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.