The variations of current on Green Island Ridge in the southeast of Taiwan
Date Issued
2014
Date
2014
Author(s)
Lin, Ting-Chun
Abstract
Kuroshio is the major current flowing through the east of Taiwan, which is originated from the North Equatorial current between 10 degrees to 20 degrees north latitude.When the North Equatorial current flows westward to the east of Philippines, it is divided into north and south branch.The north branch is the Kuroshio,and it flows along the east coast of Philippines and then truns northward to the Luzon Strait to the east of Taiwan. There were few mooring observations of the current in the southeast of Taiwan in previous studies. In this study, we used five Acoustic Doppler Current Profiler which set up on the northwest of Green Island from May 2011 to August 2012,to explore the variation of this current in the southeast of Taiwan. The current velocity data showed that the current flow is north north east at the S1 station which is near to Green Island. The velocity of the northward current can reach 2.26 m/s. Similarly, the current flow is northeast at the S5 station which is close to Taiwan, and it is parallel to the coastline of east Taiwan, and the velocity of the northward current can reach 1.77 m/s . Using Spectrum analysis to study the velocity data, the results showed of O1、K1、M2 tidal currents in this area significantly. The vertical structure of each tidal currents also showed that the tidal currents in this area are containing the barotropic tide and baroclinic tide.This study discussed the barotropic tide and baroclinic tide by depth-average separating. The results showed that the 1st baroclinic mode and 2nd baroclinic mode dominated. Further this study analyzed the current by using the sixteen days low pass filter to filter the tidal signals which are relative high frequency. After low pass filter, the current displays many of the intraseasonal variations of the low frequency.This study defined the north velocity changes more than 0.1 m/s for the event during two months. Sumed up the observation in a total of 15 consecutive months which across the summer and winter, there are 5 velocity enhancing events and 3 velocity decreasing events. Using the satellite altimetry data sea level anomaly to distinguish eddies and to study the currents on the horizontal space. The results showed that there were four times events contacted with the warm eddy within five enhancing events and two times events contacted with the cold eddy within three decreasing events. In addition, the velocity enchancing events and the decreasing events were also contacted with the path of Kuroshio shifted to the Pacific Ocean or the invasion of the South China Sea. The eddies not only changed the velocity but also change the hydrology of the vertical structure and then changed the baroclinic tidal currents.
Subjects
Kuroshio
Mooring observations
Southeast of Taiwan
sea level anomaly
tidal current
Type
thesis
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