ABSTRACT
Ionospheric electrodynamics depends, among other things, on the conductivity of the ionosphere and on the strength of thermospheric winds. The theory of ionospheric conductivity was developed by M. Hirono and W. G. Baker and D. F. Martyn. Equivalent current is not necessarily the same as the true height-integrated horizontal ionospheric electric-current density, since the true current system is three-dimensional, with significant amounts of current flowing along geomagnetic field lines the ionosphere. Numerical simulation models of the ionospheric dynamo have been used to shed light on many characteristics of ionospheric electrodynamics. Disturbances to the global current system can be produced by changes in ionospheric conductivity. Perturbations in the geomagnetic field were one of the earliest phenomena of ionospheric electrodynamics to be observed, and magnetic-perturbation data have existed for a long period of time, from points widely spread over the Earth. The influence of modified ionospheric conductivity on geomagnetic perturbations is often observed during solar flares and eclipses.
