PROJECT AURECHOES - AURORAL ECHOES AND THE TWO-STREAM INSTABILITY.
CORNELL AERONAUTICAL LAB INC BUFFALO N Y
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The literature indicates that the two-stream instability is an important causal mechanism in the production of electron-density irregularities which contribute to aspect-sensitive VHF echoes from the equatorial and auroral E regions. The two-stream-theory relationship between Doppler shift and radar frequency computed by D. T. Farley for the equatorial E region is scaled so as to represent an auroral environment at any temperature. Salient characteristics of 158 Doppler spectra, obtained during 143.5-MHz auroral backscatter experiments at Buffalo, are listed and discussed. Approximately 54 of these spectra have a single peak the appearance of two peaks in 40 of the spectra probably resulted mainly from nonuniformities in the auroral current systems. The characteristics observed by us of spectral peaks centered on Doppler velocities from 325 to 800 ms are consistent with predictions from the two-stream theory the range in values of these Doppler velocities is probably substantially due to large variations in electron temperature in the auroral E region. The available information on ion drifts is not adequate to determine whether the observed spectral peaks with Doppler velocities as great as 1800 ms could have resulted from scattering from plasma waves in regions of large ion drift and enhanced plasma temperature. It is possible that spectral content with very large Doppler velocities resulted from some other mechanism such as plasma turbulence. Author
- Atmospheric Physics