Electrodynamics in the low and middle latitude ionosphere: a tutorial

Electric fields in the low and middle latitude ionosphere result from currents driven internally by neutral winds and gravity, and externally by applied potentials. The resulting internal electric polarization fields arise from the need to make the total current divergence free. By considering the current drivers many of the attributes of the observed ion and electron drifts can be understood including the E- and F-region dynamos, the initial growth of ionospheric depletions, and effects from high latitudes. Such an exercise leads to an overall understanding of the governing principles. However, it is necessary to know all the large-scale spatial gradients in the drivers, many of which are presently unknown, in order to unravel the outstanding mysteries of the electrodynamics of the region. (C) 2004 Elsevier Ltd. All rights reserved.