Showing papers on "Internal wave published in 1984"
TL;DR: In this article, the Rossby adjustment process in the wake of a storm is studied with a view to finding, within the context of linear theory, how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer.
Abstract: The Rossby adjustment process in the wake of a storm is studied with a view to finding, within the context of linear theory, how wave dispersion in both the vertical and meridional directions spreads energy which is initially confined entirely to the mixed layer. Comparisons are made between three cases 1) a periodic storm on the f-plane (where dispersion is purely vertical); 2) a bounded storm on the f-plane; and 3) a bounded storm centered 2700 km from the equator on an equatorial beta-plane. Particular attention is paid to the initial rate of loss of energy from the mixed layer, and some simple formulas which work very well in the cases studied are derived. These show that the rate of loss goes up when the mixed-layer depth is increased, and also that the rate scales as the square of the wavenumber. Values of the rates are sufficient to provide a major source of energy for internal waves below the mixed layer. The often-observed tendency for phase lines to propagate upward is found in all case...
307 citations
TL;DR: In this paper, large amplitude internal waves were observed in the vicinity of the shelf edge and identified positively as solitons, and it was concluded that the associated amount of mixing is sufficient to supply the required nutrients to the euphotic zone.
Abstract: During a measurement program on the Scotian Shelf off Nova Scotia, large amplitude internal waves were observed in the vicinity of the shelf edge. Some were identified positively as solitons. The observations provide insight into the soliton generation process and explain the role they play in the transfer of energy from tides to ocean mixing. It is found that the shoreward propagating energy in the baroclinic tide, which is generated at the shelf edge, is dissipated by way of the large-amplitude, short internal waves. Based on observed dissipation rates of solitary waves, it is concluded that the associated amount of mixing is sufficient to supply the required nutrients to the euphotic zone.
292 citations
TL;DR: In this article, the interaction of weakly nonlinear long internal gravity waves is studied, and it is shown that each wave satisfies a Korteweg-de Vries equation, and the main effect of the interaction is described by a phase shift.
Abstract: The interaction of weakly nonlinear long internal gravity waves is studied. Weak interactions occur when the wave phase speeds are unequal; this case includes that of a head-on collision. It is shown that each wave satisfies a Korteweg-de Vries equation, and the main effect of the interaction is described by a phase shift. Strong interactions occur when the wave phase speeds are nearly equal although the waves belong to different modes. This case is described by a pair of coupled Korteweg-de Vries equations, for which some preliminary numerical results are presented.
216 citations
TL;DR: In this article, the authors examined the evolution of a field of internal waves launched by stratified flow over symmetric topography in mean flows which reverse direction at some height above the surface.
Abstract: We examine the evolution of a field of internal waves launched by stratified flow over symmetric topography in mean flows which reverse direction at some height above the surface. With the gradient Richardson number at this “critical level” in the undisturbed flow restricted to values greater than 0.25, the nonlinear interaction in the region is such that the surface strongly reflects large amplitude internal waves incident upon it. When the critical level is located near certain discrete heights above the ground the incident and reflected waves interfere constructively and the wave amplitude in the low levels is resonantly enhanced by a large factor. These results are related to our previous analyses of the process by which breaking internal waves are able to induce intense downslope windstorms.
168 citations
TL;DR: In this paper, the Zakharov integral equation for surface gravity waves is modified to include higher-order (quintet) interactions, for water of constant (finite or infinite) depth.
Abstract: The Zakharov integral equation for surface gravity waves is modified to include higher-order (quintet) interactions, for water of constant (finite or infinite) depth. This new equation is used to study some aspects of class I (4-wave) and class II (5-wave) instabilities of a Stokes wave.
141 citations
TL;DR: In this article, a stably-stratified nighttime boundary layer perturbed by Kelvin-Helmholtz internal waves with critical levels around 600 m was observed, although the time-mean gradient Richardson numbers were large and positive.
Abstract: Observations have been made of a stably-stratified nighttime boundary layer perturbed by Kelvin-Helmholtz internal waves with critical levels around 600 m. Significant turbulence intensities were measured although the time-mean gradient Richardson numbers were large and positive. It is shown by constructing energy budgets of wave and turbulent components separately that there is an essential flow of kinetic energy from wave to turbulence and that the mechanics of this exchange process depend upon the nonlinear character of the wave field. Turbulent energy budgets were followed through a wave cycle and revealed that turbulence production occurred during only one quarter of a wave period, the rest of the time being taken up by redistribution of turbulent kinetic energy (tke) among the three orthogonal components, relaxation under the effects of density stratification and dissipation. The principal path of energy dissipation is through conversion of vertical component tke to density fluctuations, wh...
126 citations
TL;DR: In this article, a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area of the Gulf of California by the Seasat synthetic aperture radar (SAR).
Abstract: Pronounced signatures of internal waves were detected repeatedly in the Gulf of California by the Seasat synthetic aperture radar (SAR). A series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area. It was found that the number of observed wave groups was highly correlated with the strength of the local tides: the maximum number occurred during spring tides and the minimum number occurred during neap tides, indicating that the internal waves were tidally forced. Most of the wave activity was found to the north of 28 deg N where the tides were the strongest in the Gulf. The application of a simple, nonlinear internal wave model to the observations indicated that the peak-to-peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2. The estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 x 10 to the 15th erg/s, representing only 10 percent of the rate of the dissipation of the dominant M2 tide in the Gulf.
125 citations
TL;DR: In this paper, the authors examined longitudinally asymmetric features of gravity wave propagation in a sudden warming, using observed geostrophic wind fields in the stratosphere for three days of winter 1979.
Abstract: Longitudinally asymmetric features of gravity wave propagation in a sudden warming are examined theoretically, using observed geostrophic wind fields in the stratosphere for three days of winter 1979. It is shown that the wind patterns accompanying a sudden warming act to reduce, but not eliminate, quasi-stationary gravity wave propagation to the mesosphere. The onset of large-amplitude planetary waves leads to the formation of propagating zones and forbidden zones for gravity waves of intermediate horizontal scale (50–200 km). Lateral ray movement and horizontal refraction are secondary but observable effects for these waves. To the extent that these waves are excited isotropically in the troposphere, it is possible to evaluate the direction and magnitude of the average wavevector reaching the mesosphere as follows. Stationary waves with wavevector orthogonal to the local mean flow are selectively absorbed in the stratosphere, implying that for these waves the average wavevector transmitted to t...
111 citations
TL;DR: In this paper, the propagation and refraction of stationary inertia-gravity waves in the winter stratosphere is examined with ray tracing, and the mean flow shear has enhanced unstable wave breaking by compressing, the wave packet and decreasing the absolute value of wave action density required for breaking.
Abstract: The propagation and refraction of stationary inertia–gravity waves in the winter stratosphere is examined with ray tracing. Due to their smaller vertical group velocity these waves experience more lateral ray movement and horizontal refraction that the simple gravity waves recently discussed by Dunkerton and Butchart. Stationary waves are rotated by the transverse horizontal shear and propagate into the polar night jet. Circumstances are found in which the mean flow shear has enhanced unstable wavebreaking by compressing, the wave packet and decreasing the absolute value of wave action density required for breaking. In some other places, reflection from the caustic is more likely.
110 citations
TL;DR: In this article, the power spectral densities (PSD) of five profiles were presented and they closely fit a straight line on a log-log graph even to wavelengths as small as 40m, and the average slope is −2.7 ±.2 (standard error = 0.1).
Abstract: Vertical profiles of scalar horizontal winds have been measured at high resolution (10m) in the 13 to 37 km region of the stratosphere. This resolution (at that range of altitude) represents the state-of-the-art, and is unique. Our goal was to ascertain whether or not the internal waves of the stratosphere behave consistently with the Garrett-Munk model which was originally created for oceanic internal waves. The power spectral densities (PSD's) of five profiles are presented and it is found that (a) they closely fit a straight line on a log-log graph even to wavelengths as small as 40m, and (b) the average slope is −2.7 ± .2 (standard error = 0.1). We conclude that (a) stratospheric internal waves obey the Garrett-Munk model for vertical wave numbers, and (b) there is no statistically significant evidence for a break in the curve at high wave numbers when due allowance is made for aliasing effects.
104 citations
TL;DR: In this paper, a model of the radial, time dependent spreading of a shallow buoyant layer over a motionless, deep ambient layer is developed, which includes fronts as discontinuities and treats the remainder of the plume flow as inviscid, gravitational spreading controlled by nonlinear, internal waves.
Abstract: Shallow buoyant, surface plumes in coastal waters sometimes develop by nearly radial spreading from a continuous source, such as at a river mouth. Such plumes often display a ring structure where buoyant water is concentrated between fronts at both the leading and trailing edges of the expanding ring. These rings often occur in multiple, concentric forms. A model of the radial, time dependent spreading of a shallow buoyant layer over a motionless, deep ambient layer is developed. It includes fronts as discontinuities and treats the remainder of the plume flow as inviscid, gravitational spreading controlled by nonlinear, internal waves. Calculations by the method of characteristics are presented that show the evolution of a clear ring structure. The combination of rapid spreading in the radial geometry together with reflection of internal waves off the frontal boundary at the plume leading edge is shown to be necessary for ring formation. A mechanism is suggested for the formation of multiple rings through the shear flow instability inherent in radial spreading.
TL;DR: In this article, an independent estimate of the frequency-wavenumber spectrum of near-inertial waves for the Sargasso Sea in late summer was made using 8 time series of horizontal velocity from a single moored vertical array and 58 vertical profiles from a horizontal array of expendable velocity profilers.
Abstract: Independent estimates of the frequency–wavenumber spectrum of near-inertial waves for the Sargasso Sea in late summer were made using 8 time series of horizontal velocity from a single moored vertical array and 58 vertical profiles of horizontal velocity from a horizontal array of expendable velocity profilers. The profiler data were analyzed to produce an internal wave frequency-wavenumber spectrum with sufficient resolution to resolve the details of the inertial peak and compute the vertical energy flux. Comparison with the lower resolution spectrum from the moored array shows qualitative agreement; the differences are most likely due to biases in both techniques and to intermittency of the internal wave field. These data reveal a marked asymmetry of the near-inertial internal wave field, with a net downward enemy flux of 0.12±0.12 ergs cm−2 s−1. The downward propagating waves have more energy, a larger horizontal scale and a lower frequency than the upward propagating waves. The magnitude of t...
TL;DR: In this article, the drift velocities in bottom boundary layers due to edge waves show spatial patterns of convergence and divergence which may move sediment to form either regular crescentic or cuspate features when only one edge wave mode dominates, or a bewildering array of bars, bumps and holes when several phase-locked modes exist together.
TL;DR: In this article, a 3D neutral wind model is developed and used together with an atmospheric model in a gravity-wave ray-tracing analysis, which shows that the thermospheric wind can act as a filter for waves travelling at unfavorable angles to the mean flow, via the mechanisms of reflection and critical coupling.
TL;DR: In this article, the authors used linearized internal wave models incorporating linear drag to explain the frequency response of phase velocity but are less successful with the attenuation coefficient, which is well explained by the model of the outer area of the kelp.
Abstract: Coastal kelp stands are a unique physical environment having high drag distributed throughout the water column. Temperature records from locations at increasing distances into the kelp show a damping of high-frequency variance and a slowing of wave propagation at low frequencies. This behavior at low frequencies is more a diffusion than a wave process. Linearized internal wave models incorporating linear drag successfully explain the frequency response of phase velocity but are less successful with the attenuation coefficient. The attenuation coefficient is well explained by the model of the outer area of the kelp but is overestimated in the kelp stand interior. In the outer area phase velocity is about 0.12 m s−1 at 100 cpd (cycles per day), a third of that at 1 cpd; attenuation coefficient is 7.5 km−1 at 100 cpd, 1.5 km−1 at 1 cpd.
TL;DR: In this paper, an 18-day sequence of velocity profiles of the top 600 m of the sea was collected off the coast of Southern California using a pair of Doppler sonars mounted on the Research Platform FLIP.
Abstract: In May 1980 an 18-day sequence of velocity profiles of the top 600 m of the sea was collected off the coast of Southern California. The measurements were obtained using a pair of Doppler sonars mounted on the Research Platform FLIP. From these data, estimates of the wavenumber-frequency spectrum of the oceanic internal wavefield are obtained. The spectra are characterized by a series of ridges, which occur at near-internal and tidal frequencies as well as higher harmonics and sums of these fundamentals. The ridges run parallel to the wavenumber axis. There is a pronounced near-inertial spectral peak. The near-inertial motions are dominated by a few identifiable wave groups. There is a net downward energy propagation in the near-inertial frequency band. The vertical-wavenumber dependence of a the spectrum is decidedly asymmetric in this region. The asymmetry extends to five times the inertial frequency, making much of the so-called continuum asymmetric. A high-wavenumber cutoff at approximately 60...
TL;DR: In this paper, the authors show that even when the unstable shear in the tropospheric jet is confined to a shallow sublayer, producing markedly small-scale Kelvin-Helmholtz instabilities, upscale scattering to the large-scale waves is an efficient process.
Abstract: Upscale scattering of Kelvin-Helmholtz waves to gravity shear waves involves the nonlinear interaction of two Kelvin-Helmholtz waves with wavenumbers k and k′ to produce a wave with wavenumber k−k′. Calculations show that the process produces long-wavelength radiating gravity waves in atmospheric conditions that favor the Kelvin-Helmholtz instabilities. Both line and continuum evaluations are presented in the context of the unstable tropospheric jet. It is shown that even when the unstable shear in the jet is confined to a shallow sublayer, producing markedly small-scale Kelvin-Helmholtz instabilities, upscale scattering to the large-scale waves is an efficient process.
TL;DR: In this paper, the three-dimensional structure of the near-inertial frequency internal wave field was measured at two open ocean sites using expendable velocity profilers and the energy density was roughly equal to Munk's (1981) universal value.
Abstract: The three-dimensional structure of the near-inertial frequency internal wave field was measured at two open ocean sites using expendable velocity profilers. Both wave fields appear to be dominantly wind forced although their vertical structure and horizontal scales are quite different. The HYDRO-79 data were taken in the Sargasso Sea in September 1979. The internal wave field is predominantly downward propagating and vertically uniform, when WKB scaled, in the upper 800 m of the ocean. The energy density is roughly equal to Munk's (1981) universal value. The STKEX data were taken during a period of strong storms in the northeastern Pacific Ocean in November 1980. In the upper few hundred meters the wave field is five times larger horizontally and five times more energetic, when WKB scaled, than the HYDRO-79 wave field. Measurements made after the passage of a strong cold front show an even more energetic and larger scale wave field extending to 500 m. Comparison with the simulations of Price (198...
TL;DR: In this paper, the general structure of stratified airflow over a single hill of height H and length L 1 is studied in detail and shown to be determined by the upwind velocity profile, the magnitude of a characteristic Froude number and the dimensions of the hill.
Abstract: Methods for calculating, interpolating and idealising air flow in complex terrain are reviewed. Then the general structure of stratified airflow over a single hill of height H and length L1 is studied in detail and shown to be determined by the upwind velocity profile, the magnitude of a characteristic Froude number and the dimensions of the hill. Let N(L1) be the buoyancy frequency upwind at a height L1, and u* and U0 be the upwind friction and mean velocity respectively; then the flow is effectively neutral if u*/NL1>1. But if u*/NL1>1 and u0/NL1>1, the stratification is weak enough to affect the upwind turbulence and velocity profile but not the dynamics of the flow over the hill. If U0/NL1 1 the buoyancy forces are strong enough to affect the mean flow over the hill but not strong enough to prevent it passing over the top. In this regime the flow is very sensitive to the form of the upwind temperature profile. If U0/NH>1, much of the flow passes round the hill. A similar classification, with different flow patterns, is appropriate for unstably stratified flows. When the wind is weak enough, local slope winds can dominate. Results from the analysis of these different regimes are described and compared with laboratory of field measurements where possible. It is shown how some of these results can be extended to groups of hills.
TL;DR: In this paper, the amplification and attenuation of small-scale acoustic-gravity waves in Venus's atmosphere is studied with a plane-wave model that realistically simulates height variations in structure and zonal circulation.
Abstract: The amplification and attenuation of small-scale acoustic-gravity waves in Venus's atmosphere is studied with a plane-wave model that realistically simulates height variations in structure and zonal circulation. Forcing for these waves could be convective activity at cloud heights or close to the surface, or turbulence arising from small-scale shear instability of the zonal flow; the model treats both surface forcing and cloud-level forcing by diabatic heating variations in the low-stability layer near the base of the clouds. Waves are attenuated in this cloud-level, low-static-stability layer. Slowly moving waves with small vertical length scales are attenuated by eddy diffusivity. Westward moving waves can undergo critical level absorption. A net enhancement in wave amplitude is ago possible because waves can be trapped between the surface and the base of the low stability layer at about 50 km. Observations of small-scale wave activity at the cloud tops and above can be used to explore uncertai...
01 Jan 1984
TL;DR: The simple theory for the effect of gravity wave breaking on eddy diffusion and on mean stress is reviewed in this article, where attempts are made to identify the magnitudes of known mechanisms for generating gravity waves.
Abstract: The simple theory for the effect of gravity wave breaking on eddy diffusion and on mean stress is reviewed. Attempts are made to identify the magnitudes of known mechanisms for generating gravity waves. The relation between observed periods and unobserved horizontal wavenumbers is discussed. Finally the role of group velocity, wave packets and wave inhomogeneity is discussed.
TL;DR: In this article, the authors examined the available evidence for the frequency regimes, excitation and damping mechanisms of the core waves and concluded that although the waves may exist theoretically, their detection and interpretation as a method for determining the buoyancy frequency is a difficult proposition.
TL;DR: Theoretical studies predict a parametric instability of finite-amplitude internal gravity waves, which hitherto has been observed only in laboratory experiments as discussed by the authors, and the occurrence of this process in the atmosphere is of basic interest because finite amplitude gravity waves which are almost ubiquitous especially at upper atmospheric heights, would produce unstable flows even at large Richardson numbers.
Abstract: Theoretical studies predict a parametric instability of finite-amplitude internal gravity waves which hitherto has been observed only in laboratory experiments. The occurrence of this process in the atmosphere is of basic interest because finite-amplitude gravity waves, which are almost ubiquitous especially at upper atmospheric heights, would produce unstable flows even at large Richardson numbers. Maximum entropy power spectra of a strong internal gravity wave in the thermosphere, which was generated by a volcanic eruption and detected on records of the Doppler shift of high-frequency radio waves, in fact show good agreement with the spectra of synthetic Doppler records obtained from a calculated unstable gravity wave. The frequencies and wavenumbers observed in the gravity wave domain satisfy in particular the theoretically predicted resonance conditions. The observed Doppler records also show two significant lines in the acoustic domain which probably result from a nonlinear interaction with ...
TL;DR: A quasi-periodic wind oscillation with an apparent 20-50 hour period was observed at between 16 and 20 km in every experiment conducted during three periods from 1979 to 1981 with the Arecibo UHF radar as mentioned in this paper.
Abstract: A quasi-periodic wind oscillation with an apparent 20-50 hour period was observed at between 16 and 20 km in every experiment conducted during three periods from 1979 to 1981 with the Arecibo UHF radar. The wave disappeared near 20 km, where the mean zonal flow had easterly shear with height. This phenomenon is discussed in terms of wave absorption at a critical level, and it is suggested that the wave had a westward horizontal phase speed of 10-20 m/sec. On the basis of a relationship from f-plane theory in which the Doppler-shifted wave frequency approaches the Coriolis frequency at the critical level, an intrinsic period and horizontal wavelength at the wave-generated height of 20-30 hours and about 2000 km, respectively, are inferred.
01 Jan 1984
TL;DR: In this article, the influence of the fine-structure field on the character of large-scale dispersion of an odorous substance leads to a hypothesized mechanism for olfactory orientation.
Abstract: Some characteristic properties of vertical fine structure and microstructure in natural waters are surveyed. Ubiquitous thermal microstructure, by its anisotrophy due to shear in the fine-structure gradient layers, is a property that could be used by fishes to orient relative to the local current shear. The geostrophic shear causes a bias in the probability of breaking of internal waves, depending on the direction of wave travel relative to the shear. By this mechanism the direction of major ocean currents may be mirrored in local microstructure. The influence of the fine-structure field on the character of large-scale dispersion of an odorous substance leads to a hypothesized mechanism for olfactory orientation. Some results from ultrasonic tracking of Atlantic salmon and European eels are given to show that fish do perceive and react to vertical fine structure.
TL;DR: In this paper, it was shown that nonlinear internal waves, generated within the Strait of Gibraltar, propagated eastward about 50 km into the western Mediterranean Sea and appeared as energetic packets of 30 minute period waves.
Abstract: Current measurements revealed that nonlinear internal waves, generated within the Strait of Gibraltar, propagated eastward about 50 km into the western Mediterranean Sea and appeared as energetic packets of 30 minute period waves. The waves had a net eastward transport in the upper layer such that during a ten day period the waves carried one-third of the climatic transport. This partitioning of transport, normally carried by a narrow current, may have altered the strengths of the Atlantic inflow current and the anticyclonic Alboran Sea gyre.
TL;DR: In this paper, a new mechanism of instability in stratified fluid caused by internal wave radiation from a shear layer is explained in terms of the negative energy wave concept, and the dispersion relation and non-linear stage of the process are analyzed through a model with tangential velocity discontinuity.
Abstract: The paper deals with a new mechanism of instability in stratified fluid caused by internal wave radiation from a shear layer. This radiation instability may be explained in terms of the negativeenergy wave concept. These waves are able to grow due to radiation losses. The dispersion relation and non-linear stage of the process are analyzed through a model with tangential velocity discontinuity. The non-linear description is based on a long-wave approximation leading to an evolution equation of the Korteweg-de Vries type with certain additional terms responsible for instability as well as dissipation due to turbulence. Approximate solutions of the equation are obtained which, in particular, describe the evolution of solitons including explosive growth and approaching the steady state.
TL;DR: In this paper, the effect of horizontally inhomogeneous flows on internal wave propagation in a stratified ocean with a constant Brunt-Vaisala frequency was analyzed using wave-normal surfaces.
Abstract: The effect of horizontally inhomogeneous flows on internal wave propagation in a stratified ocean with a constant Brunt-Vaisala frequency is analysed. Dispersion characteristics of internal waves in a moving fluid and kinematics of wave packets in smoothly inhomogeneous flows are considered using wave-normal surfaces. It is shown that internal-wave blocking and short-wave transformation may occur in longitudinally inhomogeneous flows. For parallel flows internal-wave trapping is possible in the vicinity of the limiting layer where the wave frequency in the locally comoving frame of reference coincides with the Brunt-Vaisala frequency. Internal-wave trapping also takes place in jet-type flows in the vicinity of the flow-velocity maximum. WKB solutions of the equation describing internal-wave propagation in a parallel horizontally inhomogeneous flow in the linear approximation are obtained. Singular points of this equation and the related effect of internal-wave amplification (overreflection) under the action of the flow are investigated. The spectrum and the growth rate of internal-wave localized modes in a jet-type flow are obtained.
TL;DR: The R/V Endeavor encountered a strong front in the core of the warm core ring 82B on June 22, 1982, while participating in a multi-ship study as mentioned in this paper.
Abstract: On June 22, 1982, the R/V Endeavor, while participating in a multi-ship study of a warm core ring 82B, encountered a strong front in the core of the ring. The vessel was headed on a radial section outward from ring center while a CTD was repeatedly raised and lowered between 10 and 300 m. Current profiles in the upper 100 m were obtained continuously with a Doppler acoustic profiling system. Above the shallow 45 m seasonal thermocline, a current jet of 4 km width was encountered having a central core of relatively light water and a maximum current of 1.1 m/s. This jet was both highly nonlinear and totally unexpected. A high frequency packet of directional internal waves was acoustically observed in the seasonal thermocline at the outer edge of the jet. Vertical velocities were large enough (6 cm/s) as to be directly observable in the Doppler returns. The waves were propagating from the northeast, parallel to the ship track, and orthogonal to the jet toward the center of the warm core ring. While a nonlinear, centrifugal term was required for the force balance of the jet, the high-frequency internal wave packet could be explained with linear, gravest-mode wave dynamics.