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Item Ionospheric disturbances in a large area of the terrestrial globe by two strong solar flares of September 6, 2017, the strongest space weather events in the last decade(Elsevier) Fagundes, Paulo Roberto; Pezzopane, Michael; Habarulema, John Bosco; Venkatesh, Karnam; Dias, Maukers Alem Lima; Tardelli, Alexandre; Abreu, Alessandro José de; Pillat, Valdir Gil; Pignalberi, Alessio; Bolzan, Maurício José Alves; Ribeiro, Brunno Augusto Gomes; Vieira, Francisco; Raulin, Jean-Pierre; Denardini, Clezio Marcos; Seemala, Gopi K.; Arcanjo, Mateus de OliveiraOn September 6, 2017, the solar active region AR 2673 emitted two solar flares: the first at 08:57 UT (X2.2) and the second at 11:53 UT (X9.3); both were powerful enough to black-out high and low frequency radio waves (where UT is universal time). The X9.3 was the strongest solar flare event in the past decade. In this study, we took the advantage of these two extreme flare events to investigate cor- responding effects on the ionosphere using multi-instrument observations from magnetometers, Global Positioning System – Total Elec- tron content (GPS-TEC) receivers, ionosondes and Swarm satellites over a large geographical extent covering South American, African and European sectors. During the X2.2 flare, European and African sectors were sunlit and during X9.3 European, African, and South American sectors were sunlit and exposed to the solar flare radiation. During the X2.2 flare, there was an ionosonde blackout for a dura- tion of about 45 min, while during the X9.3 flare this blackout lasted for 1 h and 30 min. The blackout are seen over a large global extent which demonstrates the severity of solar flare events in disrupting the radio communication. The horizontal component of Earth’s geo- magnetic field has shown ripples and enhancements during these flare events. The ionospheric Vertical Total Electron Content (VTEC) showed a positive phase along with an intensification of the Equatorial Ionization Anomaly (EIA) over the South American and African sectors. The dynamical and physical processes associated with the TEC and EIA variabilities due to solar flare are discussed.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.