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

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.

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Diurnal to Seasonal Variations in Ocean Chlorophyll and Ocean Currents in the North of Taiwan Observed by Geostationary Ocean Color Imager and Coastal Radar

Remote Sensing ◽

10.3390/rs12172853 ◽

2020 ◽

Vol 12 (17) ◽

pp. 2853

Author(s):

Po-Chun Hsu ◽

Ching-Yuan Lu ◽

Tai-Wen Hsu ◽

Chung-Ru Ho

Keyword(s):

Seasonal Variations ◽

Chlorophyll Concentration ◽

Ocean Color ◽

Tidal Currents ◽

Ocean Currents ◽

Ocean Dynamics ◽

Northern Coast ◽

The North ◽

The Kuroshio ◽

Kuroshio Region

The waters in the north of Taiwan are located at the southern end of the East China Sea (ECS), adjacent to the Taiwan Strait (TS), and the Kuroshio region. To understand the physical dynamic process of ocean currents and the temporal and spatial distribution of the ocean chlorophyll concentration in the north of Taiwan, hourly coastal ocean dynamics applications radar (CODAR) flow field data and geostationary ocean color imager (GOCI) data are analyzed here. According to data from December 2014 to May 2020, the water in the TS flows along the northern coast of Taiwan into the Kuroshio region with a velocity of 0.13 m/s in spring and summer through the ECS. In winter, the Kuroshio invades the ECS shelf, where the water flows into the TS through the ECS with a velocity of 0.08 m/s. The seasonal variation of ocean chlorophyll concentration along the northwestern coast of Taiwan is obvious, where the average chlorophyll concentration from November to January exceeds 2.0 mg/m3, and the lowest concentration in spring is 1.4 mg/m3. It is apparent that the tidal currents in the north of Taiwan flow eastward and westward during ebb and flood periods, respectively. Affected by the background currents, the flow velocity exhibits significant seasonal changes, namely, 0.43 m/s in summer and 0.27 m/s in winter during the ebb period and is 0.26 m/s in summer and 0.45 m/s in winter during the flood period. The chlorophyll concentration near the shore is also significantly affected by the tidal currents. Based on CODAR data, virtual drifter experiments, and GOCI data, this research provides novel and important knowledge of ocean current movement process in the north of Taiwan and indicates diurnal to seasonal variations in the ocean chlorophyll concentration, facilitating future research on the interaction between the TS, ECS, and Kuroshio.

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Seasonal Variation of Space/Time Statistics of Short-Term Sea Surface Temperature Variability in the Kuroshio Region

Journal of Oceanography ◽

10.1007/s10872-005-0078-3 ◽

2005 ◽

Vol 61 (4) ◽

pp. 709-720 ◽

Cited By ~ 7

Author(s):

Kohtaro Hosoda ◽

Hiroshi Kawamura

Keyword(s):

Seasonal Variation ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Space Time ◽

Temperature Variability ◽

Sea Surface ◽

Short Term ◽

The Kuroshio ◽

Kuroshio Region

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Interannual variability of larval fish assemblages associated with water masses in winter in the Taiwan Strait during 2007–2013

Fisheries Science ◽

10.1007/s12562-020-01489-z ◽

2021 ◽

Author(s):

Yu-Kai Chen ◽

Chia-Yi Pan ◽

Yi-Chen Wang ◽

Hsiu-Ju Tseng ◽

Bo-Kun Su ◽

...

Keyword(s):

Fish Assemblages ◽

Larval Fish ◽

Taiwan Strait ◽

Assemblage Structure ◽

Sea Surface ◽

Coastal Current ◽

Annual Variations ◽

Frontal Zones ◽

The Taiwan Strait

AbstractIn this study, the interannual variations of ichthyoplankton assemblages in the Taiwan Strait (TS) during the winters of 2007–2013 were determined. The cold China Coastal Current (CCC) and Mixed China Coastal Water (MCCW) intruded into the TS and impinged with the warm Kuroshio Branch Current (KBC) with annual variations. Consequently, the ichthyoplankton community in the TS was mainly structured into two assemblages characterized by differing environmental conditions. The composition of the warm KBC assemblage was relatively stable and was characterized by Diaphus B and Bregmaceros spp. By contrast, the cold MCCW assemblage demonstrated considerable variations over the years, with demersal Gobiidae and Scorpaenidae families considered the most representative. In addition, Benthosema pterotum and Trichiurus spp. were common in both KBC and MCCW assemblages. The distribution of the KBC assemblage demonstrated sharp boundaries in the frontal zones, whereas changes in the assemblage structure between the frontal zones were gradual for the MCCW assemblage, particularly when demersal taxa were dominant. Sea surface temperature and salinity were most strongly associated with variability in the assemblage structure during the study period. Thus, this paper provides a better understanding of long-term larval fish dynamics during winter in the TS.

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Radiocesium in the Taiwan Strait and the Kuroshio east of Taiwan from 2018 to 2019

Scientific Reports ◽

10.1038/s41598-021-01895-y ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Wei-Jen Huang ◽

Ming-Ta Lee ◽

Kuei-Chen Huang ◽

Kai-Jung Kao ◽

Ming-An Lee ◽

...

Keyword(s):

Water Column ◽

Surface Waters ◽

Half Life ◽

North Pacific Ocean ◽

Taiwan Strait ◽

Depth Range ◽

Near Surface ◽

Activity Concentrations ◽

The Taiwan Strait ◽

The Kuroshio

AbstractThe release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling 137Cs (half-life, 30.2 year) and 134Cs (half-life, 2.06 year) activity concentrations in the Kuroshio east of Taiwan and the Taiwan Strait (latitude 20° N–27° N, longitude 116° E–123° E) remain unclear. This study collected seawater samples throughout this region and analyzed 134Cs and 137Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all 134Cs activity concentrations were below the detection limit (0.5 Bq m−3). Analyses of water column 137Cs profiles revealed a primary concentration peak (2.1–2.2 Bq m−3) at a depth range of 200–400 m (potential density σθ: 25.3 to 26.1 kg m−3). The PCA result suggests that this primary peak was related to density layers in the water column. A secondary 137Cs peak (1.90 Bq m−3) was observed in the near-surface waters (σθ = 18.8 to 21.4 kg m−3) and was possibly related to upwelling and river-to-sea mixing on the shelf. In the Taiwan Strait, 137Cs activity concentrations in the near-surface waters were higher in the summer than in the winter. We suggest that upwelling facilitates the vertical transport of 137Cs at the shelf break of the western NPO.

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Regional Defence

10.3366/edinburgh/9781474446228.003.0004 ◽

2020 ◽

pp. 66-100

Author(s):

Bhubhindar Singh

Keyword(s):

Taiwan Strait ◽

The North ◽

The Us ◽

Taiwan Strait Crisis ◽

The Taiwan Strait ◽

Nuclear Crisis

The chapter shows how the Japanese security policymaking elite utilised the North Korean Nuclear Crisis in 1993–4, the Taiwan Strait Crisis in 1996 and the Taepodong Crisis in 1999 to authorise the SDF to adopt a regional defence role within the US–Japan alliance.

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On the Interpretation of the North Atlantic Averaged Sea Surface Temperature

Journal of Climate ◽

10.1175/jcli-d-19-0158.1 ◽

2020 ◽

Vol 33 (14) ◽

pp. 6025-6045

Author(s):

Jing Sun ◽

Mojib Latif ◽

Wonsun Park ◽

Taewook Park

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

North Atlantic ◽

Climate Models ◽

Ocean Dynamics ◽

Sea Surface ◽

The North ◽

Sst Variability ◽

The North Atlantic ◽

Different Time Scales

AbstractThe North Atlantic (NA) basin-averaged sea surface temperature (NASST) is often used as an index to study climate variability in the NA sector. However, there is still some debate on what drives it. Based on observations and climate models, an analysis of the different influences on the NASST index and its low-pass filtered version, the Atlantic multidecadal oscillation (AMO) index, is provided. In particular, the relationships of the two indices with some of its mechanistic drivers including the Atlantic meridional overturning circulation (AMOC) are investigated. In observations, the NASST index accounts for significant SST variability over the tropical and subpolar NA. The NASST index is shown to lump together SST variability originating from different mechanisms operating on different time scales. The AMO index emphasizes the subpolar SST variability. In the climate models, the SST-anomaly pattern associated with the NASST index is similar. The AMO index, however, only represents pronounced SST variability over the extratropical NA, and this variability is significantly linked to the AMOC. There is a sensitivity of this linkage to the cold NA SST bias observed in many climate models. Models suffering from a large cold bias exhibit a relatively weak linkage between the AMOC and AMO and vice versa. Finally, the basin-averaged SST in its unfiltered form, which has been used to question a strong influence of ocean dynamics on NA SST variability, mixes together multiple types of variability occurring on different time scales and therefore underemphasizes the role of ocean dynamics in the multidecadal variability of NA SSTs.

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