A theoretical model for ionospheric electric fields at mid-and low-latitudes is developed.In the geomagnetic dipolar coordinate system,we deduce a partial differential equation of electricpotential from the ionospheric dynamo theory.The deduced equation is taken as the fundamentalequation for the present model.The principal parameters for the model input,the thermosphericneutral winds,the densities and temperatures of electrons,ions and neutral atoms and molecules,are obtained from the empirical models HWM93,IRI90 and MSISE90,respectively.In terms of therelaxation iteration method,the partial equations for electric potential are solved successfully,andthen,the ionospheric electric potential,fields,and currents are derived.Our model can reproducethe main features of the ionospheric electrodynamical processes such as the equatorial electric jet(EEJ),so it will be a useful tool for studying the upper atmosphere and ionosphere.
