Magnetic storm associated perturbations of the upper atmosphere

Abstract

This review attempts to summarize what is presently known about the large-scale morphology and the physics of magnetic storm associated perturbations of the upper atmosphere. First the dissipation of electrical energy and the resulting basic atmospheric disturbance effects at higher latitudes are described. These include large plasma and neutral wind velocities, high plasma and neutral gas temperatures, and changes in the neutral gas composition. Parts of these perturbations are transported toward lower latitudes by traveling atmospheric disturbances and by large-scale wind circulation. Traveling atmospheric disturbances, for example, are thought to be responsible for the transient density perturbations observed at equatorial latitudes; large-scale winds are made responsible for the transport of composition perturbations toward middle latitudes. Local time and seasonal variations are attributed to the interaction of magnetospheric storm and solar radiation driven winds. Since charged particles are firmly embedded in their neutral gas environment, any perturbation of the neutral atmosphere will cause ionospheric disturbance effects. These include short-duration positive storms due to traveling atmospheric disturbances, long-duration positive storms due to changes in the large-scale wind circulation, and negative storm effects due to neutral composition changes. Even though significant progress has been made in understanding upper atmospheric storms, many open questions remain, and some of these are summarized at the end of this review.