[A-OS12] Ocean Science Revealed by Global Observation System

[AOS12-P07] Observations of Surface Currents of Nanwan Bay Using High Frequency Radar

*Shaohua Chen^1,2, Ying-Chih Fang², Shi-Ming Chen¹ (1.Taiwan Ocean Research Institute, National Applied Research Laboratories, 2.Department of Oceanography, College of Marine Sciences, National Sun Yat-sen University)

Keywords:HF radar, Nanwan Bay, Surface Current Mapping

The Taiwan Ocean Research Institute (TORI) has maintained and operated an around-Taiwan high-frequency radar (HFR) network since 2009. There are 3 HFRs covering Nanwan Bay providing hourly surface current observations with a spatial resolution of 1 km and a maximum range of 40 km offshore, with records from 2014 to date. This study analyzes this high-resolution HFR-derived surface current data to understand the characteristics of ocean circulation, seasonal variations, and tidal current patterns in the bay. Surface currents there are primarily driven by a mixture of diurnal and semidiurnal tides. The surface tidal currents are eastward during the ebb phase and westward during the flood phase. The dominant tidal constituents are the semidiurnal M₂ and diurnal K₁ and O₁ components, which exhibit stronger semidiurnal energy during spring, summer, and autumn. In winter, however, the situation changes with the K₁ component developing greater energy. Tidal kinetic energy (KE) spatial distribution in summer months encompasses one regional low inside the bay and another low near the southern flank of the radar footprint. Areas farther offshore contain tidal KEs about 5 times larger than these low areas. In addition, spatial distribution of KE of the mean flow is not consistent with the tidal component in the different seasons, suggesting processes other than tides are in play. These results underscore the seasonal dynamics of Nanwan Bay and highlight the importance of high-resolution radar data in understanding coastal circulation patterns.