Naturally enhanced ion-acoustic spectra and their interpretation

K.J.F. Sedgemore-Schulthess, J.P. St. Maurice

    Research output: Contribution to journalReviewpeer-review


    Incoherent scatter radars are designed to detect scatter from thermal fluctuations in the ionosphere. These fluctuations contain, among other things, features associated with ion-acoustic waves driven by random motions within the plasma. The resulting spectra are generally broad and noisy, but nevertheless the technique can, through a detailed analysis of spectra, be used to measure a range of physical parameters in the Earth's upper atmosphere, and provides a powerful diagnostic in studies of magnetosphere-ionosphere coupling, thermosphere dynamics and the geospace environment in general. In recent years there has been much interest in naturally occurring (as opposed to artificially stimulated) enhanced ion-acoustic spectra seen in the auroral zone and cusp/cleft region. A study of the plasma instability processes that lead to such spectra will help us to better understand auroral particle acceleration, wave-particle and wave-wave interactions in the ionosphere, and their association with magnetospheric processes. There is now a substantial body of literature documenting observations of enhanced ion-acoustic spectra, but there remains controversy over generation mechanisms. We present a review of literature documenting observations of naturally enhanced ion-acoustic spectra, observed mainly along the geomagnetic field direction, along with a discussion of the theories put forward to explain such phenomena.
    Original languageEnglish
    JournalSurveys in Geophysics
    Issue number1
    Pages (from-to)55-92
    Publication statusPublished - 2001


    • Ionosphere
    • Aurora
    • Incoherent scatter
    • Magnetosphere
    • Plasma instabilities


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