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1.
An investigation of the properties of low-frequency internal waves in the northeastern China Seas 总被引：1，自引：0，他引：1
A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed
to analyze the observation data. Analysis of some data gathered in the northestern China Seas revealed strong semidiurnal
internal tides and near-inertial internal waves at the stations in the East China Sea and near-inertial waves but no semidiurnal
internal tides at the station in the centre of the Yellow Sea. The geographic properties of low-frequency internal waves in
the region are discussed primarily on the basis of the mechanism of internal tide generation on the continental shelfbreak,
and the mechanisms of local generation and global generation.
Project supported by the National Natural Science Foundation of China. 相似文献
2.
The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body.The model incorporates body geometry,propeller forcing,and stratification magnitude of seawater.The generation mechanism and wave properties are discussed based on model results.It was found that the generation of the wave and its properties depend greatly on the body speed.Only when that speed exceeds some critical value,between 1.5 and 4.5 m/s,can the moving body generate wake-collapse internal waves,and with increases of this speed,the time of generation advances and wave amplitude increases.The generated wake-collapse internal waves are confirmed to have characteristics of the second baroclinic mode.As the body speed increases,wave amplitude and length increase and its waveform tends to take on a regular sinusoidal shape.For three linearly temperature-stratified profiles examined,the weaker the stratification,the stronger the wake-collapse internal wave. 相似文献
3.
Some approximate formulas, based on the internal- wave directional spectral model established by Schott and Willebrand (1973),
of vertically standing wavemode eigenfunctions and a dispersion relation of internal waves in shallow seas are presented.
An optimization method to estimate internal wave directional spectra is described and the confidence interval expression of
the estimates is established.
The GM spectral model of oceanic internal waves cannot be used in shallow seas (01 bers, 1983). Internal waves in shallow
seas have two origins: oceanic (those generated in and propagating from the deep sea and ocean) and local (Phillips, 1977).
As both reveal obvious propagation orientations, it is important to investigate the directional properties of the internal
wave field. Though cross correlation function or cross-spectrum analyses can reveal the directional properties in some degree
(Fang et al., 1984, and Fang, 1987), internal- wave directional spectrum analysis can further estimate the main propagation
directions of wave components with different modenumbers and frequencies. So the latter is a more effective analysis tool.
Because internal- wave directional spectrum analysis requires high quality data and long computer time, there are very few
study reports so far on this subject. Among them. Schott and Willebrands' (1973) work is noteworthy. On the supposition, of
linearization, they derived an internal- wave directional spectrum model. Internal-wave directional-spectra in shallow seas
are investigated in the present study with their work as reference.
Project supported by the National Natural Science Foundation of China. 相似文献
4.
A distinct type of nonlinear internal-wave packet, with the largest internal solitary wave in the middle of the packet, was
regularly observed in the South China Sea during the Asian Seas International Acoustics Experiment in 2001. Data analysis
shows that the occurrence of the distinct internal wave packet is closely related with the occurrence of lower-high internal
tides; the internal tides are mixed in the experimental area and, thus, there is diurnal inequality between the heights of
two neighboring internal tides. Modeling of internal tides and internal solitary waves in a shoaling situation suggests that
this type of wave packet can be generated in the South China Sea by the large shoaling of internal solitary waves and internal
tides. Both the internal solitary waves and the internal tides come from the direction of Luzon Strait. The initial large
internal solitary waves contribute to the occurrence of the largest internal solitary wave in the middle of the packet and
the waves behind the largest internal solitary wave, while the shoaling internal tides bring about the nonlinear internal
waves in front of the largest internal solitary wave via interaction with the local shelf topography. 相似文献
5.
Ocean internal waves appear as irregular bright and dark stripes on synthetic aperture radar(SAR) remote sensing images. Ocean internal waves detection in SAR images consequently constituted a difficult and popular research topic. In this paper, ocean internal waves are detected in SAR images by employing the faster regions with convolutional neural network features(Faster R-CNN) framework; for this purpose, 888 internal wave samples are utilized to train the convolutional network and identify internal waves. The experimental results demonstrate a 94.78% recognition rate for internal waves, and the average detection speed is 0.22 s/image. In addition, the detection results of internal wave samples under dif ferent conditions are analyzed. This paper lays a foundation for detecting ocean internal waves using convolutional neural networks. 相似文献
6.
Impacts of internal waves on chlorophyll a distribution in the northern portion of the South China Sea 总被引：1，自引：0，他引：1
Internal waves can bring nutrients to the upper level of water bodies and facilitate phytoplankton photosynthesis. Internal
waves occur frequently in the northern portion of the South China Sea and inflict an important effect on chlorophyll a distribution. In this study, in-situ observation and satellite remote sensing data were used to study the effects of internal
waves on chlorophyll a distribution. Based on the in-situ observations, lower chlorophyll a concentrations were present in the middle and bottom level in areas in which internal waves occur frequently, while the surface
chlorophyll a distribution increased irregularly, and a small area with relatively higher chlorophyll a concentrations was observed in the area around the Dongsha Island. Satellite remote sensing showed that the chlorophyll a
concentration increased in the area near Dongsha Island, where internal waves frequently occurred. The results of the increased
chlorophyll a concentration in the surface water near Dongsha Island in the northern portion of the South China Sea indicated
that internal waves could uplift phytoplankton and facilitate phytoplankton growth. 相似文献
7.
Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology for calculating density perturbation and energy flux of internal waves only using a velocity field that is based on linearized equations for internal waves. The method was tested by numerical simulations of internal waves generated by tidal flowing over a Gaussian topography in a stratified fluid. The density perturbations and energy fluxes determined using our method that only used velocity data agreed with density perturbations and energy fluxes determined by the equation of state based on temperature data. The mean relative error (MRE) and root mean square error (RMSE) between the two methods were lower than 5% and 10% respectively. In addition, an experiment was performed to exam our method using the velocity field measured by Particle Image Velocimetry (PIV), and the setup of the experiment is consistent with the numerical model. The results of the experiments calculated by the methods using PIV data were also generally equal to those of the numerical model. 相似文献
8.
Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean . Bottom intensifications are caused by many factors .e.g. upstream blocking , which is the result of nonlinear interaction among waves . The energy may decay very fast so that internal tides are mostly locally generated .Internal tides may have considerable residual currents.In a 3-D frame, numerical study revealed that internal waves may interfere with each other to cause strong motions fer from the generation sources.The mechanism that determines how the lee waves break to form various nonlinear waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytic study is difficult , so numerical method may be effective . A radiation condition on the open boundary must be employed. A complete 3-D model may gain interesting result.Study on internal tides in China is limited to field observations and data analysis . 相似文献
9.
A continuously stratified nonlinear model is set up to study the impact of topographical character on the generation of internal solitary waves over a sill by tidal flow. One of the reasons why almost all of the generated internal solitary waves propagate westward in the northern South China Sea is explained. The model simulations describe the generation and propagation of internal waves well. When the strength of imposed barotropic tides and the water stratification stay unchanged, the steepness of the sill slope can control both (a) whether or not the waves induced over a sill by tidal flow are linear internal waves or nonlinear internal solitary waves, and (b) the amplitude of the internal solitary waves generated. If the steepness of the sill is asymmetric, the nonlinear internal solitary waves may be induced on the steeper side of the sill. These conclusions are supported by a numerical experiment with a monthly-mean stratification and an actual seafloor topography from the Luzon Strait. 相似文献
10.
In a two-dimensional and linear framework, a transformation was developed to derive eigensolutions of internal waves over a subcritical hyperbolic slope and to approximate the continental slope and shelf. The transformation converts a hyperbolic slope in physical space into a flat bottom in transform space while the governing equations of internal waves remain hyperbolic. The eigensolutions are further used to study the evolution of linear internal waves as it propagates to subcritical continental slope and shelf. The stream function, velocity, and vertical shear of velocity induced by internal wave at the hyperbolic slope are analytically expressed by superposition of the obtained eigensolutions. The velocity and velocity shear increase as the internal wave propagates to a hyperbolic slope. They become very large especially when the slope of internal wave rays approaches the topographic slope, which is consistent with the previous studies. 相似文献
11.
A preliminary theoretical and experimental study was conducted on internal wave modes and their weak nonlinear resonant interaction in a nonlinearly stratified fluid . An asymptotical solution of the modes and a dispersion relation of internal waves in a stratified fluid with density profile similar to that in our experiment were obtained theoretically . The resonant-interaction mechanism to 2nd order approximation is also discussed . The resonant interaction of the 3rd and 4th mode internal waves excited by the unstable 1st mode wave is analyzed on the basis of data obtained by conductivity probes. The resonant-interaction condition, , is examined . It is shown that the resonant instability increases with pycnocline thickness and wave maker driving frequency . 相似文献
12.
Many observations show that in the Yellow Sea internal tidal waves (ITWs) possess the remarkable characteristics of internal Kelvin wave, and in the South Yellow Sea (SYS) the nonlinear evolution of internal tidal waves is one of the mechanisms producing internal solitary waves (ISWs), which is different from the generation mechanism in the case where the semidiurnal tidal current flows over topographic drops. In this paper, the model of internal Kelvin wave with continuous stratification is given, and an elementary numerical study of nonlinear evolution of ITWs is made for the SYS, using the generalized KdV model (GKdV model for short) for a continuous stratified ocean, in which the different effects of background barotropic ebb and flood currents are considered. Moreover, the parameterization of vertical turbulent mixing caused by ITWs and ISWs in the SYS is studied, using a parameterization scheme which was applied to numerical experiments on the breaking of ISWs by Vlasenko and Hutter in 2002. It is found that the vertical turbulent mixing caused by internal waves is very strong within the upper layer with depth less than about 30m, and the vertical turbulent mixing caused by ISWs is stronger than that by ITWs. 相似文献
13.
Laboratory experiments were conducted to investigate the evolution of interfacial internal solitary waves(ISWs) incident on a triangular barrier. ISWs with different amplitudes were generated by gravitational collapse. The ISW energy dissipation and turbulence processes were calculated as waves passed over the triangular barrier. Experimental results showed that ISWs were reflecting back off the triangular barrier, and shoaling ISWs led to wave breaking and mixing when waves propagated over the obstacle. Wave instability created the dissipation of energy as it was transmitted from waves to turbulence. The rate of ISW energy dissipation, the maximum turbulent dissipation, and the buoyancy diffusivity linearly increased with the increase in the incident wave energy. 相似文献
14.
Remote sensing and in situ observations of internal tides, solitary waves and bores in shallow water are briefly reviewed in this paper. The emphasis is laid on interpreting SAR images based on oceanographic measurements, and analyzing characteristics of internal waves in the China Seas. Direc-tions for future research are discussed. 相似文献
15.
The South China Sea (SCS) is one of the most active areas of internal waves. We undertook a program of physical oceanography
in the northern South China Sea from June to July of 2009, and conducted a 1-day observation from 15:40 of June 24 to 16:40
of June 25 using a chain of instruments, including temperature sensors, pressure sensors and temperature-pressure meters at
a site (117.5°E, 21°N) northeast of the Dongsha Islands. We measured fluctuating tidal and subtidal properties with the thermistor-chain
and a ship-mounted Acoustic Doppler Current Profiler, and observed a large-amplitude nonlinear internal wave passing the site
followed by a number of small ones. To further investigate this phenomenon, we collected the tidal constituents from the TPXO7.1
dataset to evaluate the tidal characteristics at and around the recording site, from which we knew that the amplitude of the
nonlinear internal wave was about 120 m and the period about 20 min. The horizontal and vertical velocities induced by the
soliton were approximately 2 m/s and 0.5 m/s, respectively. This soliton occurred 2–3 days after a spring tide. 相似文献
16.
The directional-spectrum model of internal waves in shallow seas given by Xiao and Fang (1991) was used to analyze the observation
data gathered in April, 1981, in the sea off Sydney, Australia. Some reasonable results were obtained. The energy ratio between
Wavemodes 1 and 2 was about 2 for most frequencies and was up to 8 at ω=0.23 cph. Wave components with frequencies 0.1–0.8
cph were generated in the deep sea, and propagated onshore, while those with frequencies higher than 0.8 cph were locally
generated by the interaction between longshore currents and bottom topography.
Several surveys were carried out in the sea off Sydney, Australia (Cresswell, 1974, Cresswell and Boland, 1981, and Fang,
Boland and Cresswell, 1984). The survey performed in April 1981 by Fang, Boland and Cresswell (1984) was outstandingly successful.
To draw some deterministic and stochastic characters of internal waves, Fang, Boland and Cresswell (1984) and Fang (1987)
analyzed these data gathered in 1981 and obtained some reasonable results. 相似文献
17.
Shipboard X-band radar images acquired on 24 June 2009 are used to study nonlinear internal wave characteristics in the northeastern
South China Sea. The studied images show three nonlinear internal waves in a packet. A method based on the Radon Transform
technique is introduced to calculate internal wave parameters such as the direction of propagation and internal wave velocity
from backscatter images. Assuming that the ocean is a two-layer finite depth system, we can derive the mixed-layer depth by
applying the internal wave velocity to the mixed-layer depth formula. Results show reasonably good agreement with in-situ
thermistor chain and conductivity-temperature-depth data sets. 相似文献
18.
Large amplitude internal solitary waves (ISWs) often exhibit highly nonlinear effects and may contribute significantly to
mixing and energy transporting in the ocean. We observed highly nonlinear ISWs over the continental shelf of the northwestern
South China Sea (19°35′N, 112°E) in May 2005 during the Wenchang Internal Wave Experiment using in-situ time series data from
an array of temperature and salinity sensors, and an acoustic Doppler current profiler (ADCP). We summarized the characteristics
of the ISWs and compared them with those of existing internal wave theories. Particular attention has been paid to characterizing
solitons in terms of the relationship between shape and amplitude-width. Comparison between theoretical prediction and observation
results shows that the high nonlinearity of these waves is better represented by the second-order extended Korteweg-de Vries
(KdV) theory than the first-order KdV model. These results indicate that the northwestern South China Sea (SCS) is rich in
highly nonlinear ISWs that are an indispensable part of the energy budget of the internal waves in the northern South China
Sea. 相似文献
19.
By using a coordinate transformation, an exact solution of internal tides with sub-inertial frequency isobtained when the bottom slope is linear and the Vaisala frequency is constant. Accordingly thedispersion relations of free waves are presented. This solution is suitable for general coastal low-frequencybaroclinic waves with zero alongshore wavenumber. 相似文献
20.
Scattering process of internal waves propagating over a subcritical strait slope onto a shelf region
DAI Dejun WANG Wei QIAO Fangli YUAN Yeli 《中国海洋大学学报(英文版)》2005,4(4):377-382
The scattering process, which means the redistribution of energy fluy in modenumber space, is analyzed for internal waves propagating from the abyssal ocean onto a subcritical strait slope and then a shelf region. In light of Wunsch＇s work, the waves are analytically expressed as superimposition of eigensolutions distribution of energy flux in the shelf region： one is the ratio of water depth in and the other is the ratio of the slope of the internal tide rays to the topographic energy flux distribution： the energy flux is focused around one modenumber or case, the range of modenumbers where energy flux is distributed is narrow. Two parameters have evident effects on the the shelf region to that in the abyssal ocean slope. Generally, there are two patterns of focused around two modenumbers. In any case, the range of modenumbers where energy flux is distributed is narrow. 相似文献