Modeling the three-dimensional structure of ionospheric electrodynamics

Ionospheric electric fields and currents are driven by collisionalinteraction between thermospheric winds and ions, bymagnetospherically driven convection and field-aligned currents athigh latitudes, by gravitational and pressure-gradient forces on theionospheric plasma, and by weak currents from the lower atmosphere.The electrodynamics of the ionospheric E and F regions are stronglycoupled. For time scales longer than a few minutes the electric fieldis electrostatic. The electric potential is nearly constant alonggeomagnetic-field lines, and can be represented in two dimensions in acoordinate system aligned with the magnetic field. The currentdensity, however, varies in all three dimensions. The associatedperturbations of the geomagnetic field induce currents in the Earth,which modify the perturbations. We are developing a model of ionospheric electrodynamics that takes into account all of the sourcesand calculates the three-dimensional structure of currents andtheir associated magnetic perturbation fields at high spatialresolution. This model will be used to simulate ionospheric drifts aswell as geomagnetic perturbations at the ground, at low-Earth-orbitsatellite heights, and within the E-region ionosphere. When coupledwith a dynamical model of the thermosphere and ionosphere it can beused to assimilate electrodynamic data into the model. In thispresentation we discuss the modeling principles and present resultsrelevant to the electrodynamics of the middle and low latitudeionosphere below 200 km, including the effects of coupling withF-region electrodynamics and the expected observable effects onrockets and on low Earth orbit satellites.