensified flows in the Peng-hu Channel when the southwest monsoon prevails. The second and third types of drifter tracks are under the influence of strong northeast monsoon. The drifters are carried onto the shelf of East China Sea from the Kuroshio or the East China Sea, and then move southward along the TS. Some drifters are grounded at the west coast of Taiwan, and the others drift through the TS. The third type of drifter tracks show that drifters start from the Luzon Strait and move northward into the TS. However, they can only reach the neighboring area of Peng-Hu archipelagoes, then they change the direction of drifting to the south or southwest and toward the SCS. The fourth type is that drifters are carried northward from the SCS into the northern TS under the weak northeast wind, and then veer to the south when the northeast monsoon intensifies. The fifth type of drifter tracks demonstrates the flow pattern of the northern TS when the northeast monsoon diminishes. This flow pattern belongs to the Taiwan Warm Current (TWC) in wintertime. The surface speed of TWC is about 0.2~0.4 m/s northward. The second, fourth and fifth flow patterns in the TS have not been quite discovered in previous studies. In-situ marine observations right beneath typhoons are very scanty and valuable. In this study we have found several events with some drifters happened to get caught by typhoons. The maximum speed of drifters near the typhoon center is found to be about 2 m/s. The SST, which is observed by the drifter, reduces 2~4¢J after the typhoon passes. Our results indicate that for the case of the Typhoon Haitang the Matsu weather station measured a sudden increase of wind speed of about 3 m/s every hour, and the corresponding drifter speed increases 0.52 m/s. There were two events in summer of 2006 when the Typhoon Billis and Saomai passed the northern region of Taiwan, and some drifters located at the Kuroshio to the north of typhoon were carried rapidly onto the ECS shelf with a maximum speed of about 1.1 m/s. This result indicates that the Kuroshio waters can penetrate into the ECS shelf by means of the passage of typhoon in this region during summertime.
Three cruises with the shipboard ADCP were performed by three research vessels concurrently along two transects during 2002-2004. Various phase averaging methods were employed to eliminate tidal effects. The calculated volume transport of the TS for the period of August 2002, September 2003 and March 2004 is 3.4, 3.6 and 2.8 Sv, respectively. These transport values are compatible with the output of EASCNFS model. The estimated uncertainty of the residual flow through the Peng-hu Channel derived from the 5-phase-averaging, 4-phase-averaging, 3-phase-averaging and 2-phase-averaging methods is 0.3, 0.3, 1.3 and 4.6 cm/s, respectively. Procedures for choosing a best phase average method to remove tidal currents in any particular region are also suggested.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0212108-193625 |
| Date | 12 February 2008 |
| Creators | Chang, Yu-Chia |
| Contributors | Jian-Hwa Hu, Ching-Sheng Chern, James T. Liu, Ruo-Shan Tseng, Yu-Hwai Wang, Joe 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-0212108-193625 |
| Rights | unrestricted, Copyright information available at source archive |
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