EFFECTS OF ELECTRICAL COUPLING ON EQUATORIAL IONOSPHERIC PLASMA MOTIONS - WHEN IS THE F-REGION A DOMINANT DRIVER IN THE LOW-LATITUDE DYNAMO

Previous studies of the low-latitude atmospheric dynamo have concluded that the E region dynamo is the principal source of electric fields during the day, with the F region dynamo being of significant importance in the postsunset period. By computing field line integrals of the Hall and Pedersen conductivities and wind-driven currents from a sophisticated F region model, we find that the F region may provide a significant contribution to the dynamo electric field at all local times in a limited altitude and latitude region. Though the peak value of the Pedersen conductivity in the E region is larger than the peak value of the F region Pedersen conductivity, the field line integrated Pedersen conductivity of the F region can be significantly larger than the integrated Pedersen conductivity of the E region. This effect is most pronounced for low-latitude flux tubes with apex altitudes slightly above the F peak. This is due to the unique geometry of the equatorial geomagnetic field in which the field line path length through the F region is much greater than the field line path length through the E region. This effect decreases with increasing latitude as the field lines become more vertical and the path lengths through the appropriate parts of E and F regions become more comparable. We examine the consequences of this effect upon the low-latitude drifts derived from three dynamo circuit assumptions and compare the results to average drifts observed at Jicamarca, Peru.