Our long-term goal is to locate the source of non-linear internal waves (NLIWs) in the northern S... more Our long-term goal is to locate the source of non-linear internal waves (NLIWs) in the northern South China Sea (SCS), study their generation mechanism and establish the capability to predict its generation time and propagation path. OBJECTIVES In 2005, locate NLIWs with satellite image analysis and field data collection, and study their characteristics. In 2006, study the evolution of NLIWs from internal tide. In 2007, study their generation mechanism, and derive a model to predict their generation and propagation.
Terrestrial, Atmospheric and Oceanic Sciences, 1994
The first analysis of a Synthetic Aperture Radar (SAR) image over Tai wan area is presented. This... more The first analysis of a Synthetic Aperture Radar (SAR) image over Tai wan area is presented. This image was obtained from the Russian Almaz satellite of pass 7519. The brightness of the SAR images represents the backscattering cross section of the sea surface or the roughness of the sea surface that responds dynamically to the surface wind, the surfactant concen tration and the divergence of surface current. Because SAR uses microwave as a working frequency, it can provide an on-fragmented image of the sea surface with the least interference from the cloud or weather system. In this study, weather maps, wave analysis maps, ship data, satellite thermal images and bathymetric charts were used to interpret the brightness variations of the SAR image northeast of Taiwan, and a wealth of oceanic features-slicks, sur face waves, packets of internal waves, current, bottom topography, vortices, ships and ship wakes were found. These features should be further validated with shipborne measurements, satellite IR data, and SAR images from other satellites, like the first European Space Agency. remote sensing satellite, the ERS-1.
The water characteristics of the East China Sea depend on influxes from river runoff , the Kurosh... more The water characteristics of the East China Sea depend on influxes from river runoff , the Kuroshio, and the Taiwan Strait. A three-year observation using an acoustic Doppler current profiler (ADCP) operated on a ferry provides the first nearly continuous data set concerning the seasonal flow pattern and the volume transport from the Taiwan Strait to the East China Sea. The observed volume transport shows strong seasonality and linkage to the along-strait wind stress. An empirical regression formula between the volume transport and wind was derived to fill the gaps of observation so as to obtain a continuous data set. Based on this unique data set, the three-year mean of monthly volume transport is northeastward throughout the year, large (nearly 3 Sv) in summer and low (nearly zero) in winter. The China Coastal Current flows southward in winter, while the northward-flowing Taiwan Strait Current may reverse direction during severe northeasterly winds in the winter or under typhoons. The sea level difference across Taiwan Strait is closely correlated to the transport through the strait, and their relation is found seasonally nearly stable.
The Journal of the Acoustical Society of America, 2013
Ocean current profiling using ocean acoustic tomography (OAT) was conducted in the Kuroshio Curre... more Ocean current profiling using ocean acoustic tomography (OAT) was conducted in the Kuroshio Current southeast of Taiwan from August 20 to September 15, 2009. Sound pulses were transmitted reciprocally between two acoustic stations placed near the underwater sound channel axis and separated by 48 km. Based on the result of ray simulation, the received signals are divided into multiple ray groups because it is difficult to resolve the ray arrivals for individual rays. The average differential travel times from these ray groups are used to reconstruct the vertical profiles of currents. The currents are estimated with respect to the deepest water layer via two methods: An explicit solution and an inversion with regularization. The strong currents were confined to the upper 200 m and rapidly weakened toward 500 m in depth. Both methods give similar results and are consistent with shipboard acoustic Doppler current profiler results in the upper 150 m. The observed temporal variation demonstrates a similar trend to the prediction from the Hybrid Coordinate Ocean Model.
The northeast South China Sea is perhaps the largest internal tide energy source in the world. Th... more The northeast South China Sea is perhaps the largest internal tide energy source in the world. The temporal variability of internal tides was investigated on the basis of 8-month moored acoustic Doppler current profiler observations on the continental slope at the Dongsha Plateau. The daily amplitude and phase of diurnal and semidiurnal internal tides were determined from complex demodulation, and the dominant spatial and temporal patterns were extracted with empirical orthogonal function (EOF) analysis. The EOF modal structures showed good agreement with the normal mode solution, although vertical phase propagations were apparent. The first semidiurnal EOF mode corresponded to the first normal mode, and the first two diurnal EOF modes corresponded to the second and third normal modes, respectively. The modal structure and energy flux also were consistent with previous observations near the shelf break from the Asian Seas International Acoustic Experiment. On the other hand, the amplitudes of diurnal and semidiurnal EOF modes both indicated large irregular fortnightly variations that were not phase locked (incoherent) with astronomical forcing. The study highlighted the importance of incoherent internal tidal motion, which accounted for about three fourths of the observed tidal energy.
New evidence based on recent satellite data is presented to provide a rare opportunity in quantif... more New evidence based on recent satellite data is presented to provide a rare opportunity in quantifying the long-speculated contribution of tropical cyclones to enhance ocean primary production. In July 2000, moderate cyclone Kai-Tak passed over the South China Sea (SCS). During its short 3-day stay, Kai-Tak triggered an average 30-fold increase in surface chlorophyll-a concentration. The estimated carbon fixation resulting from this event alone is 0.8 Mt, or 2-4% of SCS's annual new production. Given an average of 14 cyclones passing over the SCS annually, we suggest the long-neglected contribution of tropical cyclones to SCS's annual new production may be as much as 20-30%.
The Kuroshio volume transport (KVT) at 24.5øN near Taiwan was directly measured for the first tim... more The Kuroshio volume transport (KVT) at 24.5øN near Taiwan was directly measured for the first time during the period from September 1994 to May 1996 through the channel between Taiwan and Iriomote, Japan. Adjusted sea level difference anomaly (SLDA) across the Kuroshio is examined as a proxy for long-term monitoring of KVT. Regression analyses were performed on the directly measured KVT and SLDA between Ishigaki and sea level stations on the Taiwan side (Keelung, Kenfang and Suao). The best estimators of KVT are: (1) KVT1-0.32xSLDA1 (Ishigaki-Suao) + 20.85 Sv + 2.3 Sv for daily KVT and (2) KVTlo-0.37 x SLDAlo(Ishigaki-Suao) + 20.87 Sv 4-1.4 Sv for 10-day low-passed KVT.
The common geostrophic estimation of ocean current velocity uses only water temperature and condu... more The common geostrophic estimation of ocean current velocity uses only water temperature and conductivity profiles. The geostrophic volume transport of a western boundary current, like the Taiwan Current (Kuroshio east of Taiwan), between the coast and its eastern boundary can be easily estimated based on hydrographic survey data. But the eastern boundary of the Taiwan Current is very uncertain due to extremely variable hydrographic conditions. This uncertainty is strongly correlated with the propagating mesoscale eddies originating from the interior of the western North Pacific Ocean. The uncertainty of estimated transport can be greatly reduced if eddy distribution is considered when determining the integration boundaries with the assistance of satellite altimeter measurements. Eight hydrographic surveys east of Taiwan between November 1992 and June 1996 are demonstrated in this study. The average geostrophic transport of the Taiwan Current with a reference set to 1000 dbar at 22°N...
Considerable westward or nothwestward propagating eddies were found east of Taiwan that cross-exp... more Considerable westward or nothwestward propagating eddies were found east of Taiwan that cross-explains the anomalies in the repeated hydrography, trajectory of drifting buoys and altimetric analyses. The sea level differences (SLD) across the Taiwan Current (Kuroshio) in the East Taiwan Channel (ETC) are utilized in order to examine the possible implication of eddies in the Taiwan Current transport. It is
Our long-term goal is to locate the source of non-linear internal waves (NLIWs) in the northern S... more Our long-term goal is to locate the source of non-linear internal waves (NLIWs) in the northern South China Sea (SCS), study their generation mechanism and establish the capability to predict its generation time and propagation path. OBJECTIVES In 2005, locate NLIWs with satellite image analysis and field data collection, and study their characteristics. In 2006, study the evolution of NLIWs from internal tide. In 2007, study their generation mechanism, and derive a model to predict their generation and propagation.
Terrestrial, Atmospheric and Oceanic Sciences, 1994
The first analysis of a Synthetic Aperture Radar (SAR) image over Tai wan area is presented. This... more The first analysis of a Synthetic Aperture Radar (SAR) image over Tai wan area is presented. This image was obtained from the Russian Almaz satellite of pass 7519. The brightness of the SAR images represents the backscattering cross section of the sea surface or the roughness of the sea surface that responds dynamically to the surface wind, the surfactant concen tration and the divergence of surface current. Because SAR uses microwave as a working frequency, it can provide an on-fragmented image of the sea surface with the least interference from the cloud or weather system. In this study, weather maps, wave analysis maps, ship data, satellite thermal images and bathymetric charts were used to interpret the brightness variations of the SAR image northeast of Taiwan, and a wealth of oceanic features-slicks, sur face waves, packets of internal waves, current, bottom topography, vortices, ships and ship wakes were found. These features should be further validated with shipborne measurements, satellite IR data, and SAR images from other satellites, like the first European Space Agency. remote sensing satellite, the ERS-1.
The water characteristics of the East China Sea depend on influxes from river runoff , the Kurosh... more The water characteristics of the East China Sea depend on influxes from river runoff , the Kuroshio, and the Taiwan Strait. A three-year observation using an acoustic Doppler current profiler (ADCP) operated on a ferry provides the first nearly continuous data set concerning the seasonal flow pattern and the volume transport from the Taiwan Strait to the East China Sea. The observed volume transport shows strong seasonality and linkage to the along-strait wind stress. An empirical regression formula between the volume transport and wind was derived to fill the gaps of observation so as to obtain a continuous data set. Based on this unique data set, the three-year mean of monthly volume transport is northeastward throughout the year, large (nearly 3 Sv) in summer and low (nearly zero) in winter. The China Coastal Current flows southward in winter, while the northward-flowing Taiwan Strait Current may reverse direction during severe northeasterly winds in the winter or under typhoons. The sea level difference across Taiwan Strait is closely correlated to the transport through the strait, and their relation is found seasonally nearly stable.
The Journal of the Acoustical Society of America, 2013
Ocean current profiling using ocean acoustic tomography (OAT) was conducted in the Kuroshio Curre... more Ocean current profiling using ocean acoustic tomography (OAT) was conducted in the Kuroshio Current southeast of Taiwan from August 20 to September 15, 2009. Sound pulses were transmitted reciprocally between two acoustic stations placed near the underwater sound channel axis and separated by 48 km. Based on the result of ray simulation, the received signals are divided into multiple ray groups because it is difficult to resolve the ray arrivals for individual rays. The average differential travel times from these ray groups are used to reconstruct the vertical profiles of currents. The currents are estimated with respect to the deepest water layer via two methods: An explicit solution and an inversion with regularization. The strong currents were confined to the upper 200 m and rapidly weakened toward 500 m in depth. Both methods give similar results and are consistent with shipboard acoustic Doppler current profiler results in the upper 150 m. The observed temporal variation demonstrates a similar trend to the prediction from the Hybrid Coordinate Ocean Model.
The northeast South China Sea is perhaps the largest internal tide energy source in the world. Th... more The northeast South China Sea is perhaps the largest internal tide energy source in the world. The temporal variability of internal tides was investigated on the basis of 8-month moored acoustic Doppler current profiler observations on the continental slope at the Dongsha Plateau. The daily amplitude and phase of diurnal and semidiurnal internal tides were determined from complex demodulation, and the dominant spatial and temporal patterns were extracted with empirical orthogonal function (EOF) analysis. The EOF modal structures showed good agreement with the normal mode solution, although vertical phase propagations were apparent. The first semidiurnal EOF mode corresponded to the first normal mode, and the first two diurnal EOF modes corresponded to the second and third normal modes, respectively. The modal structure and energy flux also were consistent with previous observations near the shelf break from the Asian Seas International Acoustic Experiment. On the other hand, the amplitudes of diurnal and semidiurnal EOF modes both indicated large irregular fortnightly variations that were not phase locked (incoherent) with astronomical forcing. The study highlighted the importance of incoherent internal tidal motion, which accounted for about three fourths of the observed tidal energy.
New evidence based on recent satellite data is presented to provide a rare opportunity in quantif... more New evidence based on recent satellite data is presented to provide a rare opportunity in quantifying the long-speculated contribution of tropical cyclones to enhance ocean primary production. In July 2000, moderate cyclone Kai-Tak passed over the South China Sea (SCS). During its short 3-day stay, Kai-Tak triggered an average 30-fold increase in surface chlorophyll-a concentration. The estimated carbon fixation resulting from this event alone is 0.8 Mt, or 2-4% of SCS's annual new production. Given an average of 14 cyclones passing over the SCS annually, we suggest the long-neglected contribution of tropical cyclones to SCS's annual new production may be as much as 20-30%.
The Kuroshio volume transport (KVT) at 24.5øN near Taiwan was directly measured for the first tim... more The Kuroshio volume transport (KVT) at 24.5øN near Taiwan was directly measured for the first time during the period from September 1994 to May 1996 through the channel between Taiwan and Iriomote, Japan. Adjusted sea level difference anomaly (SLDA) across the Kuroshio is examined as a proxy for long-term monitoring of KVT. Regression analyses were performed on the directly measured KVT and SLDA between Ishigaki and sea level stations on the Taiwan side (Keelung, Kenfang and Suao). The best estimators of KVT are: (1) KVT1-0.32xSLDA1 (Ishigaki-Suao) + 20.85 Sv + 2.3 Sv for daily KVT and (2) KVTlo-0.37 x SLDAlo(Ishigaki-Suao) + 20.87 Sv 4-1.4 Sv for 10-day low-passed KVT.
The common geostrophic estimation of ocean current velocity uses only water temperature and condu... more The common geostrophic estimation of ocean current velocity uses only water temperature and conductivity profiles. The geostrophic volume transport of a western boundary current, like the Taiwan Current (Kuroshio east of Taiwan), between the coast and its eastern boundary can be easily estimated based on hydrographic survey data. But the eastern boundary of the Taiwan Current is very uncertain due to extremely variable hydrographic conditions. This uncertainty is strongly correlated with the propagating mesoscale eddies originating from the interior of the western North Pacific Ocean. The uncertainty of estimated transport can be greatly reduced if eddy distribution is considered when determining the integration boundaries with the assistance of satellite altimeter measurements. Eight hydrographic surveys east of Taiwan between November 1992 and June 1996 are demonstrated in this study. The average geostrophic transport of the Taiwan Current with a reference set to 1000 dbar at 22°N...
Considerable westward or nothwestward propagating eddies were found east of Taiwan that cross-exp... more Considerable westward or nothwestward propagating eddies were found east of Taiwan that cross-explains the anomalies in the repeated hydrography, trajectory of drifting buoys and altimetric analyses. The sea level differences (SLD) across the Taiwan Current (Kuroshio) in the East Taiwan Channel (ETC) are utilized in order to examine the possible implication of eddies in the Taiwan Current transport. It is
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