Characteristic Analysis of Sea Surface Currents around Taiwan Island from CODAR Observations

Yu-Hao Tseng,Quanan Zheng,Chung-Ru Ho,Ching-Yuan Lu

doi:10.3390/rs13153025

Abstract

Sea surface currents observed by high-frequency (HF) radars have been widely used in ocean circulation research. In this study, hourly sea surface currents observed by the Taiwan Coastal Ocean Dynamics Applications Radar (CODAR) system from 2015 to 2019 were analyzed by the empirical orthogonal function (EOF) analysis to reveal the characteristics of the sea surface currents around Taiwan Island. The study area is divided into two regions, the Kuroshio region east of Taiwan Island and the Taiwan Strait west of Taiwan Island. In the Kuroshio region, the first EOF mode shows that the Kuroshio is characterized by higher current speeds with greater variability in summer. The second and third EOF modes present a dipole eddy pair and single eddy impingement on the Kuroshio during different periods. The seasonal variation of the dipole eddy pair indicates that the cyclonic/anticyclonic eddy on the north/south side appears more frequently in summer. Single eddy impingement occurs at multiple periods, including daily, intraseasonal, interseasonal, and annual periods. For the Taiwan Strait, the first EOF mode displays the tide signals. The tides enter the Taiwan Strait from the north and south, forming strong sea surface currents around the northern tip of Taiwan Island and the Penghu Archipelago. The second EOF mode exhibits the seasonal changes of the sea surface currents driven by the monsoon winds. The sea surface currents in the northern Taiwan Strait are relatively strong, possibly due to the narrow and shallow terrain there. The high spatiotemporal resolution of sea surface currents derived from CODAR observations provide more detailed characteristics of sea surface circulation around Taiwan Island.

Highlights

Taiwan Island is located in the southwest region of the North Pacific Ocean
The high spatiotemporal resolution of sea surface currents derived from Coastal Ocean Dynamics Application Radar (CODAR) observations provide more detailed characteristics of sea surface circulation around Taiwan Island
In the east of Taiwan Island, the Kuroshio, as a western boundary current in the North Pacific, is featured by a width of about 200 km, seasonal flow patterns with the surface velocity in excess of 1.0 m/s, and interactions with westward-propagating mesoscale eddies originating from the Subtropical Counter Current [1,2,3,4,5]

Summary

Introduction

The sea surface currents that surround the island manifest complex spatiotemporal variability. Understanding their variations is important for navigational safety, search and rescue, and all marine resources development industries. In the east of Taiwan Island, the Kuroshio, as a western boundary current in the North Pacific, is featured by a width of about 200 km, seasonal flow patterns with the surface velocity in excess of 1.0 m/s, and interactions with westward-propagating mesoscale eddies originating from the Subtropical Counter Current [1,2,3,4,5]. Radar theory was developed [13], lowing the theory, further high-frequency (HF) radar theory was developed [13], andand twotwo-dimensional ocean diagrams. 3–10 MHz are used by long-range radars, and

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Results

Conclusion