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  • 1
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    F region electron density irregularity spectra near auroral acceleration and shear regions (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two orbits of the Atmosphere Explorer D yielded data on F region electron irregularities in the high latitude ionosphere. Data were taken with a retarding potential analyzer, an ion drift meter, a low energy electron experiment and a photoelectron spectrometer. Auroral forms were simultaneously visually sighted by DMSP spacecraft. The irregularities were associated with auroral excitation and large structured flow regions. Steep spectra with one-dimensional spectral index values for wavelengths over 1 km were observed in the acceleration region. Large amplitude irregularities appeared in large structured flow regions and displayed shallow spectra, indicating the presence of large power spectral densities at scale lengths of about 100 m. It is suspected that large velocities or shears in the velocities in adjacent precipitation regions cause the F region density perturbations.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5554-556
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    NASA TECHNICAL REPORTS
  • 2
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    Plasma structuring by the gradient drift instability at high latitudes and comparison with velocity shear driven processes (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Using results of the in situ measurements made by the DE 2 satellite, the nature of plasma structuring at high latitudes, caused by the gradient drift instability process, is described. Using noon-midnight and dawn-dusk orbits of the DE 2 satellite, it was possible to examine the simultaneous density and electric field spectra of convecting large-scale plasma density enhancements in the polar cap known as 'patches', in directions parallel and perpendicular to their antisunward convection. The results provide evidence for the existence of at least two generic classes of instabilities operating in the high-latitude ionosphere: one driven by large-scale density gradients in a homogeneous convection field with respect to the neutrals, and the other driven by the structured convection field itself in an ambient ionosphere where density fluctuations are ubiquitous.
    Keywords: GEOPHYSICS
    Type: AD-A227847 , Journal of Geophysical Research (ISSN 0148-0227); 95; 7799-781
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    NASA TECHNICAL REPORTS
  • 3
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    Geoid height versus topography for oceanic plateaus and swells (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Gridded geoid height data (Marsh et al.l, 1986) and gridded bathymetry data (Van Wykhouse, 1973) are used to estimate the average compensation depths of 53 oceanic swells and plateaus. The relationship between geoid height and topography is examined using Airy and thermal compensation models. It is shown that geoid height is linearly related to topography between wavelengths of 400 and 4000 m as predicted by isostatic compensation models. The geoid/topography ratio is dependent on the average depth of compensation. The intermediate geoid/topography ratios of most thermal swells are interpreted as a linear combination of the decaying thermal swell signature and that of the persisting Airy-compensated volcanic edifice.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 7403-741
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  • 4
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    Simultaneous density and electric field fluctuation spectra associated with velocity shears in the auroral oval (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A detailed study is presented of simultaneous density and electric field fluctuation spectra over a large-scale length range seen in association with large structured convective plasma flows, field-aligned currents, and particle precipitation at high latitudes. The data were obtained for two Dynamics Explorer 2 orbits at two different altitudes within the F region and the topside ionosphere. The observations are compared with results of nonlinear simulations of shear flow-driven instabilities and predictions based on two-dimensional turbulence arguments, with particular reference to the Kelvin-Helmholtz process.
    Keywords: GEOPHYSICS
    Type: AD-A190920 , AFGL-TR-88-0024 , Journal of Geophysical Research (ISSN 0148-0227); 93; 115-136
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