Significant Electric Field Perturbations in Low Latitude Ionosphere due to the Passage of Two Consecutive ICMEs During 6-8 September 2017

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 (similar to 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 similar 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 similar 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 similar to 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. Key Points Extreme electric field perturbations in equatorial ionosphere are driven by prompt penetration (PP) of solar wind electric field and substorm Additional role of substorm is shown in driving unusually large disturbance dynamo (DD) electric field perturbations in equatorial ionosphere Unusually large PP and DD electric fields generated super fountain and suppressed plasma fountain, respectivelly