Abstract:
The equatorial zonal electric field responses to prompt penetration of eastward convection electric
fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the
intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F
layer to >550 km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs
were found to extend up to 27.13°N and 25.98°S magnetic dip latitudes indicating their altitude development to
~1670 km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes),
no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations
due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric
disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the
premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage
Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due
to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to
confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly
enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector.
The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at
dusk sector in the presence of convection electric fields associated with the onset of a substorm under
southward interplanetary magnetic field Bz
