Electric Fields in the Middle Atmosphere

Abstract

All of the solar electromagnetic energy impinging on the earth must pass through the middle atmosphere in some form. This weakly conducting region between the cloud tops and the ionosphere has often been considered to be electrically passive. This paper will review what is known about the large scale electrodynamics of the middle atmosphere and present the results of some recent research which contradicts the historical view of the region. One key to understanding middle atmospheric electrodynamics is a good understanding of the temporally and spatially varying electrical conductivity. With the knowledge of the conductivity, the middle atmospheric effects of external electric generators can often be determined by solving a time dependent boundary value problem often referred to as "mapping" the electric field. This has been a useful technique for study of current generators both below and above the middle atmosphere. Furthermore, contrary to the classical picture, there may be sources of electric fields within the middle atmosphere. Certainly there are sources of variability in the conductivity which actively modify the expected signal from external generators. The many-fold increase in available electric parameter data from within the middle atmosphere has been a great stimulus to recent research. However, this review will conclude that these measurements have tended to raise more questions than answers. That is a clear indication that the field of middle atmospheric electrodynamics is ripe for breakthrough research which will only come as a result of a new and vigorous measurement program.