Sporadic E Theory. I. Collision-Geomagnetic Equilibrium

A simple equilibrium theory of ionization transport in the ionosphere is described which predicts a tendency for thin layers of overdense ionization (sporadic E layers) to form in the E-region. Such layers can be produced by the dominance of any of five mechanisms of ionization convergence. Three of these mechanisms involve the neutral wind shear and two involve the neutral wind. The theory assumes that ambipolar diffusion of the electrons and heavy positive ions takes place under the influence of the forces due to neutral collisions and the geomagnetic field. The layer formation tendency is strongest for the principal part of the wind shear convergence mechanism in the lower E-region at those altitudes where the neutral vorticity is antiparallel to the geomagnetic field, land in the upper E-region where the neutral vorticity is perpendicular to the geomagnetic field in the westward (eastward) sense in the northern (southern) geomagnetic hemisphere. The layer formation tendency is strongest for the wind convergence mechanism in the middle E-region. The altitudes of these layers may be predicted by constructing the equilibrium ion drift velocity convergence profile from the observed neutral wind profile. This is done for four experiments carried out in December 1962 and close agreement is found between the predictions of the theory and the observed characteristics of four out of six sporadic E layers, providing convincing proof of the existence of a wind shear transport mechanism.