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  • 學位論文

東北季風期間黑潮入侵東海南部陸棚對臺灣東北部海岸水溫及水位之影響及其動力現象之探討

Influences of the Wintertime Kuroshio Intrusion on the Temperature and Sea Level along the Northeastern Coast of Taiwan and the Investigation of Its Dynamics

指導教授 : 詹森
共同指導教授 : 陳世楠(Shih-Nan Chen)

摘要


本研究分析佈放於彭佳嶼、草里、馬崗及南方澳溫壓測站資料,經過截斷頻率1/20 day-1的低通濾波處理後,發現於東北季風盛行期(10-4月)彭佳嶼測站會發生兩次異常增溫現象,草里、馬崗及南方澳則僅發生一次。配合衛星影像資料SST、SSTA、SSH、地轉流及SLA,與氣象測站之平均風速風向和平均氣溫資料,及浮標軌跡和CTD資料等來探討因不同的黑潮入侵現象而造成沿岸測站低頻水溫及水位變動的特性及可能的動力機制。 彭佳嶼每年東北季風盛行期發生的兩次低頻異常增溫現象,配合平均浮標軌跡及平均SLA結果推論可能對應是兩個不同類型之黑潮入侵現象,第一類現象發生期間通常為10-12月,黑潮表層流左側先向臺灣東北海岸靠近,入侵陸棚的區域位於彭佳嶼東北方,屬小規模入侵現象,原因為強勁持續的東北季風,引致海洋上層的艾克曼輸送使黑潮偏向西北方發生入侵陸棚的現象,僅彭佳嶼觀測到明顯的異常增溫現象,蘇澳站水位反應較彭佳嶼早。第二類現象發生在12-3月間,約由棉花峽谷及北棉花峽谷間上陸棚,屬大規模入侵現象,原因為北方冷空氣南移,陸棚水持續冷卻而下沉,另方面黑潮在宜蘭海脊南端混合層因東北季風造成的攪拌致厚度加大,使得黑潮流經宜蘭海脊後往北至沖繩海槽易發生渦管拉伸現象,由正相對渦度帶動表層海流逆時針轉而產生大規模入侵的現象,因入侵區域距彭佳嶼較近,而後黑潮表層暖水往沿岸擴大,彭佳嶼站水位較蘇澳站早反應,水溫反應順序為彭佳嶼、馬崗、草里及南方澳,其中馬崗及草里僅供參考,原因為可能受近岸水團、臺灣海峽水或大陸沿岸流的多種影響。

並列摘要


This study utilizes the sea level and temperature data from four tide gauge stations in the northeastern coast of Taiwan (Pengjiayu, Caoli, Magang, and Nanfan-Ao) and satellite remote sensing data to analyze the wintertime Kuroshio intrusion onto the East China Sea shelf. The low-pass filtered temperature (cutoff frequency at 1/20 day-1) shows two temperature anomalies at Penjiayu during the northeasterly monsoon period. The temperature increase anomalies range between 0.5 and 2.5℃ with a period of about 3 to 10 weeks. The temperature anomalies are linked to the shelf intrusion of the Kuroshio, which could be related to two different processes. The first process occurs between October and December, which is attributed to the monsoon-driven, northwestward Ekman drift of the Kuroshio. This type of intrusion is classified as small scale with a relatively short cross shelf penetration and causes temperature rise only at Penjiayu. The low-pass filtered sea level variations were observed at several stations with Su-Ao sea level reacting prior to Penjiayu. The second process occurred during December and March is a larger scale intrusion, beginning at an area between Mien-Hua Canyon and North Mien-Hua Canyon before the warm water of the Kuroshio moves towards the northern coast of Taiwan. This Kuroshio intrusion should be caused by the density difference between the mixed layer of the Kuroshio south of I-Lan Ridge and that of the East China Sea, where shelf water becomes denser and then subsided after extended periods of atmospheric cooling. The thickening of the mixed layer south of I-Lan Ridge, on the other hand, enhances water column compression and stretching over the ridge and the deep Okinawa Trough, respectively, and thus causes cyclonic intrusion onto the shelf due to the relatively vorticity disturbance.

參考文獻


Stephen Pond and George L. Pickard (1983), Introductory Dynamical Oceanography, 2nd ed., Butterworth Heinemann, Inc., 266–267 pp.
Benoit Cushman-Roison (2006), Introduction to geophysical fluid dynamics, 2nd ed., Prentice-Hall, Inc., 185-186 pp.
Chao S.-Y. (1991), Circulation of the East China Sea, a numerical study, J. Oceanogr., 42, 273–295.
Chern C.-S., and J. Wang (1990), On the mixing of waters at a northern offshore area of Taiwan, Terrestrial Atmospheric and Oceanic Sciences, 1(3), 297–306.
Chern C.-S. and J. Wang (1992b), On the seasonal variation of the Kuroshio intrusion onto the East China Sea, Acta Oceanographica Taiwanica, 29, 1–17.

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