This investigation shows that the significant electric field disturbances in the dip‐equatorial ionosphere during the geomagnetic storm of 6–8 September 2017 are due to the passage of two consecutive interplanetary coronal mass ejections (ICMEs). During the passage of the first ICME sheath, a long duration (∼10 hr) prompt penetration (PP) event is operational in which 60‐min periodic component is found to be present in vertical drift as well as in equatorial electrojet, but the 45‐min periodicity, though present, is not significant in equatorial electrojet. On 8 September, the shock associated with the second ICME enhances the F region vertical plasma drift to ∼150 m/s in the evening hours which is one of the highest vertical drift ever measured over Jicamarca. The same PP electric field causes unusually large enhancement of the equatorial electrojet strength to ∼135 nT in the early morning hours over the Philippine sector. The disturbance dynamo (DD) that follows the storm causes an upward vertical drift of ∼55 m/s during postmidnight hours over Jicamarca which is one of the highest observed. These unusually large electric field perturbations cause significant changes in the F region plasma fountain. It is shown that these electric field perturbations cannot be accounted by PP/DD electric field associated with the geomagnetic storm only and significant contribution from substorm is conspicuous. Therefore, the present investigation highlights the need to evaluate the role of substorm in unusually large electric field perturbations over equatorial ionosphere.
The variability in the low latitude F region plasma distribution is greatly controlled by the equatorial F region plasma fountain process (Anderson, 1973a, 1973b). This process generates two ionization crests around ±15° geomagnetic latitudes and an ionization trough over the dip equator. This is known as equatorial ionization anomaly (EIA). Meridional winds cause asymmetry in the intensity and location of the EIA crest regions (e.g., Anderson, 1973a). The plasma distribution over the EIA crest regions shows day-today variability (e.g., Huang et al., 1989) as well as seasonal and solar activity dependences (e.g., Chakrabarty et al., 2012; Huang & Cheng, 1995; Mo et al., 2018). Understanding the plasma density variability over the EIA crest region is important as it is one of the most L-band scintillation affected regions in the globe (e.g.,
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