Physics of Electric Discharges in Atmospheric Gases: An Informal Introduction

A short account of the physics of electrical discharges in gases is given from the viewpoint of its historical evolution and application to planetary atmospheres. As such it serves as an introduction to the papers on particular aspects of electric discharges contained in this issue, in particular in the chapters on lightning and the discharges which in the last two decades have been observed to take place in Earth’s upper atmosphere. In addition to briefly reviewing the early history of gas discharge physics we discuss the main parameters affecting atmospheric discharges like collision frequency, mean free path and critical electric field strength. Any discharge current in the atmosphere is clearly carried only by electrons. Above the lower boundary of the mesosphere the electrons must be considered magnetized with the conductivity becoming a tensor. Moreover, the collisional mean free path in the upper atmosphere becomes relatively large which lowers the critical electric field there and more easily enables discharges than at lower altitudes. Finally we briefly mention the importance of such discharges as sources for wave emission.