Please use this identifier to cite or link to this item: http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/101423
Title: 南海渦漩、暖流及颱風溫降之數值模擬與動力解釋
Simulations and interpretations on mesoscale eddy, Warm Current, and typhoon-induced temperature drop in the South China Sea
Authors: 吳朝榮
Wu, Chau-Ron
江紫綾
Chiang, Tzu-Ling
Keywords: 中尺度渦漩
南海暖流
海表面溫降
mesoscale eddy
South China Sea Warm Current
sea surface temperature drop
Issue Date: 2010
Abstract: 本研究使用一個南海區域的數值模式(South China Sea model)模擬向西移動的中尺度渦漩行為、冬季之南海暖流(South China Sea Warm Current)及颱風造成的海表面溫降,並解釋這些現象的動力過程與形成機制。由南海模式之海表面高度距平值顯示,起源於呂宋海峽附近之中尺度渦漩脫離後會向西移動,進而影響南海北部的水文及環流。此渦漩脫離的週期在冬天較短為40~50天,夏天較長為80~120天,此與黑潮入侵之季節性變化有關。南海模式也能成功地模擬出南海暖流。經由多個數值試驗得知,黑潮的存在並不會影響南海暖流的形成與否。冬季時東北季風的間歇性減弱(wind relexation),才是南海暖流產生的主要原因。也就是說,東北季風時期,海水會在東京灣(Gulf of Tonkin)岸邊堆積,使得海平面升高,待東北季風減弱後,海水回流進而形成南海暖流。我們也利用模式重新確認了暖流的發源處是在東京灣,而非過去所認為的海南島東南方。南海模式亦成功模擬了2000年夏季啟德颱風(Kai-Tak)在南海北部所造成的強烈海表面溫降。並利用數值試驗得知:湧升及垂直混合機制各自所占的表面降溫比例分別為62%與31%。啟德颱風能夠造成如此強烈之表面溫降原因為:一、颱風來臨前有異常淺的溫躍層存在,所以次表層的冷水較容易被帶到表面;二、颱風本身之移動速率較慢,因此由颱風引起之湧升效應更為強烈。
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.
URI: http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=%22http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=id=%22GN0895440015%22.&%22.id.&
http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/101423
Other Identifiers: GN0895440015
Appears in Collections:學位論文

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