Study of Kuroshio cut off by cyclonic eddy off eastern Taiwan

• Main Authors: Liu, Tsung-Ming, 劉宗銘
• Other Authors: Zheng, Zhe-Wen
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/4by79e

碩士 === 國立臺灣師範大學 === 地球科學系 === 107 === This research focus on the influence of cyclonic eddy on Kuroshio on outer region of eastern Taiwan sea. According to data of satellite altimeter, during the study period (January 1993 to April 2016), cyclonic eddy moved westward to the outer region of eastern Taiwan sea (123°E) for 18 times, among eight of them. When there is Kuroshio intrusion at Luzon Strait. The eddy westward path can be roughly divided into these three types: (1) moves from east of Luzon Island to northwest (18°N~20°N) (2) moves from east of Luzon Strait to west (20°N~22°N) (3) moves westward from Taiwan eastern sea (22°N~23°N). This study focus on the third cyclonic eddy moving path: a further analysis on west moving cyclonic eddy event at outer eastern region of Taiwan sea, and found that when the cyclonic eddy moves westward to 123°E, the Kuroshio met a cyclonic eddy, it results a decrease in velocity for the flow of Kuroshio. Followed by an intrusion into the Luzon Strait at upstream of Kuroshio, and occurs a clockwise eddy in the southwest of Taiwan. The other part of the Kuroshio flows eastward, and then northward when it flows along the cyclonic eddy counterclockwise, attaining a same result as Kuo & Chern (2011). When the cyclonic eddy is transmitted from the east to the west of the Kuroshio, and move westward to the longitude of 123°E, the vorticity of the cyclonic eddy begins to weaken, which may be influenced by a northward flowing Kuroshio, results it to move northward, according to definition by Liang et al. (2003), where the boundary for east of Kuroshio is 123°E. After further simulation using ROMS model (Regional Ocean Modeling System), a same result appeared that the eddy at east coast of Taiwan weakened, when met Kuroshio and appeared the phenomenon of intrusion into Luzon Strait at upstream of Kuroshio. A clockwise eddy was also found in the southwest of Taiwan. From the geostrophic field output by ROMS model, the vorticity calculated for Luzon Strait shows when the cyclonic eddy collides Kuroshio, the vorticity value increases significantly, so the changes could be concluded that the vorticity is influenced by the intrusion of Kuroshio into the Luzon Strait. Furthermore, the vorticity change could be used to explain the phenomenon of Kuroshio intrusion into Luzon Strait. When the west shifted cyclonic eddy met Kuroshio, resulted Kuroshio has a weakened northward flow on east coast of Taiwan, which in turn weakens the velocity of Kuroshio flow on the eastern side of the Luzon Strait. The vorticity in Luzon Strait area changes (positive vorticity becomes smaller), in order to maintain the conservation vorticity of in the region, and so when westward Kuroshio moves in and invades Luzon Strait too (positive vorticity increases).