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  • 1
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    Global large scale structures in the F region (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Measurements of neutral densities, temperatures and ion density and temperature by the Atmosphere Explorer C and E satellites exhibit fluctuations made up of coherent waves of scale size from hundreds to thousands of kilometers. The fluctuations in the AE-C data are found at times of low magnetic activity to extend from the auroral region in one hemisphere across the equator to the corresponding region in the other hemisphere with little change in apparent wavelength. The fluctuations in the AE-E data similarly exhibit at times of low magnetic activity nearly uniform wave structure encircling the equatorial belt. Typical examples of waves of more than 1000 km apparent wavelength in both the AE-C and AE-E data are presented. These observations during quiet times may be explained by a system of quasi-stationary waves excited by the auroral belts that are distributed about the Earth possibly with tidal or sub-tidal periods and scale lengths determined by the structure of the belts. According to this interpretation, Traveling Ionospheric Disturbance (TID's) are manifestations of transient wave systems moving past a ground observatory that result from changes in magnetic activity with periods and scale sizes associated with the regions of enhanced auroral activity. Some evidence suggesting tidal-like stationary waves from the Millstone Hill incoherent scatter radar is presented.
    Keywords: GEOPHYSICS
    Type: NASA. Goddard Space Flight Center Thermosphere Dynamics Workshop, Volume 2; p 119-135
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  • 2
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    Large-scale waves in the ionosphere observed by the AE satellite (1981)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Atmospheric Explorer (AE) satellite data were used to establish whether coherent waves in the gravity wave range are present in both neutral and ionized media in the thermosphere. The AE-C data in particular are shown. Data consist of the in situ argon, helium, nitrogen, and oxygen densities, plasma density, and ion and electron temperatures. Filtering provides the fluctuation signals for each which are spectrum analyzed for power and cross spectra. The observed frequencies are essentially proportional to the spatial wavenumbers along the satellite track. Scale sizes range from thousands to tens of kilometers.
    Keywords: GEOPHYSICS
    Type: AGARD The Phys. Basis of the Ionosphere in the Solar-Terrest. System; 10 p
    Format: text
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  • 3
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    A morphological study of waves in the thermosphere using DE-2 observations (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Theoretical model and data analysis of DE-2 observations for determining the correlation between the neutral wave activity and plasma irregularities have been presented. The relationships between the observed structure of the sources, precipitation and joule heating, and the fluctuations in neutral and plasma parameters are obtained by analyzing two measurements of neutral atmospheric wave activity and plasma irregularities by DE-2 during perigee passes at an altitude on the order of 300 to 350 km over the polar cap. A theoretical model based on thermal nonlinearity (joule heating) to give mode-mode coupling is developed to explore the role of neutral disturbance (winds and gravity waves) on the generation of plasma irregularities.
    Keywords: GEOPHYSICS
    Type: NASA-CR-176775 , NAS 1.26:176775 , POLY-MRI-1451-86
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  • 4
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    Large-scale waves in the thermosphere observed by the AE-C satellite (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Wavelike perturbations in the ionosphere are known as traveling ionospheric disturbances (TID's). For the detection of wavelike perturbations in neutral density, velocity, and temperature, it is necessary to employ satellite-borne experiments. Experiments conducted with the aid of satellites so far provide little evidence that wavelike perturbations in the neutrals and the ions are correlated. The present investigation is concerned with a detailed examination of the wavelike perturbations observed during a representative Atmosphere Explorer C satellite orbit. Details regarding the analyzed data are discussed along with the employed data processing procedures. Attention is given to coherent relationships between the ion variations and the neutral variations over a wide range of scale sizes and over global distances.
    Keywords: GEOPHYSICS
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-22; 340-352
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  • 5
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    Medium scale gravity waves in the thermosphere observed by the AE-C satellite (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is pointed out that the measurements of the Atmosphere Explorer (AE) have made it possible to detect large- and medium-scale waves in neutrals and ions in the thermosphere. Gross et al. (1983, 1984) have reported on large-scale waves throughout a major portion of an orbit of AE-C with scale sizes from hundreds to thousands of kilometers. The present investigation is concerned with a more limited portion of the same orbit, taking into account a part in the Northern Hemisphere from about 10 deg to 54 deg latitude. The data consist of 1.0-s samples for ions and 1.5-s samples for neutrals. The data indicate fluctuations of oxygen, nitrogen, helium, and electron density, and temperature fluctuations. The structures formed by the fluctuations appear to be made up of waves having wavelengths in the range from 100 to over 400 km. The cross-correlation function demonstrates strong association between N2 and O with a peak value of 0.88 for waves of wavelengths on the order of 250-300 km.
    Keywords: GEOPHYSICS
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-23; 139-149
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  • 6
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    Uniformly spaced field-aligned ionization ducts (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A number of interesting cases of combination mode ducted echoes for mid- and low-latitude regions are presented that show nearly uniformly spaced multiple combination mode traces on the ionograms in the frequency range above 1 MHz. These traces suggest that a parallel system of field-aligned ducts is present. Ray tracing studies are made to determine the structure that would explain the observations using the electron density profile derivable from the vertical trace and assuming field-aligned ducts. Spacing perpendicular to the ducts is found to be as much as 70 km. Some of these parallel duct structures are found to extend to the conjugate hemisphere, possibly to the F peak.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 8986-899
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  • 7
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    Errors incurred in profile reconstruction and methods for increasing inversion accuracies for occultation type measurements (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method for augmenting the occultation experiment is described for slightly refractive media. This method which permits separation of the components of the gradient of refractivity, appears applicable to most of the planets for a major portion of their atmospheres and ionospheres. The analytic theory is given, and the results of numerical tests with a radially and angularly varying model of an ionosphere are discussed.
    Keywords: GEOPHYSICS
    Type: NASA. Ames Res. Center Math. of Profile Inversion; 15 p
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  • 8
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    Ionospheric disturbances and gravity waves (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The response of ionization to a gravity wave moving through the ionosphere is studied. Hydrodynamic equations are used, and local thermodynamic equilibrium is imposed for simplicity. The treatment involves a perturbation analysis, and the background medium is assumed to be time stationary, horizontally stratified, and known. It is shown that ionization may be locally resonant at each level for certain frequencies and directions, for which condition neutral and ionized particles are considered closely or critically coupled. The phase direction for this critical coupling is always downward in the absence of a magnetic field. A magnetic field results in two resonant directions for the same frequency, and these directions are mostly downward. Observed TID's associated with gravity waves may be indicative of such resonances. It is also noted that strong coupling may occur to neutral acoustic waves at high altitudes. Previous investigations restrict their use of momentum equations to the diffusion equation. The analysis also shows that such restrictions result in the neglect of terms arising from momentum transport due to any background ambipolar diffusion velocity and wave motion. These terms are mostly relevant at higher altitudes.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; July 1
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  • 9
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    Investigation of planetary ionospheres (1967)
    In:  CASI
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    Publication Date: 2019-06-27
    Description: Feasibility of using radio sounding techniques to investigate ionospheric properties of planets
    Keywords: GEOPHYSICS
    Type: NASA-CR-689
    Format: application/pdf
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  • 10
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    Large scale waves in the thermosphere observed by the AE-C satellite (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Atmospheric Explorer C (AE-C) data are analyzed to study wavelike perturbations in the thermosphere at an altitude of about 260 km. Four geophysical parameters are analyzed. These are nitrogen and oxygen densities, electron density and ion temperature as measured by three different instruments on board AE-C. The data are processed by normalizing them to their average values and their fluctuations are obtained by passing the normalized data through a high pass filter. These fluctuations exhibit strong periodicities that persist throughout the records, regardless of the filter cutoff frequency. The fluctuations are cross correlated by direct comparison, by comparison of their spectral content as obtained by the MEM and FFT, and by computing cross correlation functions.
    Keywords: GEOPHYSICS
    Type: A Morphological Study of Waves in the Thermosphere; 82 p
    Format: text
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