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研究生:梁家睿
研究生(外文):Jia-ruei Liang
論文名稱:利用LoweredADCP與CTD剖面資料估算台灣西南海域之紊流擴散
論文名稱(外文):Estimates of turbulent mixing in the seas off the Southwestern Taiwan from Lowered ADCP and CTD profiles
指導教授:曾若玄曾若玄引用關係
指導教授(外文):Ruo-Shan Tseng
學位類別:碩士
校院名稱:國立中山大學
系所名稱:海洋生物科技暨資源學系研究所
學門:自然科學學門
學類:海洋科學學類
論文種類:學術論文
論文出版年:2010
畢業學年度:98
語文別:中文
論文頁數:117
中文關鍵詞:內潮內孤立波高屏海底峽谷黑潮紊流
外文關鍵詞:Thorpe scaleKuroshioGaoping Submarine Canyoninternal solitonturbulenceinternal tides
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本研究利用下放式都普勒海流剖面儀(Lowered ADCP)及溫鹽深儀(CTD)所觀測的剖面,根據紊流理論運算以求得垂直渦流擴散係數K (vertical eddy diffusivity),主要使用Thorpe scale分析法計算Kz,再輔以流切(shear)的垂直波數能譜法(vertical wave number spectral)計算Ksh,針對內潮、深海大洋、內孤立波及黑潮等四種不同情況探討影響紊流擴散的因素。
首先在高屏海底峽谷(Gaoping submarine canyon)的開口處完成兩個航次 (2008年7月和12月)的定點測站之27(夏季)及40(冬季)小時連續觀測,結果顯示此地內潮呈現50及100m的垂直位移,顯著的半日潮週期且上下層流速成相反的第一斜壓模流場等特性;兩個季節漲潮時紊流混合的擴散率皆明顯大於退潮時期,冬季觀測時適逢大潮,漲潮時的Kz超過0.01 m2 s-1,大於蒙特利海底峽谷(Monterey Canyon)的紊流擴散率。冬季時因混合層增厚,流速增加,造成的紊流擴散較為強烈。
2008年5月的聯合探測結果指出,南海SEATS測站於3000m以上Kz平均值為3×10-4 m2 s-1,而 Ksh約為1.8×10-4 m2 s-1,接近海底的Kz的平均值則增大為2.5×10-3 m2/s,不論上層海洋或是海底的Kz都比一般大洋的平均值較高,這可能與南海環境有關。SEATS測站Kz剖面在300-700 m處幾乎為零,表示分層也較為明顯,不容易有紊流發生。
2007年5月於南海北部之內波實驗結果指出,深水區在內孤立波通過後造成Kz的垂直分佈產生了變化,表面混合不明顯,主要在400 m以下逐漸增大至底層;淺水區在內孤立波通過時受到陸棚地形影響,產生破碎後的消散作用,混合擴散明顯增強,最大值(~1 m2 s-1)出現於180 m的深度。
2007年10月於蘭嶼附近完成之黑潮實驗結果指出,黑潮流場的 Kz在表層超過10-2 m2 s-1,主要是受到黑潮強勁流速的影響;靠近蘭嶼處有一深達3000m的海溝存在,地形與底層流作用,使得底層Kz皆超過1 m2 s-1,顯示底層的混合以地形影響為主,產生與內孤立波同量級的紊流擴散。
In this study, vertical profiles of velocity and hydrographic properties measured by the Lowered ADCP and CTD, respectively are used to calculate the vertical eddy diffusivity K based on small-scale turbulence theory. Two methods are used to estimate K, that is, the Thorpe scale analysis method (designated as Kz) and vertical wave number shear spectral method (designated as Ksh). Four different experiments with different flow conditions and bathymetry, i.e., internal tides, deep open-ocean, nonlinear internal waves and Kuroshio, are conducted and their K values are estimated and discussed.
The internal tides at the mouth of Kao-Ping Submarine Canyon (KPSC) are observed during July and December (spring tide) of 2008. In each cruise the LADCP/CTD casts are repeated every two hours and last 27 and 40 hours, respectively. The results indicate the existence of strong, semi-diurnal internal tides with vertical displacement of 50~100 m and the nature of first baroclinic mode. Turbulent mixing during flood is significantly stronger than that during ebb. Note that in the winter experiments the Kz can reach 0.01 m2 s-1, which is even larger than the reported Kz values in other submarine canyons of the world, suggesting strong mixing processes are taking place in the KPSC.
From the LADCP/CTD data of the joint hydrographic survey on May 2008 at SEATS station of the South China Sea, the estimated average values of Kz and Ksh in the upper 3000 m are about 3×10-4 m2 s-1 and 1.8×10-4 m2 s-1, respectively. The average value of Kz near the ocean bottom increases to 2.5×10-3 m2 s-1. These estimated Kz are somewhat larger than the reported values in the open ocean. On the other hand, Kz values between 300 and 700 m deep are almost zero, indicating that turbulent mixing is inhibited in the stratified layer.
Nonlinear internal waves are tracked in the South China Sea during May 2007. Our results show that after the internal solitons passed in the deep waters, the Kz profiles change significantly, surface mixing is weak, and Kz increases gradually from 400 m deep to the ocean bottom. In the shallow water region, shoaling effect of the nonlinear internal waves lead to enhanced energy dissipation and higher values of Kz, with the maximum value reaches 1 m2 s-1 near 180m depth.
The flow structure of Kuroshio current between Taiwan and Lanyu is observed in October 2007. The results show that Kz in the surface layer is high (~10-2 m2 s-1), obviously due to strong Kuroshio flows there. At the 3000 m deep submarine trench near Lanyu, the Kz in the bottom layer is also very high (~ 1 m2 s-1 ), indicating that effective turbulent mixing in the bottom layer is mainly due to topography, which has similar level as the nonlinear internal waves.
章次 頁次
謝誌…………………………………………… Ⅰ
中文摘要……………………………………… Ⅱ
英文摘要……………………………………… Ⅳ
目錄…………………………………………… Ⅵ
圖目錄………………………………………… IX
表目錄…………………………………………XIV
ㄧ、 緒論……………………………………… 1
二、儀器與現場觀測……………………………8
2.1 LADCP與CTD剖面…………………………8
2.2 高屏海底峽谷內潮實驗 ………………… 12
2.3 南海北部內孤立波實驗 ………………… 13
2.4 2008聯合觀測實驗-南海SEATS測站……15
2.5 蘭嶼附近之黑潮流場實驗 ……………… 17
三、資料分析方法…………………………… 25
3.1 Thorpe scale方法…………………………25
3.2 垂直波數能譜法-剪切 …………………… 28
四、結果 ……………………………………… 34
4.1 高屏海底峽谷內潮於垂直混合…………… 34
4.1.1 CTD水文剖面資料…………………… 34
4.1.2 LADCP流速剖面資料…………………35
4.1.3 夏季紊流擴散………………………… 37
4.1.4 冬季紊流擴散………………………… 39
4.2 SEATS測站之紊流擴散……………………41
4.3 南海內孤立波之紊流擴散…………………44
4.3.1 深水區內波與擴散率………………… 44
4.2.2 陸棚區內波與擴散率………………… 46
4.4 蘭嶼附近黑潮流場之紊流擴散……………48
五、 討論……………………………………… 83
5.1 內潮與紊流特性之季節變化………………83
5.1.1 浮力頻率與流速剪切………………… 83
5.1.2 紊流混合之季節差異………………… 84
5.2 深海大洋紊流擴散之垂直分佈 ……………86
5.3 內孤立波效應下的紊流混合……………… 87
5.4 黑潮造成紊流擴散之空間變化………… 88
六、結論…………………………………………96
參考文獻…………………………………………99

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