On the mechanisms favoring the development of plasma irregularities and zonal drift reversals during mild geomagnetic conditions

Equatorial spread F plumes were observed on two consecutive nights by the 14-panel Advanced Modular Incoherent Scatter Radar (AMISR-14) at Jicamarca. These events occurred under unfavorable seasonal and solar flux conditions, during a period that can be categorized as geomagnetically quiet. The 2D representation provided by the AMISR-14 system also revealed that the zonal drift of one of the plumes reversed from east to west on the second night. These observations motivated a multi-instrumental and multi-location investigation to study the processes that produced favorable conditions for the plume development and the possible mechanisms leading to the reversal of the irregularity zonal drift on the second night.
The results revealed simultaneous events over the Peruvian and the Brazilian regions, indicating a non-local process. The results also suggest that, even under very mild geomagnetic perturbation conditions, recurring penetration of electric fields in the equatorial ionosphere can occur promptly, modifying the equatorial electrodynamics and creating favorable conditions for the plume development. The results also confirmed that the eastward penetration electric fields, combined with the upsurge of Hall conductivity in the nighttime, typically associated with the presence of sporadic E layers, are likely to be the mechanism leading to the reversal in the irregularity zonal drift over these regions.