2022 Vol. 44, No. 6
Display Method:
2022, 44(6): 1-9.
doi: 10.12284/hyxb2022049
Abstract:
Tidal-current-asymmetry (TCA) influences sediment transport and geomorphologic changes. It is of paramount importance to understand the current asymmetry in this area in context of a long-term scale with consideration of development and protection of the coastal resources. The radial sand ridges (RSR) in the South Yellow Sea is patterned with strong tidal forcing and complex hydrodynamic environment. This paper simulated tidal current field in the RSR based on the Delft3D model and used combined harmonic analysis and skewness theory to analyze the spatial distribution of the TCA under varied shoreline conditions. The results show that peak-current-asymmetry (PCA) in the RSR is mostly flood-dominant and slack-water-asymmetry (SWA) also shows positive, meaning the flooding duration is shorter than the ebbing duration. Both the positively-dominant PCA and negatively-dominant SWA are mainly affected by the nonlinear interactions between the semidiurnal diurnal tides (M2, S2) and shallow water tides (M4, MS4). As the shoreline gradually moves towards sea during 1984 to 2014, although the nature of\begin{document}$ {\gamma }_{\mathrm{P}\mathrm{C}\mathrm{A}} $\end{document} ![]()
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Tidal-current-asymmetry (TCA) influences sediment transport and geomorphologic changes. It is of paramount importance to understand the current asymmetry in this area in context of a long-term scale with consideration of development and protection of the coastal resources. The radial sand ridges (RSR) in the South Yellow Sea is patterned with strong tidal forcing and complex hydrodynamic environment. This paper simulated tidal current field in the RSR based on the Delft3D model and used combined harmonic analysis and skewness theory to analyze the spatial distribution of the TCA under varied shoreline conditions. The results show that peak-current-asymmetry (PCA) in the RSR is mostly flood-dominant and slack-water-asymmetry (SWA) also shows positive, meaning the flooding duration is shorter than the ebbing duration. Both the positively-dominant PCA and negatively-dominant SWA are mainly affected by the nonlinear interactions between the semidiurnal diurnal tides (M2, S2) and shallow water tides (M4, MS4). As the shoreline gradually moves towards sea during 1984 to 2014, although the nature of
2022, 44(6): 10-21.
doi: 10.12284/hyxb2022057
Abstract:
Data assimilation can estimate the uncertain parameters in the numerical model while adjusting the state variables with observations to improve the simulation results through enhancing the numerical model. Based on the ensemble adjustment Kalman filter (EAKF) and the external mode of the Princeton ocean model with generalized coordinate system (POMgcs), a bathymetry estimate is performed in the M2 constituent simulation of the Bohai Sea and part of the Yellow Sea. The results of the ideal data assimilation experiment or identical twin experiment show that the EAKF method can retrieve the “truth” bathymetry. In the practical data assimilation experiment of the NAO.99Jb and tide gauge data, by comparing with the 34 tide gauges, the model simulated amplitude and phase lag errors of M2 constituent are reduced by 40.27% and 49.19%, respectively, by use of the posterior estimate of the bathymetry.
Data assimilation can estimate the uncertain parameters in the numerical model while adjusting the state variables with observations to improve the simulation results through enhancing the numerical model. Based on the ensemble adjustment Kalman filter (EAKF) and the external mode of the Princeton ocean model with generalized coordinate system (POMgcs), a bathymetry estimate is performed in the M2 constituent simulation of the Bohai Sea and part of the Yellow Sea. The results of the ideal data assimilation experiment or identical twin experiment show that the EAKF method can retrieve the “truth” bathymetry. In the practical data assimilation experiment of the NAO.99Jb and tide gauge data, by comparing with the 34 tide gauges, the model simulated amplitude and phase lag errors of M2 constituent are reduced by 40.27% and 49.19%, respectively, by use of the posterior estimate of the bathymetry.
2022, 44(6): 22-36.
doi: 10.12284/hyxb2022035
Abstract:
In this paper, surface characteristics of mesoscale eddies in the Japan Sea (JES), including size, polarity, life cycle, amplitude, and trajectory, are analyzed by using eddy datasets and sea level anomaly altimeter data from 1993 to 2019. Over the 27-year period, a total of 1429 eddies were detected with nearly equal number of cyclonic and anticyclonic eddies (CEs and AEs, respectively). Strong seasonal variability was observed for both polarities of eddy. The eddies were most generated in autumn, followed by winter and the least in the spring. Mesoscale eddies are prone to generate in the Ulleung Basin and Yamato Basin, which distributed in a southwest-northeast zonal belt. Among them, ACs are dominant in the southern JES, while CEs in the northern JES near the Tsugaru Strait. The western and southern movements of the mesoscale eddies were driven by the East Korean Warm Current and Tsushima Warm Current. In the northern JES, the mesoscale eddies were more related to the Liman cold current and subpolar front current. Further studies shown that dynamical instability is an important reason for the generation of eddies in autumn and winter. However, semi-enclosed basins, local flow fields, and complex air-sea interactions may all have a certain impact on the generation and dissipation of the mesoscale eddies.
In this paper, surface characteristics of mesoscale eddies in the Japan Sea (JES), including size, polarity, life cycle, amplitude, and trajectory, are analyzed by using eddy datasets and sea level anomaly altimeter data from 1993 to 2019. Over the 27-year period, a total of 1429 eddies were detected with nearly equal number of cyclonic and anticyclonic eddies (CEs and AEs, respectively). Strong seasonal variability was observed for both polarities of eddy. The eddies were most generated in autumn, followed by winter and the least in the spring. Mesoscale eddies are prone to generate in the Ulleung Basin and Yamato Basin, which distributed in a southwest-northeast zonal belt. Among them, ACs are dominant in the southern JES, while CEs in the northern JES near the Tsugaru Strait. The western and southern movements of the mesoscale eddies were driven by the East Korean Warm Current and Tsushima Warm Current. In the northern JES, the mesoscale eddies were more related to the Liman cold current and subpolar front current. Further studies shown that dynamical instability is an important reason for the generation of eddies in autumn and winter. However, semi-enclosed basins, local flow fields, and complex air-sea interactions may all have a certain impact on the generation and dissipation of the mesoscale eddies.
2022, 44(6): 37-47.
doi: 10.12284/hyxb2022043
Abstract:
This study mainly uses the GECCO2 reanalysis data from 1958 to 2016 to analyze the spatiotemporal characteristics of the southern Indian Ocean sea surface temperature anomalies (SSTA) winter-to-winter recurrence through lag correlation analysis, and investigate the roles of oceanic reemergence mechanism and atmospheric forcing. The results show that the winter-to-winter recurrence of SSTA occurs south of 15ºS in the southern Indian Ocean, especially between Madagascar and southwestern Australia (15º–45ºS, 70º–100ºE). The recurrence mainly occurs in the winter of the following year, but there are also some areas where the recurrence occurs in the following fall and continue to the subsequent winter. Further analysis shows that the difference between the deep winter mixed layer and shallow summer mixed layer, known as the oceanic reemergence mechanism, is the main cause of the recurrence of SSTA in the southern Indian Ocean. In addition, the net heat flux also directly contributes to the recurrence of SSTA in southern Madagascar and southwestern Australia.
This study mainly uses the GECCO2 reanalysis data from 1958 to 2016 to analyze the spatiotemporal characteristics of the southern Indian Ocean sea surface temperature anomalies (SSTA) winter-to-winter recurrence through lag correlation analysis, and investigate the roles of oceanic reemergence mechanism and atmospheric forcing. The results show that the winter-to-winter recurrence of SSTA occurs south of 15ºS in the southern Indian Ocean, especially between Madagascar and southwestern Australia (15º–45ºS, 70º–100ºE). The recurrence mainly occurs in the winter of the following year, but there are also some areas where the recurrence occurs in the following fall and continue to the subsequent winter. Further analysis shows that the difference between the deep winter mixed layer and shallow summer mixed layer, known as the oceanic reemergence mechanism, is the main cause of the recurrence of SSTA in the southern Indian Ocean. In addition, the net heat flux also directly contributes to the recurrence of SSTA in southern Madagascar and southwestern Australia.
2022, 44(6): 48-57.
doi: 10.12284/hyxb2022053
Abstract:
Hydrographic data collected from March to April 2014 by CTD-SRDL mounted on northern elephant seal were analyzed to study the distribution and decline of the temperature inversion over the eastern continental slope in Gulf of Alaska. The results show that temperature inversion occurred significantly in this region. Temperature difference was between 0.2°C and 1.6°C and thickness of temperature inversion was between 20 m and 280 m, respectively. The temperature difference increased northward along the continental slope, while the thickness thickened from 50°N to 58°N, but the average thickness at north of 58°N was relative thinner. The temperature inversion was decay during March 25 to April 22, 2014. The subsurface maximum temperature continued to fall, the temperature difference tended to be weaker, and the thickness presented a thinning tendency. Numerical results of a one-dimensional model reveal that, the temperature at the upper mixed layer increased by heating on the sea surface, but the temperature at the bottom of the mixed layer remained low, therefore the minimum temperature of temperature inversion change was not notable. With a strong temperature gradient in the subsurface, the subsurface maximum temperature dropped pronouncedly due to the turbulent diffusion, which is the main reason for temperature inversion decline. Turbulent diffusion modified temperature and salinity in subsurface water to be uniform, thus it is important to study this process for the formation and evolution of temperature inversion.
Hydrographic data collected from March to April 2014 by CTD-SRDL mounted on northern elephant seal were analyzed to study the distribution and decline of the temperature inversion over the eastern continental slope in Gulf of Alaska. The results show that temperature inversion occurred significantly in this region. Temperature difference was between 0.2°C and 1.6°C and thickness of temperature inversion was between 20 m and 280 m, respectively. The temperature difference increased northward along the continental slope, while the thickness thickened from 50°N to 58°N, but the average thickness at north of 58°N was relative thinner. The temperature inversion was decay during March 25 to April 22, 2014. The subsurface maximum temperature continued to fall, the temperature difference tended to be weaker, and the thickness presented a thinning tendency. Numerical results of a one-dimensional model reveal that, the temperature at the upper mixed layer increased by heating on the sea surface, but the temperature at the bottom of the mixed layer remained low, therefore the minimum temperature of temperature inversion change was not notable. With a strong temperature gradient in the subsurface, the subsurface maximum temperature dropped pronouncedly due to the turbulent diffusion, which is the main reason for temperature inversion decline. Turbulent diffusion modified temperature and salinity in subsurface water to be uniform, thus it is important to study this process for the formation and evolution of temperature inversion.
2022, 44(6): 58-67.
doi: 10.12284/hyxb2022047
Abstract:
A multivariate long short term memory (LSTM) neural network model was developed for the Pacific decadal oscillation (PDO) index time series prediction using sea level pressure, sea level height, ocean heat content data and sea ice concentration from 1921 to 2020 as forecast elements of the PDO index. The PDO index prediction results of different time series from 2011 to 2020 were compared and analyzed, and finally the PDO index forecasting from 2021 to 2030 is realized by using the multivariate LSTM neural network model. The results show that the average correlation coefficient and root mean square error of the predicted value and the observed value of the multivariate LSTM model after cross-validation are 0.70 and 0.62, respectively. PDO will remain in the cold phase in the next ten years, and the PDO index will fluctuate twice, there will be a minimum in 2025. Compared with other time series forecasting models, the multivariate LSTM neural network model used in this paper has less error in forecasting results and good fitting effect, which can be used as a new method of predicting PDO index.
A multivariate long short term memory (LSTM) neural network model was developed for the Pacific decadal oscillation (PDO) index time series prediction using sea level pressure, sea level height, ocean heat content data and sea ice concentration from 1921 to 2020 as forecast elements of the PDO index. The PDO index prediction results of different time series from 2011 to 2020 were compared and analyzed, and finally the PDO index forecasting from 2021 to 2030 is realized by using the multivariate LSTM neural network model. The results show that the average correlation coefficient and root mean square error of the predicted value and the observed value of the multivariate LSTM model after cross-validation are 0.70 and 0.62, respectively. PDO will remain in the cold phase in the next ten years, and the PDO index will fluctuate twice, there will be a minimum in 2025. Compared with other time series forecasting models, the multivariate LSTM neural network model used in this paper has less error in forecasting results and good fitting effect, which can be used as a new method of predicting PDO index.
2022, 44(6): 68-79.
doi: 10.12284/hyxb2022041
Abstract:
Based on a tripod measurement in the Laizhou Bay from October 21 to November 6, 2018, the unit-width bottom sediment transport rate and the effects of strong winds on bottom sediment transport are analyzed using the ensemble empirical mode decomposition, the Hilbert-Huang transform and the wavelet analysis method. The resuluts show thta the unit-width sediment transport rate can be divided into four intrinsic mode functions with increased periods including the high-frequency, tidal-period, low-frequency and long-period. The high-frequency and tidal-period components have the highest variance contribution rate and energy, indicating their greatest impact on sediment transport. The marginal spectrum shows a significant period of 13.3 h in the east-west direction, and a period larger than 11 h in the north-south direction. The net bottom sediment fluxes in the east-west and north-south directions are 305.77 kg/m and 597.25 kg/m, respectively; and the high-frequency and low-frequency component contribute least while the residual-current component contributes most. Winds work on the time-frequency distribution of the unit-width sediment transport rate mainly through the turbulence and waves during the wind decrease periods, which enhances the low-frequency domain significantly, and further induces the high-frequency fluctuations with periods about 1 h. The cross-wavelet analysis shows the winds and the unit-width sediment transport rate have a strong coherence on the low-frequency band; and the latter lags behind the former by 1/4 to 1/2 period. In addition, the wind-waves enhance the asymmetric sediment transport between flood and ebb tidal phase, which increases the net sediment flux of tidal period.
Based on a tripod measurement in the Laizhou Bay from October 21 to November 6, 2018, the unit-width bottom sediment transport rate and the effects of strong winds on bottom sediment transport are analyzed using the ensemble empirical mode decomposition, the Hilbert-Huang transform and the wavelet analysis method. The resuluts show thta the unit-width sediment transport rate can be divided into four intrinsic mode functions with increased periods including the high-frequency, tidal-period, low-frequency and long-period. The high-frequency and tidal-period components have the highest variance contribution rate and energy, indicating their greatest impact on sediment transport. The marginal spectrum shows a significant period of 13.3 h in the east-west direction, and a period larger than 11 h in the north-south direction. The net bottom sediment fluxes in the east-west and north-south directions are 305.77 kg/m and 597.25 kg/m, respectively; and the high-frequency and low-frequency component contribute least while the residual-current component contributes most. Winds work on the time-frequency distribution of the unit-width sediment transport rate mainly through the turbulence and waves during the wind decrease periods, which enhances the low-frequency domain significantly, and further induces the high-frequency fluctuations with periods about 1 h. The cross-wavelet analysis shows the winds and the unit-width sediment transport rate have a strong coherence on the low-frequency band; and the latter lags behind the former by 1/4 to 1/2 period. In addition, the wind-waves enhance the asymmetric sediment transport between flood and ebb tidal phase, which increases the net sediment flux of tidal period.
2022, 44(6): 80-88.
doi: 10.12284/hyxb2022051
Abstract:
In order to better understand the sedimentary rate changes in the Caroline area which is located in the north of West Pacific Warm Pool, a comprehensive dating method was carried out by using radiocarbon testing(14C), oxygen isotope and paleomagnetism on a gravity core from the Caroline area of the western Pacific Ocean. 14C data provide the age of the upper section since 44.3 ka BP for this core. Subsequently, the age framework since MIS4 (about 80 ka) which corresponds to the depth of 125 cm was established by using oxygen isotope and relative paleointensity (RPI) data, while the upper part also considered the 14C data. Further analysis revealed that there was an obvious sedimentary discontinuity at the depth of 126 cm to 127 cm in this core, although it has been beyond the range of 14C dating, but the paleomagnetic results show that the core formed in Brunhes period, and the relationship between RPI and oxygen isotope data under the hiatus provide a robust evidence that the age is from 180 ka to 130 ka in the bottom. At the end the deposition rate of the core was obtained, which is 1 cm/ka to 2 cm/ka, and it is consistent before and after the deposition hiatus. At the same time, the disparity of the deposition rate for each dating method indicated that there was a large deviation of 14C data in one layer maybe due to the high rate of foraminiferal shell breaking.
In order to better understand the sedimentary rate changes in the Caroline area which is located in the north of West Pacific Warm Pool, a comprehensive dating method was carried out by using radiocarbon testing(14C), oxygen isotope and paleomagnetism on a gravity core from the Caroline area of the western Pacific Ocean. 14C data provide the age of the upper section since 44.3 ka BP for this core. Subsequently, the age framework since MIS4 (about 80 ka) which corresponds to the depth of 125 cm was established by using oxygen isotope and relative paleointensity (RPI) data, while the upper part also considered the 14C data. Further analysis revealed that there was an obvious sedimentary discontinuity at the depth of 126 cm to 127 cm in this core, although it has been beyond the range of 14C dating, but the paleomagnetic results show that the core formed in Brunhes period, and the relationship between RPI and oxygen isotope data under the hiatus provide a robust evidence that the age is from 180 ka to 130 ka in the bottom. At the end the deposition rate of the core was obtained, which is 1 cm/ka to 2 cm/ka, and it is consistent before and after the deposition hiatus. At the same time, the disparity of the deposition rate for each dating method indicated that there was a large deviation of 14C data in one layer maybe due to the high rate of foraminiferal shell breaking.
2022, 44(6): 89-105.
doi: 10.12284/hyxb2022061
Abstract:
Magnetic mineral diagenesis is an important early diagenetic process after the burial of sediments and its proper identification is the precondition of interpretations for the mineral magnetic properties in the sediments. This study carried out analyses of sedimentary facies, room temperature magnetic and thermomagnetic properties in a Holocene Core MZ collected in the Shunde Plain of the Zhujiang River Delta to identify the vertical changes in the assemblage of magnetic minerals, so as to explore the early diagenetic stages and possible linkage to the sedimentary facies. The results show that the Holocene sedimentary sequence of Core MZ includes tidal channel, embayment, and deltaic successions from bottom upward. The magnetic properties at room temperature lack correlation with sedimentary facies and demonstrate features of strong early diagenesis. In addition, the magnetic properties of the late Holocene sediments were strongly influenced by the human activities. The early diagenesis mainly includes the dissolution of magnetic minerals and the formation of authigenic pyrite. Greigite was also identified in the upper section of the delta-front succession and the bottom of embayment succession. The concentration of greigite increases with depth in the embayment succession. According to the magnetic mineral assemblages, we infer different formation mechanism of greigite in the two successions. We suggest that the greigite in the delta-front facies was formed in the sulfate reduction stage of early diagenesis, whilst it was formed in the anaerobic oxidation stage of methane in the embayment facies. These phenomena indicate that sedimentary environment has impacts on the early diagenetic stage of magnetic minerals by controlling the availability of organic matter and sulfate.
Magnetic mineral diagenesis is an important early diagenetic process after the burial of sediments and its proper identification is the precondition of interpretations for the mineral magnetic properties in the sediments. This study carried out analyses of sedimentary facies, room temperature magnetic and thermomagnetic properties in a Holocene Core MZ collected in the Shunde Plain of the Zhujiang River Delta to identify the vertical changes in the assemblage of magnetic minerals, so as to explore the early diagenetic stages and possible linkage to the sedimentary facies. The results show that the Holocene sedimentary sequence of Core MZ includes tidal channel, embayment, and deltaic successions from bottom upward. The magnetic properties at room temperature lack correlation with sedimentary facies and demonstrate features of strong early diagenesis. In addition, the magnetic properties of the late Holocene sediments were strongly influenced by the human activities. The early diagenesis mainly includes the dissolution of magnetic minerals and the formation of authigenic pyrite. Greigite was also identified in the upper section of the delta-front succession and the bottom of embayment succession. The concentration of greigite increases with depth in the embayment succession. According to the magnetic mineral assemblages, we infer different formation mechanism of greigite in the two successions. We suggest that the greigite in the delta-front facies was formed in the sulfate reduction stage of early diagenesis, whilst it was formed in the anaerobic oxidation stage of methane in the embayment facies. These phenomena indicate that sedimentary environment has impacts on the early diagenetic stage of magnetic minerals by controlling the availability of organic matter and sulfate.
2022, 44(6): 106-115.
doi: 10.12284/hyxb2022055
Abstract:
The Jiaomen outlet is the main flood and sediment discharge of the Zhujiang River. It is connected with Humen outlet through a lateral branch, namely the Fuzhou Channel. The flow and sediment division ratio of the bifurcated Jiaomen outlet are important for flood control and navigation safety of the Guangdong-Hong Kong-Macao Greater Bay Area. Focusing on the flow division ratio of the Fuzhou Channel, this study designed a series of scaled physical experiments to explore the relationship between flow division ratio of the Fuzhou Channel and the flow of Jiaomen outlet and adjacent Humen outlet. The dimension of the physical model is based on morphological characteristics in the vicinity of the Jiaomen outlet nowadays. Results of the experiment are in good agreement with the filed measurements under two different flow conditions, demonstrating a reliable model performance. Subsequently, series of experiments have been carried out by varying upstream discharges of Humen and Jiaomen. Experimental results indicate that the division ratio of the Fuzhou Channel depicts a positive relationship with the flow velocity ratio between Humen and Jiaomen. Thus, the flow division ratio of the Fuzhou Channel depends on both Humen and Jiaomen. The experimental results further suggest that, under present geomorphic situation, if the upstream velocity ratio between Humen and Jiaomen decreases to 0.35, the Fuzhou Channel would shift from the main branch to secondary. The research results can provide a reference for the artificial regulation of Jiaomen outlet and its flood and navigation safety.
The Jiaomen outlet is the main flood and sediment discharge of the Zhujiang River. It is connected with Humen outlet through a lateral branch, namely the Fuzhou Channel. The flow and sediment division ratio of the bifurcated Jiaomen outlet are important for flood control and navigation safety of the Guangdong-Hong Kong-Macao Greater Bay Area. Focusing on the flow division ratio of the Fuzhou Channel, this study designed a series of scaled physical experiments to explore the relationship between flow division ratio of the Fuzhou Channel and the flow of Jiaomen outlet and adjacent Humen outlet. The dimension of the physical model is based on morphological characteristics in the vicinity of the Jiaomen outlet nowadays. Results of the experiment are in good agreement with the filed measurements under two different flow conditions, demonstrating a reliable model performance. Subsequently, series of experiments have been carried out by varying upstream discharges of Humen and Jiaomen. Experimental results indicate that the division ratio of the Fuzhou Channel depicts a positive relationship with the flow velocity ratio between Humen and Jiaomen. Thus, the flow division ratio of the Fuzhou Channel depends on both Humen and Jiaomen. The experimental results further suggest that, under present geomorphic situation, if the upstream velocity ratio between Humen and Jiaomen decreases to 0.35, the Fuzhou Channel would shift from the main branch to secondary. The research results can provide a reference for the artificial regulation of Jiaomen outlet and its flood and navigation safety.
2022, 44(6): 116-127.
doi: 10.12284/hyxb2022045
Abstract:
To investigate the characteristics of the flow field around non-submerged structures under solitary waves, a numerical model of the interaction between solitary waves and marine structures is established based on the meshless SPH method. By calculating and analyzing the characteristics of the wave surface, velocity, vorticity, and structure force under different amplitude solitary waves, the influence of relative wave height on the flow field around the non-submerged structure was explored. The results show that the flow field characteristics are closely related to the relative wave height. With a little relative wave height, the wave surface, velocity, vorticity, and structure force are smooth while the flow field fluctuate around the structure due to that the wave crest climbs to the top of the structure and collide with the water in the tank after passing the structure when the relative wave height is large than 0.2. The fluctuation amplitude of wave surface, velocity, vorticity and structure force increased with the increase of relative wave height, resulting in a more complex flow field. Meanwhile, the horizontal and vertical negative force of the structure are larger, the distribution of vorticity around the structure gradually develops to the depth and downstream direction.
To investigate the characteristics of the flow field around non-submerged structures under solitary waves, a numerical model of the interaction between solitary waves and marine structures is established based on the meshless SPH method. By calculating and analyzing the characteristics of the wave surface, velocity, vorticity, and structure force under different amplitude solitary waves, the influence of relative wave height on the flow field around the non-submerged structure was explored. The results show that the flow field characteristics are closely related to the relative wave height. With a little relative wave height, the wave surface, velocity, vorticity, and structure force are smooth while the flow field fluctuate around the structure due to that the wave crest climbs to the top of the structure and collide with the water in the tank after passing the structure when the relative wave height is large than 0.2. The fluctuation amplitude of wave surface, velocity, vorticity and structure force increased with the increase of relative wave height, resulting in a more complex flow field. Meanwhile, the horizontal and vertical negative force of the structure are larger, the distribution of vorticity around the structure gradually develops to the depth and downstream direction.
2022, 44(6): 128-139.
doi: 10.12284/hyxb2022039
Abstract:
The coastal current presents complex changes in spatiotemporal scale due to various dynamic processes and shoreline islands. High frequency surface wave radar has become an effective method to solve these problems because of its wide coverage area and high temporal resolution. Several years ocean current data was collected in Zhoushan sea area, the dynamic processes of the ocean in tide cycle, extreme events, intermonth and interannual time scales in this area were interpreted by using tidal current harmonic analysis, low pass filtering and correlation analysis. The results depicted that the Zhoushan sea area is a regular semi-diurnal tide area, and the current movement is mainly in the form of rotating current. The distribution of current velocity in investigation area illustrated a decreasing trend from northeast to southwest. Interannual variation of residual current in the Zhoushan sea area is not significant, however the obvious intermonth variation characteristic of the residual current was detected. In winter, the flow is southward, and its larger near shore than outside sea. On the contrary, the flow velocity is stronger and the spatial distribution is more uniform in summer. The correlation between wind and residual current was analyzed, during strong winds, the correlation coefficient between wind speed and residual current velocity ranged from 0.48 to 0.90, and the correlation coefficient between wind direction and residual current direction ranged from 0.55 to 0.68. When extreme events occur, the correlation coefficients of velocity and direction are 0.92 and 0.91, respectively. By way of conclusion, the analysis of high frequency surface wave radar data can well reflect the temporal and spatial characteristics of ocean currents in Zhoushan sea area, which provide a basis for marine disaster monitoring, pollutants and algal bloom transport research.
The coastal current presents complex changes in spatiotemporal scale due to various dynamic processes and shoreline islands. High frequency surface wave radar has become an effective method to solve these problems because of its wide coverage area and high temporal resolution. Several years ocean current data was collected in Zhoushan sea area, the dynamic processes of the ocean in tide cycle, extreme events, intermonth and interannual time scales in this area were interpreted by using tidal current harmonic analysis, low pass filtering and correlation analysis. The results depicted that the Zhoushan sea area is a regular semi-diurnal tide area, and the current movement is mainly in the form of rotating current. The distribution of current velocity in investigation area illustrated a decreasing trend from northeast to southwest. Interannual variation of residual current in the Zhoushan sea area is not significant, however the obvious intermonth variation characteristic of the residual current was detected. In winter, the flow is southward, and its larger near shore than outside sea. On the contrary, the flow velocity is stronger and the spatial distribution is more uniform in summer. The correlation between wind and residual current was analyzed, during strong winds, the correlation coefficient between wind speed and residual current velocity ranged from 0.48 to 0.90, and the correlation coefficient between wind direction and residual current direction ranged from 0.55 to 0.68. When extreme events occur, the correlation coefficients of velocity and direction are 0.92 and 0.91, respectively. By way of conclusion, the analysis of high frequency surface wave radar data can well reflect the temporal and spatial characteristics of ocean currents in Zhoushan sea area, which provide a basis for marine disaster monitoring, pollutants and algal bloom transport research.
2022, 44(6): 140-149.
doi: 10.12284/hyxb2022037
Abstract:
Rip current is a kind of high speed offshore current which occurs frequently in coastal. Based on Castelle’s rip current classification model, Google Earth images of 14 beaches in Guangdong Province were interpreted and classified, and the application of rip current classification model in remote sensing images was discussed. The results show that in high risk months, the composition of rip currents is relatively simple, the mixed rips are few, and the bathymetrically-controlled rip currents play a dominant role, and the number of rip currents remains at a high level. In the middle risk months, the proportion of hydrodynamically-controlled rip currents and mixed rips increases, while the proportion of bathymetrically-controlled rip currents still has a certain proportion. There is little or no rip currents in low-risk months. The structure of rip current is closely related to the state of beach. For the beach in the bay, the length of the bay affects the number of rip currents, and the concave degree of the bay affects the composition ratio of different types of rip currents. Considering the limitations of experimental conditions, this law needs to be further studied and verified in combination with the actual terrain and landform. The classification results obtained according to the interpretation criteria presented in this paper are in good agreement with the risk evaluation model proposed by previous authors, which further demonstrates the effectiveness of the interpretation criteria and provides some reference value for the future research and classification of rip currents.
Rip current is a kind of high speed offshore current which occurs frequently in coastal. Based on Castelle’s rip current classification model, Google Earth images of 14 beaches in Guangdong Province were interpreted and classified, and the application of rip current classification model in remote sensing images was discussed. The results show that in high risk months, the composition of rip currents is relatively simple, the mixed rips are few, and the bathymetrically-controlled rip currents play a dominant role, and the number of rip currents remains at a high level. In the middle risk months, the proportion of hydrodynamically-controlled rip currents and mixed rips increases, while the proportion of bathymetrically-controlled rip currents still has a certain proportion. There is little or no rip currents in low-risk months. The structure of rip current is closely related to the state of beach. For the beach in the bay, the length of the bay affects the number of rip currents, and the concave degree of the bay affects the composition ratio of different types of rip currents. Considering the limitations of experimental conditions, this law needs to be further studied and verified in combination with the actual terrain and landform. The classification results obtained according to the interpretation criteria presented in this paper are in good agreement with the risk evaluation model proposed by previous authors, which further demonstrates the effectiveness of the interpretation criteria and provides some reference value for the future research and classification of rip currents.
2022, 44(6): 150-163.
doi: 10.12284/hyxb2022059
Abstract:
Affected by fluvial sediment discharge, wind waves and tides, etc., suspended sediment in estuaries and adjacent waters has significant temporal and spatial changes. Based on the GOCI remote sensing images at hourly resolution, this paper uses the optimal remote sensing inversion algorithm, combined with spatial analysis and statistical methods to deeply study the temporal and spatial dynamic characteristics and driving mechanism of suspended sediment in the Yellow River Estuary and adjacent waters. The results show that the impact of fluvial sediment discharge on the concentration of suspended sediment is concentrated in the nearshore area of the estuary. The impact of high fluvial sediment discharge on the distribution of suspended sediment concentration can reach about 20 km offshore and spread to the Gudong nearshore area. Strong winds can cause intensive resuspension of sediment near the old river mouth of Qingshuigou, forming a high-concentration suspended sediment area. The flood and ebb tides have a significant impact on the hourly-scale suspended sediment concentration, and affect the dispersal of suspended sediment from north to south. The variation and dispersal range of the suspended sediment concentration in the spring tide are larger than that of the neap tide due to different tidal flow velocities. There is an obvious negative correlation between water depth and suspended sediment concentration. According to the difference of driving factors, the suspended sediment concentration present exponential, power function, and linear relationships with the increase of water depth.
Affected by fluvial sediment discharge, wind waves and tides, etc., suspended sediment in estuaries and adjacent waters has significant temporal and spatial changes. Based on the GOCI remote sensing images at hourly resolution, this paper uses the optimal remote sensing inversion algorithm, combined with spatial analysis and statistical methods to deeply study the temporal and spatial dynamic characteristics and driving mechanism of suspended sediment in the Yellow River Estuary and adjacent waters. The results show that the impact of fluvial sediment discharge on the concentration of suspended sediment is concentrated in the nearshore area of the estuary. The impact of high fluvial sediment discharge on the distribution of suspended sediment concentration can reach about 20 km offshore and spread to the Gudong nearshore area. Strong winds can cause intensive resuspension of sediment near the old river mouth of Qingshuigou, forming a high-concentration suspended sediment area. The flood and ebb tides have a significant impact on the hourly-scale suspended sediment concentration, and affect the dispersal of suspended sediment from north to south. The variation and dispersal range of the suspended sediment concentration in the spring tide are larger than that of the neap tide due to different tidal flow velocities. There is an obvious negative correlation between water depth and suspended sediment concentration. According to the difference of driving factors, the suspended sediment concentration present exponential, power function, and linear relationships with the increase of water depth.
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