Showing papers on "Atmospheric wave published in 1969"

Atmospheric Tides: Thermal and Gravitational

Abstract: 1. Introductory and Historical.- 1.1. Introduction: Pytheas, Bacon, Newton and Laplace.- 1.2. The Barometric and Other Daily Variations.- 1.2A. True or Apparent Time, and Mean Time.- 1.2B. The Harmonic Dial.- 1.3. Thermal Tides and Kelvin's Resonance Theory.- 1.4. More Realistic Atmospheric Models.- 1.5. The Phase of S2 (p).- 1.6. Doubts as to the Resonance Theory.- 1.7. Renewed Hope in the Resonance Theory.- 1.8. Atmospheric Oscillations as Studied by Weekes and Wilkes.- 1.9. Rockets Exclude Resonance.- 1.10. Ozone Absorption of Radiation the Main Cause of S2(p).- 1.11. Upper Air Data.- 1.12. Theoretical Calculations of the Diurnal Thermal Tide.- 1.13. Other Features of Atmospheric Oscillations.- 2S. The Solar Daily Atmospheric Oscillations As Revealed By Meteorological Data.- 2S.1. The Material Studied Ground Level Data.- 2S.2. Harmonic Analysis of S The Non-Cyclic Variation.- 2S.3. The Seasonal Variation of S.- 2S.3A. Daily Seasonal Integers ? (Sigma) or SN (Bartels, 1954).- 2S.4. The World-Wide Distribution of S, Particularly of S(p).- 2S.4A. S2(p).- 2S.4A.1. Types of Associated Legendre Functions.- 2S.4A.2. The Spherical Harmonic Expression of S2(p).- 2S.4B. S1(p).- 2S.4C. S3(p).- 2S.4D. S4(p).- 2S.5. The Daily Variation of Air Temperature T.- 2S.6. The Daily Wind Variation S(V).- 2S.7. Atmospheric Daily Changes above Ground Level.- 2S.7A. Daily Variations between the Ground and 30 km.- 2S.7B. Daily Variations from 30 km-60 km.- 2S.7C. Daily Variations from 80-120 km.- 2S.7D. Daily Variations in the Thermosphere.- 2S.7E. Analysis of Data Covering Only a Fraction of a Day.- 2L. The Lunar Atmospheric Tide As Revealed By Meteorological Data.- 2L.1. Introduction.- 2L.2. The Tropical Lunar Air Tide.- 2L.3. The Lunar Air Tide Outside the Tropics.- 2L.4. The Month and the Lunar Day.- 2L.4A. The Main Harmonic Components of the Lunar Tidal Potential.- 2L.5. Methods of Computation of L from Observed Data Early Methods Based on Apparent Lunar Time.- 2L.6. The Chapman-Miller (or C-M) Method for Meteorological Variables.- 2L.6A. Use of the Integers Mu (or ?) instead of the Integers Nu or Nu? (or v?).- 2L.6B. The Components Sp.- 2L.7. Vector Probable Errors.- 2L.8. The Determination of L2 from Only a Few Meteorological Readings per Day.- 2L.9. The Lunar Semidiurnal Barometric Tide L2 (p).- 2L.10. The Expression of L2 (p) in Spherical Harmonic Functions.- 2L. 11. The Asymmetry of L2 (p) Relative to the Equator, and its Seasonal Variation.- 2L.12. Comparison of L2(p) and S2(p).- 2L.13. The Lunar Tidal Wind Variation.- 2L.14. The Lunar Tidal Variation of Air Temperature.- 2L.15. The Lunar Tidal Changes of Height of Various Pressure Levels.- 2L.16. Brief Mention of the Lunar Geomagnetic Tide.- 3. Quantitative Theory Of Atmospheric Tides And Thermal Tides.- 3.1. Introduction.- 3.2. Equations.- 3.3. Methods of Solution.- 3.3A. Laplace's Tidal Equation.- 3.3B. Vertical Structure Equation.- 3.3C. Outline of Overall Procedure.- 3.4. Sources of Excitation.- 3.4A. Gravitational Excitation.- 3.4B. Thermal Excitation Due to Exchange of Heat with the Ground.- 3.4C. Thermal Excitation Due to Direct Atmospheric Absorption of Insolation.- 3.4D. Summary.- 3.5. Explicit Solutions.- 3.5A. The Migrating Solar Semidiurnal Thermal Tide.- 3.5B. The Solar Diurnal Thermal Tide.- 3.5C. The Lunar Semidiurnal Tide.- 3.5D. Other Components.- 3.6. Shortcomings of Present Calculations.- 3.6A. Surface Topography.- 3.6B. Dissipation.- 3.6B.1. Infrared Cooling.- 3.6B.2. Molecular Viscosity and Conductivity.- 3.6B.3. Ion Drag and Thermal Tides in the Ionosphere.- 3.6C. Non-Linear Effects.- 3.6D. Neglect of Mean Winds and Horizontal Temperature Gradients.- 3.6E. Additional Remarks.- 3.7. Comparison of Theory with Data.- List of Symbols for Chapter 3.- Guide To The Figures And Tables.- References.- Index Of Names.- Index Of Subjects.- Index Of Places.

Acoustic methods for the remote probing of the lower atmosphere

Abstract: The potential usefulness of acoustic methods for the remote probing of the lower atmosphere is reviewed. Starting with a comparison of the effects of temperature, wind, and humidity fluctuations upon the refractive index of air to electromagnetic and acoustic waves, it is shown that the fluctuations in acoustic refractive index may be expected to be about 1000 times stronger than in the radio case. The opportunities for passive and for line-of-sight remote acoustical sensing of the troposphere offered by this relatively strong interaction are briefly identified. Since the scattered power is proportional to the square of the refractive index fluctuations, the scatter of acoustic waves may be expected to be roughly one million times stronger than for radio waves. Based on the theoretical work of Kallistratova (but including the effects of atmospheric absorption), the system parameters required for effective acoustic echo-sounding of the lower atmosphere are deduced. It is concluded that the acoustic sounding technique could be developed to monitor, to heights of at least 1500 meters, 1) the vertical profile of wind speed and direction, 2) the vertical profile of humidity, 3) the location and intensity of temperature inversions, 4) the three-dimensional spectrum of mechanical turbulence, and 5) the three-dimensional spectrum of temperature inhomogeneity (i.e., of optical refractive index fluctuation). Typical time and height resolutions for the proposed acoustic echo-sounders could be of the order 10 seconds and 10 meters; the spatial wave number explored could range from about 10-2m-1to about 400 m-1.

Probing the clear atmosphere with high power, high resolution radars

Abstract: Observations of radar echoes from the clear atmosphere are presented and the scattering mechanisms responsible for the two basic types of clear-air echoes are discussed. The commonly observed dot echo originates from a point in space and usually shows little variation in echo intensity over periods of about 0.1 second. The results of the most recent investigations of these clear-air dot targets are consistent with the conclusion that most, if not all, of the dot echoes are caused by insects or birds. The second type of clear-air radar echo appears diffuse in space, and signal intensities vary considerably over periods of less than 0.1 second. The echoes often occur in thin horizontal layers or as boundaries of convective activity; these are characterized by sharp gradients of refractive index. The reflectivity-wavelength dependence of these echoes is consistent with the theory of scattering by fluctuations in refractive index, and the signal intensities can be accounted for by the spectral characteristics of refractive-index variations observed directly. Some features of clear-air atmospheric structures as observed with radar are presented. These structures include thin stable inversions, convective thermals, Benard convection cells, breaking gravity waves, and high tropospheric layers which are sufficiently turbulent to affect aircraft.

Fluctuations of a focused beam wave for atmospheric turbulence probing

Abstract: This paper demonstrates that a focused beam wave may be effectively used to probe the atmospheric turbulence. Unlike plane and spherical waves, the focused beam has two parameters, i.e., the beam size and the radius of curvature of phase front at the aperture which may be easily varied experimentally. General formulations for the amplitude and phase correlation functions and structure functions of a focused beam wave are given including the effects of wind velocity and time delay. The effects of the beam size and the focal length on the spectral and spatial filter functions and temporal frequency spectrum are examined in detail including the effects of separation, wind velocity, and time delay. Using these functions, procedures are shown to probe the form of the spectral density of the index of refraction, the structure constant, and the wind velocity along the path.

On the observed large-scale atmospheric wave motions

Abstract: On the basis of data from the whole Earth during different periods of the International Geophysical Year the large-scale wave motions at the 500 mb level, and to some extent the 1000 mb level, are studied. The waves are represented by spherical harmonic components of the height field for the whole Earth as well as for each of the two hemispheres. The relative importance of the different components in the expansion of the height field for the whole Earth is illustrared, and the seasonal variations at the two hemispheres are considered. The motion of the different wave components is investigated by computing mean values of the 24-hours phase angle changes. Except for the most large-scale, quasi-stationary components the mean velocities are found to be quite well in agreement with the Rossby-Haurwitz formula for the wave motions in a barotropic, non-divergent model with a solid rotating basic flow. The fluctuations of the quasi-stationary waves are studied by means of quadrature spectrum analysis and by application of different time filters. A certain part of the regular fluctuations seems to be attributed to various westward wave motions with different velocities of propagation. Each of these westward wave motions seems to be composed of more spherical harmonic components with different amplitudes. The quantitative results concerning the velocities of propagation and the amplitudes are generally supporting the idea that these wave motions may be explained essentially by the Rossby effect, for the most large-scale components combined with a divergence effect. DOI: 10.1111/j.2153-3490.1969.tb00427.x

Experiments on the generation of small water waves by wind

Abstract: The generation and growth of small water waves by a turbulent wind has been investigated in a laboratory channel. The evolution of these oscillations with fetch was traced from their inception with amplitudes in the micron range under conditions of steady air flow. The experiments revealed that the waves are generated at all air velocities in small bursts consisting of groups of waves of nearly constant frequency. After travelling for some distance downstream, these wavelets attain sufficient amplitude to become visible. For this condition, a wind speed critical to raise waves is well defined. After the first wavelets appear, two new stages of growth are identified at longer fetches if the air speed remains unchanged. In the first of these, the wave component associated with the spectral peak grows faster with fetch than any other part of the wave spectrum of the initial waves until its amplitude attains an upper limit consistent with Phillips's equilibrium range, which appears to be universal for wind waves on any body of water. If the air flow is not changed, then the frequency of this dominant wave remains constant with fetch up to equilibrium. This frequency tends to decrease, however, with increasing wind shear on the water. In the second stage of growth, only the energy of wave components with spectral densities lower than the equilibrium limit tend to increase with fetch so that the wave spectrum is maintained near equilibrium in the high-frequency range of the spectrum.The origin of the first waves and the rate of their subsequent growth was examined in the light of possible generating mechanisms. There was no indication that they were produced by direct interaction of the water surface with the air turbulence. Neither could any significant feedback of the waves into the turbulence structure be detected. The growth of the waves was found to be in better agreement with theoretical predictions. Under the shearing action of the wind, the first waves were found to grow exponentially. The growth rates agreed with the estimates from the viscous shearing mechanism of Miles (1962a) to a fractional error of 61% or less. A slight improvement was obtained with the viscous theory of Drake (1967) in which Miles’ model is extended to include the effect of the drift current induced by the wind in the water. Since the magnitude of the water currents observed in the tunnel is very small, this improvement is not significant.

On the Role of Joule Heating as a Source of Gravity-Wave Energy above 100 km

Abstract: Observations of ionospheric disturbances by various investigators have led to the suggestion that auroral energy may be coupled to atmospheric wave motions through joule heating. A linear model of internal gravity-wave generation by joule heating in the region of the auroral electrojet (100–150 km above the earth's surface) is investigated. Heat conduction, viscosity and reflection of wave energy by atmospheric inhomogeneities are not considered. The computed value of the upward wave-energy flux from the source region is of order 0.1–1 erg cm−2 sec−1 and is of sufficient magnitude to be of importance in the energetics of the F region. Shortcomings of the present model are discussed, with emphasis on how the physical features which have been neglected might affect the present results.

Propagators of atmospheric motions 2. Excitation by switch‐on sources

Abstract: The excitation of various atmospheric wave motions by switch-on sources is investigated. An asymptotic description of the propagation of the transient forerunners and the stationary forced motion contained within a Brillouin front is given. Three-dimensional Rossby waves generated in an unbounded atmosphere by a traveling point source and several kinds of oscillating point sources are discussed. Also given is the solution for the switch-on of a horizontally traveling gravity wave or vertically traveling atmospheric acoustic wave. Various one-dimensional switch-on Rossby wave problems in a periodic domain are solved in terms of image sources.

A multiwavelength line-of-sight experiment for remote atmospheric sensing

Abstract: Simultaneous measurements have been made on a 3.57- km line-of-sight atmospheric path using a phase quadrature technique at 10.4 GHz, plus a combination of near-infrared and 23.8-GHz transmissometers operating in oxygen and water vapor absorption bands, respectively. The latter two systems provide the separate dry and wet terms of integrated radio refractivity for use in interpretation of the 10.4-GHz phase data. Direct measurement of the statistics of the phase quadrature components of the incoherent scattered field yields several incoherent field parameters not obtained before in line-of-sight experiments. The usefulness of these parameters for atmospheric characterization is being investigated. On this short path the incoherent field is primarily at phase quadrature to the coherent field, and this component is normally distributed, implying a predominantly near-field situation. The postulated decrease of the ratio of quadrature component variances, and of their cross correlation, with spectral frequency has been verified. The agreement noted between transmissometer data and 10.4-GHz phase data in the near field transfers to agreement with 10.4-GHz amplitude data in the far field. This difference, noted in a comparison of measurement spectra, is a helpful analytical tool in the characterization of the atmospheric turbulence wave number spectrum.

Comparison Between Formulas for Ionospheric Radio Propagation and Atmospheric Wave Propagation

Abstract: Attention is drawn to similarities between certain magnetoionic formulas in ionospheric radio propagation and corresponding formulas for acoustic-gravity waves. Acoustic waves are similar to radio waves with frequencies above the electron gyrofrequency, whereas gravity waves are similar to whistlers.

Atmospheric sound propagation

Abstract: The propagation of sound waves at infrasonic frequencies (oscillation periods 1.0 - 1000 seconds) in the atmosphere is being studied by a network of seven stations separated geographically by distances of the order of thousands of kilometers. The stations measure the following characteristics of infrasonic waves: (1) the amplitude and waveform of the incident sound pressure, (2) the direction of propagation of the wave, (3) the horizontal phase velocity, and (4) the distribution of sound wave energy at various frequencies of oscillation. Some infrasonic sources which were identified and studied include the aurora borealis, tornadoes, volcanos, gravity waves on the oceans, earthquakes, and atmospheric instability waves caused by winds at the tropopause. Waves of unknown origin seem to radiate from several geographical locations, including one in the Argentine.

Laser-induced sonic waves in air

Abstract: Sonic waves induced by the shock of the laser-produced vapor from brass and graphite are observed in air at atmospheric pressure, using high-speed shadowgraphs. The energy transferred from the laser-produced vapor to the sonic wave is estimated to be about 10-1of the laser energy.

Evidence for strongly damped gravity waves in the earth's atmosphere

Abstract: Data from a series of pitot tube rocket soundings of the atmosphere are examined. The experiments consist of four soundings carried out over a twoday period at Fort Churchill, Canada in January and February 1967 by Smith, Theon and Horvath. Temperature data from the four soundings were averaged, and a smooth curve was drr-.wn through the points. A hydrostatically determined atmosphere based on the above lapse rate was calculated. Deviations from the above mean atmosphere were calculated, and a wavelike structure was observed. The waves grow very slowly below approximately 80 km, and acquire a more rapid growth rate at higher altitudes. The density and temperature variations have a wavelength of 10-20 km and appear to consistently be about 180 degrees out of phase. The pressure variation is somewhat irregular. However, in regions '%,here pressure variation is well behaved it is out of phase with temperature and density by about 90 degrees. Volland's theory of thermally damped gravity waves was used to compute wave patterns like those observed experimentally. A highly damped., upward propagating wave gives good results. Damping by conduction, turbulence and radiative transfer is examined, and turbulence is found to be the most important. *NRC-NASA Research Associate I

Acoustic Waves in the Ionosphere

Abstract: : Acoustic wave characteristics in the upper atmosphere are deduced from temporal and spatial electron density variations obtained with the Arecibo back-scatter sounder. A theory is developed which relates the observed wave characteristics to the power spectrum of the wave sources. (Author)