A Digest of Electrodynamic Coupling and Layer Instabilities in the Nighttime Midlatitude Ionosphere

Abstract

The basic elements of electrodynamic coupling and positive feedback between a sporadic E (E s ) layer and the F layer of the nighttime midlatitude ionosphere are briefly described. This coupled system is interesting because each layer, in isolation, can be unstable to perturbations in vertical displacement (i.e., the so-called E s layer and Perkins instabilities). The two processes are similar generically and can be referred to as layer instabilities. Moreover, both have maximum growth rates when frontal perturbations are aligned northwest to southeast in azimuth (northern hemisphere), which leads to interactive behavior with positive feedback because the polarization electric fields that arise from both processes are in phase and additive. Consequently, the growth rates of both instabilities are enhanced by their mutual presence; the largest enhancement, however, occurs in the structuring of the F layer. Some of the interesting aspects of coupled-system behavior are described and discussed.