Electrostatic noise generated by the auroral electron beam

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Abstract
Refraction of electrostatic noise in the whistler and upper hybrid modes out of the spatially limited amplification region of the auroral electron beam limits the amplitude of the noise produced. Power flux spectra are calculated by using the linear electrostatic growth rate and allowing for ray refraction in the direction perpendicular to the auroral arc. A graphical algorithm is developed for predicting the power flux spectra of whistler and upper hybrid noise for a wide range of ionospheric and beam parameters. Predicted power flux spectral shapes and intensities for the whistler mode are in good agreement with observations of VLF hiss. The power flux in the upper hybrid mode can exceed the whistler mode power flux in the region of the ionosphere where the electron plasma frequency is larger than the electron cyclotron frequency. A distinction based on the beam intensity is made between quiet and intense arcs. Quasi‐linear and nonlinear processes are not important in quiet arcs but may produce observable effects in intense arcs. In particular, intense electrostatic noise near the plasma frequency may produce deep density cavities that radiate electromagnetic kilometric radiation.