Measurements of HF-enhanced plasma and ion lines at EISCAT with high-altitude resolution

Details Measurements of HF-enhanced plasma and ion lines at EISCAT with high-altitude resolution Measurements of HF-enhanced plasma and ion lines at EISCAT with high-altitude resolution

Apr 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000jgr...105.7429r&link_type=abstract

Journal of Geophysical Research, Volume 105, Issue A4, p. 7429-7440

Physics

Plasma Physics

26

Ionosphere: Active Experiments, Space Plasma Physics: Active Perturbation Experiments, Space Plasma Physics: Nonlinear Phenomena, Space Plasma Physics: Turbulence

Scientific paper

Measurements of plasma and ion lines induced during HF ionospheric interaction experiments have been made with the European Incoherent Scatter (EISCAT) facility at Troms[do] with sufficiently high-altitude resolution to compare with theories of Langmuir turbulence. Recent Langmuir turbulence models predict a change from broad structureless spectra to line or cascade spectra within a few hundred meters for VHF (224 MHz) observations assuming typical ionospheric density gradients. In a campaign in May 1994 we found VHF spectra that were grouped into two regions separated in altitude by ~2 km, with broad, unstructured plasma line spectra in the upper region and cascade type spectra in the lower region. The ion line channels showed detectable spectra mainly in the upper altitude region, which corresponds to that which had the broad plasma lines. The background ionospheric density profile showed an unusually low plasma density gradient near the HF reflection heights, thus allowing the two regions, which are normally so close together that one only sees a transition from one type of spectra to the other, to be clearly separated in height. Thus, in the high-latitude ionosphere there can, at times, be a simultaneous existence in spatially separate regions of cavitation (often referred to as strong turbulence) and cascading (normally associated with saturated parametric decay) as predicted by some simulations. Another new feature is a height variation in the plasma line cascades with the highest-order cascades strongest at the lowest heights, in accordance with expectations based on the parametric decay instability.

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