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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1965

Magneto-gravity waves

Small amplitude low frequency waves in plasma of infinite conductivity under influence of constant external gravitational and magnetic fields

ATMOSPHERIC CONDUCTIVITY↗
NASA NTRS1974

Computer extension and analytic continuation of Stokes' expansion for gravity waves

Stokes' infinitesimal-wave expansion for steady progressive free-surface waves has been extended to high order using a computer to perform the coefficient arithmetic. Stokes' expansion has been found to be incapable of yielding the highest wave for any value of the water depth since convergence is limited by a square-root branch-point some distance short of the maximum. By reformulating the problem using a different independent parameter, the highest waves are obtained correctly. Series summation and analytic continuation are facilitated by the use of Pade approximants. The method is valid in principle for any finite value of the wavelength and solutions of high accuracy can be obtained for most values of the wave height and water depth.

Schwartz, L. W.↗
NASA NTRS1975

Neutral composition gravity waves in the thermosphere observed by ESRO 4

Neutral composition waves with a wave length of about 5000 km and a wave period of about 2.5 hours were observed by ESRO 4 in the altitude region of 250 km. The amplitudes are of the order of 25 percent for Ar, 15 percent for N2, and roughly 10 percent for He and O at 25 percent geographic latitude. The wave amplitudes are seen to decrease towards lower latitudes suggesting that the composition waves are launched by auroral sources. Simultaneous ground based ionosonde measurements of the F2 layer critical frequency at mid and low latitudes show a wave period consistent with the satellite observations. The theoretical investigation with a multi-component model shows that diffusion plays a major role in explaining these wave phenomena. The phase and amplitude relation between atmospheric constituents are sensitive to the altitude region in which energy is deposited thus suggesting that Joule heating or soft particle precipitation are the predominant energy sources.

Trinks, H.↗
NASA NTRS1976

The leaking mode problem in atmospheric acoustic-gravity wave propagation

The problem of predicting the transient acoustic pressure pulse at long horizontal distances from large explosions in the atmosphere is examined. Account is taken of poles off the real axis and of branch line integrals in the general integral governing the transient waveform. Perturbation techniques are described for the computation of the imaginary ordinate of the poles and numerical studies are described for a model atmosphere terminated by a halfspace with c = 478 m/sec above 125 km. For frequencies less than 0.0125 rad/sec, the GR sub 1 mode, for example, is found to have a frequency dependent amplitude decay of the order of 0.0001 nepers/km. Examples of numerically synthesized transient waveforms are exhibited with and without the inclusion of leaking modes. The inclusion of leaking modes results in waveforms with a more marked beginning rather than a low frequency oscillating precursor of gradually increasing amplitude. Also, the revised computations indicate that waveforms invariably begin with a pressure rise, a result supported by other theoretical considerations and by experimental data.

Kinney, W. A.↗
NASA NTRS1977

The influence of the directional energy distribution on the nonlinear dispersion relation in a random gravity wave field

The influence of the directional distribution of wave energy on the dispersion relation is calculated numerically using various directional wave spectrum models. The results indicate that the dispersion relation varies both as a function of the directional energy distribution and the direction of propagation of the wave component under consideration. Furthermore, both the mean deviation and the random scatter from the linear approximation increase as the energy spreading decreases. Limited observational data are compared with the theoretical results. The agreement is favorable.

Huang, N. E.↗
NASA NTRS1981

Correlative study of thermospheric gravity waves and tropospheric vorticity area index

Based on the occurrence frequency of wave-like structures in 23,691 individual measurements of thermospheric density, it is demonstrated that there is no significant hemispherical correlation between satellite-measured thermospheric wave-like structures and the tropospheric vorticity area index in the epoch 1974-1976. However, in the northern polar zone, (60-90 deg) N, wave occurrence frequency is greater for large values of the 500 mb vorticity area index.

Chiu, Y. T.↗
NASA NTRS1981

Spacecraft-Doppler gravity-wave detection. II - Results

A description is presented of the results of experiments conducted to detect very-low-frequency (VLF)-band gravitational radiation. The experiments are based on Doppler tracking of the Voyager I spacecraft. There were basically two kinds of experiments performed. The first was concerned with the detection of solitary bursts of gravitational radiation such as might emanate from a single violent astrophysical event. There were no positive results of the search for such burst events at a level of 3 x 10 to the -14th, nearly two orders of magnitude away from the required sensitivity. The second kind of experiment performed was related to an attempt to detect the isotropic background of cosmic gravitational radiation. The negative results fail by a little over an order of magnitude to limit radiation below the existing limits due to cosmic evolution. In summary, there was no detection of gravitational radiation at an amplitude of 3 x 10 to the -14th for VLF waves of frequency around 0.001 Hz.

Hellings, R. W.↗
NASA NTRS1983

Gravity waves in the thermosphere observed by the AE satellites

Atmospheric Explorer (AE) satellite data were used to investigate the spectra characteristics of wave-like structure observed in the neutral and ionized components of the thermosphere. Power spectral analysis derived by the maximum entropy method indicate the existence of a broad spectrum of scale sizes for the fluctuations ranging from tens to thousands of kilometers.

Gross, S. H.↗