Showing papers on "Longitudinal wave published in 2004"

Ultrasonic Waves in Solid Media

Abstract: Preface 1. Introduction 2. Dispersion principles 3. Unbounded isotropic and anisotropic media 4. Reflection and refraction 5. Oblique incidence 6. Wave scattering 7. Surface and subsurface waves 8. Waves in plates 9. Interface waves 10. Layer on a half space 11. Waves in rods 12. Waves in hollow cylinders 13. Guided waves in multiple layers 14. Source influence 15. Horizontal shear 16. Waves in an anisotropic layer 17. Elastic constant determination 18. Waves in viscoelastic media 19. Stress influence 20. Boundary element methods Bibliography Appendices A. Ultrasonic nondestructive testing principles, analysis and display technology B. Basic formulas and concepts in the theory of elasticity C. Basic formulas in complex variables D. Schlieren imaging and dynamic photoelasticity E. Key wave propagation experiments Index.

Shoaling of subharmonic gravity waves

Abstract: [1] In this paper the energy budget of wave group-induced subharmonic gravity waves in the nearshore region is examined on the basis of the energy equation for long waves in conjunction with analyses of a high-resolution laboratory data set of one-dimensional random wave propagation over a barred beach. The emphasis is on the growth of forced subharmonics and the deshoaling of the reflected free waves in the shoaling zone. The incident lower-frequency subharmonics are nearly fully reflected at the shoreline, but the higher-frequency components appear to be subject to a significant dissipation in a narrow inshore zone including the swash zone. The previously reported phase lag of the incident forced waves behind the short-wave groups is confirmed, and its key role in the transfer of energy between the grouped short waves and the shoaling bound waves is highlighted. The cross-shore variation of the local mean rate of this energy transfer is determined. Using this as a source function in the wave energy balance allows a very accurate prediction of the enhancement of the forced waves in the shoaling zone, where dissipation is insignificant. The phase lag appears to increase with increasing frequency, which is reflected in a frequency-dependent growth rate, varying very nearly from the free-wave variation ∼ h -1/4 (Green's law) for the lower frequencies to the shallow-water equilibrium limit for forced subharmonics ∼h -5/2 for the higher frequencies. This observed frequency dependence is tentatively generalized to a dependence on a normalized bed slope, controlling whether a so-called mild-slope regime or a steep-slope regime prevails, in which enhanced incident forced waves dominate over breakpoint-generated waves or vice versa.

The Fresnel volume and transmitted waves

Abstract: In seismic imaging experiments, it is common to use a geometric ray theory that is an asymptotic solution of the wave equation in the high-frequency limit. Consequently, it is assumed that waves propagate along infinitely narrow lines through space, called rays, that join the source and receiver. In reality, recorded waves have a finite-frequency content. The band limitation of waves implies that the propagation of waves is extended to a finite volume of space around the geometrical ray path. This volume is called the Fresnel volume. In this tutorial, we introduce the physics of the Fresnel volume and we present a solution of the wave equation that accounts for the band limitation of waves. The finite-frequency wave theory specifies sensitivity kernels that linearly relate the traveltime and amplitude of band-limited transmitted and reflected waves to slowness variations in the earth. The Fresnel zone and the finite-frequency sensitivity kernels are closely connected through the concept of constructive interference of waves. The finite-frequency wave theory leads to the counterintuitive result that a pointlike velocity perturbation placed on the geometric ray in three dimensions does not cause a perturbation of the phase of the wavefield. Also, it turns out that Fermat’s theorem in the context of geometric ray theory is a special case of the finite-frequency wave theory in the limit of infinite frequency. Last, we address the misconception that the width of the Fresnel volume limits the resolution in imaging experiments.

Stationary optical wave fields with arbitrary longitudinal shape by superposing equal frequency Bessel beams: Frozen Waves.

Abstract: In this paper it is shown how one can use Bessel beams to obtain a stationary localized wave field with high transverse localization, and whose longitudinal intensity pattern can assume any desired shape within a chosen interval 0

Waves in the ocean and atmosphere : introduction to wave dynamics

Abstract: 1 Introduction.- 2 Kinematic Generalization.- 3 Equations of Motion Surface Gravity Waves.- 4 Fields of Motion in Gravity Waves and Energy.- 5 The Initial Value Problem.- 6 Discussion of Initial Value Problem [Continued).- 7 Internal Gravity Waves.- 8 Internal Waves, Group Velocity and Reflection.- 9 WKB Theory for Internal Gravity Waves.- 10 Vertical Propagation of Waves: Steady Flow and the Radiation Condition.- 11 Rotation and Potential Vorticity.- 12 Large-Scale Hydrostatic Motions.- 13 Shallow Water Waves in a Rotating Fluid Poincare and Kelvin Waves.- 14 Rossby Waves.- 15 Rossby Waves (Continued), Quasi-Geostrophy.- 16 Energy and Energy Flux in Rossby Waves.- 17 Laplace Tidal Equations and the Vertical Structure Equation.- 18 Equatorial Beta-Plane and Equatorial Waves.- 19 Stratified Quasi-Geostrophic Motion and Instability Waves.- 20 Energy Equation and Necessary Conditions for Instability.- 21 Wave-Mean Flow Interaction.- Problems.- References.

Enhanced ultrasound transmission through the human skull using shear mode conversion

Abstract: A new transskull propagation technique, which deliberately induces a shear mode in the skull bone, is investigated. Incident waves beyond Snell’s critical angle experience a mode conversion from an incident longitudinal wave into a shear wave in the bone layers and then back to a longitudinal wave in the brain. The skull’s shear speed provides a better impedance match, less refraction, and less phase alteration than its longitudinal counterpart. Therefore, the idea of utilizing a shear wave for focusing ultrasound in the brain is examined. Demonstrations of the phenomena, and numerical predictions are first studied with plastic phantoms and then using an ex vivo human skull. It is shown that at a frequency of 0.74 MHz the transskull shear method produces an amplitude on the order of—and sometimes higher than—longitudinal propagation. Furthermore, since the shear wave experiences a reduced overall phase shift, this indicates that it is plausible for an existing noninvasive transskull focusing method [Clement, Phys. Med. Biol. 47(8), 1219–1236 (2002)] to be simplified and extended to a larger region in the brain.

Global P and PP traveltime tomography: rays versus waves

Abstract: SUMMARY This paper presents a comparison of ray-theoretical and finite-frequency traveltime tomography for compressional waves. Our data set consists of 86 405 long-period P and PP‐P traveltimes measured by cross-correlation. The traveltime of a finite-frequency wave is sensitive to anomalies in a hollow banana-shaped region surrounding the unperturbed ray path, with the sensitivity being zero on the ray. Because of the minimax nature of the surface-reflected PP wave, its sensitivity is more complicated. We compute the 3-D traveltime sensitivity efficiently by using the paraxial approximation in conjunction with ray theory and the Born approximation. We compare tomographic models with the same χ 2 fit for both ray theory and finite-frequency analysis. Depending on the depth and size of the anomaly, the amplitudes of the velocity perturbations in the finite-frequency tomographic images are 30‐50 per cent larger than in the corresponding ray-theoretical images, demonstrating that wave front healing cannot be neglected when interpreting long-period seismic waves. The images obtained provide clear evidence that a limited number of hotspots are fed by plumes originating in the lower mantle.

Generation and classification of localized waves by Lorentz transformations in Fourier space.

Abstract: The Lorentz transformations of propagation-invariant localized waves (also known as nondispersive or nondiffracting or undistorted progressive waves) are studied in the frequency-momentum space For supports of wave functions in this space rules of transformation are derived which allow one to group all localized waves into distinct classes: subluminal, luminal, and superluminal localized waves It is shown that for each class there is an inertial frame in which any given localized wave takes a particularly simple form In other words, any localized wave is nothing but a relativistically aberrated and Doppler shifted version of a simple ``seed'' wave Also discussed are the relations of the physical (subluminal) Lorentz tranformation to other mathematical tranformations used in the literature on localized waves, as well as physical interpretation of the substantial changes that localized waves undergo if observed and generated in different inertial frames

Reverse propagation of sound in the gerbil cochlea.

Abstract: It is commonly believed that the cochlea emits sounds through backward-traveling waves. In the present experiment using a scanning-laser interferometer, I detected forward-traveling but not backward-traveling waves and found that the stapes vibrates earlier than the basilar membrane. These results contradict the current theory and show that the ear emits sounds through the cochlear fluids as compression waves rather than along the basilar membrane as backward-traveling waves.

Plane waves with negative phase velocity in Faraday chiral mediums.

Abstract: The propagation of plane waves in a Faraday chiral medium is investigated. Conditions for the phase velocity to be directed opposite to the direction of power flow are derived for propagation in an arbitrary direction; simplified conditions which apply to propagation parallel to the distinguished axis are also established. These negative phase-velocity conditions are explored numerically using a representative Faraday chiral medium, arising from the homogenization of an isotropic chiral medium and a magnetically biased ferrite. It is demonstrated that the phase velocity may be directed opposite to power flow, provided that the gyrotropic parameter of the ferrite component medium is sufficiently large compared with the corresponding nongyrotropic permeability parameters.

Calculation of sound propagation in nonuniform flows: Suppression of instability waves

Abstract: Acoustic waves propagating through nonuniform flows are subject to convection and refraction. Most noise prediction schemes use a linear wave operator to capture these effects. However, the wave operator can also support instability waves that, for a jet, are the well-known Kelvin-Helmholtz instabilities. These are convective instabilities that can completely overwhelm the acoustic solution downstream of the source location. A general technique to filter out the instability waves is presented. A mathematical analysis is presented that demonstrates that the instabilities are suppressed if a time-harmonic response is assumed, and the governing equations are solved by a direct solver in the frequency domain. Also, a buffer-zone treatment for a nonreflecting boundary condition implementation in the frequency domain is developed

MHD wave propagation in the neighbourhood of a two-dimensional null point

Abstract: The nature of fast magnetoacoustic and Alfven waves is investigated in a zero β plasma. This gives an indication of wave propagation in the low β solar corona. It is found that for a two-dimensional null point, the fast wave is attracted to that point and the front of the wave slows down as it approaches the null point, causing the current density to accumulate there and rise rapidly. Ohmic dissipation will extract the energy in the wave at this point. This illustrates that null points play an important role in the rapid dissipation of fast magnetoacoustic waves and suggests the location where wave heating will occur in the corona. The Alfven wave behaves in a different manner in that the wave energy is dissipated along the separatrices. For Alfven waves that are decoupled from fast waves, the value of the plasma β is unimportant. However, the phenomenon of dissipating the majority of the wave energy at a specific place is a feature of both wave types.

The Effects of Stratification on Oscillating Coronal Loops

Abstract: Recent observations by the Solar and Heliospheric Observatory (SOHO) and the Transition Region and Coronal Explorer (TRACE) have confirmed previous theoretical predictions that coronal loops may oscillate. These oscillations and their damping are of fundamental importance, because they can provide diagnostics of the coronal plasma. In the present paper, we perform numerical hydrodynamic calculations of a one-dimensional loop model to investigate the effects of stratification on damping of longitudinal waves in the hot coronal loops observed by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on board the SOHO satellite. In particular, we study the dissipation by thermal conduction and by compressive viscosity of standing slow magnetosonic disturbances in loops of semicircular shape. For the parameter regime that characterizes the SUMER hot loops, we find that stratification results in a ~10%-20% reduction of the wave-damping time compared to the nonstratified loop models because of increased dissipation by compressive viscosity due to gravity. We show that temperature oscillations are more strongly dissipated by thermal conduction, while density and velocity waves are mostly damped by compressive viscosity. However, the decay time of the oscillations is always governed by the thermal conduction timescale. The scalings of the decay time with wave period, temperature, and loop length all point toward higher dissipation rates in the stratified, hotter loops because of the increased effects of thermal conduction and compressive viscosity.

Sonic boom in soft materials: The elastic Cerenkov effect

Abstract: We report an experimental evidence of an elastic sonic boom in soft materials. Our approach is based on the ultrasonic remote generation, inside soft media, of a supersonic moving source radiating shear waves in a Mach cone. In analogy with the Cerenkov electromagnetic radiation emitted by a beam of charged particles moving at a speed greater than the speed of light, an intense shear wave is radiated in soft materials. Such Mach waves are sensitive to medium elasticity inhomogeneities and are of great interest for ultrasound-based medical imaging applications.

Solitary waves observed in the auroral zone: the Cluster multi-spacecraft perspective

Abstract: We report on recent measurements of solitary waves made by the Wideband Plasma Wave Receiver located on each of the four Cluster spacecraft at 4.5-6.5 R E (well above the auroral acceleration region) as they cross field lines that map to the auroral zones. These solitary waves are observed in the Wideband data as isolated bipolar and tripolar waveforms. Examples of the two types of pulses are provided. The time durations of the majority of both types of solitary waves observed in this region range from about 0.3 up to 5ms. Their peak-to-peak amplitudes range from about 0.05 up to 20mV/m, with a few reaching up to almost 70mV/m. There is essentially no potential change across the bipolar pulses. There appears to be a small, measurable potential change, up to 0.5V, across the tripolar pulses, which is consistent with weak or hybrid double layers. A limited cross-spacecraft correlation study was carried out in order to identify the same solitary wave on more than one spacecraft. We found no convincing correlations of the bipolar solitary waves. In the two cases of possible correlation of the tripolar pulses, we found that the solitary waves are propagating at several hundred to a few thousand km/s and that they are possibly evolving (growing, decaying) as they propagate from one spacecraft to the next. Further, they have a perpendicular (to the magnetic field) width of 50km or greater and a parallel width of about 2-5km. We conclude, in general, however, that the Cluster spacecraft at separations along and perpendicular to the local magnetic field direction of tens of km and greater are too large to obtain positive correlations in this region. Looking at the macroscale of the auroral zone at 4.5-6.5 R E , we find that the onsets of the broadband electrostatic noise associated with the solitary waves observed in the spectrograms of the WBD data are generally consistent with propagation of the solitary waves up the field lines (away from Earth), or with particles or waves propagating up the field line, which leads to local generation of the solitary waves all along the field lines. A discussion of the importance of these solitary waves in magnetospheric processes and their possible generation mechanisms, through electron beam instabilities and turbulence, is provided.

Guided circumferential shear horizontal waves in an isotropic hollow cylinder

Abstract: Guided time-harmonic shear horizontal (SH) waves propagating in the circumferential direction of an isotropic hollow cylinder are studied. The dispersion equation as well as the displacement and stress field across the wall thickness is derived analytically. Compared with the SH waves in a plate, a quantitative guideline of how well a plate model can approximate a pipe in the circumferential direction is given for defect characterization purpose. The work is also crucial for initiating work efforts on three-dimensional wave scattering for pipeline inspection.

Reservoir Fluids Identification Using Vp/Vs Ratio?

Abstract: Sonic travel time of compressional wave is generally used as porosity tool for given lithology. Introducing shear wave travel time is very helpful in determining mechanical rock properties. It is found that compressional wave is sensitive to the saturating fluid type. The use of the ratio of compressional wave velocity to shear wave velocity, Vp/Vs, is a good tool in identifying fluid type. The fact that compressional wave velocity decreases and shear wave velocity increases with the increase of light hydrocarbon saturation, makes the ratio of Vp/Vs more sensitive to change of fluid type than the use of Vp or Vs separately. Field examples are given to identify fluids type (water, oil and gas) using the Vp/Vs ratio. Field examples have shown that shear travel time decreases while compressional travel time increases when the water saturated points become gas or light oil saturated points in the studied sections. The decrease of shear travel time (increase of shear wave velocity) is due to the decrease of density and the absorption of deformation by free gas in pores. The increase of compressional travel time (decrease of compressional wave velocity) is due to the decrease of bulk modulus of reservoir rocks which compensates the decrease of rock density.

Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

Abstract: . In this paper, in terms of an axisymmetric model of the magnetosphere, we formulate the criteria for which the Alfven waves in the magnetosphere can be toroidally and poloidally polarized (the disturbed magnetic field vector oscillates azimuthally and radially, respectively). The obvious condition of equality of the wave frequency ω to the toroidal (poloidal) eigenfrequency ΩTN (ΩPN) is a necessary and sufficient one for the toroidal polarization of the mode and only a necessary one for the poloidal mode. In the latter case we must also add to it a significantly stronger condition ∣ΩTN–ΩPN∣/ΩTN ≫ m–1 where m is the azimuthal wave number, and N is the longitudinal wave number. In cold plasma (the plasma to magnetic pressure ratio β = 0) the left-hand side of this inequality is too small for the routinely recorded (in the magnetosphere) second harmonic of radially polarized waves, therefore these waves must have nonrealistically large values of m. By studying several models of the magnetosphere differing by the level of disturbance, we found that the left-hand part of the poloidality criterion can be satisfied by taking into account finite plasma pressure for the observed values of m ∼ 50 – 100 (and in some cases, for even smaller values of the azimuthal wave numbers). When the poloidality condition is satisfied, the existence of two types of radially polarized Alfven waves is possible. In magnetospheric regions, where the function ΩPN is a monotonic one, the mode is poloidally polarized in a part of its region of localization. It propagates slowly across magnetic shells and changes its polarization from poloidal to toroidal. The other type of radially polarized waves can exist in those regions where this function reaches its extreme values (ring current, plasmapause). These waves are standing waves across magnetic shells, having a poloidal polarization throughout the region of its existence. Waves of this type are likely to be exemplified by giant pulsations. If the poloidality condition is not satisfied, then the mode is toroidally polarized throughout the region of its existence. Furthermore, it has a resonance peak near the magnetic shell, the toroidal eigenfrequency of which equals the frequency of the wave. Key words. Magnetospheric physics (plasmasphere; MHD waves and instabilities) – Space plasma physics (kinetic and MHD theory)

Utilization of high-frequency Rayleigh waves in near-surface geophysics

Abstract: Rayleigh waves, surface waves that travel along a “free” surface such as the earth-air or the earth-water interface, are usually characterized by relatively low velocity, low frequency, and high amplitude. Rayleigh waves are the result of interfering P and SV waves. Particle motion of the fundamental mode of Rayleigh waves in a homogeneous medium moving from left to right is elliptical in a counter-clockwise (retrograde) direction along the free surface. As depth increases, the particle motion becomes prograded and is still elliptical when reaching sufficient depth. The motion is constrained to a vertical plane consistent with the direction of wave propagation.

The evolution and subsequent dynamics of waves on a vertically falling liquid film

Abstract: The spatiotemporal evolution of periodic waves on a vertically falling water film was investigated at the Reynolds number Re=15–75 via physical and numerical experiments. Small periodic waves excited at a low frequency grow directly into teardrop-shaped tall pulses, small waves of an intermediate frequency first grow into close-packed humps and then into pulses sandwiching single capillary ripples, and small waves of a high frequency grow into nearly sinusoidal waves. The initial wave evolution causes the waves to accelerate at low frequencies or to decelerate at intermediate and high frequencies. The maximum deceleration occurs with the growth into the close-packed humps which then undergo the transition to the pulses without a change of the wave frequency, associated with rapid acceleration. Subsequently, the quasisteady, nearly sinusoidal waves of small amplitudes and short-separation pulses further develop into nearly solitary tall pulses through transitions of wave coalescence, associated with growth of transverse wavefront variation. The nearly sinusoidal waves of large amplitudes rapidly increase the transverse variations of wavefronts and then fade away. These spatiotemporal evolution scenarios are consistent with the predictions from the stability analysis of steady-state traveling waves and the numerical simulations of the temporal evolution of periodic waves reported in the literature. A comparison with the evolution of noise-driven natural waves suggests that the natural waves greatly compress the scenario of waves at an intermediate frequency and rapidly grow into nearly solitary pulses following the scenario. Furthermore, it was revealed that these evolution scenarios resemble the ones observed on falling films inclined slightly from the horizontal.

Cracks in Rubber under Tension Exceed the Shear Wave Speed

Abstract: The shear wave speed is an upper limit for the speed of cracks loaded in tension in linear elastic solids. We have discovered that in a non-linear material, cracks in tension (Mode I) exceed this sound speed, and travel in an intersonic range between shear and longitudinal wave speeds. The experiments are conducted in highly stretched sheets of rubber; intersonic cracks can be produced simply by popping a balloon.

Internal wave tunnelling

Abstract: We present the first laboratory evidence of internal gravity wave tunnelling through weakly stratified fluid patches and we derive analytic theories for energy transmission by the waves in two distinct circumstances. In one, the computed transmission coefficient is directly analogous to the textbook calculation for quantum tunnelling of a free electron incident upon a potential barrier. In the other, we consider the partial reflection and transmission of internal waves through a mixed region bounded by discontinuities in the density profile. The results reveal a linear resonance between vertically propagating internal waves and interfacial waves that exist on either flank of the mixing region. The resonance permits perfect transmission of internal waves that would otherwise strongly reflect from the weakly stratified region. We discuss a specific application of our results to deep convective storm-generated internal waves that tunnel through the mesosphere to the ionosphere.

The damping of slow MHD waves in solar coronal magnetic fields. III. The effect of mode coupling

Abstract: The properties of slow MHD waves in a two dimensional model are investigated, in a low-beta plasma. Including a horizontal density variation causes "phase mixing" and coupling between slow and fast MHD waves. The effects of different density profiles, different driving frequencies, different values for the viscosity coefficient and plasma beta (<1) are studied. Using numerical simulations, it was found that the behaviour of the perturbed velocity was strongly dependent on the values of the parameters. From analytical approximations, a strong interaction with the fundamental, normal modes of the system was found to play an important role. The coupling to the fast wave proved to be an inefficient way to extract energy from the driven slow wave and is unlikely to be responsible for the rapid damping of propagating slow MHD waves, observed by TRACE. The "phase mixing" of the slow waves due to the (horizontal) density inhomogeneity does cause a significant amount of damping, but is again unlikely to be sufficiently strong to explain the rapid observed damping.

Generation and propagation of water waves in a two-dimensional numerical viscous wave flume

Abstract: This study investigated the generation and propagation of water waves in a numerical viscous wave flume. The numerical scheme developed by Huang and collaborators for solving the unsteady two-dimensional Navier–Stokes equations for wavemaking problems was employed to generate different incident waves, including small- and finite-amplitude waves and solitary waves. The accuracy of the numerical results for the wave and velocity profiles was verified by comparison with the analytical solutions. The wave propagation in a numerical wave flume was also investigated. For periodic gravity waves on finite water depth, the results showed that waves with larger Ursell numbers are more stable than those with smaller Ursell numbers. The propagation of solitary waves in the channel is stable. For stable waves, the wave height attenuation caused by the energy dissipation in the wave motion was shown to be consistent with the theoretical results.

The application of the constants of motion to nonlinear stationary waves in complex plasmas: a unified fluid dynamic viewpoint

Abstract: Perturbation reductive procedures, as used to analyse various weakly nonlinear plasma waves (solitons and periodic waves), normally lead to the dynamical system being described by KdV, Burgers' or a nonlinear Schrodinger-type equation, with properties that can be deduced from an array of mathematical techniques. Here we develop a fully nonlinear theory of one-dimensional stationary plasma waves, which elucidates the common nature of various diverse wave phenomena. This is accomplished by adopting an essentially fluid dynamic viewpoint. In this unified treatment the constants of the motion (for mass, momentum and energy) lead naturally to the construction of the wave structure equations. It is shown, for example, that electrostatic, Hall–magnetohydrodynamic and ion–cyclotron–acoustic nonlinear waves all obey first-order differential equations of the same generic type for the longitudinal flow field of the wave. The equilibrium points, which define the soliton amplitude, are given by the compressive and/or rarefactive roots of a total plasma ‘energy’ or ‘momentum’ function characterizing the wave type. This energy function, which is an algebraic combination of the Bernoulli momentum and energy functions for the longitudinal flow field, is the fluid dynamic counterpart of the pseudo-potentials, which are characteristic of system structure equations formulated in other than fluid variables. Another general feature of the structure equation is the phenomenon of choked flow, which occurs when the flow speed becomes sonic. It is this trans-sonic property that limits the soliton amplitudes and defines the critical collective Mach numbers of the waves. These features are also obtained in multi-component plasmas where, for example, in a bi-ion plasma, momentum exchanges between protons and heavier ions are mediated by the Maxwell magnetic stresses. With a suitable generalization of the concept of a sonic point in a bi-ion system and the corresponding choked flow feature, the wave structures, although now more complicated, can also be understood within this overall fluid framework. Particularly useful tools in this context are the momentum hodograph (an algebraic relation between the bi-ion speeds and the electron speed, or magnetic field, which follows from the conservation of mass, momentum and charge-neutrality) and a generalized Bernoulli energy density for each species. Analysis shows that the bi-ion solitons are essentially compressive, but contain the remarkable feature of the presence of a proton rarefactive core. A new type of soliton, called an ‘oscilliton’ because embedded spatial oscillations are superimposed on the classical soliton, is also described and discussed. A necessary condition for the existence of this type of wave is that the linear phase velocity must exhibit an extremum where the phase speed matches the group speed. The remarkable properties of this wave are illustrated for the case of both whistler waves and bi-ion waves where, for the latter, the requisite condition is met near the cross-over frequencies. In the case of the whistler oscilliton, which propagates at speeds in excess of one half of the Alfven speed (based on the electrons), an analytic solution has been constructed through a phase-portrait integral of the system in which the proton and electron dynamics must be placed on the same footing. The relevance of the different wave structures to diverse space environments is briefly discussed in relation to recently available high-time and spatial resolution data from satellite observations.