Response of the Equatorial Ionosphere over the South American Region to 8 September 2017 Geomagnetic Storm

This study delved into the response of the equatorial ionosphere in the South American region to the geomagnetic storm in September 2017. Six global positioning system (GPS) receivers, positioned along 45° W and 70° W, were utilized to estimate the daily variation of total electron content (TEC). A pair of magnetometers measured the strength of the equatorial electrojet (EEJ) (inferred E × B drift), and the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite revealed changes in the thermospheric neutral composition before, during, and after the geomagnetic storm on September 8, 2017. The pre-storm effect and occurrence of solar flares, accompanied by solar bursts are responsible for the significant enhancement in TEC magnitudes days prior to geomagnetic storm event. However, the significant enhancement observed in the TEC magnitude during the main phase of the geomagnetic storm was primarily driven by DP2 (disturbance polar number 2), created by the daytime prompt penetration of electric field (PPEF) signature. Other mechanisms responsible for this enhancement included the increase in thermospheric neutral composition, O/N₂ ratio, and more ionization of electrons due to the increase in solar flux. Furthermore, the drastic increase in the amplitude of the morning-afternoon magnetometer-inferred upward-directed E × B drift during the main phase of the storm, compared to the quiet periods, was attributed to the magnetic signature (DP2) due to PPEF. Additionally, the inhibition of ionospheric irregularities at the equatorial ionosphere during the main phase of the geomagnetic storm may be associated with the storm-time occurrence.