IMF By-driven electric field disturbances over the equator during northward IMFs: PPEF responses

This article provides the first evidence of equatorial and low-latitude ionospheric electric field disturbances driven by quasi-periodic variations in the interplanetary magnetic field (IMF) By component, under a constant northward IMF Bz (∼+15 nT), solar wind dynamic pressure (∼8 nPa), solar wind velocity (∼450 km/s), and positive Sym-H (+10 nT). The virtual height of the F layer (h’F), measured by ionosondes at opposite longitudes in the American (Jicamarca, 11.9°S, −76.0°E; Fortaleza, 3.9°S, −38.52°E) and Indian (Trivandrum, 8.5°N, 77.0°E; Tirunelveli, 8.73°N, 77.7°E) sectors, shows electric field disturbances with opposite polarities during the day and night, driven by changes in the IMF. During northward IMF Bz conditions, vertical E × B plasma drifts measured by the Jicamarca Incoherent Scatter Radar (ISR), along with equatorial electrojet (EEJ) observations, reveal westward electric field disturbances on the dayside. Conversely, on the nightside, ionosonde measurements at Trivandrum and Tirunelveli show eastward electric field perturbations. Notably, quasi-periodic electric field fluctuations with prominent periodicities of approximately 15 min are observed in both the IMF By and ionospheric parameters, such as dh'F/dt and EEJ, in both local time sectors. These fluctuations are most likely driven by modulations in high-latitude disturbance polar (DP2) currents. SuperDARN ionospheric convection maps display enhanced convection, rotation, and expansion, which appear to influence the equatorial electric field. The presence of northward Bz (NBZ) currents and reverse convection patterns likely contributes to the observed westward electric field perturbations at low latitudes.