Equatorial westward electrojet impacting equatorial ionization anomaly development during the 6 April 2000 superstorm

We investigate the forward plasma fountain and the equatorial ionosphere in the topside region during the 6 April 2000 superstorm in the Australian sector at ~0900 LT. Space‐ and ground‐based multi‐instrument measurements, Coupled Thermosphere‐Ionosphere‐Plasmasphere Electrodynamics (CTIPe) simulations, and field‐aligned observations comprise our results. These reveal an unusual storm development during which the eastward prompt penetration electric (E) field (PPEF) developed and operated under the continuous effects of the westward disturbance dynamo E‐field (DDEF) while large‐scale traveling ionospheric disturbances (TIDs) traveled equatorward and generated strong equatorward wind surges. We have identified the eastward PPEF by the superfountain effect causing the equatorial ionization anomaly (EIA)'s development with crests situated at ~±28°N (geomagnetic) in the topside ionosphere at ~840 km altitude. The westward DDEF's occurrence is confirmed by mapping the “anti‐Sq” current system wherein the equatorial westward current created a weak long‐lasting westward electrojet event. Line plots of vertical drift data tracked large‐scale TIDs. Four scenarios, covering ~3.5 h in universal time, demonstrate that the westward DDEF became superimposed on the eastward PPEF. As these E‐fields of different origins became mapped into the F region, they could interact. Consequently, the eastward PPEF‐related equatorial upward E × B drift became locally reduced by up to 75 m/s near the dip equator by the westward DDEF‐related equatorial downward E × B drift. Meanwhile, the EIA displayed a better development as equatorial wind surges, reproduced by CTIPe, increased from 501 to 629 m/s, demonstrating the crucial role of mechanical wind effects keeping plasma density high.

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