2023 Vol. 45, No. 7
Display Method:
2023, 45(7): 1-7.
doi: 10.12284/hyxb2023121
Abstract:
As a frontier subject of nonlinear science, wave-current interaction has been studied by many scholars. This paper will explore the wave-current interaction under the serious sea conditions in the Northwest Pacific during the influenced by No.1 super Typhoon “Nepartak” in 2016. The results indicate that wave-current coupling model can effectively improve the simulation accuracy of significant wave height (SWH) under serious sea conditions. The influence of wave-current interaction on SWH is closely related to the angle between wave direction and sea surface current direction: when wave direction is close to current direction, wave-current interaction will decrease the SWH; in those areas where the wave and the current have the opposite direction, wave-current interaction will increase the SWH; the closer the angle between the wave and the current is to 90°, the less influence wave-current interaction has on the SWH. The maximum SWH difference whether including wave-current interaction or not is about 1.5 m.
As a frontier subject of nonlinear science, wave-current interaction has been studied by many scholars. This paper will explore the wave-current interaction under the serious sea conditions in the Northwest Pacific during the influenced by No.1 super Typhoon “Nepartak” in 2016. The results indicate that wave-current coupling model can effectively improve the simulation accuracy of significant wave height (SWH) under serious sea conditions. The influence of wave-current interaction on SWH is closely related to the angle between wave direction and sea surface current direction: when wave direction is close to current direction, wave-current interaction will decrease the SWH; in those areas where the wave and the current have the opposite direction, wave-current interaction will increase the SWH; the closer the angle between the wave and the current is to 90°, the less influence wave-current interaction has on the SWH. The maximum SWH difference whether including wave-current interaction or not is about 1.5 m.
2023, 45(7): 8-24.
doi: 10.12284/hyxb2023101
Abstract:
Based on the tide level data along the tidal reach of Xijiang River from 2015 to 2017, we applied the nonstationary tidal harmonic analysis model NS-TIDE to study the spatial and temporal variation characteristics of the amplitude and phase of different cycles of tidal constituent, the change of tidal dynamics composition and tidal wave deformation characteristics, and discussed the causes of tidal level deformation and the reversal of the lowest low waters along the tidal reach. The results show that, unlike the diurnal constituent and semi-diurnal constituent along the tidal reach that have amplitude decay and phase increment, the shallow water component amplitude increases and then decreases, the amplitude of MSf is increasing, and the phase is changing alternately; the decay rate of each tidal amplitude is higher in the flood season than in the dry season, and the phase changes more in the flood season, indicating that the tidal wave propagates upstream more slowly under the top support of river discharge. Due to the influence of river discharge and topography, the amplitude of MSf is larger in the flood season and upstream section of the river, and the tidal dynamic composition changes from the main tidal constituent to the secondary tidal constituent; the change of amplitude ratio of M4 and M2 indicates significant tidal deformation, and the reversal of the lowest low waters when the amplitude ratio of MSf to M2 and S2 is relatively large.
Based on the tide level data along the tidal reach of Xijiang River from 2015 to 2017, we applied the nonstationary tidal harmonic analysis model NS-TIDE to study the spatial and temporal variation characteristics of the amplitude and phase of different cycles of tidal constituent, the change of tidal dynamics composition and tidal wave deformation characteristics, and discussed the causes of tidal level deformation and the reversal of the lowest low waters along the tidal reach. The results show that, unlike the diurnal constituent and semi-diurnal constituent along the tidal reach that have amplitude decay and phase increment, the shallow water component amplitude increases and then decreases, the amplitude of MSf is increasing, and the phase is changing alternately; the decay rate of each tidal amplitude is higher in the flood season than in the dry season, and the phase changes more in the flood season, indicating that the tidal wave propagates upstream more slowly under the top support of river discharge. Due to the influence of river discharge and topography, the amplitude of MSf is larger in the flood season and upstream section of the river, and the tidal dynamic composition changes from the main tidal constituent to the secondary tidal constituent; the change of amplitude ratio of M4 and M2 indicates significant tidal deformation, and the reversal of the lowest low waters when the amplitude ratio of MSf to M2 and S2 is relatively large.
2023, 45(7): 25-39.
doi: 10.12284/hyxb2023099
Abstract:
Under the background of global climate change, the extreme storm surge events caused by tropical cyclones in the Changjiang River Estuary and adjacent coastal area present non-stationary feature. In this study, a storm surge model for the Changjiang River Estuary was constructed using the ADCIRC model to reproduce the storm surges during 241 tropical cyclones affecting the Changjiang River Estuary from 1979 to 2019. By combining the non-stationary generalized extreme value distribution with the state space approach, a statistical model for capturing the non-stationarity of extreme storm surges was built to investigate the spatiotemporal variability of the extreme storm surges in the Changjiang River Estuary and its adjacent coastal area. The statistical model can well reproduce the non-stationary feature of extreme storm surges, which was mainly represented by the time-dependent location parameter. The time-dependent location parameters at the tidal gauge stations were stationary before 2008 and presented increasing trends afterwards, which was mainly caused by the increase of the annual second- and third-largest storm surges. The reoccurrence period of storm surge event with 100-year return period under the stationary assumption was reduced to around 40–80 years, indicating an increased flood risk in the Changjiang River Estuary. Combined with the changes in the intensity and path of the tropical cyclones that caused the annual second- and third-largest storm surges, it was concluded that the increasing trends of extreme storm surges were mainly caused by the increase in the intensity of the tropical cyclone that tracking northward to the offshore of the Changjiang River Estuary and veering eastwards.
Under the background of global climate change, the extreme storm surge events caused by tropical cyclones in the Changjiang River Estuary and adjacent coastal area present non-stationary feature. In this study, a storm surge model for the Changjiang River Estuary was constructed using the ADCIRC model to reproduce the storm surges during 241 tropical cyclones affecting the Changjiang River Estuary from 1979 to 2019. By combining the non-stationary generalized extreme value distribution with the state space approach, a statistical model for capturing the non-stationarity of extreme storm surges was built to investigate the spatiotemporal variability of the extreme storm surges in the Changjiang River Estuary and its adjacent coastal area. The statistical model can well reproduce the non-stationary feature of extreme storm surges, which was mainly represented by the time-dependent location parameter. The time-dependent location parameters at the tidal gauge stations were stationary before 2008 and presented increasing trends afterwards, which was mainly caused by the increase of the annual second- and third-largest storm surges. The reoccurrence period of storm surge event with 100-year return period under the stationary assumption was reduced to around 40–80 years, indicating an increased flood risk in the Changjiang River Estuary. Combined with the changes in the intensity and path of the tropical cyclones that caused the annual second- and third-largest storm surges, it was concluded that the increasing trends of extreme storm surges were mainly caused by the increase in the intensity of the tropical cyclone that tracking northward to the offshore of the Changjiang River Estuary and veering eastwards.
2023, 45(7): 40-55.
doi: 10.12284/hyxb2023115
Abstract:
Phytoplankton blooms in polar regions with seasonal sea ice cover show a unimodal seasonality. However, the bloom processes are controlled by multiple physical and biogeochemical factors, including sea ice, light availability, mixed layer depth, and nutrients; those may result in great uncertainties in simulating phytoplankton bloom by the Earth System Models (ESMs). In this study, the results of 11 Coupled Model Intercomparison Phase-6 (CMIP6) ESMs were analyzed and evaluated with various types of observational products in order to determine whether those ESMs can correctly model the phytoplankton blooms in three Arctic shelf seas, Barents Sea, Chukchi Sea, and Bering Sea. By calculating multiple indices that represent light and nutrient limitations, the error sources of simulated surface chlorophyll a concentrations were comprehensively analyzed. Our results show that the 11 ESMs can be divided into three groups based on ice-adjusted photoperiod, rate of change of mixed layer depth, and surface nitrate concentration. Some groups are characterized by the smallest bias between modeled indices and observation-based reference, and those ESMs perform best in simulating phytoplankton bloom characteristics. The other groups of ESMs differ significantly from the reference values in terms of surface nitrate and/or rate of change of mixed layer depth, resulting in delayed occurrences of annual chlorophyll a peak concentration and greater differences in corresponding peak values. In general, in addition to the two primary constraints of light and nutrients, the ESMs should also well represent the upper mixed layer controlled by temperature and salinity distributions, so as to accurately simulate the seasonal variation of surface chlorophyll a concentration. The above analyses indicate ESMs can be used in assessing polar planktonic ecosystems, and there is room for improving ecosystem-related parametrization in future ESM development.
Phytoplankton blooms in polar regions with seasonal sea ice cover show a unimodal seasonality. However, the bloom processes are controlled by multiple physical and biogeochemical factors, including sea ice, light availability, mixed layer depth, and nutrients; those may result in great uncertainties in simulating phytoplankton bloom by the Earth System Models (ESMs). In this study, the results of 11 Coupled Model Intercomparison Phase-6 (CMIP6) ESMs were analyzed and evaluated with various types of observational products in order to determine whether those ESMs can correctly model the phytoplankton blooms in three Arctic shelf seas, Barents Sea, Chukchi Sea, and Bering Sea. By calculating multiple indices that represent light and nutrient limitations, the error sources of simulated surface chlorophyll a concentrations were comprehensively analyzed. Our results show that the 11 ESMs can be divided into three groups based on ice-adjusted photoperiod, rate of change of mixed layer depth, and surface nitrate concentration. Some groups are characterized by the smallest bias between modeled indices and observation-based reference, and those ESMs perform best in simulating phytoplankton bloom characteristics. The other groups of ESMs differ significantly from the reference values in terms of surface nitrate and/or rate of change of mixed layer depth, resulting in delayed occurrences of annual chlorophyll a peak concentration and greater differences in corresponding peak values. In general, in addition to the two primary constraints of light and nutrients, the ESMs should also well represent the upper mixed layer controlled by temperature and salinity distributions, so as to accurately simulate the seasonal variation of surface chlorophyll a concentration. The above analyses indicate ESMs can be used in assessing polar planktonic ecosystems, and there is room for improving ecosystem-related parametrization in future ESM development.
Temperature profile inversion in the South China Sea under the constraint of depth-fixed temperature
2023, 45(7): 126-136.
doi: 10.12284/hyxb2023097
Abstract:
In order to quickly obtain a large-scale, quasi-real-time internal structure of the ocean, sea surface remote sensing data are widely used to construct the vertical structure of the temperature profiles, but satellite remote sensing can only obtain relatively accurate ocean surface or near-surface data. In order to improve the accuracy of temperature profile inversion, this paper takes the depth-fixed temperature as the constraint, and the nonlinear mapping between the temperature profiles and the sea surface remote sensing data such as sea surface temperature (SST) and sea level anomaly (SLA) is generated through the radial basis function (RBF) neural network, and discuss the theoretical basis for constrained depth selection. The inversion results of the temperature profiles in the South China Sea show that the first empirical orthogonal function (EOF) coefficient can characterize the vertical displacement of the thermocline. And there is a strong correlation between the temperature at the depth corresponding to the extreme point of the first EOF and the first EOF coefficient. Therefore, when the temperature at this depth is added as a constraint, the inversion accuracy of the thermocline is about 0.35℃ higher than that of only using sea surface remote sensing data, and the mean root mean square error of temperature profile inversion is about 0.33℃.
In order to quickly obtain a large-scale, quasi-real-time internal structure of the ocean, sea surface remote sensing data are widely used to construct the vertical structure of the temperature profiles, but satellite remote sensing can only obtain relatively accurate ocean surface or near-surface data. In order to improve the accuracy of temperature profile inversion, this paper takes the depth-fixed temperature as the constraint, and the nonlinear mapping between the temperature profiles and the sea surface remote sensing data such as sea surface temperature (SST) and sea level anomaly (SLA) is generated through the radial basis function (RBF) neural network, and discuss the theoretical basis for constrained depth selection. The inversion results of the temperature profiles in the South China Sea show that the first empirical orthogonal function (EOF) coefficient can characterize the vertical displacement of the thermocline. And there is a strong correlation between the temperature at the depth corresponding to the extreme point of the first EOF and the first EOF coefficient. Therefore, when the temperature at this depth is added as a constraint, the inversion accuracy of the thermocline is about 0.35℃ higher than that of only using sea surface remote sensing data, and the mean root mean square error of temperature profile inversion is about 0.33℃.
2023, 45(7): 56-68.
doi: 10.12284/hyxb2023105
Abstract:
Rare earth elements (REE) and their relationships with biogenic silica (BSiO2), magnetic susceptibility, Al2O3 and Fe2O3 in Core DC-11 were analyzed to reveal sediment provenances and transport history by iceberg-current-atmosphere since 34 ka BP in the southeastern Scotia Sea, Antarctica. Temporal variation of REE is similar to that of Al2O3, indicating they mainly occur in terrigenous detritus and BSiO2 has obvious dilution effect on them. Sediments with high REE concentration, flat shale-normalized pattern, weak positive Eu anomaly, and high LaN/YbN ratio during the last glacial period indicated they are transferred from the Weddell Sea and eroded from the bordering lands with relatively old crust. The increases in magnetic susceptibility, ΔAl2O3, TFe2O3/Eu ratio indicated an enhanced input of dust from South America during this period. In early Deglaciation (19.6−14.1 ka BP), increasing Eu positive anomaly and lower LaN/YbN ratio indicated the southern branch of Antarctic Circumpolar Current (ACC) strengthened and contributed more sediments from the South Shetland Islands and Antarctic Peninsula due to the southward shifts of oceanic fronts, while decreasing magnetic susceptibility, ΔAl2O3, TFe2O3/Eu ratios showed rapid decrease in dust supply from South America. During the Antarctic Cold Reversal period (ACR, 14.1−12.9 ka BP), sediments from the South Shetland Islands and Antarctic Peninsula decreased sharply due to cold condition and weakened ACC branch, the weakest Eu positive anomaly and highest LaN/YbN ratio indicated that the sediments from the Weddell Sea dominated in the core again, and the peak of ice raft debris indicated ice rafting is vital or dominant agent. In the late Deglaciation (12.9−11.7 ka BP), the return of ACC branch to the South Shetland Islands and Antarctic Peninsula contributed more to the sediments in Core DC-11; in Holocene (11.7−0 ka BP), the ACC branch in the area between the South Shetland Islands and Antarctic Peninsula was generally enhanced, and its contribution to core sediments increased to be roughly equivalent to the amount of sediments from the Weddell Sea.
Rare earth elements (REE) and their relationships with biogenic silica (BSiO2), magnetic susceptibility, Al2O3 and Fe2O3 in Core DC-11 were analyzed to reveal sediment provenances and transport history by iceberg-current-atmosphere since 34 ka BP in the southeastern Scotia Sea, Antarctica. Temporal variation of REE is similar to that of Al2O3, indicating they mainly occur in terrigenous detritus and BSiO2 has obvious dilution effect on them. Sediments with high REE concentration, flat shale-normalized pattern, weak positive Eu anomaly, and high LaN/YbN ratio during the last glacial period indicated they are transferred from the Weddell Sea and eroded from the bordering lands with relatively old crust. The increases in magnetic susceptibility, ΔAl2O3, TFe2O3/Eu ratio indicated an enhanced input of dust from South America during this period. In early Deglaciation (19.6−14.1 ka BP), increasing Eu positive anomaly and lower LaN/YbN ratio indicated the southern branch of Antarctic Circumpolar Current (ACC) strengthened and contributed more sediments from the South Shetland Islands and Antarctic Peninsula due to the southward shifts of oceanic fronts, while decreasing magnetic susceptibility, ΔAl2O3, TFe2O3/Eu ratios showed rapid decrease in dust supply from South America. During the Antarctic Cold Reversal period (ACR, 14.1−12.9 ka BP), sediments from the South Shetland Islands and Antarctic Peninsula decreased sharply due to cold condition and weakened ACC branch, the weakest Eu positive anomaly and highest LaN/YbN ratio indicated that the sediments from the Weddell Sea dominated in the core again, and the peak of ice raft debris indicated ice rafting is vital or dominant agent. In the late Deglaciation (12.9−11.7 ka BP), the return of ACC branch to the South Shetland Islands and Antarctic Peninsula contributed more to the sediments in Core DC-11; in Holocene (11.7−0 ka BP), the ACC branch in the area between the South Shetland Islands and Antarctic Peninsula was generally enhanced, and its contribution to core sediments increased to be roughly equivalent to the amount of sediments from the Weddell Sea.
2023, 45(7): 168-182.
doi: 10.12284/hyxb2023055
Abstract:
Most of the small rivers in the Shandong Peninsula have clear sediment sources and relatively small mineral deposition differentiation, and their study can provide regional similarities for the analysis of the sources of large rivers into the sea, as well as the characteristics of the material sources in the Shandong Peninsula for the deposition of the Yellow Sea shelf and Bohai Sea shelf. In this paper, the distribution patterns of detrital minerals in surface sediment samples taken from riverbeds, estuaries and beaches were analysed at multiple grain levels, taking the Xin’an River, a small short-source river in the northeastern part of the Shandong Peninsula, as an example. The study shows that the Xin’an River basin and beach sediments are mostly medium and fine sands, with moderate heavy mineral content in the whole sample, ranging from 1.47% to 8.19%. Twenty-seven heavy minerals and eight light minerals occur, with the main heavy minerals hornblende (41.7%), chlorite (16.7%), actinolite (10.6%) and limonite (6.7%) and the main light minerals quartz (49.0%), plagioclase (26.5%) and potassium feldspar (20.7%), which are much more abundant than the other detrital minerals in the riverbed, estuary and beach, and the mineral assemblage remains constant, with less significant variation in relative content between them, while there is a significant non-linear correlation between non-dominant mineral species and clastic grain size. Mineral species and content in the Xin’an River are controlled by the regional lithological sources, i.e. acidic and moderately acidic intrusive rocks and regional metamorphic rocks, and the relatively stable output of amphibole group minerals across the different features of the Xin’an River is responsible for their homogeneity. The short source rivers of the Shandong Peninsula are derived from similar geological features and rock types, although the types and content of detrital minerals vary. The main controlling factors for mineral composition variation are regional sources and particle size sorting, followed by sedimentary environmental differences. In contrast, the high content of mica group and carbonate minerals in a specific grain size and the low content of amphibole group minerals are the aspects that distinguish the Huanghe River from the river source materials in the northern and southern coastal waters of the Shandong Peninsula.
Most of the small rivers in the Shandong Peninsula have clear sediment sources and relatively small mineral deposition differentiation, and their study can provide regional similarities for the analysis of the sources of large rivers into the sea, as well as the characteristics of the material sources in the Shandong Peninsula for the deposition of the Yellow Sea shelf and Bohai Sea shelf. In this paper, the distribution patterns of detrital minerals in surface sediment samples taken from riverbeds, estuaries and beaches were analysed at multiple grain levels, taking the Xin’an River, a small short-source river in the northeastern part of the Shandong Peninsula, as an example. The study shows that the Xin’an River basin and beach sediments are mostly medium and fine sands, with moderate heavy mineral content in the whole sample, ranging from 1.47% to 8.19%. Twenty-seven heavy minerals and eight light minerals occur, with the main heavy minerals hornblende (41.7%), chlorite (16.7%), actinolite (10.6%) and limonite (6.7%) and the main light minerals quartz (49.0%), plagioclase (26.5%) and potassium feldspar (20.7%), which are much more abundant than the other detrital minerals in the riverbed, estuary and beach, and the mineral assemblage remains constant, with less significant variation in relative content between them, while there is a significant non-linear correlation between non-dominant mineral species and clastic grain size. Mineral species and content in the Xin’an River are controlled by the regional lithological sources, i.e. acidic and moderately acidic intrusive rocks and regional metamorphic rocks, and the relatively stable output of amphibole group minerals across the different features of the Xin’an River is responsible for their homogeneity. The short source rivers of the Shandong Peninsula are derived from similar geological features and rock types, although the types and content of detrital minerals vary. The main controlling factors for mineral composition variation are regional sources and particle size sorting, followed by sedimentary environmental differences. In contrast, the high content of mica group and carbonate minerals in a specific grain size and the low content of amphibole group minerals are the aspects that distinguish the Huanghe River from the river source materials in the northern and southern coastal waters of the Shandong Peninsula.
2023, 45(7): 69-78.
doi: 10.12284/hyxb2023078
Abstract:
Occasional species are vulnerable to external threats such as environmental changes and human activities and have important values in biodiversity conservation. However, due to their limited availability of data and associated difficulties in statistical analysis, there are few studies on the spatial distribution and their relationships with environmental factors. In this study, based on the fishery resource surveys in the Haizhou Bay conducted from 2013 to 2019, we analyzed the relationships between the distribution and environmental factors for three occasional species, Coilia mystus, Odontamblyopus rubicundus and Erisphex pottii, using generalized additive model (GAM) and random forest (RF) model. The models were compared according to their goodness of fit and the predictive performances were evaluated using cross-validation. The results showed that depth was the most significant factor affecting the distribution of C. mystus and O. rubicundus in spring and autumn, the sea bottom temperature was the most important environmental factor influencing the distribution of E. pottii in autumn. The distribution model of C. mystus had the highest deviance explanation, followed by O. rubicundus, and E. pottii had the lowest deviance explanation. The deviance explanation by the distribution models of C. mystus, O. rubicundus and E. pottii were all lower in spring than in autumn. The cross-validation showed that the area under the curve (AUC) of the three species ranged from 0.70 to 0.85, and only the AUC of C. mystus reached 0.9 in autumn; meanwhile, the AUC of the GAM prediction results were larger than those of the RF model, indicating that the prediction performance of the GAM was better than that of the RF model for the occasional species. This study would provide a reference for the selection of models for future studies of occasional species, and have guiding significance for the conservation of the occasional species.
Occasional species are vulnerable to external threats such as environmental changes and human activities and have important values in biodiversity conservation. However, due to their limited availability of data and associated difficulties in statistical analysis, there are few studies on the spatial distribution and their relationships with environmental factors. In this study, based on the fishery resource surveys in the Haizhou Bay conducted from 2013 to 2019, we analyzed the relationships between the distribution and environmental factors for three occasional species, Coilia mystus, Odontamblyopus rubicundus and Erisphex pottii, using generalized additive model (GAM) and random forest (RF) model. The models were compared according to their goodness of fit and the predictive performances were evaluated using cross-validation. The results showed that depth was the most significant factor affecting the distribution of C. mystus and O. rubicundus in spring and autumn, the sea bottom temperature was the most important environmental factor influencing the distribution of E. pottii in autumn. The distribution model of C. mystus had the highest deviance explanation, followed by O. rubicundus, and E. pottii had the lowest deviance explanation. The deviance explanation by the distribution models of C. mystus, O. rubicundus and E. pottii were all lower in spring than in autumn. The cross-validation showed that the area under the curve (AUC) of the three species ranged from 0.70 to 0.85, and only the AUC of C. mystus reached 0.9 in autumn; meanwhile, the AUC of the GAM prediction results were larger than those of the RF model, indicating that the prediction performance of the GAM was better than that of the RF model for the occasional species. This study would provide a reference for the selection of models for future studies of occasional species, and have guiding significance for the conservation of the occasional species.
2023, 45(7): 90-101.
doi: 10.12284/hyxb2023080
Abstract:
In this study, hydrodynamic characteristics of transformation and breaking processes of the undular tidal bore on the uneven seabed have been numerically investigated by applying a nonhydrostatic numerical wave model (NHWAVE). Effects of tidal bore height, initial water depth and bed slope on the hydrodynamics of tidal bore are discussed in detail. Research findings indicates that the tidal bore height and initial water depth have significant effects on the transformation and breaking processes of the undular tidal bore on the uneven seabed. However, different bed slope on the undular tidal bore hydrodynamic characteristics of the influence of less. The existence of bed slope can lead to a significant increase in the height of the undular tidal bore, causing dramatic changes in the maximum water level along the range, and make the tidal bore propagation speed is reduced. The average speed of water depth tends to increase with the tidal bore height, as well as the height difference between the upstream and downstream tidal bore height. When increasing the water depth, the tidal difference between the upstream and downstream tidal bore height decreases, and the surface velocity decreases monotonically with the average velocity of water depth. The research findings drawn from this study can have certain reference significances for the accurate understanding of the hydrodynamics of tidal bore on the uneven seabed. It provides a scientific basis for the engineering design and safety assessment of wading buildings in the tidal river section.
In this study, hydrodynamic characteristics of transformation and breaking processes of the undular tidal bore on the uneven seabed have been numerically investigated by applying a nonhydrostatic numerical wave model (NHWAVE). Effects of tidal bore height, initial water depth and bed slope on the hydrodynamics of tidal bore are discussed in detail. Research findings indicates that the tidal bore height and initial water depth have significant effects on the transformation and breaking processes of the undular tidal bore on the uneven seabed. However, different bed slope on the undular tidal bore hydrodynamic characteristics of the influence of less. The existence of bed slope can lead to a significant increase in the height of the undular tidal bore, causing dramatic changes in the maximum water level along the range, and make the tidal bore propagation speed is reduced. The average speed of water depth tends to increase with the tidal bore height, as well as the height difference between the upstream and downstream tidal bore height. When increasing the water depth, the tidal difference between the upstream and downstream tidal bore height decreases, and the surface velocity decreases monotonically with the average velocity of water depth. The research findings drawn from this study can have certain reference significances for the accurate understanding of the hydrodynamics of tidal bore on the uneven seabed. It provides a scientific basis for the engineering design and safety assessment of wading buildings in the tidal river section.
2023, 45(7): 102-109.
doi: 10.12284/hyxb2023051
Abstract:
Polar ships always collide with various types of sea ice in varying degrees during their voyages in ice-covered regions, so sufficient fatigue strength reserves are essential. This paper proposes a cumulative damage analysis method for ice-induced fatigue on polar ship structures based on field measured ice loads. Firstly, according to the statistical analysis of the field data of ice thickness and sailing speed of RV Xue Long during the China’s 8th Arctic Scientific Expedition, ice-induced fatigue conditions are constructed within the ice thickness range of 0.5−2.5 m and the sailing speed range of 2−12 kn. The joint probability distribution of the two parameters is taken as the occurrence probability of fatigue conditions. Then, the time histories of ice loads under typical conditions are identified based on the support vector machine method. The key positions and corresponding hot spot stresses are determined by dynamic analysis. The rainflow counting algorithm is adopted to count the number of stress cycles. Finally, the fatigue damage during the voyage is further calculated by S-N curve and Miner linear cumulative damage theory, which verifies the ice navigation safety of RV Xue Long. This paper has certain reference significance for the ice-resistant design and safety evaluation of polar ship structures.
Polar ships always collide with various types of sea ice in varying degrees during their voyages in ice-covered regions, so sufficient fatigue strength reserves are essential. This paper proposes a cumulative damage analysis method for ice-induced fatigue on polar ship structures based on field measured ice loads. Firstly, according to the statistical analysis of the field data of ice thickness and sailing speed of RV Xue Long during the China’s 8th Arctic Scientific Expedition, ice-induced fatigue conditions are constructed within the ice thickness range of 0.5−2.5 m and the sailing speed range of 2−12 kn. The joint probability distribution of the two parameters is taken as the occurrence probability of fatigue conditions. Then, the time histories of ice loads under typical conditions are identified based on the support vector machine method. The key positions and corresponding hot spot stresses are determined by dynamic analysis. The rainflow counting algorithm is adopted to count the number of stress cycles. Finally, the fatigue damage during the voyage is further calculated by S-N curve and Miner linear cumulative damage theory, which verifies the ice navigation safety of RV Xue Long. This paper has certain reference significance for the ice-resistant design and safety evaluation of polar ship structures.
2023, 45(7): 79-89.
doi: 10.12284/hyxb2023093
Abstract:
In the real sea state, the differences in directions of component waves result in three-dimensional short-crested waves, which have many different characteristics compared to two-dimensional long-crested waves. Therefore, in present study, the whole generation and evolution processes of short-crested freak waves are experimentally simulated by dispersive and directional focusing of component waves, in order to examine the external features and relationship of the abnormal large waves occurring during the processes. The results indicate that the abnormal large wave evolves symmetrically along the peak wave direction and undergoes a three- or four-stage process, each stage is indicated by the characteristic parameters of the abnormal large wave, it implies that the characteristic parameters can be used to identify the stage which the large abnormal wave is in and predict the variation tendency; and that compared to the two-dimensional cases, the “wave group” and “deep trough” stages are likely to be skipped, as a result, the spatio-temporal spans of the generation and evolution processes are smaller for the three-dimensional cases, it implies that in three-dimensional wave fields, the deep troughs and successive large waves (wave group) associated with freak waves may have a low probability of occurrence.
In the real sea state, the differences in directions of component waves result in three-dimensional short-crested waves, which have many different characteristics compared to two-dimensional long-crested waves. Therefore, in present study, the whole generation and evolution processes of short-crested freak waves are experimentally simulated by dispersive and directional focusing of component waves, in order to examine the external features and relationship of the abnormal large waves occurring during the processes. The results indicate that the abnormal large wave evolves symmetrically along the peak wave direction and undergoes a three- or four-stage process, each stage is indicated by the characteristic parameters of the abnormal large wave, it implies that the characteristic parameters can be used to identify the stage which the large abnormal wave is in and predict the variation tendency; and that compared to the two-dimensional cases, the “wave group” and “deep trough” stages are likely to be skipped, as a result, the spatio-temporal spans of the generation and evolution processes are smaller for the three-dimensional cases, it implies that in three-dimensional wave fields, the deep troughs and successive large waves (wave group) associated with freak waves may have a low probability of occurrence.
2023, 45(7): 183-194.
doi: 10.12284/hyxb2023113
Abstract:
Seagrass coverage ratio is an important indicator reflecting the ecological status of seagrass beds. In this paper, through the design of aerial photography scheme and flight condition test, the high-resolution seagrass image map of the Dongjiao Coconut Forest sea area was obtained by using UAV aerial photography. Combined with the image classification tools of ArcGIS software and 3D tools, a new method for calculating the coverage ratio of seagrass were obtained and the coverage of seagrass was calculated. The station location of simulating survey method of the traditional seagrass coverage ratio was compared and discussed. Seagrasses in the coastal sea bed of the Dongjiao Coconut Forest are distributed on the coral reefs within 300 m from the shore with patches and intervals. Using the new method, the concentrated distribution area of seagrass at sea bed of the Dongjiao Coconut Forest is about 23 221 m2, and average concentration distribution ratio is 17.79%. The distribution area of seagrass in this study area is about 16 423 m2, and the coverage ratio of seagrass is 12.58%. The coverage ratio of seagrass is higher, and the ecological condition of seagrass bed is good. Sargassum is densely distributed in the southeast area of the study area, with a distribution area of 755.6 m2 and a coverage of 0.5%, and grows as a single cylinder floating. By simulating the investigation station location of the sample frame method and sample line method of traditional seagrass coverage survey, seagrass coverage ratio changes with different stations, sample frame, and sample line positions changing randomly, which is the reason for the representativeness and comparability of the traditional survey results. The research results of this project have the promotion and application value in the investigation of seagrass ecological monitoring area.
Seagrass coverage ratio is an important indicator reflecting the ecological status of seagrass beds. In this paper, through the design of aerial photography scheme and flight condition test, the high-resolution seagrass image map of the Dongjiao Coconut Forest sea area was obtained by using UAV aerial photography. Combined with the image classification tools of ArcGIS software and 3D tools, a new method for calculating the coverage ratio of seagrass were obtained and the coverage of seagrass was calculated. The station location of simulating survey method of the traditional seagrass coverage ratio was compared and discussed. Seagrasses in the coastal sea bed of the Dongjiao Coconut Forest are distributed on the coral reefs within 300 m from the shore with patches and intervals. Using the new method, the concentrated distribution area of seagrass at sea bed of the Dongjiao Coconut Forest is about 23 221 m2, and average concentration distribution ratio is 17.79%. The distribution area of seagrass in this study area is about 16 423 m2, and the coverage ratio of seagrass is 12.58%. The coverage ratio of seagrass is higher, and the ecological condition of seagrass bed is good. Sargassum is densely distributed in the southeast area of the study area, with a distribution area of 755.6 m2 and a coverage of 0.5%, and grows as a single cylinder floating. By simulating the investigation station location of the sample frame method and sample line method of traditional seagrass coverage survey, seagrass coverage ratio changes with different stations, sample frame, and sample line positions changing randomly, which is the reason for the representativeness and comparability of the traditional survey results. The research results of this project have the promotion and application value in the investigation of seagrass ecological monitoring area.
2023, 45(7): 110-125.
doi: 10.12284/hyxb2023111
Abstract:
Fully integrating the use of satellite remote sensing and in-situ observation information to build a high-quality underwater temperature and salinity fields is a frontier topic in the development of marine scientific research. Currently, the vast majority of assimilation systems use assimilation schemes that require the assumption that elements have some artificially predetermined relationship between the surface and underwater. As a result, the temperature and salinity analysis field was more man-made and could not objectively reflect the real state of the ocean. This paper proposed a scheme that did not make any relationship assumptions, only relied on the complementary effects of different types of observation data in time and space, and combined the satellite remote sensing and in-situ observations for spatio-temporal four-dimensional multiscale objective analysis. Compared with the experimental results of assimilating these two types of observation data separately, it was found that the method could not only obtain more accurate temperature and salinity profile structure characteristics, but also reflect the detailed information of the mesoscale changes in the sea surface, the multi-scale information in the observation data was extracted to the maximum, and the effect of “1 + 1 > 2” was realized, and constructed a completely objective temperature and salinity analysis field. The results also showed that assimilating satellite remote sensing sea surface salinity data can effectively improve the analysis of temperature and salinity, which proved that the role of satellite remote sensing sea surface salinity observation on temperature and salinity assimilation could not be ignored.
Fully integrating the use of satellite remote sensing and in-situ observation information to build a high-quality underwater temperature and salinity fields is a frontier topic in the development of marine scientific research. Currently, the vast majority of assimilation systems use assimilation schemes that require the assumption that elements have some artificially predetermined relationship between the surface and underwater. As a result, the temperature and salinity analysis field was more man-made and could not objectively reflect the real state of the ocean. This paper proposed a scheme that did not make any relationship assumptions, only relied on the complementary effects of different types of observation data in time and space, and combined the satellite remote sensing and in-situ observations for spatio-temporal four-dimensional multiscale objective analysis. Compared with the experimental results of assimilating these two types of observation data separately, it was found that the method could not only obtain more accurate temperature and salinity profile structure characteristics, but also reflect the detailed information of the mesoscale changes in the sea surface, the multi-scale information in the observation data was extracted to the maximum, and the effect of “1 + 1 > 2” was realized, and constructed a completely objective temperature and salinity analysis field. The results also showed that assimilating satellite remote sensing sea surface salinity data can effectively improve the analysis of temperature and salinity, which proved that the role of satellite remote sensing sea surface salinity observation on temperature and salinity assimilation could not be ignored.
2023, 45(7): 137-146.
doi: 10.12284/hyxb2023109
Abstract:
Based on the statistical data of direct economic losses of typhoon storm surge in China from 1989 to 2021, the economic losses of storm surge disasters in China during 32 years showed a significant downward trend, showing a thick-tailed distribution as a whole, and a normal distribution after logarithmic processing. The periodic changes of the direct economic losses of typhoon storm surge in China were analyzed by Morlet wavelet analysis method. According to the t-test, there were two quasi-high-frequency oscillations in the whole region, 1−2 years and 7−8 years oscillation , but the annual cycle gradually shortened to 3−5 years with the change of time. It indicated that the economic loss sequence of storm surge had high-frequency oscillation and multi-period nested low-frequency oscillation. On this basis, Daubechies wavelet decomposition was used to separate high frequency signal and low frequency signal. According to the results of root mean square error (RMSE) and signal-to-noise ratio, Daubechies wavelet base was set the vanishing moment is 7 and the number of decomposition layers is 2 for the direct economic loss time series of typhoon storm surges in China from 1989 to 2021, which had the optimal decomposition and reconstruction effect. Based on the results of stationarity test and white noise test of wavelet coefficients of each decomposition layer, the combined wavelet decomposed−ARMA model was established. The simulation accuracy and prediction accuracy were both better than that of single Autoregressive Integrated Moving Average model and Fourier series expansion model, which verified the reliability and superiority of wavelet decomposition method for rapid assessment of economic loss of typhoon storm surge in China.
Based on the statistical data of direct economic losses of typhoon storm surge in China from 1989 to 2021, the economic losses of storm surge disasters in China during 32 years showed a significant downward trend, showing a thick-tailed distribution as a whole, and a normal distribution after logarithmic processing. The periodic changes of the direct economic losses of typhoon storm surge in China were analyzed by Morlet wavelet analysis method. According to the t-test, there were two quasi-high-frequency oscillations in the whole region, 1−2 years and 7−8 years oscillation , but the annual cycle gradually shortened to 3−5 years with the change of time. It indicated that the economic loss sequence of storm surge had high-frequency oscillation and multi-period nested low-frequency oscillation. On this basis, Daubechies wavelet decomposition was used to separate high frequency signal and low frequency signal. According to the results of root mean square error (RMSE) and signal-to-noise ratio, Daubechies wavelet base was set the vanishing moment is 7 and the number of decomposition layers is 2 for the direct economic loss time series of typhoon storm surges in China from 1989 to 2021, which had the optimal decomposition and reconstruction effect. Based on the results of stationarity test and white noise test of wavelet coefficients of each decomposition layer, the combined wavelet decomposed−ARMA model was established. The simulation accuracy and prediction accuracy were both better than that of single Autoregressive Integrated Moving Average model and Fourier series expansion model, which verified the reliability and superiority of wavelet decomposition method for rapid assessment of economic loss of typhoon storm surge in China.
2023, 45(7): 147-157.
doi: 10.12284/hyxb2023070
Abstract:
Red tide is a major marine ecological disaster in China. Effectively monitoring the occurrence and spatial distribution of red tide is of great significance for their prevention and control. Traditional red tide monitoring is mainly conducted by watercolor satellites with low spatial resolution. However, there are monitoring blind areas for frequent small-scale red tides. GF-1 WFV remote sensing images, featuring high spatial resolution and a wide imaging range, can be used to monitor small-scale red tides. However, the traditional method for watercolor satellites cannot be used for GF-1 WFV satellite data as GF-1 WFV remote sensing images are characterized by low spectral resolution and few bands. And it is hard to extract the information about red tide as they differ in both shape and scale. Due to diverse shapes of the red tide distribution, this paper proposes a scale-adaptive red tide detection network (SARTNet) for GF-1 WFV sensing images. This network adopts a two-layer backbone structure to integrate the shape and detail features of red tide and introduces an attention mechanism to model the correlation between features of red tides at different scales, thereby improving its performance in detecting red tides that are complexly distributed. The experimental results show that the red tide detection performance of SARTNet is better than that of the existing methods, with an F1 score above 0.89; and it is less affected by environmental factors, with few missing and misstated pixels for red tide information at different scales.
Red tide is a major marine ecological disaster in China. Effectively monitoring the occurrence and spatial distribution of red tide is of great significance for their prevention and control. Traditional red tide monitoring is mainly conducted by watercolor satellites with low spatial resolution. However, there are monitoring blind areas for frequent small-scale red tides. GF-1 WFV remote sensing images, featuring high spatial resolution and a wide imaging range, can be used to monitor small-scale red tides. However, the traditional method for watercolor satellites cannot be used for GF-1 WFV satellite data as GF-1 WFV remote sensing images are characterized by low spectral resolution and few bands. And it is hard to extract the information about red tide as they differ in both shape and scale. Due to diverse shapes of the red tide distribution, this paper proposes a scale-adaptive red tide detection network (SARTNet) for GF-1 WFV sensing images. This network adopts a two-layer backbone structure to integrate the shape and detail features of red tide and introduces an attention mechanism to model the correlation between features of red tides at different scales, thereby improving its performance in detecting red tides that are complexly distributed. The experimental results show that the red tide detection performance of SARTNet is better than that of the existing methods, with an F1 score above 0.89; and it is less affected by environmental factors, with few missing and misstated pixels for red tide information at different scales.
2023, 45(7): 158-167.
doi: 10.12284/hyxb2023117
Abstract:
Estuaries are the main channels for land-derived pollutants to enter the sea. Under the background of rapid global climate change and intensified human activities, the flux of river pollutants into the sea has increased sharply, resulting in serious ecological problems such as water pollution and ecological damage in estuaries, bays and their adjacent marginal seas. This paper selects the Jiulong River Estuary, which is significantly affected by strong tides, extreme events and human activities, and applied a biomarker tool−coprostanol to trace the environmental fecal pollution, explore the enter the sea behavior (“to”) of fecal pollutants (“source”) in the Jiulong River Estuary after entering the river, and reveal the spatial and temporal distribution characteristics and controlled factors (“sink”) of fecal organic matter within the estuary. The study found that the estuarine runoff process and tidal action in different seasons affect the spatial and temporal distribution of fecal organic pollutants, and the tidal process has a greater impact on the occurrence of coprostanol in the water environment of the middle and upper reaches of the estuary, showing a tidal cycle of low concentration at high tide and high concentration at low tide. The occurrence characteristics of coprostanol in the land-sea transport process in the estuarine area are also controlled by the complex water body and sediment dynamic process in the maximum turbidity zone, which has a certain purification effect on fecal organic pollutants. The study also shows that the spatiotemporal distribution characteristics of coprostanol in estuarine areas are closely related to human activities by comparing the nutrient inputs from rivers such as ammonia and nitrogen dominated by anthropogenic contributions.
Estuaries are the main channels for land-derived pollutants to enter the sea. Under the background of rapid global climate change and intensified human activities, the flux of river pollutants into the sea has increased sharply, resulting in serious ecological problems such as water pollution and ecological damage in estuaries, bays and their adjacent marginal seas. This paper selects the Jiulong River Estuary, which is significantly affected by strong tides, extreme events and human activities, and applied a biomarker tool−coprostanol to trace the environmental fecal pollution, explore the enter the sea behavior (“to”) of fecal pollutants (“source”) in the Jiulong River Estuary after entering the river, and reveal the spatial and temporal distribution characteristics and controlled factors (“sink”) of fecal organic matter within the estuary. The study found that the estuarine runoff process and tidal action in different seasons affect the spatial and temporal distribution of fecal organic pollutants, and the tidal process has a greater impact on the occurrence of coprostanol in the water environment of the middle and upper reaches of the estuary, showing a tidal cycle of low concentration at high tide and high concentration at low tide. The occurrence characteristics of coprostanol in the land-sea transport process in the estuarine area are also controlled by the complex water body and sediment dynamic process in the maximum turbidity zone, which has a certain purification effect on fecal organic pollutants. The study also shows that the spatiotemporal distribution characteristics of coprostanol in estuarine areas are closely related to human activities by comparing the nutrient inputs from rivers such as ammonia and nitrogen dominated by anthropogenic contributions.
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