Excitation of short-scale field-aligned electron density irregularities by ionospheric topside sounders

S. P. Kuo

Research output: Contribution to journalArticle

Abstract

Generation of short-scale field-aligned electron density irregularities on a short timescale (≪ 1 s) by ionospheric topside sounder pulses is studied. It is a four-wave parametric coupling process, in which a sounder-launched Z mode pump wave decays into two electron Bernstein sidebands and a geomagnetic field-aligned density irregularity. The dispersion relation of the parametric coupling process has been derived and analyzed. The results show that meter-scale field-aligned electron density irregularities (FAI) can be excited with growth rates of the order of 105 s-1 under the resonance conditions that fo≅fp≅ nfc, where fo, fp, and fc are the pump wave frequency, electron plasma frequency, and electron cyclotron frequency, respectively, and n is an integer. The excited FAI extend along the magnetic field toward the satellite path, causing the incoherent scattering of the subsequently transmitted sounding pulses. This is suggested to be a possible cause of long-duration Z mode echoes appearing on the Alouette 2 ionograms when fo ≅ fp≅ nfc, as reported by Benson [1997]. It is found that the threshold field of the instability decreases with increased n. It may explain why long-duration Z mode echoes were only observed when n ≥ 4.

Original languageEnglish (US)
Article number1999JA900232
Pages (from-to)19889-19894
Number of pages6
JournalJournal of Geophysical Research: Space Physics
Volume104
Issue numberA9
StatePublished - 1999

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