Ze-Nan Zhu - Academia.edu (original) (raw)
Papers by Ze-Nan Zhu
Journal of Physical Oceanography
Topographic Rossby waves (TRWs) play an important role in deep-ocean dynamics and abyssal intrase... more Topographic Rossby waves (TRWs) play an important role in deep-ocean dynamics and abyssal intraseasonal variations. Observational records from 15 current- and pressure-recording inverted echo sounders (CPIESs) and two moorings deployed in the northern Manila Trench (MT), South China Sea (SCS), for over 400 days were utilized to analyze the widely existing near-21-day bottom-trapped TRWs in the trench. The TRWs were generally generated in winter and summer, dominated by perturbations in the upper ocean. Kuroshio intrusion and its related variabilities contributed to the perturbations in winter, whereas the perturbations generated north of Luzon Island dominated in summer. Eddies north of Luzon propagated northwestward in the summer of 2018; however, these eddies caused the Kuroshio meanderings in the Luzon Strait (LS) in the summer of 2019. The variations in the Kuroshio path and the Kuroshio-related eddies induced TRWs in the deep ocean in regions with steep topography. However, the...
Journal of Physical Oceanography
The Kuroshio intrusion into the South China Sea (SCS) in summer is weak and has rarely been repor... more The Kuroshio intrusion into the South China Sea (SCS) in summer is weak and has rarely been reported by in situ observations. Here, we describe a new form of Kuroshio water intrusion that is strongest during the summer, the North Luzon Warm Eddy (NLWE), which is an anticyclonic eddy originating north of Luzon Island. During early July to mid-September 2018, two NLWEs moving northwestward were captured by a mooring array consisting of 27 current- and pressure-recording inverted echo sounders (CPIESs). The three-dimensional CPIES estimates reveal that the NLWEs carried large amounts of saline Kuroshio waters (S > 34.7 psu) in the subsurface, which was also evidenced by Argo float profiles. The Kuroshio intrusion was confined to waters shallower than the 14.8 °C isotherm. Historical data for NLWEs suggest that they occur mostly during the summer but are absent between November to March, which is attributed to seasonal wind stress curl (WSC). However, because the seasonal signal of W...
Remote Sensing, Jul 5, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Journal of Physical Oceanography
South China Sea (SCS) abyssal circulation largely contributes to water renewal, energy budget, an... more South China Sea (SCS) abyssal circulation largely contributes to water renewal, energy budget, and sedimentary processes in the deep ocean. The three-dimensional abyssal circulation west of the Luzon Strait (LS) in the northern SCS was investigated using an array comprising 27 current- and pressure-recording inverted echo sounders. Over 400 days of measurements from June 2018 to July 2019 showed a narrow and strong (∼70 km, ∼2.3 cm s−1 at 2500 dbar) northward current near the steep eastern boundary, while a wide and weak (∼180 km, ∼1.5 cm s−1 at 2500 dbar) southwestward current lies along the subdued western boundary. The circulation showed conspicuous cyclonic patterns with a volume transport of ∼1.21 ± 0.93 Sv (1 Sv ≡ 106 m3 s−1) and ∼1.59 ± 0.95 Sv below 2500 dbar along the eastern and western boundaries, respectively. The current near the LS was strong in late autumn and early winter but weak in late winter and spring, following the seasonal variation of LS deep-water overflow. ...
Japan Geoscience Union, Mar 14, 2019
Remote Sensing, 2022
The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisite... more The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisited to elucidate the propagation and generation characteristics of the M2 and M4 tidal currents with a second CAT experiment, which was conducted from 3–6 April 2018 (local time). Two-dimensional flow fields of the M2 and M4 tidal currents and the residual current were reconstructed using a coast-fitting inversion model with the reciprocal travel-time data of five acoustic stations. The M2 tidal current is a progressive-type wave that propagates eastward at a speed of 0.7 ms−1, much slower than expected for free progressive tides in this region (19 ms−1). The M4 nonlinear current constructed an out-of-phase relationship between the western and eastern halves of the tomography domain, implying the generation of standing-type waves. Such nonlinear processes led to flood- and ebb-dominant tidal current asymmetries for the western and eastern halves of the model domain, respectively. The two-d...
Japan Geoscience Union, Mar 14, 2019
Bottom pressure, current and temperature are observed by eleven current and pressure-recording in... more Bottom pressure, current and temperature are observed by eleven current and pressure-recording inverted echo sounders in the South China Sea from 2016 to 2019.
Ocean Dynamics, 2021
Herein, tidal current and associated nonlinear currents were measured using nine coastal acoustic... more Herein, tidal current and associated nonlinear currents were measured using nine coastal acoustic tomography (CAT) systems surrounding the tomography domain in Xiangshan Bay from 12:00 on December 10 to 12:00 on December 11, 2019 (local time, UTC+8). The distributions of M2 and M4 tidal currents, which were dominant in the bay, were reconstructed by the coast-fitting method (CFM) using the differential travel time data obtained along the 36 transmission paths. The tidal currents for both M2 and M4 showed a significant contrast in current directions and phases between the eastern and western halves of the tomography domain. For M2, progressive- and standing-type waves were generated in the eastern and western halves, respectively. The M4 currents were out-of-phase (with a time lag of 3 h) between the eastern and western halves. Furthermore, it was found that the M4 current in the western half was considerably influenced by the 6-h seiches resonating in the Xiangshan Fjord on the western side of the tomography domain. The observation and inversion errors were significantly smaller than the amplitudes of the M2 and M4 currents.
OCEANS 2018 MTS/IEEE Charleston, 2018
Eleven sets of coastal acoustic tomography (CAT) systems were successfully deployed in Dalian Bay... more Eleven sets of coastal acoustic tomography (CAT) systems were successfully deployed in Dalian Bay (DLB) during March 7–8, 2015, aiming to reconstruct the tidal current fields. The number of successful reciprocal transmission lines was 51, which may be the maximum number in ocean acoustic tomography history. The inverse method results showed that the velocity amplitudes in DLB were 0.75 ms-1 near the bay mouth and 0.30 ms-1in the inner bay. Furthermore, the travel time difference data were also assimilated into the Finite-Volume Community Ocean Model based on the ensemble Kalman Filter method. The assimilation showed similar results to those of the inverse method. Both the inverse method and data assimilation effectively reconstructed the tidal current, with a mean root mean square difference of 0.05 ms-1when compared to the Acoustic Doppler Current Profile data. Meanwhile, a tidal vortex west of Dasanshan Island was more effectively shown by assimilation rather than inversion.
A 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations i... more A 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations in March 2013, to measure the tidal current in the strait. The horizontal distributions of the tidal currents were calculated by inverse analysis of CAT data. The diurnal tidal current constituents were found to dominate: the ratio of the amplitudes O1, K1, M2, S2, and MSF was 1.00 : 0.60 : 0.47 : 0.21 : 0.11. The residual currents flowed westward in the northern QS and turned southward in the southern QS. The residual current velocities were larger in the northern area than in the southern area, with a maximum westward velocity of 12.4 cm·s-1 in the northern QS. Volume transport estimated using the CAT data varied between -0.710 Sv and 0.859 Sv, with residual current transport of -0.044 Sv, where negative values indicate westward. This is the first estimation, from synchronous measurements, of major tidal current constituents, residual currents, and volume transport in this strait.
2016 IEEE/OES China Ocean Acoustics (COA), 2016
An experiment for synchronous mapping of current velocity (V<sub>CAT</sub>) and tempe... more An experiment for synchronous mapping of current velocity (V<sub>CAT</sub>) and temperature (T<sub>CAT</sub>) distributions was successfully carried out using four coastal acoustic tomography (CAT) systems, from March 17 to April 1, 2013, in the Qiongzhou Strait, China. During the CAT observation period, shipboard acoustic Doppler current profiler (ADCP) surveys were also performed to observe the current velocity (V<sub>ADCP</sub>) and temperature (T<sub>ADCP</sub>) for the purpose of comparison with the CAT data. Position offsets, including a long-time averaged offset and a short-period fluctuation offset, were corrected for temperature estimation. The horizontal distribution of V<sub>CAT</sub> and T<sub>CAT</sub> was reconstructed by an inverse technique using the CAT data. V<sub>CAT</sub> was nearly parallel to the strait while T<sub>CAT</sub> was higher in the southern area than in th...
Journal of Ocean University of China, 2021
In this study, power spectral density and inverse analyses were performed to obtain the frequency... more In this study, power spectral density and inverse analyses were performed to obtain the frequency characteristics and spatial distribution of temperature in the Qiongzhou Strait using reciprocal sound transmission data obtained in a coastal acoustic tomography experiment conducted in 2013. The results reveal three dominant types of internal tides (diurnal, semidiurnal, and terdiurnal). Spectral analysis of the range-average temperature deviation along the northern and southern transmission paths shows that along the northern path, the energy of the diurnal internal tides was significantly larger than that of the semidiurnal tides. The semidiurnal internal tides, in contrast, were more pronounced along the southern path. A terdiurnal spectrum with an energy level equivalent to that of the semidiurnal internal tide was discernable for both the northern and southern paths. These three types of internal tides can also be recognized in the time variation of the zonal-average temperature deviation. The diurnal internal tides were strengthened along the northern coast, implying their westward propagation and the existence of coastally trapped effects. The other two types of internal tides, which have smaller wavelengths than the diurnal internal tides, were less resolved over the entire tomographic domain due to the insufficient resolution of the inversion. The data quality was verified to be satisfactory by error estimation.
Journal of Geophysical Research: Oceans, 2021
Frontiers in Earth Science, 2021
To continuously monitor the discharge of the Yangtze River, two coastal acoustic tomography (CAT)... more To continuously monitor the discharge of the Yangtze River, two coastal acoustic tomography (CAT) systems with synchronized transmission were deployed at the Datong hydrometric station of the Yangtze River from July 2018 to January 2021. To accurately estimate the discharge of the Yangtze River, the cross-sectional averaged flow velocity and area data were estimated by establishing two empirical relationships: one between the range-averaged flow velocity measured by acoustic Doppler current profiler (ADCP) and the reciprocal travel time difference measured by CAT, and the other between the ADCP-measured cross-sectional area and the water-surface elevation (stage). Compared with the discharges directly measured by ADCP, our estimation had the root mean square error of 946 m3/s, accounting for 2.5% of the mean discharge. The discharges varied from 10,981 to 81,807 m3/s over the 2.5-years observational period, with a mean of 30,708 m3/s. The annual mean discharge was 29,163 and 34,763 ...
Journal of Geophysical Research: Oceans, 2021
Journal of Physical Oceanography, 2021
Topographic Rossby waves (TRWs) are oscillations generated on sloping topography when water colum... more Topographic Rossby waves (TRWs) are oscillations generated on sloping topography when water columns travel across isobaths under potential vorticity conservation. From our large-scale observations from 2016 to 2019, near-65-day TRWs were first observed in the deep basin of the South China Sea (SCS). The TRWs propagated westward with a larger wavelength (235 km) and phase speed (3.6 km day−1) in the north of the array and a smaller wavelength (80 km) and phase speed (1.2 km day−1) toward the southwest of the array. The ray-tracing model was used to identify the energy source and propagation features of the TRWs. The paths of the near-65-day TRWs mainly followed the isobaths with a slightly downslope propagation. The possible energy source of the TRWs was the variance of surface eddies southwest of Taiwan. The near-65-day energy propagated from the southwest of Taiwan to the northeast and southwest of the array over ~100–120 and ~105 days, respectively, corresponding to a group veloci...
Acta Oceanologica Sinica, 2020
Between June 2015 and June 2017, two pressure-recording inverted echo sounders (PIESs) and five c... more Between June 2015 and June 2017, two pressure-recording inverted echo sounders (PIESs) and five current and pressure-recording inverted echo sounders (CPIESs) deployed along a section across the Kerama Gap acquired a dataset of ocean bottom pressure records in which there was significant 21-day variability (P bot21). The P bot21 , which was particularly strong from July-December 2016, was coherent with wind stress curl (WSC) on the continental shelf of the East China Sea (ECS) with a squared coherence of 0.65 for a 3-day time lag. A barotropic ocean model demonstrated the generation, propagation, and dissipation of P bot21. The modeled results show that the P bot21 driven by coastal ocean WSC in the ECS propagated toward the Ryukyu Island Chain (RIC), while deep ocean WSC could not induce such variability. On the continental shelf, the P bot21 was generated nearly synchronously with the WSC from the coastline to the southeast but dissipated within a few days due to the effect of bottom friction. The detection of P bot21 by the moored array was dependent on the 21-day WSC patterns on the continental shelf. The P bot21 driven southeast of the Changjiang Estuary by the WSC was detected while the P bot21 generated northeast of the Changjiang Estuary was not.
Sensors, 2020
Coast-fitting tomographic inversion that is based on function expansion using three types of norm... more Coast-fitting tomographic inversion that is based on function expansion using three types of normal modes (the Dirichlet, Neumann, and open boundary modes) is proposed to reconstruct current fields from the coastal acoustic tomography (CAT) data. The superiority of the method was validated while using CAT data that were obtained in 2015 in the Dalian Bay. The semidiurnal tidal and residual current fields were accurately reconstructed over the entire model domain surrounded by coasts and open boundaries. The proposed method was effective, particularly around the peripheral regions of the tomography domain and the near-coast regions outside the domain, where accurate results are not expected from the conventional inverse method based on function expansion by Fourier function series with no coast fittings. The error velocity for the semidiurnal tidal currents was 2.2 cm s−1, which was calculated from the root-mean-square-difference between the CAT-observed and inverted range-averaged c...
Journal of Physical Oceanography
Topographic Rossby waves (TRWs) play an important role in deep-ocean dynamics and abyssal intrase... more Topographic Rossby waves (TRWs) play an important role in deep-ocean dynamics and abyssal intraseasonal variations. Observational records from 15 current- and pressure-recording inverted echo sounders (CPIESs) and two moorings deployed in the northern Manila Trench (MT), South China Sea (SCS), for over 400 days were utilized to analyze the widely existing near-21-day bottom-trapped TRWs in the trench. The TRWs were generally generated in winter and summer, dominated by perturbations in the upper ocean. Kuroshio intrusion and its related variabilities contributed to the perturbations in winter, whereas the perturbations generated north of Luzon Island dominated in summer. Eddies north of Luzon propagated northwestward in the summer of 2018; however, these eddies caused the Kuroshio meanderings in the Luzon Strait (LS) in the summer of 2019. The variations in the Kuroshio path and the Kuroshio-related eddies induced TRWs in the deep ocean in regions with steep topography. However, the...
Journal of Physical Oceanography
The Kuroshio intrusion into the South China Sea (SCS) in summer is weak and has rarely been repor... more The Kuroshio intrusion into the South China Sea (SCS) in summer is weak and has rarely been reported by in situ observations. Here, we describe a new form of Kuroshio water intrusion that is strongest during the summer, the North Luzon Warm Eddy (NLWE), which is an anticyclonic eddy originating north of Luzon Island. During early July to mid-September 2018, two NLWEs moving northwestward were captured by a mooring array consisting of 27 current- and pressure-recording inverted echo sounders (CPIESs). The three-dimensional CPIES estimates reveal that the NLWEs carried large amounts of saline Kuroshio waters (S > 34.7 psu) in the subsurface, which was also evidenced by Argo float profiles. The Kuroshio intrusion was confined to waters shallower than the 14.8 °C isotherm. Historical data for NLWEs suggest that they occur mostly during the summer but are absent between November to March, which is attributed to seasonal wind stress curl (WSC). However, because the seasonal signal of W...
Remote Sensing, Jul 5, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Journal of Physical Oceanography
South China Sea (SCS) abyssal circulation largely contributes to water renewal, energy budget, an... more South China Sea (SCS) abyssal circulation largely contributes to water renewal, energy budget, and sedimentary processes in the deep ocean. The three-dimensional abyssal circulation west of the Luzon Strait (LS) in the northern SCS was investigated using an array comprising 27 current- and pressure-recording inverted echo sounders. Over 400 days of measurements from June 2018 to July 2019 showed a narrow and strong (∼70 km, ∼2.3 cm s−1 at 2500 dbar) northward current near the steep eastern boundary, while a wide and weak (∼180 km, ∼1.5 cm s−1 at 2500 dbar) southwestward current lies along the subdued western boundary. The circulation showed conspicuous cyclonic patterns with a volume transport of ∼1.21 ± 0.93 Sv (1 Sv ≡ 106 m3 s−1) and ∼1.59 ± 0.95 Sv below 2500 dbar along the eastern and western boundaries, respectively. The current near the LS was strong in late autumn and early winter but weak in late winter and spring, following the seasonal variation of LS deep-water overflow. ...
Japan Geoscience Union, Mar 14, 2019
Remote Sensing, 2022
The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisite... more The first coastal acoustic tomography (CAT) experiment site of the Neko-Seto Channel was revisited to elucidate the propagation and generation characteristics of the M2 and M4 tidal currents with a second CAT experiment, which was conducted from 3–6 April 2018 (local time). Two-dimensional flow fields of the M2 and M4 tidal currents and the residual current were reconstructed using a coast-fitting inversion model with the reciprocal travel-time data of five acoustic stations. The M2 tidal current is a progressive-type wave that propagates eastward at a speed of 0.7 ms−1, much slower than expected for free progressive tides in this region (19 ms−1). The M4 nonlinear current constructed an out-of-phase relationship between the western and eastern halves of the tomography domain, implying the generation of standing-type waves. Such nonlinear processes led to flood- and ebb-dominant tidal current asymmetries for the western and eastern halves of the model domain, respectively. The two-d...
Japan Geoscience Union, Mar 14, 2019
Bottom pressure, current and temperature are observed by eleven current and pressure-recording in... more Bottom pressure, current and temperature are observed by eleven current and pressure-recording inverted echo sounders in the South China Sea from 2016 to 2019.
Ocean Dynamics, 2021
Herein, tidal current and associated nonlinear currents were measured using nine coastal acoustic... more Herein, tidal current and associated nonlinear currents were measured using nine coastal acoustic tomography (CAT) systems surrounding the tomography domain in Xiangshan Bay from 12:00 on December 10 to 12:00 on December 11, 2019 (local time, UTC+8). The distributions of M2 and M4 tidal currents, which were dominant in the bay, were reconstructed by the coast-fitting method (CFM) using the differential travel time data obtained along the 36 transmission paths. The tidal currents for both M2 and M4 showed a significant contrast in current directions and phases between the eastern and western halves of the tomography domain. For M2, progressive- and standing-type waves were generated in the eastern and western halves, respectively. The M4 currents were out-of-phase (with a time lag of 3 h) between the eastern and western halves. Furthermore, it was found that the M4 current in the western half was considerably influenced by the 6-h seiches resonating in the Xiangshan Fjord on the western side of the tomography domain. The observation and inversion errors were significantly smaller than the amplitudes of the M2 and M4 currents.
OCEANS 2018 MTS/IEEE Charleston, 2018
Eleven sets of coastal acoustic tomography (CAT) systems were successfully deployed in Dalian Bay... more Eleven sets of coastal acoustic tomography (CAT) systems were successfully deployed in Dalian Bay (DLB) during March 7–8, 2015, aiming to reconstruct the tidal current fields. The number of successful reciprocal transmission lines was 51, which may be the maximum number in ocean acoustic tomography history. The inverse method results showed that the velocity amplitudes in DLB were 0.75 ms-1 near the bay mouth and 0.30 ms-1in the inner bay. Furthermore, the travel time difference data were also assimilated into the Finite-Volume Community Ocean Model based on the ensemble Kalman Filter method. The assimilation showed similar results to those of the inverse method. Both the inverse method and data assimilation effectively reconstructed the tidal current, with a mean root mean square difference of 0.05 ms-1when compared to the Acoustic Doppler Current Profile data. Meanwhile, a tidal vortex west of Dasanshan Island was more effectively shown by assimilation rather than inversion.
A 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations i... more A 15-day coastal acoustic tomography (CAT) experiment was carried out at four acoustic stations in March 2013, to measure the tidal current in the strait. The horizontal distributions of the tidal currents were calculated by inverse analysis of CAT data. The diurnal tidal current constituents were found to dominate: the ratio of the amplitudes O1, K1, M2, S2, and MSF was 1.00 : 0.60 : 0.47 : 0.21 : 0.11. The residual currents flowed westward in the northern QS and turned southward in the southern QS. The residual current velocities were larger in the northern area than in the southern area, with a maximum westward velocity of 12.4 cm·s-1 in the northern QS. Volume transport estimated using the CAT data varied between -0.710 Sv and 0.859 Sv, with residual current transport of -0.044 Sv, where negative values indicate westward. This is the first estimation, from synchronous measurements, of major tidal current constituents, residual currents, and volume transport in this strait.
2016 IEEE/OES China Ocean Acoustics (COA), 2016
An experiment for synchronous mapping of current velocity (V<sub>CAT</sub>) and tempe... more An experiment for synchronous mapping of current velocity (V<sub>CAT</sub>) and temperature (T<sub>CAT</sub>) distributions was successfully carried out using four coastal acoustic tomography (CAT) systems, from March 17 to April 1, 2013, in the Qiongzhou Strait, China. During the CAT observation period, shipboard acoustic Doppler current profiler (ADCP) surveys were also performed to observe the current velocity (V<sub>ADCP</sub>) and temperature (T<sub>ADCP</sub>) for the purpose of comparison with the CAT data. Position offsets, including a long-time averaged offset and a short-period fluctuation offset, were corrected for temperature estimation. The horizontal distribution of V<sub>CAT</sub> and T<sub>CAT</sub> was reconstructed by an inverse technique using the CAT data. V<sub>CAT</sub> was nearly parallel to the strait while T<sub>CAT</sub> was higher in the southern area than in th...
Journal of Ocean University of China, 2021
In this study, power spectral density and inverse analyses were performed to obtain the frequency... more In this study, power spectral density and inverse analyses were performed to obtain the frequency characteristics and spatial distribution of temperature in the Qiongzhou Strait using reciprocal sound transmission data obtained in a coastal acoustic tomography experiment conducted in 2013. The results reveal three dominant types of internal tides (diurnal, semidiurnal, and terdiurnal). Spectral analysis of the range-average temperature deviation along the northern and southern transmission paths shows that along the northern path, the energy of the diurnal internal tides was significantly larger than that of the semidiurnal tides. The semidiurnal internal tides, in contrast, were more pronounced along the southern path. A terdiurnal spectrum with an energy level equivalent to that of the semidiurnal internal tide was discernable for both the northern and southern paths. These three types of internal tides can also be recognized in the time variation of the zonal-average temperature deviation. The diurnal internal tides were strengthened along the northern coast, implying their westward propagation and the existence of coastally trapped effects. The other two types of internal tides, which have smaller wavelengths than the diurnal internal tides, were less resolved over the entire tomographic domain due to the insufficient resolution of the inversion. The data quality was verified to be satisfactory by error estimation.
Journal of Geophysical Research: Oceans, 2021
Frontiers in Earth Science, 2021
To continuously monitor the discharge of the Yangtze River, two coastal acoustic tomography (CAT)... more To continuously monitor the discharge of the Yangtze River, two coastal acoustic tomography (CAT) systems with synchronized transmission were deployed at the Datong hydrometric station of the Yangtze River from July 2018 to January 2021. To accurately estimate the discharge of the Yangtze River, the cross-sectional averaged flow velocity and area data were estimated by establishing two empirical relationships: one between the range-averaged flow velocity measured by acoustic Doppler current profiler (ADCP) and the reciprocal travel time difference measured by CAT, and the other between the ADCP-measured cross-sectional area and the water-surface elevation (stage). Compared with the discharges directly measured by ADCP, our estimation had the root mean square error of 946 m3/s, accounting for 2.5% of the mean discharge. The discharges varied from 10,981 to 81,807 m3/s over the 2.5-years observational period, with a mean of 30,708 m3/s. The annual mean discharge was 29,163 and 34,763 ...
Journal of Geophysical Research: Oceans, 2021
Journal of Physical Oceanography, 2021
Topographic Rossby waves (TRWs) are oscillations generated on sloping topography when water colum... more Topographic Rossby waves (TRWs) are oscillations generated on sloping topography when water columns travel across isobaths under potential vorticity conservation. From our large-scale observations from 2016 to 2019, near-65-day TRWs were first observed in the deep basin of the South China Sea (SCS). The TRWs propagated westward with a larger wavelength (235 km) and phase speed (3.6 km day−1) in the north of the array and a smaller wavelength (80 km) and phase speed (1.2 km day−1) toward the southwest of the array. The ray-tracing model was used to identify the energy source and propagation features of the TRWs. The paths of the near-65-day TRWs mainly followed the isobaths with a slightly downslope propagation. The possible energy source of the TRWs was the variance of surface eddies southwest of Taiwan. The near-65-day energy propagated from the southwest of Taiwan to the northeast and southwest of the array over ~100–120 and ~105 days, respectively, corresponding to a group veloci...
Acta Oceanologica Sinica, 2020
Between June 2015 and June 2017, two pressure-recording inverted echo sounders (PIESs) and five c... more Between June 2015 and June 2017, two pressure-recording inverted echo sounders (PIESs) and five current and pressure-recording inverted echo sounders (CPIESs) deployed along a section across the Kerama Gap acquired a dataset of ocean bottom pressure records in which there was significant 21-day variability (P bot21). The P bot21 , which was particularly strong from July-December 2016, was coherent with wind stress curl (WSC) on the continental shelf of the East China Sea (ECS) with a squared coherence of 0.65 for a 3-day time lag. A barotropic ocean model demonstrated the generation, propagation, and dissipation of P bot21. The modeled results show that the P bot21 driven by coastal ocean WSC in the ECS propagated toward the Ryukyu Island Chain (RIC), while deep ocean WSC could not induce such variability. On the continental shelf, the P bot21 was generated nearly synchronously with the WSC from the coastline to the southeast but dissipated within a few days due to the effect of bottom friction. The detection of P bot21 by the moored array was dependent on the 21-day WSC patterns on the continental shelf. The P bot21 driven southeast of the Changjiang Estuary by the WSC was detected while the P bot21 generated northeast of the Changjiang Estuary was not.
Sensors, 2020
Coast-fitting tomographic inversion that is based on function expansion using three types of norm... more Coast-fitting tomographic inversion that is based on function expansion using three types of normal modes (the Dirichlet, Neumann, and open boundary modes) is proposed to reconstruct current fields from the coastal acoustic tomography (CAT) data. The superiority of the method was validated while using CAT data that were obtained in 2015 in the Dalian Bay. The semidiurnal tidal and residual current fields were accurately reconstructed over the entire model domain surrounded by coasts and open boundaries. The proposed method was effective, particularly around the peripheral regions of the tomography domain and the near-coast regions outside the domain, where accurate results are not expected from the conventional inverse method based on function expansion by Fourier function series with no coast fittings. The error velocity for the semidiurnal tidal currents was 2.2 cm s−1, which was calculated from the root-mean-square-difference between the CAT-observed and inverted range-averaged c...