Electric fields deduced from the thermospheric model

Dynamo effects arising from the horizontal pressure gradient force of the thermosphere are investigated theoretically. The global thermospheric model used in the derivation of the dynamo current is such that the thermosphere varies horizontally only in the diffusosphere above the turbopause level (assumed to be at 110 km), although the effects of the variation of the turbosphere temperature are briefly discussed. It has been shown that the dynamo current integrated along the magnetic field lines amounts to of the order of 10 A/km, which is comparable to the Sq current. A major portion of the integrated dynamo current provides a two-dimensionally irrotational, or divergent, component that gives rise to the polarization electric field, so that the divergent component may be canceled by the return current's flowing mainly at the highly conductive E region under the influence of the polarization electric field and also flowing along the field lines under the influence of the field-aligned component of the electric field at extremely small magnitudes. The plasma drifts driven by the electric field obtained from the present model suggest the important role of the F region dynamo, especially upon phenomena such as the equatorial evening enhancement of the vertical drift revealed by Jicamarca data and the semidiurnal behavior of the plasma drift at middle latitudes indicated by Millstone Hill data.