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Item Occurrence of Ionospheric irregularities over Brazil and Africa during the 2019 Antarctic minor sudden stratospheric warming(Elsevier) Agyei-Yeboah, Ebenezer; Fagundes, Paulo Roberto; Tardelli, Alexandre; Pillat, Valdir Gil; Vieira, Francisco; Arcanjo, Mateus de OliveiraThe influence of sudden stratospheric warming (SSW) on the ionosphere and ionospheric irregularities has been studied extensively over the years. However, majority of these investigations have been conducted using warming events originating from the northern hemisphere. Only a few studies have been done on ionospheric variations due to the Antarctic SSW events and to the best of our knowledge, there have not been any studies on southern hemisphere SSW and the occurrence of ionospheric irregularities. In this study, the occurrence of ionospheric irregularities during the 2019 minor Southern hemisphere (SH)/Antarctic SSW is investigated. The event occurs in a relatively calm solar and geomagnetic activity period which makes it possible to identify the effects of SSW on the occurrence of irregularities. Three ionosondes located in different latitudinal regions in Brazil as well as a network of ground-based GPS receiver stations located in both Brazil and Africa were used for this undertaking. Complimentary data from the same ionosonde stations using the same months from 2017 and 2018 were also used. On average more Spread-F was observed in 2019 than in 2017 or 2018 at all stations. ROT observations showed more occurrence in the Brazil sectors followed by West Africa and thenEast Africa. It was observed that the occurrence frequency decreased between 8% and 46 % from the pre-SSW phase to ascending/peak phases and from 2018 to 2019 for the peak phase.Item Morphological Features of Ionospheric Scintillations During High Solar Activity Using GPS Observations Over the South American Sector(Advancing Earth and Space Sciences) Jesus, Rodolfo de; Batista, Inez Staciarini; Takahashi, Hisao; Barros, Diego; Figueiredo, Cosme Alexandre Oliveira Barros; Abreu, Alessandro José de; Jonah, Olusegun Folarin; Fagundes, Paulo Roberto; Venkatesh, KarnamThe main objective of this study is to investigate the ionospheric irregularities observed by Global Positioning System‐total electron content (GPS‐TEC) receivers during the high solar activity years of 2013 and 2014 at different stations in the equatorial and low‐latitude regions in the South American sector. The ionospheric parameters used in this investigation are the TEC, the rate of change of the TEC index (ROTI), and the amplitude scintillation index (S4). In the South American sector, the ROTI and S4 indices showed that the ionospheric irregularities have an annual variation with maximum occurrence from September to April, between 20:00 LT and 02:00 LT, and no occurrence from May to August. Also, strong phase fluctuations (ROTI >1) are observed over South America at 19 LT in October and November. Morlet wavelet analysis of ROTI and S4 showed that planetary wave‐scale periods ranging from 2 to 8 days are predominant during September–March at 20–02 LT in South America. In addition, using a keogram it was possible to evaluate the distance between adjacent ionospheric plasma depletions, and this result is presented and discussed. The longitudinal distances between adjacent bubbles vary around ~600–1000 km, which is larger than values reported in most previous studies.