高頻雷達觀測臺灣西南海域冬季表面流路徑

Pathways of the surface current off southwest Taiwan in winter : Observations from HF Radar

汪威(Wei Wang)

指導教授 ： 楊穎堅

共同指導教授 ： 詹森

國立臺灣大學/理學院/海洋研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.00949

摘要

分析國家實驗研究院臺灣海洋科技研究中心之高頻測流雷達系統於2013年11月至2014年2月期間的觀測資料，研究臺灣西南海域冬天期間表面流場的變化。研究結果發現表面流場有一些的短期變化，其中值得注意的是2013年11月期間，澎湖群島南方附近進入週期十數天的逆鐘向旋轉流場，以及在2014年1至2月於高雄及安平外海形成週期十數天的順鐘向旋轉流場。
利用實向量經驗正交函數(Real-vector Empirical Orthogonal Function, REOF)分析測流雷達的觀測資料，可得到三個主要模態，其總變異量約為臺灣西南海域變異量之74 %；Mode1呈現高雄及安平外海為順鐘向流場結構且與呂宋海峽西側海面高度變化有關；Mode2呈現臺灣西南海域為南北向海流進出澎湖水道的流場結構；而Mode3則是呈現澎湖群島南方附近海域東北-西南走向的流場結構，並與此區域東北風變化有關。
此外，Mode2與Mode3相互結合，可得到臺灣西南海域有傳播模態(Propagating mode)現象發生。主要傳播模態現象為在澎湖群島與高雄及安平外海之間，持續週期約10-15天，間歇性的產生順鐘向或逆鐘向旋轉流場，而其傳遞方向由Mode2與Mode3之相位軌跡判斷。如果相位軌跡為順鐘向，代表東北風增強期間會弱化觀測區內的北上海流，致使澎湖群島南方附近產生逆鐘向的旋轉流場，並往高雄及安平外海傳遞。當相位軌跡為逆鐘向，代表東北風減弱使臺灣西南海域南方與澎湖群島南方海域的海流分別呈現往南與東北向之流場結構，使高雄及安平外海產生順鐘向旋轉流場，並往澎湖群島南方海域傳遞。

關鍵字

臺灣西南海域 ； 表面海流 ； 高頻測流雷達

並列摘要

Variations of the surface currents in the sea Southwest of Taiwan (SWT) were investigated by High Frequency Radar (HF Radar), which had measured surface currents from Nov. 2013 to Feb. 2014. Several short-term changes in surface currents have been found. One notable change is that the rotating currents have produced with a period for about ten days between the Anping-Kaohsiung and Penghu Islands. For example, the cyclonic rotation currents were found in Nov. 2013 whereas the anti-cyclonic rotation currents were found in Jan. 2014 to Feb. 2014.
Using Real-vector empirical orthogonal function (REOF) to analyze surface currents in the SWT has revealed that almost 74 % of total variances of currents in first three modes. A large clockwise current structure was presented near Anping-Kaohsiung coast in Mode1, which indicated that surface currents have changed with sea surface high of west side of Luzon Strait. Surface currents were showed northward current structure in the SWT in Mode2. Surface currents were showed northeastward current structure in the South of Penghu Islands in Mode3, which was affected by the northeast monsoon in this area.
In addition, when Mode2 and Mode3 combined with each other, they can obtain a propagating mode in the SWT. The main propagating features propagated cyclonic or anti-cyclonic rotation currents between the Anping-Kaohsiung and Penghu Islands. The propagating direction was determined by the phase trajectory of mode amplitude in the Mode2 and Mode3. If phase trajectory was clockwise, the strong NE monsoon would counter the northward current in the SWT. The results in the South of the Penghu Islands have produced the cyclonic rotation currents, and have propagated to the coast of Anping-Kaohsiung. When the phase trajectory was counterclockwise, and the NE monsoon weakened, southward and northeastward current structure was presented in the Southern of SWT and South of Penghu Islands respectively. The results near the coast of Anping-Kaohsiung have produced the anti-cyclonic rotation currents, and have propagated to the South of the Penghu Islands.

並列關鍵字

Sea southwest of Taiwan ； Surface currents ； HF Radar

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