Implications of flow angle stabilization on coherent E region spectra

Abstract

Recent perpendicular particle simulations of the Farley‐Buneman instability show good agreement with the linear dispersion relation: the phase velocity is proportional to the electric field. This is in contrast with the usually quoted nonlinear theory, which states that the phase velocity at any direction does not rise much above the ion acoustic velocity Cs. However, the simulations also produce a flow angle shift in the spatial power spectrum such that the most intense modes have phase velocities close to Cs. Using simple analytical formulae based on these simulations, we synthesize coherent spectra assuming a turbulent microstructure of the scattering volume. In this way, the observed type 1 characteristics can be reproduced, and also spectra similar to type 4 can be generated. A new interpretation of the Cs saturation observed in the equatorial electrojet is thus presented, and the difference between equatorial and auroral coherent spectra becomes understandable.