Theory of the geomagnetic daily disturbance variations

Abstract

The worldwide ionospheric current system predicted by a previously described theory of the auroral electrojets is computed. Tidal air motions are neglected at first, and the high-latitude current system is assumed to be due entirely to the interaction of magnetospheric rotation with the belt of energetic protons trapped in the distorted geomagnetic field. For a given geomagnetic distortion and trapped proton distribution, the computed current system strongly resembles Chapman's idealized Ds, current system, if sufficiently high E-region electron concentrations independent of geographical position are assumed. As the assumed electron concentrations are decreased, however, the intensity of the computed current system is reduced, first in the auroral zone and then at all latitudes; at the same time the phase of the current system is advanced in the polar cap and is retarded at low latitudes. In view of this limitation of the current system by the available electron concentrations, the large disturbance variations observed during an intense geomagnetic storm can be explained by the present theory only if, in addition to an enhancement in the trapped proton density, greatly enhanced E-region electron concentrations are assumed, particularly in the auroral zone. Such enhanced electron concentrations are known to occur when blanketing sporadic E is observed. The observed correlation between blanketing sporadic E and the strength of the electrojet current is thus predicted by the present theory. The interaction of the tidal wind system with the belt of trapped protons is also considered. The resulting auroral electrojet currents oppose the Ds a current system if the usually accepted pattern of upper atmospheric tidal winds is assumed; the existence of a different wind pattern at high latitudes, at least during geomagnetic storms, is a possibility that cannot altogether be excluded, although it appears unlikely. If the majority of energetic particles in the radiation belt were electrons, their interaction with the usually accepted tidal wind pattern would result in the correct phase for the Ds current system; satellite observations indicate, however, that the majority of the energetic particles are protons. The present theory can also account for the generation of meridional static electric fields of the type that, according to a theory of Megill and Carleton, cause midlatitude red arcs.