Journal of Geophysical Research
The first successful measurements of plasma lines in the auroral E layer were made in January 1976 using the Chatanika incoherent scatter radar. Although they are considerably weaker than the signal from the ion component, the plasma line signals are readily detectable. Typical signal-to-noise ratios were about 4%. In this series of experiments, plasma lines were observed in the interval between 3.8 and 6.0 MHz, which corresponds to phase energies between 0.55 and 1.4 eV. They were found between 98 and 134 km; the derived plasma wave intensities varied between 0.06 and 1.0 eV, and the enhancements between 4 and 30 times the thermal level. There was a marked altitude dependence: the weakest waves were at the lowest altitudes, and the strongest were just below the maximum altitudes. There was no discernible frequency dependence at the lowest altitudes, but at the highest altitudes the lower-frequency plasma waves were stronger. These variations are probably related to the altitude variations of the suprathermal electron spectrum and of the electron temperature.
Wickwar, V. B. (1978), Plasma Lines in the Auroral E Layer, J. Geophys. Res., 83(A11), 5186–5190, doi:10.1029/JA083iA11p05186.