[1] We use extensive incoherent scatter radar observations made at the Jicamarca Radio Observatory between 1970 and 2003 to study and model empirically the equatorial zonal plasma drifts near the F region peak using Bernstein polynomials as base functions. Our quiet-time model results confirm that the daytime drifts are westward and are nearly season and solar cycle independent. The nighttime drifts are eastward, have larger magnitudes, and increase strongly with solar flux, particularly near equinox and December solstice. Enhanced geomagnetic activity drives small eastward perturbation drifts during the day and much larger westward disturbance drifts at night. The nighttime drift perturbations are largest near midnight and increase strongly with solar flux near equinox and December solstice but are essentially absent near June solstice. The Jicamarca zonal disturbance drifts can be largely accounted for by disturbance dynamo electric fields with a dominant time delay of about 3-15 hours following enhanced geomagnetic activity. In the postmidnight sector, there are also smaller westward disturbance drifts associated with time delays of about 15-24 hours and perhaps even longer. Our results strongly suggest that the longitudinal dependence of both the quiet and disturbed equatorial nighttime zonal drifts varies with season.

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During a stratospheric balloon flight on April 9, 1980, large scale electric fields have been measured, for the first time, at the Brazilian Magnetic Anomaly with a double‐probe detector. We report here the results of this flight performed during a time interval with fair weather at the observing region and enhanced geomagnetic activity. These results suggest that a BAND of precipitating energetic particles, moving equatorwards with respect to the balloon, could have produced a conductivity enhancement down to the middle atmosphere, distorting the vertical atmospheric electric field and giving rise to the type of horizontal fields observed.

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Abstract-Theproblem of downward mapping of equatorial Ionospheric electric fields is studied in two dimensions employing the finite elements and finite differences numerical techniques. The solutions obtained for low latitudes are compared with known results for high latitudes. It is found that equatorial ionospheric electric fields of scale lengths of the order of 100 km or more reach balloon heights (30-40 km) without undergoing noticeable attenuation.However, in the case of equatorial ionospheric electric tields of scale lengths of a few tens of kilometers it is found that these fields reach balloon heights with severe attenuation.