Auroral E-region diagnosis by means of nonlinearly stabilized plasma waves.

Results from a rocket experiment (Bahnsen et al., 1978) where simultaneous and accurate data are obtained on the electric field, as well as on extremely low-frequency electrostatic plasma-density waves in the dayside auoral ionospheric E-region are reexamined. The observations in the auroral ionosphere of plasma-wave phase velocities which are equal to the ion acoustic speed rather than to the differential electron-ion drift velocity as predicted by linear theories, are explained by the slight modification of the linear theory suggested by Sudan (1983). The modification depends on the average wave-fluctuation level, and continues until the growth rate is zero and the wave amplitude is stable. The observed wave-potential amplitudes and the relative density fluctuations are found to be in agreement with the modified linear equations.