本文利用Sb-ADCP的流速資料，CTD水文資料及衛星影像來探討小琉球島後尾流的機制，研究結果顯示當尾流在小琉球北邊時，產生順時針及逆時針的渦漩其渦度達 0.01 s ，此二個旋轉方向相反的渦漩在小琉球背流面的中間產生迴流並產生不穩定的eddy shedding現象。當尾流出現在小琉球南邊時，產生二個固定成對且方向相反的穩定渦漩，二個渦漩之間有迴流流向島嶼。
分析位於小琉球沿岸的底碇式ADCP資料顯示，小琉球東北方靠近海岸的地方主要以半日潮為主，半日潮流橢圓主軸方向平行於小琉球東北方的海岸地形（東北-西南向），其振幅約為全日潮二倍，軸向為東北東與西南西做往復運動，潮流橢圓型態甚為狹長。海流在漲潮時段流向東北且產生沈降流，而在退潮時段流向西南且產生湧昇流。海流較大的時段集中在大潮。
探討湧昇現象時採用了三個航次的CTD資料，研究結果顯示受到島嶼尾流影響的地區渦漩中心不論順時針或反時針皆為輻散，呈現湧昇的狀態，此時湧昇流將深層海水帶上來，使得海水呈現溫度較低、鹽度高且溶氧量高及葉綠素濃度低的特性。反之渦漩邊緣為輻合地帶產生沉降流，此地區海水特性為溫度高、鹽度低、溶氧量低及葉綠素濃度高。而位於尾流水深60公尺處由於受到的流剪相當大造成了斜溫層，此地區混合作用旺盛。不受到尾流影響的地方，分層效應明顯，溫度、鹽度及溶氧量於水平方向的變化不大，此時沒有沉降與湧昇的現象，而在受到阻擋效應與自由流交界的地區，剪應力增加而有些混合的作用。
最後我們利用許明光及劉正千老師提供的歐洲資源衛星ERS-1/SAR雷達影像及福衛二號衛星空照圖觀察小琉球尾流，可以很清楚地看到尾流出現在小琉球的東南方，此時為大潮時段，尾流形成von Karman vortex street。而同樣大潮期間在小琉球北方也發現由懸浮物高的濁水形成一個逆時鐘的渦流，這個渦流的尺度大約直徑為4km。在衛星影像海表面葉綠素濃度圖，發現葉綠素濃度特別低的區域位於渦漩中心。綜合本研究的四個航次、黃材成老師的底碇式ADCP資料及衛星影像，發現小琉球島嶼尾流出現的時間約在大潮前後。

The objective of this study is to investigate and characterize the mechanism of the island wake behind an island called Liu Chiu Yu off the southwestern Taiwan coast based on the in-situ data of Sb-ADCP, CTD and satellite images. The findings suggest that a counter-clockwise eddy and a clockwise eddy both are with 0.01 S vortice appears in the wake of Liu Chiu Yu when the background flows are toward the northwest. The system of two eddies with opposite rotation and a central return flow develops an unsteady eddy shedding. On the other hand, when the background flows are toward the southeast, island wake generated in the lee of Liu Chiu Yu is attached system of two eddies with opposite rotation and a central return flow.
The Sb-ADCP data shows that the flow pattern in the northeastern coast of Liu Chiu Yu is mainly semidiurnal. The major axis of the ellipse of the semidiurnal current is parallel to the orientation of the coast line (northeast to southwest) and the shape of the ellipse is quite long and narrow. The amplitude of the semidiurnal current is approximately two times that of the diurnal current. Generally, the currents are stronger and the occurring probability of the island wake is higher during spring tide.
The CTD data shows that the eddy center appears to be divergent and upwelling occurs in the areas under the influence of island wakes. The upwelling pumps deep seawater to the surface and results in low temperature, high salinity, high oxygen concentration and low chlorophyll concentration. On the other hand, in the eddy edges, downwelling occur causing high temperature, low salinity, low oxygen concentration and high chlorophyll concentration. Strong shear was formed at the depth of 60m inside the island wake which generates thermocline so that the mixing phenomenon is quite obvious there. Moreover, in the regions without the influence of island wakes, the stratifying effect is clear and the horizontal variation of temperature, salinity and oxygen concentration is small. Therefore, neither upwelling nor downwelling occurs there. Furthermore, along the edge between blocking and free-stream areas, the shear stress increases and the mixing phenomenon arises to a certain degree.
The satellite images show that an island wake appears in the southeastern Liu Chiu Yu during spring tide. The island wake develops a phenomenon called von Karman vortex street. At the same time, a counter-clockwise eddy with heavy suspensions appears in the northern Liu Chiu Yu. The radius of the eddy is around 4 Km. The area of the lowest chlorophyll concentration is located at the center of the eddy. By analyzing all these data, it is concluded that the island wake in Liu Chiu Yu usually appears during spring tide.

章次 頁次

中文摘要……………………………………………………………...I
英文摘要……………………………………………………………III
目錄…………………………………………………………………IV
圖目錄………………………………………………………………VI
表目錄……………………………………………………………...XII


一、前言……………………………………………………………1
二、研究區域……………………………………………………….4
2.1 地理位置及海底地形…………………………………...4
2.2 潮汐…………………………………………………...4
2.3 海流…………………………………...........................5
2.4 風場…………………………………...........................6
三、實驗設計與現場調查………………………………………....7
3.1 海流觀測……………………………………………....7
3.1.1 Sb-ADCP…………………………………..................7
3.1.2 底碇式ADCP………………………………………..10
3.2 水文觀測…………………………………...................10
3.3 遠端遙測……………………………………………...10
四、資料分析與結果……………………………………………..12
4.1 尾流的二維流場……………………………….............12
4.1.1 C1028航次2004年12月Sb-ADCP的二維流場…12
4.1.2 C1095航次2005年9月Sb-ADCP的二維流場…..14
4.1.3 C1113航次2005年11月Sb-ADCP的二維流場….15
4.2 尾流的垂直結構…………………………………...........15
4.2.1 C1028航次2004年12月Sb-ADCP的三維流場….15
4.2.2 C1095航次2005年9月Sb-ADCP的三維流場…...16
4.2.3 C1113航次2005年11月Sb-ADCP的三維流場…..17
4.3 1145航次2006年4月二維流場與溫度剖面……………..18
4.4 水文特性………………………………….....................19
4.4.1 CTD溫度剖面…………………………………..19
4.4.1.1 C1095航次2005年9月CTD溫度剖面…………19
4.4.1.2 C1113航次2005年11月CTD溫度剖面………...20
4.4.2 溶氧量剖面…………….………….…………...21
4.4.3 葉綠素剖面………………………..…................22
4.4.4 塩度剖面…..……………………………………23
4.5 底碇式ADCP…………………………………................24
4.6 衛星影像………………………………….......................25

五、討論…………………………………..........................................26
5.1 二維流場………………………………….......................27
5.2 三維流場…………………………………………….......28
5.3 小琉球島嶼尾流的渦度與散度…………………………….29
5.4 水文觀測………………………………….......................30
5.5 定點長時間流場觀測……………………………………..33
5.6 島嶼尾流相關參數………………………………………..34
5.6.1 雷諾數…………………………………...............34
5.6.2 島嶼尾流參數…………………………………….36
六、結論…………………………………............................................37
七、參考文獻…………………………………………………………40

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