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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.
Po-Chun Hsu; Ching-Yuan Lu; Tai-Wen Hsu; Chung-Ru Ho. 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 2020, 12, 2853 .
AMA StylePo-Chun Hsu, Ching-Yuan Lu, Tai-Wen Hsu, Chung-Ru Ho. 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. 2020; 12 (17):2853.
Chicago/Turabian StylePo-Chun Hsu; Ching-Yuan Lu; Tai-Wen Hsu; Chung-Ru Ho. 2020. "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 12, no. 17: 2853.
Tidal current‐induced cyclonic eddies cause cold‐water upwelling and periodic sea surface temperature (SST) drops around the coral reef area in Nanwan Bay, which is located at the southern tip of Taiwan. This study used Himawari‐8 satellite data and tide gauge and coastal ocean dynamics application radar (CODAR) data to analyze the characteristics of the SST drops and cyclonic eddy propagation and used an oceanic general circulation model (OGCM) to simulate the tidal current flowing process. According to the CODAR data analysis, the mixed primary semidiurnal tide had an average current velocity of 0.3–0.4 m s‐1 throughout the bay, and the average life cycle of a cyclonic eddy is 6.6 hr, with a propagation speed of 0.35 m s‐1. The SST drop during the spring tide period was greater than that during the neap tide period, and the SST dropped in both summer and winter. The average daily SST drop in the summer reached 2 °C with a maximum observed value of 4.7 °C, and the SST drop rate was 0.3–0.5 °C hr‐1. The annual mean chlorophyll‐a concentration was 0.25 mg m‐3. This study explored the special properties of the Nanwan Bay coral reef area from the perspective of ocean physics to allow ecologists to facilitate the implementation of long‐term conservation and monitoring programs.
Po‐Chun Hsu; Hung‐Jen Lee; Quanan Zheng; Jian‐Wu Lai; Feng‐Chun Su; Chung‐Ru Ho. Tide‐Induced Periodic Sea Surface Temperature Drops in the Coral Reef Area of Nanwan Bay, Southern Taiwan. Journal of Geophysical Research: Oceans 2020, 125, 1 .
AMA StylePo‐Chun Hsu, Hung‐Jen Lee, Quanan Zheng, Jian‐Wu Lai, Feng‐Chun Su, Chung‐Ru Ho. Tide‐Induced Periodic Sea Surface Temperature Drops in the Coral Reef Area of Nanwan Bay, Southern Taiwan. Journal of Geophysical Research: Oceans. 2020; 125 (4):1.
Chicago/Turabian StylePo‐Chun Hsu; Hung‐Jen Lee; Quanan Zheng; Jian‐Wu Lai; Feng‐Chun Su; Chung‐Ru Ho. 2020. "Tide‐Induced Periodic Sea Surface Temperature Drops in the Coral Reef Area of Nanwan Bay, Southern Taiwan." Journal of Geophysical Research: Oceans 125, no. 4: 1.
Dynamics of ocean current-induced island wake has been an important issue in global oceanography. Green Island, a small island located off southeast of Taiwan on the Kuroshio path was selected as the study area to more understand the spatial structure and temporal variation of well-organized vortices formed by the interaction between the Kuroshio and the island. Sea surface temperature (SST) and chlorophyll-a (Chl-a) concentration data derived from the Himawari-8 satellite and the second generation global imager (SGLI) of global change observation mission (GCOM-C) were used in this study. The spatial SST and Chl-a variations in designed observation lines and the cooling zone transitions on the left and right sides of the vortices were investigated using 250 m spatial resolution GCOM-C data. The Massachusetts Institute of Technology general circulation model (MITgcm) simulation confirmed that the positive and negative vortices were sequentially detached from each other in a few hours. In addition, totals of 101 vortexes from July 2015 to December 2019 were calculated from the 1-h temporal resolution Himawari-8 imagery. The average vortex propagation speed was 0.95 m/s. Totals of 38 cases of two continuous vortices suggested that the average vortex shedding period is 14.8 h with 1.15 m/s of the average incoming surface current speed of Green Island, and the results agreed to the ideal Strouhal-Reynolds number fitting curve relation. Combined with the satellite observation and numerical model simulation, this study demonstrates the structure of the wake area could change quickly, and the water may mix in different vorticity states for each observation station.
Po-Chun Hsu; Chia-Ying Ho; Hung-Jen Lee; Ching-Yuan Lu; Chung-Ru Ho. Temporal Variation and Spatial Structure of the Kuroshio-Induced Submesoscale Island Vortices Observed from GCOM-C and Himawari-8 Data. Remote Sensing 2020, 12, 883 .
AMA StylePo-Chun Hsu, Chia-Ying Ho, Hung-Jen Lee, Ching-Yuan Lu, Chung-Ru Ho. Temporal Variation and Spatial Structure of the Kuroshio-Induced Submesoscale Island Vortices Observed from GCOM-C and Himawari-8 Data. Remote Sensing. 2020; 12 (5):883.
Chicago/Turabian StylePo-Chun Hsu; Chia-Ying Ho; Hung-Jen Lee; Ching-Yuan Lu; Chung-Ru Ho. 2020. "Temporal Variation and Spatial Structure of the Kuroshio-Induced Submesoscale Island Vortices Observed from GCOM-C and Himawari-8 Data." Remote Sensing 12, no. 5: 883.
When the Kuroshio passes Green Island off Taiwan, well-organized wakes are formed by the interaction between the Kuroshio and the island. The vertical mixing in the wake produces cold water, which entrains from the mixed layer below the surface and results in relatively colder and saltier waters with a higher chlorophyll-a concentration on the sea surface to the lee of the island. The meander of the Kuroshio maximum velocity axis has a major influence on the island wake. The shift of the Kuroshio in front of Green Island not only weakens the flow velocity but also affects the development of the wake. In the Green Island wake, the density overturns with a Thorpe scale between 2.9 m and 20.5 m and the turbulent kinetic energy dissipation rate is 0.2×10−6–8.5×10−5 Wkg−1, which corresponds to an eddy diffusivity in the range of 0.01–0.23 m2s−1. The spatial distribution patterns of the sea surface temperature (SST) in the island wake are classified into four distinct types, as obtained from moderate-resolution imaging spectroradiometer (MODIS) SST images. The most frequently occurring type is of the wake alone, which accounts for 86.7% of the island wake patterns. The other three types are a wake with a tail stretching downstream (4.0%), a wake with a small cyclonic cold core but no tail stretching downstream (6.8%) and an S-shaped meandering wake (2.5%).
Po-Chun Hsu; Kai-Ho Cheng; Sen Jan; Hung-Jen Lee; Chung-Ru Ho. Vertical structure and surface patterns of Green Island wakes induced by the Kuroshio. Deep Sea Research Part I: Oceanographic Research Papers 2018, 143, 1 -16.
AMA StylePo-Chun Hsu, Kai-Ho Cheng, Sen Jan, Hung-Jen Lee, Chung-Ru Ho. Vertical structure and surface patterns of Green Island wakes induced by the Kuroshio. Deep Sea Research Part I: Oceanographic Research Papers. 2018; 143 ():1-16.
Chicago/Turabian StylePo-Chun Hsu; Kai-Ho Cheng; Sen Jan; Hung-Jen Lee; Chung-Ru Ho. 2018. "Vertical structure and surface patterns of Green Island wakes induced by the Kuroshio." Deep Sea Research Part I: Oceanographic Research Papers 143, no. : 1-16.
The interaction of coastal water in I-Lan Bay, a bay near northeast Taiwan, and the Kuroshio Current is studied using the data from hydrologic survey and satellite remote sensing. An index for water mass distinguished is used for clarifying the origin of water mass in I-Lan Bay. The velocity profile from acoustic Doppler current profile data indicates a countercurrent that flows southward along the northeast coast of Taiwan toward I-Lan Bay with a speed around 0.1–0.2 m/s. The index of water mass indicates that the water of I-Lan Bay is mainly affected by the northern shelf waters of Taiwan and mixed with Kuroshio nearshore water, thus forming a clear ocean front between these two areas. The near surface water temperature in the I-Lan Bay is about 2 °C lower than that in the Kuroshio region. The seasonal average near surface salinity of I-Lan Bay can exist 0.4 psu fresher than the Kuroshio area. From the analysis of dynamic process, the coastal countercurrent in I-Lan Bay is primarily affected by 1) the occurrence of cold dome in northeast of Taiwan mainly occurs in summer, and 2) the wind-driven current from the Taiwan Strait along the north coast and the northeast coast of Taiwan caused by the southwesterly monsoon makes the countercurrents strongly in summer. The dynamics of the countercurrent occurrence can be explained by the Ekman transport theory.
Po-Chun Hsu; Quanan Zheng; Ching-Yuan Lu; Kai-Ho Cheng; Hung-Jen Lee; Chung-Ru Ho. Interaction of coastal countercurrent in I-Lan Bay with the Kuroshio northeast of Taiwan. Continental Shelf Research 2018, 171, 30 -41.
AMA StylePo-Chun Hsu, Quanan Zheng, Ching-Yuan Lu, Kai-Ho Cheng, Hung-Jen Lee, Chung-Ru Ho. Interaction of coastal countercurrent in I-Lan Bay with the Kuroshio northeast of Taiwan. Continental Shelf Research. 2018; 171 ():30-41.
Chicago/Turabian StylePo-Chun Hsu; Quanan Zheng; Ching-Yuan Lu; Kai-Ho Cheng; Hung-Jen Lee; Chung-Ru Ho. 2018. "Interaction of coastal countercurrent in I-Lan Bay with the Kuroshio northeast of Taiwan." Continental Shelf Research 171, no. : 30-41.
Underwater gliders are used to investigate the variations on the ocean surface and subsurface during the 14 typhoons that passed over the Kuroshio region near Taiwan in 2010–2013. Typhoon-induced subsurface layer warming, which was formed on the basis of the heat pump effect of the vertical mixing process, is observed in this study. In addition, the gliders observe the variations in salinity during the passage of the typhoons. Typhoons, accompanied by heavy rainfall, introduce a considerable amount of fresh water into the upper ocean, diluting the surface salinity. The diluted salinity accompanied deepening of the mixed layer which moved downward to the subsurface by vertical mixing, supplying fresh water to both the surface and subsurface layers. Additionally, because of vertical mixing, maximum temperature variations occur at the bottom of the mixed layer or at a level deeper than the mixed layer. Changes of the heat content show that a series of vertical mixing events occurs in the upper ocean. Pairs of salinity profiles indicate comprehensive vertical mixing in the upper ocean and yield schematics to compare typhoons with or without heavy rainfall. Higher sustained wind speeds may contribute to a considerable drop in sea surface temperature, but possibly not to the magnitude of the subsurface warming. The upper ocean thermocline gradient before a typhoon is an important factor to determine the magnitude of subsurface warming. This study concludes a glider observational result that typhoons cause subsurface layer warming and freshening in the Kuroshio region near Taiwan.
Po-Chun Hsu; Chung-Ru Ho. Typhoon-induced ocean subsurface variations from glider data in the Kuroshio region adjacent to Taiwan. Journal of Oceanography 2018, 75, 1 -21.
AMA StylePo-Chun Hsu, Chung-Ru Ho. Typhoon-induced ocean subsurface variations from glider data in the Kuroshio region adjacent to Taiwan. Journal of Oceanography. 2018; 75 (1):1-21.
Chicago/Turabian StylePo-Chun Hsu; Chung-Ru Ho. 2018. "Typhoon-induced ocean subsurface variations from glider data in the Kuroshio region adjacent to Taiwan." Journal of Oceanography 75, no. 1: 1-21.
Po-Chun Hsu; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. Satellite observations of rainfall effect on sea surface salinity in the waters adjacent to Taiwan. Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions 2017 2017, 39 .
AMA StylePo-Chun Hsu, Chen-Chih Lin, Shih-Jen Huang, Chung-Ru Ho. Satellite observations of rainfall effect on sea surface salinity in the waters adjacent to Taiwan. Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions 2017. 2017; ():39.
Chicago/Turabian StylePo-Chun Hsu; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. 2017. "Satellite observations of rainfall effect on sea surface salinity in the waters adjacent to Taiwan." Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions 2017 , no. : 39.
Po-Chun Hsu; Ming-Huei Chang; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. Investigation of the island-induced ocean vortex train of the Kuroshio Current using satellite imagery. Remote Sensing of Environment 2017, 193, 54 -64.
AMA StylePo-Chun Hsu, Ming-Huei Chang, Chen-Chih Lin, Shih-Jen Huang, Chung-Ru Ho. Investigation of the island-induced ocean vortex train of the Kuroshio Current using satellite imagery. Remote Sensing of Environment. 2017; 193 ():54-64.
Chicago/Turabian StylePo-Chun Hsu; Ming-Huei Chang; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. 2017. "Investigation of the island-induced ocean vortex train of the Kuroshio Current using satellite imagery." Remote Sensing of Environment 193, no. : 54-64.
In this study, satellite sea surface temperature (SST) dataset is used to study the wakes formed by the Kuroshio flows past Green Island, a small island located off southeast of Taiwan. Satellite thermal Infrared Imagery usually has missing data due to cloud coverage. This situation is difficult for further analyzing. To fill up the missing data and to obtain long-term information, Data Interpolating Empirical Orthogonal Functions is used in the study. These SST images without missing data are then analyzed by the Empirical Orthogonal Function (EOF) method. The first EOF mode explains 99.95% of the total variance and clearly shows a cooling area behind Green Island. Using the gradient EOF method, each mode indicates different wake features, including direction, range, and extended length of the wake. During the data period, the percentage of the wake occurrence was 59%. The average cooling SST was about 0.91±0.15°C. For the extended range of the island wake, there is 63% shorter than 20 km, and only 8% longer than 30 km. In addition, the wake area has 1–3 times higher than surrounding area in chlorophyll-a concentration due to the island mass effect.
Kai-Ho Cheng; Chung-Ru Ho; Po-Chun Hsu. Analyses of Green Island wake caused by Kuroshio from satellite imagery. 2016 Techno-Ocean (Techno-Ocean) 2017, 109 -112.
AMA StyleKai-Ho Cheng, Chung-Ru Ho, Po-Chun Hsu. Analyses of Green Island wake caused by Kuroshio from satellite imagery. 2016 Techno-Ocean (Techno-Ocean). 2017; ():109-112.
Chicago/Turabian StyleKai-Ho Cheng; Chung-Ru Ho; Po-Chun Hsu. 2017. "Analyses of Green Island wake caused by Kuroshio from satellite imagery." 2016 Techno-Ocean (Techno-Ocean) , no. : 109-112.
Satellite remote-sensing data and glider data are used to study the Kuroshio meander and surface properties, east of Taiwan. The Kuroshio meandered eastward 13 times between 1993 and 2013 because of cold eddies propagating from the western Pacific. The maximum duration of the meanders was 80 days. The farthest eastward shift of the Kuroshio axis was approximately 270 km from its original position, depending on the size of the cold eddy. Cold eddies reduce the current speed at the Kuroshio axis to 84% of its seasonal average, which is approximately 0.75 m/s. According to glider data, isopycnal uplifting is produced when cold eddies impinge on the Kuroshio, and satellite observations show that the sea surface temperature (SST) drops 1-3 °C and that the chlorophyll-a (chl-a) concentration increases up to 0.54 mg/m 3 .
Po-Chun Hsu; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. Effects of Cold Eddy on Kuroshio Meander and Its Surface Properties, East of Taiwan. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 2016, 9, 5055 -5063.
AMA StylePo-Chun Hsu, Chen-Chih Lin, Shih-Jen Huang, Chung-Ru Ho. Effects of Cold Eddy on Kuroshio Meander and Its Surface Properties, East of Taiwan. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 2016; 9 (11):5055-5063.
Chicago/Turabian StylePo-Chun Hsu; Chen-Chih Lin; Shih-Jen Huang; Chung-Ru Ho. 2016. "Effects of Cold Eddy on Kuroshio Meander and Its Surface Properties, East of Taiwan." IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 9, no. 11: 5055-5063.
The HadISST (Hadley Centre Sea Ice and Sea Surface Temperature) dataset is used to define the years of El Niño, El Niño Modoki, and La Niña events and to find out the impacts of these events on typhoon activity. The results show that the formation positions of typhoon are farther eastward moving in El Niño years than in La Niña years and much further eastward in El Niño Modoki years. The lifetime and the distance of movement are longer, and the intensity of typhoons is stronger in El Niño and in El Niño Modoki years than in La Niña years. The Accumulated Cyclone Energy of typhoon is highly correlated with the Oceanic Niño Index with a correlation coefficient of 0.79. We also find that the typhoons anomalously decrease during El Niño years but increase during El Niño Modoki years. Besides, there are two types of El Niño Modoki, I and II. The intensity of typhoon in El Niño Modoki I years is stronger than in El Niño Modoki II years. Furthermore, the centroid position of the Western Pacific Warm Pool is strongly related to the area of typhoon formation with a correlation coefficient of 0.95.
Po-Chun Hsu; Chung-Ru Ho; Shin-Jye Liang; Nan-Jung Kuo. Impacts of Two Types of El Niño and La Niña Events on Typhoon Activity. Advances in Meteorology 2013, 2013, 1 -8.
AMA StylePo-Chun Hsu, Chung-Ru Ho, Shin-Jye Liang, Nan-Jung Kuo. Impacts of Two Types of El Niño and La Niña Events on Typhoon Activity. Advances in Meteorology. 2013; 2013 (17):1-8.
Chicago/Turabian StylePo-Chun Hsu; Chung-Ru Ho; Shin-Jye Liang; Nan-Jung Kuo. 2013. "Impacts of Two Types of El Niño and La Niña Events on Typhoon Activity." Advances in Meteorology 2013, no. 17: 1-8.