探討南灣西側海岸線淺水區海水溫降機制之研究;ON THE MECHANISMS OF THE WATER COOLING IN THE SHALLOW WATER WEST OF NANWAN COASTLINE, SOUTHERN TAIWAN

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題名:	探討南灣西側海岸線淺水區海水溫降機制之研究;ON THE MECHANISMS OF THE WATER COOLING IN THE SHALLOW WATER WEST OF NANWAN COASTLINE, SOUTHERN TAIWAN
作者:	尹拉文;Irawan, Septiyadi
貢獻者:	水文與海洋科學研究所
關鍵詞:	南灣週期性海水溫降事件;內波溯升;渦漩引致之湧升流;periodic water temperature drop at Nanwan Bay;internal waves run-up;eddy-induced upwelling
日期:	2022-09-29
上傳時間:	2022-10-04 11:03:11 (UTC+8)
出版者:	國立中央大學
摘要:	台灣南部南灣的不尋常生物物理現象，例如1988年大量魚類死亡，與表面水溫驟降有關，而最近的論證表明，水體冷卻是由潮汐引起渦漩進而帶動湧升流的結果。本研究的目的為重新檢視南灣的溫降機制，重點關注其於渦漩之間的關係，並探討其它的冷卻機制，例如內波淺化。本研究使用2016年6至7月的現地量測和遙測資料，來源包括（i）本研究團隊所部設的ADCP和uCTD；（ii）台灣海洋科技研究中心的水底溫度計和岸基高頻雷達(CODAR)；（iii）日本宇宙航空研究開發機構（JAXA）的向日葵八號(Himawari-8)海表溫度。南灣海域在大潮期間會發生強烈的分層現象，滿足內波形成的必要條件。本研究發現，大潮期間的強分層現象並不總是伴隨著渦漩的紀錄。在28天的量測中，記錄到16次有渦漩的溫降事件、4次有渦漩而沒有溫降事件、9次沒有渦漩的溫降事件。溫降事件和渦漩的關係在本研究也透過海流場向量分析進行探討，包括散度、渦度、應力、Okubo-Weiss參數和瞬時分離率(Instantaneous Rate of Separation, IROS)。渦漩的存在使得場的渦度上升，而湧升流造成的溫降事件則伴隨著顯著的Okubo-Weiss參數。在溫度驟降時，內波溯升現象的發生與沒有渦漩的溫降事件高度吻合。而後將此與實驗尺度的內重力波分析進行比較，結果表明，內波的溯升被低估了，這代表此估計對於輸入參數的微小變化非常敏感。內波溯升的紀錄也受到uCTD溫度和鹽度剖面的影響，顯示出不同潮汐週期的海水分層的發展。最後，本研究統整出：在南灣的西側海岸線上，渦漩可能佔總體冷卻機制的55%，而內波溯升傳遞至海岸線的機率佔31%。;Unusual biophysical phenomenon at Nanwan Bay, Southern Taiwan, for example enormous death of fish in 1988 was associated with sudden surface water cooling. Recent arguments reveal that the cooling water was consequence of upwelling due to tide-induced cyclonic eddy. The aim of this study is to revisit the cooling mechanism in Nanwan Bay, by focusing on the relation of eddy and cold event; and exploring alternative cooling water mechanism, i.e. by internal waves shoaling. This study utilizes both in-situ measurements and remote sensing datasets which were measured during June-July 2016, including (i) ADCP & uCTD deployed by Marine Physical Observation Research Group (MPORG); (ii) bottom temperature gauges and CODAR from Taiwan Ocean Research Institute (TORI); and (iii) Himawari-8 SST by Japan Aerospace Exploration Agency (JAXA). Nanwan Bay encounters strong stratification during spring tide, which it is the ingredient of internal waves formation. This study found that the strong stratification during spring tide were not followed by sequence of cyclonic eddy. For 28 days’ measurement, there were 16 events of cold event with eddies; 4 event of eddy without cold event; and 9 events of cold event without eddy. The relation of cold event and cyclonic eddies was also investigated by some derived field vector of surface current, including divergence, vorticity, strain, Okubo-Weiss and IROS. Eddy presence increases the vorticity of the field, and upwelling cold event is followed by significant Okubo-Weiss number. The internal waves run-up was marked at which temperature drop suddenly and was highly coincident with the classification of cold event with no eddy. This marking was then compared to the internal gravity current analysis from both laboratory and numerical scaling. The comparison result showed that the internal waves run-up was underestimated, indicating that the estimation is very sensitive to the small change of the input parameter. The internal waves run-up footprint was also influenced out by temperature and salinity profile of uCTD, which showed the development of stratified water on different tide cycles. Thus, this study concludes that the eddy may play about 55% of total cooling mechanism probability at the west coastline of Nanwan, and internal waves run-up propagation to the coastline take only 31% of that probability.
顯示於類別:	[水文與海洋科學研究所] 博碩士論文

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