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2026, 48(4): 1-10.
doi: 10.12284/hyxb20260032
Abstract:
This study employs the MITgcm two-dimensional non-hydrostatic numerical model to simulate the generation, propagation, and dissipation processes of wind-generated near-inertial internal waves in the low-latitude ocean region (2°–20°N) under both the traditional approximation and the nontraditional approximation. The effects of the nontraditional approximation (retention of the horizontal component of the Coriolis parameter) on the propagation pathways, energy dissipation, and ocean interior mixing of near-inertial internal waves are systematically analyzed. The nontraditional approximation broadens the dispersion relation of internal waves, enabling near-inertial internal waves to generate sub-inertial components. Consequently, these waves can cross the inertial latitudes defined under the traditional approximation and continuously transport energy toward higher latitudes and the deep ocean. Poleward-propagating near-inertial internal waves, under the nontraditional approximation, propagate downward to the seafloor in the vicinity of the inertial latitude. After bottom reflection, wave energy accumulates within the near-bottom layer, significantly enhancing vertical shear in this region and triggering shear instability, which leads to near-inertial internal waves energy dissipation. The mean dissipation power per unit zonal width in the shear instability region is 0.25 W/m, and the associated enhanced turbulent mixing drives diapycnal volume transport in the deep ocean reaching 1.2 × 10−4 Sv. Based on the model results and a global estimate of near-inertial wave energy dissipation, this study roughly estimates that under the non-traditional approximation, wind-generated near-inertial internal waves induce deep-ocean turbulent mixing, which drives a global upwelling of approximately 1 Sv. These results indicate that the non-traditional approximation is essential for accurately quantifying near-inertial wave energy dissipation and its role in the global meridional overturning circulation.
This study employs the MITgcm two-dimensional non-hydrostatic numerical model to simulate the generation, propagation, and dissipation processes of wind-generated near-inertial internal waves in the low-latitude ocean region (2°–20°N) under both the traditional approximation and the nontraditional approximation. The effects of the nontraditional approximation (retention of the horizontal component of the Coriolis parameter) on the propagation pathways, energy dissipation, and ocean interior mixing of near-inertial internal waves are systematically analyzed. The nontraditional approximation broadens the dispersion relation of internal waves, enabling near-inertial internal waves to generate sub-inertial components. Consequently, these waves can cross the inertial latitudes defined under the traditional approximation and continuously transport energy toward higher latitudes and the deep ocean. Poleward-propagating near-inertial internal waves, under the nontraditional approximation, propagate downward to the seafloor in the vicinity of the inertial latitude. After bottom reflection, wave energy accumulates within the near-bottom layer, significantly enhancing vertical shear in this region and triggering shear instability, which leads to near-inertial internal waves energy dissipation. The mean dissipation power per unit zonal width in the shear instability region is 0.25 W/m, and the associated enhanced turbulent mixing drives diapycnal volume transport in the deep ocean reaching 1.2 × 10−4 Sv. Based on the model results and a global estimate of near-inertial wave energy dissipation, this study roughly estimates that under the non-traditional approximation, wind-generated near-inertial internal waves induce deep-ocean turbulent mixing, which drives a global upwelling of approximately 1 Sv. These results indicate that the non-traditional approximation is essential for accurately quantifying near-inertial wave energy dissipation and its role in the global meridional overturning circulation.
2026, 48(4): 11-18.
doi: 10.12284/hyxb20260038
Abstract:
Oceanic ridges can channel tsunami energy as trapped waves that propagate over distances exceeding ten thousand kilometers. Owing to their distinct propagation characteristics, these waves carry substantial energy to remote oceanic regions, posing serious threats to coastal engineering structures and to human life and property. Using potential flow theory, this study derives an analytical solution for trapped waves over a stepped ridge. It is mathematically demonstrated that trapped waves over a step-type ridge arise from wave reflection at the abrupt topographic change, and an explicit expression is provided for the critical condition required for total internal reflection to occur—thereby enabling wave trapping. The results show that lower-frequency wave components are more readily trapped by the stepped topography, and that the trapping effect becomes increasingly pronounced as the incident wave angle increases. By adopting the full-depth potential flow theory, this study overcomes the limitation of previous theories that are applicable only to shallow-water waves, thus offering reliable theoretical formulations for investigating trapped waves over realistic, steep ridge topographies.
Oceanic ridges can channel tsunami energy as trapped waves that propagate over distances exceeding ten thousand kilometers. Owing to their distinct propagation characteristics, these waves carry substantial energy to remote oceanic regions, posing serious threats to coastal engineering structures and to human life and property. Using potential flow theory, this study derives an analytical solution for trapped waves over a stepped ridge. It is mathematically demonstrated that trapped waves over a step-type ridge arise from wave reflection at the abrupt topographic change, and an explicit expression is provided for the critical condition required for total internal reflection to occur—thereby enabling wave trapping. The results show that lower-frequency wave components are more readily trapped by the stepped topography, and that the trapping effect becomes increasingly pronounced as the incident wave angle increases. By adopting the full-depth potential flow theory, this study overcomes the limitation of previous theories that are applicable only to shallow-water waves, thus offering reliable theoretical formulations for investigating trapped waves over realistic, steep ridge topographies.
2026, 48(4): 19-34.
doi: 10.12284/hyxb20260022
Abstract:
To accurately simulate nearshore wave-induced currents, this study proposes a general construction method for vertical weighting functions. Based on this method, existing depth-dependent horizontal wave radiation stress formulations are unified, and a modified formulation (Z04m) with tunable vertical distribution characteristics is derived. This formulation features a smooth and continuous vertical profile and allows for flexible adaptation to varying wave conditions and sloping topographies by adjusting a single parameter. Using a developed two-way coupled three-dimensional coastal wave-current interaction model, the applicability of different formulations is comprehensively evaluated. The model is validated against four laboratory flume experiments with varying conditions. The results show that the performance of different radiation stress formulations varies considerably in reproducing wave-induced current structures. The modified formulation outperforms the existing ones in simulating wave setup/setdown, significant wave height, and cross-shore vertical velocity profiles, with a significantly reduced root mean square error in cross-shore velocities compared with other formulations. Regarding the potential vertical momentum imbalance associated with using depth-dependent horizontal radiation stress formulations over sloping bottoms, momentum balance diagnostics based on the Roseau-type topography confirm the feasibility of the modified formulation, which includes only horizontal components. Its momentum balance characteristics are comparable to those of higher-order formulations that incorporate vertical components. The vertical momentum balance characteristics of other depth-dependent horizontal radiation stress formulations are also presented, and some are found to be imbalanced.
To accurately simulate nearshore wave-induced currents, this study proposes a general construction method for vertical weighting functions. Based on this method, existing depth-dependent horizontal wave radiation stress formulations are unified, and a modified formulation (Z04m) with tunable vertical distribution characteristics is derived. This formulation features a smooth and continuous vertical profile and allows for flexible adaptation to varying wave conditions and sloping topographies by adjusting a single parameter. Using a developed two-way coupled three-dimensional coastal wave-current interaction model, the applicability of different formulations is comprehensively evaluated. The model is validated against four laboratory flume experiments with varying conditions. The results show that the performance of different radiation stress formulations varies considerably in reproducing wave-induced current structures. The modified formulation outperforms the existing ones in simulating wave setup/setdown, significant wave height, and cross-shore vertical velocity profiles, with a significantly reduced root mean square error in cross-shore velocities compared with other formulations. Regarding the potential vertical momentum imbalance associated with using depth-dependent horizontal radiation stress formulations over sloping bottoms, momentum balance diagnostics based on the Roseau-type topography confirm the feasibility of the modified formulation, which includes only horizontal components. Its momentum balance characteristics are comparable to those of higher-order formulations that incorporate vertical components. The vertical momentum balance characteristics of other depth-dependent horizontal radiation stress formulations are also presented, and some are found to be imbalanced.
2026, 48(4): 35-46.
doi: 10.12284/hyxb20260028
Abstract:
Observational limitations constrain long-term studies of Arctic linear kinematic features (LKFs). This study systematically analyzes the long-term changes of Arctic LKFs and their climate drivers using a 28-year, ~2 km resolution pan-Arctic sea ice-ocean simulation, validated against winter RGPS data (1996–2008). We find no pronounced trend in pan-Arctic LKF number or density, though a very weak increase (0.003 a−1) aligns with thinning-enhanced fracturing. Modeled winter LKF density correlates well with RGPS observations (r = 0.57), confirming the model’s reliability in capturing the spatial distribution and seasonal variations of LKFs. Summer LKF density shows a strong negative correlation with the Arctic Dipole (AD) (r = −0.66), exceeding the Arctic Oscillation (AO) influence. While both AO and AD correlate negatively with LKF density in the central Arctic, LKF density correlates positively with AO but negatively with AD in the Kara Sea and Barents Sea, resulting in an overall stronger negative correlation with AD.
Observational limitations constrain long-term studies of Arctic linear kinematic features (LKFs). This study systematically analyzes the long-term changes of Arctic LKFs and their climate drivers using a 28-year, ~2 km resolution pan-Arctic sea ice-ocean simulation, validated against winter RGPS data (1996–2008). We find no pronounced trend in pan-Arctic LKF number or density, though a very weak increase (0.003 a−1) aligns with thinning-enhanced fracturing. Modeled winter LKF density correlates well with RGPS observations (r = 0.57), confirming the model’s reliability in capturing the spatial distribution and seasonal variations of LKFs. Summer LKF density shows a strong negative correlation with the Arctic Dipole (AD) (r = −0.66), exceeding the Arctic Oscillation (AO) influence. While both AO and AD correlate negatively with LKF density in the central Arctic, LKF density correlates positively with AO but negatively with AD in the Kara Sea and Barents Sea, resulting in an overall stronger negative correlation with AD.
2026, 48(4): 47-55.
doi: 10.12284/hyxb20260030
Abstract:
This paper briefly introduces the in-situ geoacoustic measurement system (SAS), which is based on high-frequency micro-vibration penetration technology. The system is composed of mechanical-hydraulic units, acoustic transducers, an acoustic emission and acquisition unit, an overall control unit, and auxiliary measurement units. It is designed for measuring the mid-frequency sound speed and attenuation coefficient of seafloor sediments. In April 2025, the system was deployed aboard the R/V “Xiangyanghong 01” to conduct in-situ acoustic measurements at nine stations in the northern continental shelf of South China Sea. At eight of these stations, the maximum penetration depth exceeded 3 meters, covering a frequency range of 1.6−10.0 kHz. The calculated sound speed shows distinct differences among the nine stations: the sound speed ratio at the first group of three stations varies between 1.01 and 1.03; at the second group of four stations, the ratio is significantly less than 1.0, ranging between 0.97 and 0.98; and at the third group of two stations, the ratio lies between the previous two groups, around 1.0. Comparison with synchronously obtained sediment core samples reveals a high correlation between sound velocity characteristics and the physical property parameters of sediments. When the sand content is high and the water content is low, the sound velocity in sediments exceeds that of near-bottom seawater; when the sand content is low and the water content is high, the sound velocity in sediments is lower than that of near-bottom seawater. Sand content and water content may be the primary factors determining whether sediment sound velocity is greater or less than that of near-bottom seawater. At the nine stations, sound speed dispersion is approximately 2% in coarser sandy sediments (\begin{document}$ \mathit{\Phi }= $\end{document} \begin{document}$ \mathit{\Phi }= $\end{document}
This paper briefly introduces the in-situ geoacoustic measurement system (SAS), which is based on high-frequency micro-vibration penetration technology. The system is composed of mechanical-hydraulic units, acoustic transducers, an acoustic emission and acquisition unit, an overall control unit, and auxiliary measurement units. It is designed for measuring the mid-frequency sound speed and attenuation coefficient of seafloor sediments. In April 2025, the system was deployed aboard the R/V “Xiangyanghong 01” to conduct in-situ acoustic measurements at nine stations in the northern continental shelf of South China Sea. At eight of these stations, the maximum penetration depth exceeded 3 meters, covering a frequency range of 1.6−10.0 kHz. The calculated sound speed shows distinct differences among the nine stations: the sound speed ratio at the first group of three stations varies between 1.01 and 1.03; at the second group of four stations, the ratio is significantly less than 1.0, ranging between 0.97 and 0.98; and at the third group of two stations, the ratio lies between the previous two groups, around 1.0. Comparison with synchronously obtained sediment core samples reveals a high correlation between sound velocity characteristics and the physical property parameters of sediments. When the sand content is high and the water content is low, the sound velocity in sediments exceeds that of near-bottom seawater; when the sand content is low and the water content is high, the sound velocity in sediments is lower than that of near-bottom seawater. Sand content and water content may be the primary factors determining whether sediment sound velocity is greater or less than that of near-bottom seawater. At the nine stations, sound speed dispersion is approximately 2% in coarser sandy sediments (
2026, 48(4): 56-68.
doi: 10.12284/hyxb20260024
Abstract:
The depth of closure is a key parameter in studies of sediment budget balance and coastal morphodynamics, and plays an important role in coastal erosion-related engineering applications. Traditional methods for estimating the depth of closure are mostly developed for wave-dominated coasts and generally neglect the influence of tidal currents, which limits their applicability to mesotidal embayments. Taking Haizhou Bay in the Lianyungang coastal area as a case study, this study systematically investigates the influence of tidal currents on the depth of closure by integrating field observations, numerical simulations, and theoretical analysis. The numerical results indicate that tidal currents in Haizhou Bay exhibit a decreasing trend from north to south, and that tidal forcing significantly enhances nearshore sediment mobilization. Under combined wave-current conditions, the depth of closure is estimated to range from 8.0 to 10.1 m, representing an increase of 0.4−1.3 m compared with the wave-only condition. Comparisons with historical bathymetric charts suggest that the observed depth of closure in Haizhou Bay generally falls within the range of 8.9−9.8 m, which is in good agreement with the results obtained in this study, further demonstrating the reliability of the proposed approach. The new method highlights the role of tidal currents in increasing bed shear stress in mesotidal embayments and explicitly accounts for their influence on the depth of closure, providing a sound scientific basis and technical support for coastal engineering applications in similar environments.
The depth of closure is a key parameter in studies of sediment budget balance and coastal morphodynamics, and plays an important role in coastal erosion-related engineering applications. Traditional methods for estimating the depth of closure are mostly developed for wave-dominated coasts and generally neglect the influence of tidal currents, which limits their applicability to mesotidal embayments. Taking Haizhou Bay in the Lianyungang coastal area as a case study, this study systematically investigates the influence of tidal currents on the depth of closure by integrating field observations, numerical simulations, and theoretical analysis. The numerical results indicate that tidal currents in Haizhou Bay exhibit a decreasing trend from north to south, and that tidal forcing significantly enhances nearshore sediment mobilization. Under combined wave-current conditions, the depth of closure is estimated to range from 8.0 to 10.1 m, representing an increase of 0.4−1.3 m compared with the wave-only condition. Comparisons with historical bathymetric charts suggest that the observed depth of closure in Haizhou Bay generally falls within the range of 8.9−9.8 m, which is in good agreement with the results obtained in this study, further demonstrating the reliability of the proposed approach. The new method highlights the role of tidal currents in increasing bed shear stress in mesotidal embayments and explicitly accounts for their influence on the depth of closure, providing a sound scientific basis and technical support for coastal engineering applications in similar environments.
2026, 48(4): 69-80.
doi: 10.12284/hyxb20260026
Abstract:
The hydrodynamic performance of a floating oscillating water column (OWC) breakwater under the co-action of waves and currents is numerically investigated. A time domain two-dimensional (2D) fully nonlinear numerical model was established for the OWC-breakwater, and its reliability was validated using experimental data. The effects of the current speed, the rear wall draft, and the rear wall thickness on the transmission coefficient, the reflection coefficient, and the hydrodynamic efficiency are numerically analyzed. The results indicate that under following current conditions, the transmission coefficient, reflection coefficient, and hydrodynamic efficiency of the device all exhibit a decreasing trend; whereas under opposing current conditions, the opposite trends are observed. Furthermore, increasing the rear wall draft reduces the transmission coefficient and improves the hydrodynamic efficiency, with a limited effect on the reflection coefficient. Besides, increasing the rear wall thickness also decreases the transmission coefficient and enhances hydrodynamic efficiency, while its influence on the reflection coefficient is insignificant. The findings of this study provide important references for the structural optimization and engineering design of OWC breakwaters.
The hydrodynamic performance of a floating oscillating water column (OWC) breakwater under the co-action of waves and currents is numerically investigated. A time domain two-dimensional (2D) fully nonlinear numerical model was established for the OWC-breakwater, and its reliability was validated using experimental data. The effects of the current speed, the rear wall draft, and the rear wall thickness on the transmission coefficient, the reflection coefficient, and the hydrodynamic efficiency are numerically analyzed. The results indicate that under following current conditions, the transmission coefficient, reflection coefficient, and hydrodynamic efficiency of the device all exhibit a decreasing trend; whereas under opposing current conditions, the opposite trends are observed. Furthermore, increasing the rear wall draft reduces the transmission coefficient and improves the hydrodynamic efficiency, with a limited effect on the reflection coefficient. Besides, increasing the rear wall thickness also decreases the transmission coefficient and enhances hydrodynamic efficiency, while its influence on the reflection coefficient is insignificant. The findings of this study provide important references for the structural optimization and engineering design of OWC breakwaters.
2026, 48(4): 81-93.
doi: 10.12284/hyxb20260034
Abstract:
This study conducted multi-objective intelligent prediction research on the excess pore water pressure around double-pile foundations in the seabed under wave action. Firstly, the time-history evolution and spatial distribution of excess pore water pressure around the double-pile foundation under different wave heights are analyzed by wave flume test. Secondly, the phase lag detection and dynamic alignment method are used to preprocess the data, and GRU and ELM neural networks are used for training prediction respectively. Finally, the dynamic error preferred fusion method is used to fuse the outputs of the two models. The results show that under the current test conditions, with the increase of wave height, the amplitude of excess pore water pressure in the seabed around the double-pile foundation increases significantly, showing obvious amplitude attenuation and phase lag along the depth direction, and there are obvious spatial differences in the maximum amplitude of excess pore water pressure around the double-pile foundation. In addition, the constructed fusion model performs best compared with the original model or single model evaluation metrics, where PCC is0.9827 , NSE is 0.9218 , RMSE is 0.003305 , and MAE is 0.002559 . The research results provide an effective way for the intelligent prediction of multi-objective pore pressure of seabed around pile foundation under wave action.
This study conducted multi-objective intelligent prediction research on the excess pore water pressure around double-pile foundations in the seabed under wave action. Firstly, the time-history evolution and spatial distribution of excess pore water pressure around the double-pile foundation under different wave heights are analyzed by wave flume test. Secondly, the phase lag detection and dynamic alignment method are used to preprocess the data, and GRU and ELM neural networks are used for training prediction respectively. Finally, the dynamic error preferred fusion method is used to fuse the outputs of the two models. The results show that under the current test conditions, with the increase of wave height, the amplitude of excess pore water pressure in the seabed around the double-pile foundation increases significantly, showing obvious amplitude attenuation and phase lag along the depth direction, and there are obvious spatial differences in the maximum amplitude of excess pore water pressure around the double-pile foundation. In addition, the constructed fusion model performs best compared with the original model or single model evaluation metrics, where PCC is
2026, 48(4): 94-109.
doi: 10.12284/hyxb20260010
Abstract:
High-quality underwater optical images are crucial for tasks such as digital twins of seabed scenes, benthic habitat protection, seabed mineral resource detection, and understanding unknown underwater phenomena. However, due to factors such as complex aquatic environments and lighting conditions, underwater optical images suffer from degradation issues including color distortion, blurred details, and low contrast. Existing underwater image enhancement methods often focus on optimizing enhancement algorithms themselves, lacking systematic analytical mechanisms for tracing, classifying, and grading different types of degradation. To address this, considering the complexity and heterogeneity of underwater optical imaging environments, this paper proposes an image quality enhancement strategy that takes degradation types into account. First, a degradation-type-aware network is constructed to identify underwater hazy and blurred images, achieving an accuracy of 97%, and also demonstrating a high distinguishing capability for illumination degradation types. Second, for the identified underwater hazy images, an adaptive color correction method is designed based on the statistical distribution of color bias values in real underwater images, effectively restoring color attenuation in varying degrees. Finally, a block indexing strategy is introduced to obtain more precise background light estimates, further addressing the hazy blur issue in underwater images in conjunction with the underwater dark channel prior. Experimental results on various real underwater image datasets, including UIEB and RUIE, indicate that compared to representative underwater image enhancement methods, the PSNR and SSIM metrics are improved by 22.17% and 4.5%, respectively.
High-quality underwater optical images are crucial for tasks such as digital twins of seabed scenes, benthic habitat protection, seabed mineral resource detection, and understanding unknown underwater phenomena. However, due to factors such as complex aquatic environments and lighting conditions, underwater optical images suffer from degradation issues including color distortion, blurred details, and low contrast. Existing underwater image enhancement methods often focus on optimizing enhancement algorithms themselves, lacking systematic analytical mechanisms for tracing, classifying, and grading different types of degradation. To address this, considering the complexity and heterogeneity of underwater optical imaging environments, this paper proposes an image quality enhancement strategy that takes degradation types into account. First, a degradation-type-aware network is constructed to identify underwater hazy and blurred images, achieving an accuracy of 97%, and also demonstrating a high distinguishing capability for illumination degradation types. Second, for the identified underwater hazy images, an adaptive color correction method is designed based on the statistical distribution of color bias values in real underwater images, effectively restoring color attenuation in varying degrees. Finally, a block indexing strategy is introduced to obtain more precise background light estimates, further addressing the hazy blur issue in underwater images in conjunction with the underwater dark channel prior. Experimental results on various real underwater image datasets, including UIEB and RUIE, indicate that compared to representative underwater image enhancement methods, the PSNR and SSIM metrics are improved by 22.17% and 4.5%, respectively.
2026, 48(4): 110-126.
doi: 10.12284/hyxb20260036
Abstract:
Based on observational data from four representative stations along the transect B in the Bering Sea during July 2012 (a cold year) and 2014 (a warm year), along with multiple sets of reanalysis data and climate model results, this study systematically evaluates the ability of different data sources to reproduce sea temperature structures from approximately 0 to1000 meters and their performance over multiple time scales using correlation coefficient, centered root mean square error (CRMSE), and standard deviation as evaluation metrics. The results show that the temperature variability in the upper ocean (0–200 m) is significantly higher than in the deeper layers (below 200 m). Reanalysis data generally have smaller average errors across all layers compared to climate model data. Specifically, for 2012, the error in the upper layers is about 0.3–0.5℃, while the model error is approximately 2℃; in the deep layers, the errors are about 0.1℃ and 1℃, respectively. In 2014, the errors in most models were lower than those in 2012, indicating that model performance is somewhat dependent on the climatic background. Long-term sequence analysis indicates that all data sources can reproduce the characteristic “cold winters and warm summers” seasonal cycle, but models show a systematic bias of about 1℃ in the middle layer temperature. On the interdecadal scale, the sea surface temperature anomaly (SSTA) shows consistent trends across data, while the middle layer temperature anomaly (MATA) exhibits time shifts of several years for extreme values. This study quantifies the error magnitude and uncertainty characteristics of different data in reproducing the upper ocean temperature structure in the Bering Sea, providing a quantitative reference for regional sea temperature variation analysis and multi-source data application.
Based on observational data from four representative stations along the transect B in the Bering Sea during July 2012 (a cold year) and 2014 (a warm year), along with multiple sets of reanalysis data and climate model results, this study systematically evaluates the ability of different data sources to reproduce sea temperature structures from approximately 0 to
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