非持續性的南海暖流

The Non-persistent South China Sea Warm Current

楊凱絜(Kai-Chieh Yang)

指導教授 ： 唐存勇

國立臺灣大學/理學院/海洋研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02256

摘要

無資料

關鍵字

南海暖流

並列摘要

From the previous hydrographic and numerical studies, the finding of a year round northeastward flowing South China Sea Warm Current (SCSWC) existed on the continental shelf of northern South China Sea (SCS), even during the NE monsoon season has been claimed. However, the existence and mechanism of SCSWC is still controversial because the conclusion is mostly based on one-time hydrographic survey or very short-term moored current velocity measurements. In this study, we utilize hydrographic measurements, including CTD casts and Shipboard Acoustic Doppler Current Profiler (Sb-ADCP) current velocity, moored ADCP current velocity, the QuickSCAT/National Centers for Environmental Prediction (QSCAT/NCEP) blended ocean surface wind stress, and the Tropical Rainfall Measurement Mission Microwave Imager Sea Surface Temperature (TMI/SST) data to study the currents on the shelf in the northern SCS, especially focus on SCSWC.
The composite temperature and SB-ADCP current velocity indicate that the shelf currents are toward the north, but northeastward in SW monsoon season (May – October) and northwestward in NE monsoon season (November — April). Furthermore, the present one-time hydrographic surveys and estimated geostrophic currents show that northeastward current is seen occasionally in the shelf region. The above studies are similar to previous studies in summer but has notable different in winter.
Solidly and directly, a 9-month (04/29/2005 — 01/18/2006) ADCP mooring measurement on the shelf break, which is the considered range of SCSWC, shows the SCSWC is not a persistent feature. The currents were varied. The northeastward current was seen only in winter when the NE monsoon relaxes. The similar events are seen in a 5-month bottom-mounted moored ADCP velocity measurement on the shelf during 11/5/2001 — 3/21/2002. The wintertime observation reveals that this northeastward current emerges only when the NE monsoon is relatively weak, its velocity can reach 30 cm/s near surface, and the SST increased accordingly. Obviously, the SCSWC only exists after NE monsoon relaxation in winter. Its intermittent characteristic is different from previous studies.
The output from the SCS model shows that the NE monsoon relaxation sets up a pressure gradient with sea level higher in the southwest than in the northeast and then causes a northeastward current, SCSWC. The results suggest that SCSWC is not a persistent feature. Wind relaxation could be the mechanism of SCSWC in winter.

並列關鍵字

South China Sea Warm Current

參考文獻

1. Chao, S.-Y., P.-T. Shaw and J. Wang (1995), Wind Relaxation as a Possible Cause of the South China Sea Warm Current, J. Oceanogr., 51, 111-132.

2. Gawarkiewicz, G., J. Wang, M. Caruso, S. R. Ramp, K. H. Brink and F. Bahr (2004), Shelfbreak Circulation and Thermocline Structure in the Northern South China Sea – Contrasting Spring Conditions in 2000 and 2001, IEEE J. Oceanic Engineering, 29(4), 1131-1143.

7. Guan, B. and G. Fang (2006), Winter Counter-wind Currents off the Southeastern China Coast: A Review, J. Oceanogr., 62, 1-24.

8. Guo, Z., T. Yang and D. Qiu (1985), The South China Sea Warm Current and the southwestward current on its right side in winter, Tropic Oceanology, 4(1), 1-9 (in Chinese with English abstract).

9. Hellerman, S. and M. Rosenstein (1983), Normal monthly wind stress over the world ocean with error estimates, J. Phys. Oceanogr., 13, 1093-1104.