Uargathy Inlet is a small natural tidal inlet in the northern region ol the Virginia Darner island chain. It is 100 m wide with a throat cross-sectional area of 384m2 and an average tidal prism of 6.47 x 106 m3. The i...Uargathy Inlet is a small natural tidal inlet in the northern region ol the Virginia Darner island chain. It is 100 m wide with a throat cross-sectional area of 384m2 and an average tidal prism of 6.47 x 106 m3. The inside drainage system is 7.8 km long and 2.2km wide. The main channels comprise 5.8% of the area, shallow lagoons 19.8%, and Spartina marshes 74.4% in 1970. Over the period 1851 - 1989 the inlet narrowed and migrated northward while maintaining a weakening downdrift offset. The nearby barrier island coastline’s rapid retreat (average rate 4.78m /a, 138 years retreat 660 m) was accompanied by back barrier channel and lagoon filling and a decrease in intertidal water volume which was probably the main reason for the entrance narrowing. The northward migration of the inlet was related to the dredging of the Inside Passage (before 1949) and the breaching of southern Metompkin Island (since 1957) connected with the inlet system. This altered the interior tidal circulation and likely shifted展开更多
A three-dimensional model is used to investigate the mechanism of the South China Sea (SCS) winter counter-current (also known as the SCS Warm Current, or the SCSWC), which flows against the wind. The model can re...A three-dimensional model is used to investigate the mechanism of the South China Sea (SCS) winter counter-current (also known as the SCS Warm Current, or the SCSWC), which flows against the wind. The model can reproduce the structure of the band-like currents over the northern shelf of the SCS, including the westward coastal current and slop current, and the SCSWC sandwiched in between. Sensitivity experiments are designed to understand the different roles of Ekman pumping of the SCSWC at different longitude. The results show that the Ekman pumping drives the SCSWC in the west segment. In the east, it is not the Ekman pumping but the intrusion of the Kuroshio that drives the SCSWC.展开更多
With the tides propagating from the open sea to the lagoon, the mean water level (MWL) in the inlet and lagoon becomes different from that at the open sea, and a setup/setdown is generated. The change of MWL (setup...With the tides propagating from the open sea to the lagoon, the mean water level (MWL) in the inlet and lagoon becomes different from that at the open sea, and a setup/setdown is generated. The change of MWL (setup/setdown) in the system imposes a great impact on regulating the development of tidal marshes, on determining the long-term water level for harbor maintenance, on the planning for the water front development with the flood control for the possible inundation, and on the interpretation of the historical sea level change when using tidal marsh peat deposits in the lagoon as the indicator for open sea' s sea level. In this case study on the mechanisms which control the setup/setdown in Xincun Inlet, Hainan in China, the 2-D barotropic mode of Eulerian - Lagrangian CIRCulation (ELCIRC) model was utilized. After model calibration and verification, a series of numerical experiments were conducted to examine the effects of bottom friction and advection terms, wetting and drying of intertidal areas, bathymetry and boundary conditions on the setup/setdown in the system. The modeling results show that setup occurs over the inlet and lagoon areas with an order of one tenth of the tide range at the entrance. The larger the bottom friction is, a larger setup is generated. Without the advection term, the setup is reduced clue to a decrease of water level gradient to compensate for the disappearance of the advection term. Even without overtides, a setup can still be developed in the system. Sea level rise and dredging in the inlet and tidal channel can cause a decrease of setup in the system, whereas shoaling of the system can increase the setup. The uniqueness of the Xincun Inlet with respect to MWL change is that there is no evident setdown in the inlet, which can be attributed to the complex geometry and bathymetry associated with the inlet system.展开更多
The present paper deals with the distribution patterns of heavy metals and the associated influenc- ing factors in the Yalu River Estuary and its adjacent coastal waters. Based upon the analysis of the surficial and c...The present paper deals with the distribution patterns of heavy metals and the associated influenc- ing factors in the Yalu River Estuary and its adjacent coastal waters. Based upon the analysis of the surficial and core sediments measurements, the pollution of heavy metal and potentiM ecological risk were evaluated. The burial flux and contents of heavy metals (except for copper) have been continuously increasing since the 1920s. Therefore, the gross potential ecological risk for the sedi- ments was high or very high, and the study area was endangered by heavy metals contamination. Heavy metals originated mainly from upstream pollutant input, correlation analysis showed that chromium, nickel, zinc~ cadmium, lead, arsenic, and mercury in the sediments of the middle and west channels as well as the sea area of the western Yalu River Estuary concentrations were most probably derived from similar sources. In contrast, the metal of copper most probably originated from sources different from the other metals. Preliminary studies indicate that copper contamina- tion was most likely the result of emission from mining activities situated at the upstream of the river. The contents of heavy metals in the sediments of estuarine turbidity maximum zone of Yalu River were larger than those of any other areas in the middle channel. With large portion of fine sediments, weaker hydrodynamics, and richer sources of heavy metals, the sediments of the west channel, were even more enriched with heavy metals than those of the middle channel.展开更多
Artificially induced tetraploid Pacific oyster, Crassostrea gigas Thunberg, produces more aneuploid gametes than normal diploid one, although they showed a comparable fecundity to diploidy. The meiotic chromosome conf...Artificially induced tetraploid Pacific oyster, Crassostrea gigas Thunberg, produces more aneuploid gametes than normal diploid one, although they showed a comparable fecundity to diploidy. The meiotic chromosome configuration of 3 tetraploid and 1 tetraploid/triploid mosaic males were analyzed through direct chromosome observation. A majority of metaphase I spermatocytes contained both bivalents and quadrivalents. The chromosome configuration of these males was characterized by preferential formation of bivalents to quadrivalents. Bivalents appeared in all spermatocytes and consisted of 86% of all chromosome aggregates. In comparison, quadrivalents occurred in 91% spermatocytes and consisted of only 12.6% of all chromosome aggregates. The mean bivalent frequency per spermatocyte varied between 14.4 and 17.2; while that of quadrivalents varied between 2.2 and 2.7. Most quadrivalents were tandemly chained(58%) or circled(39%). The total number of chromosome aggregates per spermatocyte ranged from 13 to 20 with an average of 17.6; while 18(16 bivalents and 2 quadrivalents) was the most frequent. Univalents and trivalents appeared in very low frequency. Aneuploid(hypotetraploid) spermatocytes were observed in a low frequency. The chromosome configuration of in the mosaic individual was similar to that of tetraploid individuals. The percentage of triploid spermatocytes(2%) of the mosaic individual was significantly lower(χ2 =30, P < 0.01) than that of triploid cells(46%) in its somatic tissue.展开更多
Large eddy simulation (LES) using the Smagorinsky eddy viscosity model is added to the two-dimensional nine velocity components (D2Q9) lattice Boltzmann equation (LBE) with multi-relaxation-time (MRT) to simul...Large eddy simulation (LES) using the Smagorinsky eddy viscosity model is added to the two-dimensional nine velocity components (D2Q9) lattice Boltzmann equation (LBE) with multi-relaxation-time (MRT) to simulate incompressible turbulent cavity flows with the Reynolds numbers up to 1 × 10^7. To improve the computation efficiency of LBM on the numerical simulations of turbulent flows, the massively parallel computing power from a graphic processing unit (GPU) with a computing unified device architecture (CUDA) is introduced into the MRT-LBE-LES model. The model performs well, compared with the results from others, with an increase of 76 times in computation efficiency. It appears that the higher the Reynolds numbers is, the smaller the Smagorinsky constant should be, if the lattice number is fixed. Also, for a selected high Reynolds number and a selected proper Smagorinsky constant, there is a minimum requirement for the lattice number so that the Smagorinsky eddy viscosity will not be excessively large.展开更多
High purity(>99.9% composition) nickel metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as a green polishing solution. Volt...High purity(>99.9% composition) nickel metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as a green polishing solution. Voltammetry and chronoamperometry tests were conducted to determine the optimum conditions for electrochemical polishing. Atomic force microscopy(AFM) revealed nanoscale effectiveness of each polishing treatment. Atomic force microscopy provided an overall observation of the material interface between the treated and unpolished regions. Surface morphology comparisons summarized electrochemical polishing efficiency by providing root-mean-square roughness averages before and after electrochemical polishing to reveal a mirror finish six times smoother than the same nickel metal surface prior to electropolishing. This transition manifested in a marked change in root-mean-squared roughness from 112.58 nm to 18.64 nm and producing a smooth mirror finish. Finally, the mechanism of the ionic liquid during electropolishing revealed decomposition of choline in the form of a transient choline radical by acceptance of an electron from the nickel-working electrode to decompose to trimethylamine and ethanol.展开更多
During the northeast monsoon season,Zhe-Min Coastal Current(ZMCC)travels along the Chinese mainland coast and carries fresh,cold,and eutrophic water.ZMCC is significantly important for the hydrodynamic processes and m...During the northeast monsoon season,Zhe-Min Coastal Current(ZMCC)travels along the Chinese mainland coast and carries fresh,cold,and eutrophic water.ZMCC is significantly important for the hydrodynamic processes and marine ecosystems along its path.Thus,this bottom-trapped plume deserves to be further discussed in terms of the major driving factor,for which different opinions exist.For this purpose,in this study,a high resolution Semi-implicit Cross-scale Hydroscience Integrated System Model(SCHISM)is established and validated.High correlation coefficients exist between along-shelf wind speeds and seasonal variations of both ZMCC volume transport and the freshwater signal.These coefficients imply that the wind is important in regulating ZMCC.However,for similar annual mean ZMCC volume transports,the extreme south boundaries of Zhe-Min Coastal Water(ZMCW)are different among different years.This difference is attracting attention and is explored in this study.According to the low wind/discharge experiment,it was found that although the volume transport of ZMCC is more sensitive to the variation of local wind speeds,the carried freshwater is limited by the Changjiang River discharge,which ultimately determines the south boundary of ZMCW.The momentum analysis at transects I and II shows that,for driving ZMCC,the along-shore wind forcing is as important as the buoyancy forcing.Note that this conclusion is supported by a zero-discharge experiment.It was also found that the buoyancy forcing varies with respect to time and space,which is due to variations of the discharge of Changjiang River.In addition,a particle tracking experiment shows that the substance carried by the Changjiang River diluted water would distribute along the Zhe-Min coastal region during the northeast monsoon season and it may escape due to the wind relaxation.展开更多
A three-dimensional numerical model, EFDC ( environmental fluid dynamics code) is applied to the Pamlico River Estuary (PRE) in eastern North Carolina of the United States to examine the wind impact on pollutant a...A three-dimensional numerical model, EFDC ( environmental fluid dynamics code) is applied to the Pamlico River Estuary (PRE) in eastern North Carolina of the United States to examine the wind impact on pollutant age distributions and residence time. A series of model experiments representing base case, remote-wind-induced water level set-up and local winds cases are conducted. Model results indicate that the pollutant mean age and the system residence time are functions of gravitational circulation in the PRE. The system responses to remote-wind-induced water level set-up are different in different portions of the PRE. Under such condition, dissolved substances in the upstream portion of the PRE have a younger age and shorter residence time (compared with the base case) , by contrast, they have a older age and longer residence time in the downstream portion of the PRE. Upriver and downriver local winds appear to have opposite impacts on pollutant age distributions. The substances are retained much longer within the PRE under upriver wind than those under downriver wind. The model results also suggest that across - river winds may lead to longer residence time through enhanced turbulence mixing, which slows down the gravitational circulation in the PRE.展开更多
The feedback between morphological evolution and tidal hydrodynamics in a wave-dominated tidal inlet, Xiaohai, China is investigated through data analysis and numerical model experiments. Historically, Xiaohai Inlet h...The feedback between morphological evolution and tidal hydrodynamics in a wave-dominated tidal inlet, Xiaohai, China is investigated through data analysis and numerical model experiments. Historically, Xiaohai Inlet had two openings, located at the north and south of Neizhi Island (a rocky outcrop), respectively. The evolution of Xiaohai Inlet was dominated by the natural process before 1972. In addition to the natural process, human interventions, including the closure of the north opening, 50% of freshwater reduction, and increase of land reclamation, have altered tidal hydrodynamics and morphological evolution since 1972. A series of numerical model simulations were conducted to investigate the influence of morphological changes on the hydrodynamics and the influence of human activities on the inlet evolution. The natural process has caused narrowing and shoaling of the inlet throat, development of the flood-tidal delta, and shoaling of the tidal channel inside the lagoon. Human interventions have accelerated these changes. Consequently, the tidal propagation from the offshore into the lagoon has been impeded and the tidal energy has been dissipated substantially. Tidal current has changed from ebb-dominant to flood-dominant in most parts of the inlet system whereas the inlet throat has remained as ebb-dominant, the tidal prism has decreased consistently, and sediment has continued to deposit inside the inlet. As a result, the changes of morphology, hydrodynamics, and sediment transport show a positive feedback. The human interventions have had both advantageous and adverse influences on the stability of the inlet. The closure of the North Opening has decreased the longshore sediment input to the inlet, and increased the tidal prism, ebb velocity, and sediment transport in the south opening, thus enhancing the inlet's stability. However, reducing the river discharge and landfill of the tidal flats has resulted in a decrease of the tidal prism, the ebb velocity, and the ability to export sediment, thus having the tendency to deteriorate the inlet's stability. A stability analysis based on a closure curve methodology has shown that Xiaohai Inlet is in a state of dynamic equilibrium at present.展开更多
Influenced by weather, the estuaries and bays often exhibit recurring oscillations in flow and water level similar to astronomical tides. The weather impact however is less regular than tides and more difficult to pre...Influenced by weather, the estuaries and bays often exhibit recurring oscillations in flow and water level similar to astronomical tides. The weather impact however is less regular than tides and more difficult to predict. The spectrum of weather induced motions in estuaries and bays is mostly at the low-frequency end with time scales longer than those of diurnal tides. The repeated weather impact produces meteorological tide: the recurring flood and ebb and flushing of the estuaries and bays but at lower frequencies than those of tides. The variation in weather conditions is quasi-periodic and of large scale nature(~1000-3000 km) because of the alternating low-and high-atmospheric pressure systems of extra-tropical cyclones and anti-cyclones and associated fronts. By examining 40 years of data between Jan. 1, 1977 and Dec. 31, 2016, we identified 1648 frontal events(averaging ~41.2±4.7 per year)influencing the northern Gulf of Mexico for time periods in the spring, fall and winter. The late spring and summer months(May, Jun, July, and August) were not included in the calculation because of much weaker activities involving synoptic weather systems with fronts during these months. It is found that the number of frontal events reached the maximum in Jan. and Dec. while the minimum occurred in April and Sept. It is found that there is an increasing trend of number of fronts over the 40-year period. Our data show that the low pass filtered water level,velocity, and vorticity(velocity shear) all vary in response to the weather and appear as the meteorological tide. The particle excursions of meteorological tides are much larger than those from the astronomical tides. In addition, the irregular nature of the meteorological tide makes the inward flux and outward flux asymmetric in general and thus it has a significant implication to dispersion and transport of waterborne materials. A scaling analysis shows that the meteorological tide generally reaches quasi-steady state;and as a result, a regression model is established which can be very useful for predicting the weather produced quasi-periodic motions.展开更多
文摘Uargathy Inlet is a small natural tidal inlet in the northern region ol the Virginia Darner island chain. It is 100 m wide with a throat cross-sectional area of 384m2 and an average tidal prism of 6.47 x 106 m3. The inside drainage system is 7.8 km long and 2.2km wide. The main channels comprise 5.8% of the area, shallow lagoons 19.8%, and Spartina marshes 74.4% in 1970. Over the period 1851 - 1989 the inlet narrowed and migrated northward while maintaining a weakening downdrift offset. The nearby barrier island coastline’s rapid retreat (average rate 4.78m /a, 138 years retreat 660 m) was accompanied by back barrier channel and lagoon filling and a decrease in intertidal water volume which was probably the main reason for the entrance narrowing. The northward migration of the inlet was related to the dredging of the Inside Passage (before 1949) and the breaching of southern Metompkin Island (since 1957) connected with the inlet system. This altered the interior tidal circulation and likely shifted
基金The Knowledge Innovation Program of the Chinese Academy of Sciences under contract No.KZCX1-YW-12-01the National Science Fund for Distinguished Young Scholars under contract No.40625017+1 种基金the National Natural Science Foundation of China(Key Program)under contract No.40830851the National Program on Key Basic Research Project(973Program)under contract No.2007CB816004
文摘A three-dimensional model is used to investigate the mechanism of the South China Sea (SCS) winter counter-current (also known as the SCS Warm Current, or the SCSWC), which flows against the wind. The model can reproduce the structure of the band-like currents over the northern shelf of the SCS, including the westward coastal current and slop current, and the SCSWC sandwiched in between. Sensitivity experiments are designed to understand the different roles of Ekman pumping of the SCSWC at different longitude. The results show that the Ekman pumping drives the SCSWC in the west segment. In the east, it is not the Ekman pumping but the intrusion of the Kuroshio that drives the SCSWC.
基金The National Natural Science Foundation of China under contract No. 40266001
文摘With the tides propagating from the open sea to the lagoon, the mean water level (MWL) in the inlet and lagoon becomes different from that at the open sea, and a setup/setdown is generated. The change of MWL (setup/setdown) in the system imposes a great impact on regulating the development of tidal marshes, on determining the long-term water level for harbor maintenance, on the planning for the water front development with the flood control for the possible inundation, and on the interpretation of the historical sea level change when using tidal marsh peat deposits in the lagoon as the indicator for open sea' s sea level. In this case study on the mechanisms which control the setup/setdown in Xincun Inlet, Hainan in China, the 2-D barotropic mode of Eulerian - Lagrangian CIRCulation (ELCIRC) model was utilized. After model calibration and verification, a series of numerical experiments were conducted to examine the effects of bottom friction and advection terms, wetting and drying of intertidal areas, bathymetry and boundary conditions on the setup/setdown in the system. The modeling results show that setup occurs over the inlet and lagoon areas with an order of one tenth of the tide range at the entrance. The larger the bottom friction is, a larger setup is generated. Without the advection term, the setup is reduced clue to a decrease of water level gradient to compensate for the disappearance of the advection term. Even without overtides, a setup can still be developed in the system. Sea level rise and dredging in the inlet and tidal channel can cause a decrease of setup in the system, whereas shoaling of the system can increase the setup. The uniqueness of the Xincun Inlet with respect to MWL change is that there is no evident setdown in the inlet, which can be attributed to the complex geometry and bathymetry associated with the inlet system.
基金The National Natural Science Foundation of China under contract Nos 40976051,40976036,40871019,40506022and 40506013
文摘The present paper deals with the distribution patterns of heavy metals and the associated influenc- ing factors in the Yalu River Estuary and its adjacent coastal waters. Based upon the analysis of the surficial and core sediments measurements, the pollution of heavy metal and potentiM ecological risk were evaluated. The burial flux and contents of heavy metals (except for copper) have been continuously increasing since the 1920s. Therefore, the gross potential ecological risk for the sedi- ments was high or very high, and the study area was endangered by heavy metals contamination. Heavy metals originated mainly from upstream pollutant input, correlation analysis showed that chromium, nickel, zinc~ cadmium, lead, arsenic, and mercury in the sediments of the middle and west channels as well as the sea area of the western Yalu River Estuary concentrations were most probably derived from similar sources. In contrast, the metal of copper most probably originated from sources different from the other metals. Preliminary studies indicate that copper contamina- tion was most likely the result of emission from mining activities situated at the upstream of the river. The contents of heavy metals in the sediments of estuarine turbidity maximum zone of Yalu River were larger than those of any other areas in the middle channel. With large portion of fine sediments, weaker hydrodynamics, and richer sources of heavy metals, the sediments of the west channel, were even more enriched with heavy metals than those of the middle channel.
文摘Artificially induced tetraploid Pacific oyster, Crassostrea gigas Thunberg, produces more aneuploid gametes than normal diploid one, although they showed a comparable fecundity to diploidy. The meiotic chromosome configuration of 3 tetraploid and 1 tetraploid/triploid mosaic males were analyzed through direct chromosome observation. A majority of metaphase I spermatocytes contained both bivalents and quadrivalents. The chromosome configuration of these males was characterized by preferential formation of bivalents to quadrivalents. Bivalents appeared in all spermatocytes and consisted of 86% of all chromosome aggregates. In comparison, quadrivalents occurred in 91% spermatocytes and consisted of only 12.6% of all chromosome aggregates. The mean bivalent frequency per spermatocyte varied between 14.4 and 17.2; while that of quadrivalents varied between 2.2 and 2.7. Most quadrivalents were tandemly chained(58%) or circled(39%). The total number of chromosome aggregates per spermatocyte ranged from 13 to 20 with an average of 17.6; while 18(16 bivalents and 2 quadrivalents) was the most frequent. Univalents and trivalents appeared in very low frequency. Aneuploid(hypotetraploid) spermatocytes were observed in a low frequency. The chromosome configuration of in the mosaic individual was similar to that of tetraploid individuals. The percentage of triploid spermatocytes(2%) of the mosaic individual was significantly lower(χ2 =30, P < 0.01) than that of triploid cells(46%) in its somatic tissue.
基金supported by College of William and Mary,Virginia Institute of Marine Science for the study environment
文摘Large eddy simulation (LES) using the Smagorinsky eddy viscosity model is added to the two-dimensional nine velocity components (D2Q9) lattice Boltzmann equation (LBE) with multi-relaxation-time (MRT) to simulate incompressible turbulent cavity flows with the Reynolds numbers up to 1 × 10^7. To improve the computation efficiency of LBM on the numerical simulations of turbulent flows, the massively parallel computing power from a graphic processing unit (GPU) with a computing unified device architecture (CUDA) is introduced into the MRT-LBE-LES model. The model performs well, compared with the results from others, with an increase of 76 times in computation efficiency. It appears that the higher the Reynolds numbers is, the smaller the Smagorinsky constant should be, if the lattice number is fixed. Also, for a selected high Reynolds number and a selected proper Smagorinsky constant, there is a minimum requirement for the lattice number so that the Smagorinsky eddy viscosity will not be excessively large.
文摘High purity(>99.9% composition) nickel metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as a green polishing solution. Voltammetry and chronoamperometry tests were conducted to determine the optimum conditions for electrochemical polishing. Atomic force microscopy(AFM) revealed nanoscale effectiveness of each polishing treatment. Atomic force microscopy provided an overall observation of the material interface between the treated and unpolished regions. Surface morphology comparisons summarized electrochemical polishing efficiency by providing root-mean-square roughness averages before and after electrochemical polishing to reveal a mirror finish six times smoother than the same nickel metal surface prior to electropolishing. This transition manifested in a marked change in root-mean-squared roughness from 112.58 nm to 18.64 nm and producing a smooth mirror finish. Finally, the mechanism of the ionic liquid during electropolishing revealed decomposition of choline in the form of a transient choline radical by acceptance of an electron from the nickel-working electrode to decompose to trimethylamine and ethanol.
基金The Scientific Research Fund of the Second Institute of Oceanography,MNR under contract Nos JG2104 and 14283the National Natural Science Foundation of China under contract Nos 41730536,42076010 and 42130403+3 种基金the Shanghai Pujiang Program under contract No.19PJ1404300the Shandong Natural Science Foundation under contract No.ZR2021MD007the Project of State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography,MNR under contract No.SOEDZZ2103the Zhejiang Provincial Natural Science Foundation of China under contract No.LY21D060003.
文摘During the northeast monsoon season,Zhe-Min Coastal Current(ZMCC)travels along the Chinese mainland coast and carries fresh,cold,and eutrophic water.ZMCC is significantly important for the hydrodynamic processes and marine ecosystems along its path.Thus,this bottom-trapped plume deserves to be further discussed in terms of the major driving factor,for which different opinions exist.For this purpose,in this study,a high resolution Semi-implicit Cross-scale Hydroscience Integrated System Model(SCHISM)is established and validated.High correlation coefficients exist between along-shelf wind speeds and seasonal variations of both ZMCC volume transport and the freshwater signal.These coefficients imply that the wind is important in regulating ZMCC.However,for similar annual mean ZMCC volume transports,the extreme south boundaries of Zhe-Min Coastal Water(ZMCW)are different among different years.This difference is attracting attention and is explored in this study.According to the low wind/discharge experiment,it was found that although the volume transport of ZMCC is more sensitive to the variation of local wind speeds,the carried freshwater is limited by the Changjiang River discharge,which ultimately determines the south boundary of ZMCW.The momentum analysis at transects I and II shows that,for driving ZMCC,the along-shore wind forcing is as important as the buoyancy forcing.Note that this conclusion is supported by a zero-discharge experiment.It was also found that the buoyancy forcing varies with respect to time and space,which is due to variations of the discharge of Changjiang River.In addition,a particle tracking experiment shows that the substance carried by the Changjiang River diluted water would distribute along the Zhe-Min coastal region during the northeast monsoon season and it may escape due to the wind relaxation.
基金The Science and Technology Special Grant of Guangdong Province of China under contract Nos2006A36503001,IFLOW-4:Coupling Watershed/Estuarine Water Quality Model,U.S.NOAA/National Sea Grant
文摘A three-dimensional numerical model, EFDC ( environmental fluid dynamics code) is applied to the Pamlico River Estuary (PRE) in eastern North Carolina of the United States to examine the wind impact on pollutant age distributions and residence time. A series of model experiments representing base case, remote-wind-induced water level set-up and local winds cases are conducted. Model results indicate that the pollutant mean age and the system residence time are functions of gravitational circulation in the PRE. The system responses to remote-wind-induced water level set-up are different in different portions of the PRE. Under such condition, dissolved substances in the upstream portion of the PRE have a younger age and shorter residence time (compared with the base case) , by contrast, they have a older age and longer residence time in the downstream portion of the PRE. Upriver and downriver local winds appear to have opposite impacts on pollutant age distributions. The substances are retained much longer within the PRE under upriver wind than those under downriver wind. The model results also suggest that across - river winds may lead to longer residence time through enhanced turbulence mixing, which slows down the gravitational circulation in the PRE.
基金The National Natural Science Foundation of China under contract No.40266001
文摘The feedback between morphological evolution and tidal hydrodynamics in a wave-dominated tidal inlet, Xiaohai, China is investigated through data analysis and numerical model experiments. Historically, Xiaohai Inlet had two openings, located at the north and south of Neizhi Island (a rocky outcrop), respectively. The evolution of Xiaohai Inlet was dominated by the natural process before 1972. In addition to the natural process, human interventions, including the closure of the north opening, 50% of freshwater reduction, and increase of land reclamation, have altered tidal hydrodynamics and morphological evolution since 1972. A series of numerical model simulations were conducted to investigate the influence of morphological changes on the hydrodynamics and the influence of human activities on the inlet evolution. The natural process has caused narrowing and shoaling of the inlet throat, development of the flood-tidal delta, and shoaling of the tidal channel inside the lagoon. Human interventions have accelerated these changes. Consequently, the tidal propagation from the offshore into the lagoon has been impeded and the tidal energy has been dissipated substantially. Tidal current has changed from ebb-dominant to flood-dominant in most parts of the inlet system whereas the inlet throat has remained as ebb-dominant, the tidal prism has decreased consistently, and sediment has continued to deposit inside the inlet. As a result, the changes of morphology, hydrodynamics, and sediment transport show a positive feedback. The human interventions have had both advantageous and adverse influences on the stability of the inlet. The closure of the North Opening has decreased the longshore sediment input to the inlet, and increased the tidal prism, ebb velocity, and sediment transport in the south opening, thus enhancing the inlet's stability. However, reducing the river discharge and landfill of the tidal flats has resulted in a decrease of the tidal prism, the ebb velocity, and the ability to export sediment, thus having the tendency to deteriorate the inlet's stability. A stability analysis based on a closure curve methodology has shown that Xiaohai Inlet is in a state of dynamic equilibrium at present.
基金The research was financially supported by the National Science Foundation and Natural Environment Research Council(Grant Nos.NSF-NERC 1736713 and NSF-NERC 1737274)Bureau of Ocean Energy Management(Grant No.M15AC000015)NOAA-NOS-IOOS-2016-2004378,through the Northern Gulf Institute by NOAA’s Office of Ocean and Atmospheric Research.
文摘Influenced by weather, the estuaries and bays often exhibit recurring oscillations in flow and water level similar to astronomical tides. The weather impact however is less regular than tides and more difficult to predict. The spectrum of weather induced motions in estuaries and bays is mostly at the low-frequency end with time scales longer than those of diurnal tides. The repeated weather impact produces meteorological tide: the recurring flood and ebb and flushing of the estuaries and bays but at lower frequencies than those of tides. The variation in weather conditions is quasi-periodic and of large scale nature(~1000-3000 km) because of the alternating low-and high-atmospheric pressure systems of extra-tropical cyclones and anti-cyclones and associated fronts. By examining 40 years of data between Jan. 1, 1977 and Dec. 31, 2016, we identified 1648 frontal events(averaging ~41.2±4.7 per year)influencing the northern Gulf of Mexico for time periods in the spring, fall and winter. The late spring and summer months(May, Jun, July, and August) were not included in the calculation because of much weaker activities involving synoptic weather systems with fronts during these months. It is found that the number of frontal events reached the maximum in Jan. and Dec. while the minimum occurred in April and Sept. It is found that there is an increasing trend of number of fronts over the 40-year period. Our data show that the low pass filtered water level,velocity, and vorticity(velocity shear) all vary in response to the weather and appear as the meteorological tide. The particle excursions of meteorological tides are much larger than those from the astronomical tides. In addition, the irregular nature of the meteorological tide makes the inward flux and outward flux asymmetric in general and thus it has a significant implication to dispersion and transport of waterborne materials. A scaling analysis shows that the meteorological tide generally reaches quasi-steady state;and as a result, a regression model is established which can be very useful for predicting the weather produced quasi-periodic motions.