西北太平洋渦旋偵測與統計分析

Abstract

西北太平洋渦漩的生成與傳遞，不僅影響了該區域的海高變化，也會影響到海洋生地化作用。本研究利用20年(1993-2012) 的衛星高度計資料，對此區域中尺度渦漩進行偵測，並且根據渦旋特性進行一系列相關統計。結果顯示，在此區域中，暖渦數量(16435) 明顯多於冷渦的數量(12333) ，除了在北緯19-21°範圍之內(冷渦數量多於暖渦數量)，暖渦主導了大部分的海域。一般而言，冷渦半徑稍大於暖渦半徑，兩者皆在20°N達到最大，並向南北逐漸減少，另外，暖渦之中心海表面高度異常變化 (Sea Level Anomaly, SLA) 平均較大於冷渦，並且隨經度向西增加，在黑潮附近達到最大，同樣地，渦旋受到向西傳播的影響，在黑潮附近數量最多，而渦旋動能(EKE)明顯在台灣東部海域為高值，主要是受到渦旋數量及中心SLA變化的影響。季節上，除了渦旋中心SLA外，冷暖渦之間差異不大。進一步分析渦旋的傳播，渦旋的平均移動速度為8.3cm/s，主要朝著西方移動，冷暖渦分別向北及向南偏轉，最後受到黑潮的阻隔，在此速度減弱，甚至消散。渦旋的傳播不僅受到背景的影響，冷暖渦獨特的性質更會造成傳播上的差異，根據傳播的統計結果，顯示暖渦擁有更完整的發展過程在長生命週期上，隨著季節的不同，冷暖渦傳播特性的差異更會影響到進入台灣東部海域的渦旋路徑。Acvity eddiesin the Northwestern Subtropical Pacific Ocean affects not only the sea surface height change in the region but also marine dynamic and biogeochemical processes. In this study, by using 20 years(1993-2012) satellite altimeter data, eddies generated within this region were detected and their stastic characteristic were analyzed. The result showed that ther are totally 12,333 cyclonic eddies(CEs) and 16,435 anticyclonic eddies(AEs)generated during this period. The number of AEs is significantly more than the number of CEs. AEs dominated the most area except the region between 19 ° N and 21 ° N that was dominated by CEs. The radius of CEs is slightly larger than those of AEs. Radius of both AEs and CEs reaches the maximum at 20 ° Nand gradually decreases southwardly and northwardly. In addition, the variation of the center Sea Level Anomaly(SLA) of AEs is stronger than CEs. The variations of SLA increased gradually westernedly. Maximum SLA appeared near the western boundary(Kuroshio). Meanwhile,with westward propagation of those eddies, energy carried by those eddies accumulated gradually near the Kuroshio. EKE dominated by eddy number and eddy center SLA shows a significantly high value near the off east coast of Taiwan. Furthermore, we analyze the characteristics of eddy propagation, most eddies propagate westward with a mean speed of 8.3cm/s. with and southward deflection for Cyclonic (anticyclonic) eddies propograted slightly northward (sothward), respectively. Finally, eddies were blocked by Kuroshio and thus weaken, or even disappear. Including local background conditions and individual properties of cyclonic and anticyclonic eddies all may cause changes of their propogration. Acoording to their propagation, it shows that AEs has a more complete development process with longer life time. The seasonal variations of proprogated chacterisitcs of AEs and CEs also affect the pathways of eddies entering into the east coast of Taiwan.