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Item Ionospheric GPS-TEC responses from equatorial region to the EIA crest in the South American sector under intense space weather conditions(Elsevier) Abreu, Alessandro José de; Correia, Emilia; Denardini, Clezio Marcos; Jesus, Rodolfo de; Venkatesh, Kavutarapu; Roberto, Marisa; Abalde, José Ricardo; Fagundes, Paulo Roberto; Bolzan, Maurício José Alves; Gende, Maurício AlfredoWe present and discuss the ionospheric F-region observations from equator to the equatorial ionization anomaly (EIA) regions over the South American sector during an intense space weather event occurred between 27 and May 29, 2017. During this geomagnetic storm, the symmetric-H (SYM-H) reached a minimum of − 142 nT at ~0700 UT on May 28, 2017. For this investigation, we analyze the vertical total electron content (VTEC) observations from a chain of nearly 120 Global Positioning System (GPS) stations. Magnetometer measurements obtained at two stations in the low latitude regions are also presented. The observations do not indicate prompt penetration electric field (PPEF) effects in the VTEC variations. Magnetometer’s observations over Cuiaba ´ (CBA) and Cachoeira Paulista (CXP) in central west and south parts of Brazil, respectively, have shown a strong crosscorrelation with SYM-H in the period between 3 and 48 h. The results also show positive ionospheric storm phase during the recovery phase on May 28, 2017. Positive effect during the recovery phase of the geomagnetic storm is possibly associated with effects of disturbances winds. During the recovery phase, a strong intensification of the EIA took place, possibly related to an additional ionization effect. The VTEC values show differences between the west and east sectors. This indicates that the EIA crest is stronger in the east sector than in the west sector, possibly due to the combination of disturbance wind effects and geomagnetic field geometry where in the east sector the field lines are more inclined.Item Effects of X2.8-class solar flare on the ionosphere occurred during the recovery phase of a geomagnetic storm over South American and Antarctic sectors(Elsevier) Abreu, Alessandro José de; Correia, Emilia; Venkatesh, Kavutarapu; Pignalberi, Alessio; Pezzopane, Michael; Pillat, Valdir Gil; Fagundes, Paulo Roberto; Gende, Mauricio Alfredo; Jesus, Rodolfo deIn this investigation, we present and discuss the effects of an X2.8-class solar flare occurred on 14 December 2023 on the ionospheric F region and on the geomagnetic field over South American and Antarctic sectors. This flare coincides with the recovery phase of a geomag- netic storm. To this end, we rely on vertical total electron content (VTEC) observations from nearly 250 Global Positioning System (GPS) receiver stations over South American and Antarctic sectors, complemented by in-situ electron density observations from Swarm satellites, magnetometer measurements, and ionospheric sounding observations from ionosondes. The magnetic observations show a large increase in the variations of the horizontal component (DH) of the geomagnetic field and equatorial electrojet (EEJ) currents at all stations, syn- chronized with the increase in X-rays flux, indicating solar flare effects or magnetic crochet on the Earth’s geomagnetic field. VTEC shows how the impact of the solar flare on the ionosphere is enhanced from east to west of South America in the equatorial and low-latitudes. VTEC from a specific GPS satellite-receiver also shows great effects at mid-latitudes. Results are confirmed and further elaborated through Swarm in-situ observations. In addition, an asymmetry is observed in the equatorial ionization anomaly (EIA), in which the eastern South American sector shows an intensified EIA compared to the western sector. Ionospheric sounding observations by ionosondes show total fade out in the echo traces of the ionograms, characterizing blackouts in the radio signals from equatorial to low-latitudes. Overall, our results show that an X-class solar flare occurring near the limb of the solar disk is capable of producing effects on the Earth’s ionosphere with similar or even stronger intensities than flares occurring at the center of the solar disk.