A theory of electrostatic fields in the ionosphere at nonpolar geomagnetic latitudes

The theoretical electrostatic coupling between the dynamo region and the F region of the ionosphere is examined at non-polar geomagnetic latitudes. It is found that, under certain conditions, significant coupling between these two regions can occur at all latitudes, even for electrostatic fields with horizontal scale sizes as small as a few kilometers. The coupling is strongest at the poles and weakest at the equator. Strong coupling will also occur between magnetically conjugate portions of the F region, while weaker but significant coupling will exist between conjugate portions of the dynamo region. The strength of the electric source field which would be produced by an irregular, horizontally stratified wind in the dynamo region is then computed, both for polar and for nonpolar latitudes. The results indicate that, to a large extent, the polarization charge that the local winds attempt to build up leaks away vertically and forms closed current loops. In other words, the ‘internal impedance’ of the thin source layer is greater than the ‘load impedance’ presented by the rest of the ionosphere. Finally, the possibility that electrostatic fields may cause significant electron-density variations in the F region is examined briefly. It is concluded that they will not.