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  • 1
    Electronic Resource
    Electronic Resource
    Flow angle dependence for the asymmetry of broad 50-MHz coherent echoes at large magnetic aspect angles (1997)
    Springer
    Annales geophysicae 15 (1997), S. 671-684 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The skewness of broad Type 2-like spectra has been studied using data collected by two orthogonal CW 50-MHz radio links with co-located scattering volumes. Geometrical aspect angles of observations were about 10. One short event was considered. For this event, the electron flow direction was changing periodically (period about 9 minutes) presumably due to the passage of a magnetospheric MHD wave through the ionosphere. It was found that for the radar observations along the electrojet flow, the skewness had the same sign as the mean Doppler shift with average absolute values in between 0.5–1.0. For observations perpendicular to the electrojet flow, spectra were more symmetrical (average skewness was around 0) and the sign of the skewness was sometimes opposite to the sign of the mean Doppler shift. These observations are interpreted in terms of contribution from both the Farley-Buneman and gradient-drift instabilities to the resultant spectrum. Differences with radar observations at small aspect angles are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-997-0760-4
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Altitude integration effects in the skewness of type-2 coherent echoes (1995)
    Springer
    Annales geophysicae 13 (1995), S. 946-953 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Possible effects of signal reception from different electrojet heights in a skewness of auroral coherent spectra are studied assuming that the “inherent” spectral line due to plasma turbulence is of type-2 and symmetrical. For reasonable ionospheric parameters, the altitude integrated spectra are expected to be skewed negatively for positive mean Doppler shift, in agreement with radar observations at small aspect angles. However, the spectra could be skewed positively if the turbulent layer or the electron density profile is shifted to high altitudes of \sim120 km. This change of spectral shape will not be observed experimentally if, at the same time, either the electron collision frequency is enhanced or the “inherent” spectral width is increased. Observational results are discussed in view of the predictions given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-995-0946-6
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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