This book resulted from lectures which I gave at the Universities of Kyoto, Cologne, and Bonn. Its objective is to summarize in a unifying way two other- wise rather separately treated subjects of atmospheric electrodynamics: elec- tric fields of atmospheric origin, in particular thunderstorm phenomena and related problems on the one hand, and magnetic fields, in particular those which are associated with electric currents of upper atmospheric origin, on the other. Geoelectricity and geomagnetism were not always considered as be- longing to quite different fields of geophysics. On the contrary, they were re- cognized by the physicists of the 19th and the beginning of the 20th century as two manifestations of one and the same physical phenomenon, which we pre- sently refer to as electromagnetic fields. This can still be visualized from the choice of names of scientific journals. For instance, there still exists the Japanese Journal of Geomagnetism and Geoelectricity, and the former name of the present American Journal of Geophysical Research was Terrestrial Magnetism and Atmospheric Electricity.
Whereas geomagnetism became the root of modern magnetospheric phys- ics culminating in the space age exploration of the earth's environment, geo- electricity evolved as a step-child of meteorology. The reason for this is clear. The atmospheric electric field observed on the ground reflects merely the local weather with all its frustrating unpredictability. The variable part of the geomagnetic field, however, is a useful indicator of ionospheric and magneto- spheric electric current systems.