Three-wave coupling in the auroral E-region : Progress in understanding ionospheric irregularities

Abstract

Analysis of a simple model for two-stream weak fluid turbulence suggests a straightforward mechanism for the excitation of plasma wave modes whose phase velocities are roughly half the ion-acoustic speed. This slow wave is linearly stable but is excited through three-wave interaction with two other waves, at least one of which is an unstable two-stream wave. All three waves satisfy the linear dispersion relation. Careful consideration of the coupling coefficients and resonance conditions shows that the driven (linearly stable) modes have k-vectors that are perpendicular to the local magnetic field and are perpendicular to the local magnetic field and are at some large angle to the Hall drift direction . These waves have phase velocicities in the neighborhood of half the ion-acoustic speed and they could be responsible for type-3 radar echoes observed at 50 MHz. This mechanism cannot, however, generate fast waves moving at type-4 velocities