| Summary: | 博士 === 國立臺灣師範大學 === 地球科學系 === 98 === Based on a well-validated South China Sea (SCS) model, the characteristics of the westward-propagating mesoscale eddies, the formation mechanism of the South China Sea Warm Current (SCSWC), and the interplay between the upper ocean and typhoon Kai-Tak (2000) are studied. By virtue of a sequence of numerical experiments, the physical processes of those phenomena are further interpreted.
On the basis of the model simulation, the sea surface height anomaly demonstrates that westward-propagating eddies originating in the vicinity of the Luzon Strait can modulate the hydrography and circulation in the northern SCS. The eddy shedding periods in December and August are around 40~50 days and 80~120 days, respectively. The seasonal variability of the Kuroshio intrusion results in more eddies in winter than in summer.
Concerning the physical and geographical origins of the SCSWC, model experiments consistently point to the wind relaxation as the dominant mechanism. The Kuroshio intrusion also helps, but is not chiefly responsible. Tracing the SCSWC to the source, we identify the elevated sea level in the Gulf of Tonkin, induced by the northeast monsoon, as the ultimate driving force. The presence of Hainan Island bears little importance in generating the SCSWC.
An unusually drastic surface cooling induced by typhoon Kai-Tak (2000) in the northern SCS is well reproduced by the model. In the case of Kai-Tak, numerical experiments demonstrate that upwelling and entrainment (vertical mixing) respectively account for 62% and 31% of the sea surface temperature drop. The conditions for Kai-Tak are the anomalously shallow thermocline in 2000 that allows subsurface cooler water to be more easily brought up to the surface, and strong wind-induced upwelling by a slow-moving storm.
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