Propagation Of Acoustic-gravity Waves Research Articles

Simulation of generation and propagation of acoustic gravity waves in the atmosphere during a rocket flight

Simulation of generation and propagation of acoustic gravity waves in the atmosphere during a rocket flight

Acoustic-gravity waves in the atmosphere with a piecewise-linear temperature profile

We consider the problem of propagation of acoustic-gravity waves in the atmosphere with a constant temperature gradient in the near-surface layer. The assumption of linear temperature dependence on height allowed us to reduce the wave equation to the hypergeometric form, regardless of the compressibility of the medium. The solution of this equation is represented in terms of degenerate hypergeometric functions. To analyze the obtained solution, we consider a two-layer model of a half-bounded atmosphere with a height-independent background temperature in the upper layer. The results are studied in detail under the approximation of an incompressible medium. For the model specified above, we find analytical expressions for the perturbation fields and obtain a characteristic equation whose solution allows us to calculate wave dispersion characteristics at frequencies close to the Brunt-Vaisala frequency for large horizontal scales as compared to the layer thickness.

Nonradial adiabatic oscillations of stars

The classication scheme of mode oscillations in stars is investigated mathematically and physically by using a new phase diagram representation. This technique is presented in order to study the basic equation of motion for linear adiabatic nonradial oscillations, and leads us to obtain an unambiguous scheme classication of modes. The order number introduced by this classication scheme only depends on the boundary conditions at the endpoints, the centre and the surface of the star. Furthermore, this classication is independent of the number of nodes of the eigenfunction used to characterize the oscillatory motion. Consequently, the sequence of ordinate eigenfrequencies becomes the signature of the oscillatory system itself. Provided that the equation of motion of linear adiabatic nonradial stellar oscillations has been reduced to a second-order dierential equation, this technique allows us to obtain a more reliable classication scheme of modes in stars. Although this phase analysis method has been presented to characterize the propagation of acoustic-gravity waves with one or two propagative regions, it can be nevertheless successfully applied to perturbative motions with more than three propagative regions, provided that a propagation diagram can be built.

Parametric generation of acoustic-gravity waves in the solar atmosphere

Based on a plane isothermal solar-atmosphere model, we investigate the parametric generation of acoustic-gravity waves (AGWs) in the approximation of a fixed field for vertically propagating disturbances. Both nonpropagating and propagating AGWs are shown to be generated at the difference frequency via the nonlinear interaction of primary waves in the frequency range “forbidden” for the propagation of AGWs during their linear generation. An acoustic wind has been found to be formed in the solar atmosphere at zero difference frequency; its velocity increases with height in inverse proportion to the decreasing ambient density. We study the nonlinear generation of AGWs at the second harmonic during the interaction of disturbances from the forbidden frequency range.

Observations of gravity waves of meteorological origin in the F-Region ionosphere

Motion of large meteorological phenomenon causes wave like structures that propagate from the troposphere to thermospheric heights. Acoustic gravity waves (AGW) caused by this phenomenon affect the neutral atmosphere and consequently the ionosphere. The changes of electron density profiles caused by AGW propagation are detected on the basis of ionospheric vertical sounding at the Průhonice observatory (central Europe). The observed wave-like structures have the propagation characteristics, which correspond to the theory of acoustic gravity waves that propagate into the ionosphere from below.

Tropospheric events and possible related gravity wave activity effects on the ionosphere

Short-term changes of electron concentration in the ionospheric F-region have been studied during a campaign of rapid sequence vertical ionospheric sounding. The wave-like structures occurred under low solar and geomagnetic activity. The most probable source of the observed waves was below the 175 km level and probably not in the auroral zone. The vertical components of propagation characteristics of the observed waves correspond to the theory of acoustic gravity wave propagation in the ionosphere and confirm the position of the source being below the studied heights. Another case studied showed the effects of passage of strong tropospheric cold front under high solar activity during February 1990.

Acoustic-gravity waves in the earth’s atmosphere (review)

We present the modern theory of small-amplitude acoustic-gravity waves (AGWs) in the Earth’s atmosphere. Main attention is paid to the propagation and radiation of AGWs by different sources. We also consider problems of their dissipation, stability, and interaction with the ionospheric plasma. Basic methods of detecting the wave processes in the upper atmosphere in the AGW frequency range are briefly discussed. Experimental data on atmospheric inhomogeneities are compared with theoretical findings.

Some results of measurement of atmospheric temperature and density using artificial periodic inhomogeneities of the ionospheric plasma

We present the preliminary results of measurement of atmospheric temperature and density at the E-region heights near Nizhny Novgorod in the 1990–1991 period (λ=56.15°N, ϕ=44.3°E). The monthly mean temperature and density are given in the height interval 100–110 km for September and October 1990. The temporal variations of temperature and density, associated with the propagation of acoustic-gravity and internal waves, are presented. The influence of natural turbulence on the measurement accuracy has been analyzed. The method is based on the generation of artificial periodic inhomogeneities (APIs) by a powerful radio wave and registration of the amplitudes of pulse probe radio waves backscattered by APIs.

Acoustic Resonance of the Atmospheric at 3.7 Hz

Vertical propagation of plane acoustic-gravity waves with horizontal wave fronts is discussed using a layer model with realistic temperature structure based on the Cospar International Reference Atmosphere, 1986. Acoustic resonance of a normal mode occurs between the ground and upper mesosphere, at a frequency of 3.64–3.69 mHz. Since acoustic waves with these frequencies are evanescent in the upper mesosphere where the acoustic cutoff is normally around 4.1 mHz, part of the wave energy propagated from below is reflected downward to interfere with the upward-propagating waves, thus causing model resonance. The computed resonant frequency coincides with the lower (3.7 mHz) of the two dominant frequencies found in the Rayleigh wave from the eruptions of El Chichon in 1982 and Mount Pinatubo in 1991. It also agrees with the lower spectral component of the ionospheric infrasonic waves observed by the high-frequency Doppler radar technique in association with severe convective storms below in the troposphere.

Acoustic gravity wave growth and damping in convecting plasma

Abstract. The propagation of acoustic gravity waves through steadily convecting plasma in the thermosphere has been analysed theoretically. The growth and damping rates of internal gravity waves due to the feedback effects of wave-modulated Joule heating and Laplace forcing have been calculated. It is found that large convection flow velocities lead to the growth of large-scale internal gravity waves, whilst small- and medium-scale waves are heavily damped, under similar conditions. It has also been shown that wave growth is favoured for waves travelling against the plasma flow direction. The effects of critical coupling when wave phase speeds match the plasma flow speed have also been investigated. The results of these calculations are discussed in the context of the atmospheric energy budget and thermosphere-ionosphere coupling.

Propagating ionospheric waves observed throughout east Asia during the WAGS October 1985 campaign

The propagation of acoustic gravity waves has been observed by an investigation of their effects upon the ionosphere over distances ranging up to 3400 km and extending from mid‐latitudes (45.4°N) to low latitudes (14.7°N) in east Asia. Recognizable wave structures were observed mainly on low sounding frequency, virtual height h'f and to a lesser extent f0F2 time variations, obtained from ionograms taken at 10 ionosonde stations, sounding at 5‐min intervals throughout the period October 15–19, 1985. Investigations were mainly confined to the nighttimes, since during the day large latitudinal gradients of ionization (associated mainly with the equatorial anomaly) together with movements of the equatorial anomaly crest obscured the observation of waves. In general, inferred propagation of the waves was southward, but three cases of northward propagation were observed, the former having a range of periods 40–210 min, while the latter were consistently about 70 min. The waves structures, mostly, differed depending upon whether they were located to the north or south of Yamagawa (31.2°N). There was some evidence of the predomination of longer‐period waves to the south, the shorter‐period waves observed to the north being apparently damped out in their propagation southward. The southward propagating waves exhibited upward energy propagation, while at Hong Kong (22.3°N) there was some evidence of downward phase propagation with a shift to lower periods at lower heights. It has not been possible to identify the origins of the detected waves, but it is clear that sources existed within and outside the latitude range covered by the ionosonde sounding stations (14.7°–45.4°N).

Generation of acoustic-gravity waves by atmospheric turbulence

Generation of acoustic-gravity waves by atmospheric turbulence

Propagation of Small-Scale Acoustic-Gravity Waves in the Venus Atmosphere

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...

On three-dimensional acoustic-gravity waves in model non-isothermal atmospheres

The propagation of acoustic-gravity waves is studied in a family of model non-isothermal atmospheres, including temperature profiles with any initial and asymptotic temperature and adjustable maximum temperature gradient. The equation for the vertical velocity of linear acoustic-gravity waves is solved exactly in terms of hypergeometric functions, the wave field being described to all orders in the scattering parameter kL, at all frequencies and distances, including wavelengths comparable to the scale of temperature change and atmospheric layers with a large temperature gradient. It is found that since the temperature is bounded, in the asymptotic regime waves grow in amplitude exponentially and phase increases linearly with altitude. The growth in amplitude is larger than exponential and the phase increases faster than linearly for atmospheres whose temperature increases with altitude, the effect being more marked for high frequency waves in regions of large temperature gradients. The accumulation of these effects leads to a wave field which is equivalent to the isothermal case at asymptotic temperature modified by a constant amplitude factor and phase shift which account for the history of propagation of the wave through the temperature gradients.

Generation and propagation of acoustic gravity waves

Generation and propagation of acoustic gravity waves

Harmonic generation of acoustic gravity waves

We have found that a wave at a particular frequency, which is approximately 0.8 times the Brunt‐Väisälä frequency, may play an outstanding role in second‐harmonic generation of acoustic gravity waves.

Theoretical properties of atmospheric acoustic-gravity waves

The theory of atmospheric acoustic-gravity wave propagation is investigated using techniques developed in ionospheric radio wave theory. It is shown that the WKB solutions for acousticgravity waves contain ‘additional memory’ as well as the familiar phase memory. The importance of the memory terms is assessed by comparison with a full wave numerical analysis. The reflection of acoustic-gravity waves and their behaviour near a resonance are also studied. A reasonable correspondence is found between the theoretical results and experimental observations on travelling ionospheric disturbances.

Atmospheric Solitary Waves

We show that the hydrodynamic equations which govern the propagation of acoustic gravity waves can have shock-like solutions.

The enigma of the continuous spectrum in acoustic gravity wave propagation in an isothermal atmosphere

Some remarks are made on the mathematical and the physical nature of the discrete and continuous spectra for propagation of acoustic gravity waves over a spherical earth with an isothermal atmosphere. It is pointed out that the continuous spectrum in flat earth models can actually be represented by discrete modes in a properly formulated spherical earth model. Also, it is of some interest to note that the Lamb-type wave always has some attenuation due to earth curvature.

Acoustic gravity wave propagation past the antipode

The previous theoretical formulations and numerical computations of pressure waveforms (such as described by Harkrider, Pierce, and Posey, and others) apply only to atmospheric traveling waves which have traveled less than 12 the distance around the earth. In the present paper, a technique resembling that previously introduced by Brune, Nafe, and Alsop [Bull. Seismol. Soc. Am. 51, 247–257 (1961)] for elastic surface waves on the earth is discussed and applied to the acoustic-gravity wave propagation past the antipode problem. The principal modification to the older theory is a shift in phase of π/2 to the Fourier transform of the wave after it has traveled over halfway round the globe from the source. The source of the wave is presumed to be a nuclear explosion of given energy E. Numerically synthesized waveforms of antipodal arrivals are exhibited and compared with those for direct arrivals. The necessary modifications to the Lamb-mode model theory of Pierce and Posey [Geophys. J. Roy. Astron. Soc. 26, 341–368 (1971)] are also described.