The formation of small-scale irregularities in the ionosphere

Abstract

This paper examines the relevance to the ionosphere of a certain plasma instability mechanism previously discussed by several authors. A linearized analysis of the mechanism is given that differs from earlier treatments in several respects and is more directly applicable to the ionosphere than to laboratory plasmas. It is found that the dynamo region of the ionosphere is likely to be unstable against the growth of irregularities in electron concentration with scale sizes in the range from a few tens of meters to a few kilometers, given the presence of steady electric fields comparable to those expected to be present from tidal dynamo action. It is further suggested that the space-charge potentials associated with the growth of the dynamo-region irregularities of larger scale size can be conducted up the magnetic field lines into the F region, generating irregularities there in the presence of a vertical gradient in ionization near the equator and in the presence of horizontal gradients at high magnetic latitudes. It is shown that this theory appears to be capable of explaining many of the observed features of F-region irregularities, including their diurnal variation and their correlation with magnetic disturbance, which is in a positive sense at high latitudes and in a negative sense in the vicinity of the dip equator. The relationship of the mechanism to earlier theories of the growth of small-scale F-region irregularities is discussed.