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Item Assessing the effects of a minor CIR‐HSS geomagnetic storm on the brazilian low‐latitude ionosphere: ground and space‐based observations(Advancing Earth and Space Sciences) Chingarandi, Frank Simbarashe; Cândido, Claudia Maria Nicoli; Guedes, Fabio Becker; Jonah, Olusegun Folarin; Santos, Stella Pires Moraes; Klausner, Virgínia; Osanyin, Taiwo OlusayoThis paper investigates the effects of a minor G1 Co-rotating Interaction Region (CIR)/High-Speed Stream (HSS)-driven geomagnetic storm that occurred on (13–14 October 2018), during deep solar minimum. We used simultaneous observations from multiple instruments, namely; ground-based Global Navigation Satellite Systems (GNSS) receivers, a Digisonde, ground magnetometers, and space-based observations from the National Aeronautics and Space Administration Global-scale Observations of Limb and Disk (GOLD) and SWARM missions. This study presents a detailed picture of the low-latitude ionosphere response over the Brazilian sector during a minor storm. Our results showed that the minor CIR/HSS-driven storm caused a positive ionospheric storm of over ∼20 TECU in magnitude. For the first time, periodic post-sunset irregularities and Equatorial Plasma Bubbles, equatorial plasma bubbles, were analyzed using GOLD FUV OI 135.6 nm emission, Total Electron Content (TEC) maps, Rate of TEC index, ROTI, and TEC gradients. Fluctuations in the interplanetary magnetic field Bz and changes in the thermospheric column density ratio (∑O/N2) are discussed as the main sources of ionospheric changes during the storm. This paper highlights the importance of monitoring and understanding the impact of Sun-Earth interactions and provides insight into the behavior of the low-latitude ionosphere during minor geomagnetic storms.Item CIR-Driven Geomagnetic Storm and High-Intensity Long-Duration Continuous AE Activity (HILDCAA) Event: Effects on Brazilian Equatorial and Low-Latitude Ionosphere-Observations and Modeling(MDPI) Abaidoo, Samuel; Klausner, Virginia; Candido, Claudia Maria Nicoli; Pillat, Valdir Gil; Godoy, Stella Pires de Moraes Santos Ribeiro; Guedes, Fabio Becker; Toledo, Josiely Aparecida do Espirito Santo; Trigo, Laura LuizThis paper investigates the effects of a Corotating Interaction Region (CIR)/High-Speed Stream (HSS)-driven geomagnetic storm from 13 to 23 October 2003, preceding the well-known Halloween storm. This moderate storm exhibited a prolonged recovery phase and persistent activity due to a High-Intensity Long-Duration Continuous AE Activity (HILDCAA) event. We focus on low-latitude ionospheric responses induced by Prompt Penetration Electric Fields (PPEFs) and Disturbance Dynamo Electric Fields (DDEFs). To assess these effects, we employed ground-based GNSS receivers, Digisonde data, and satellite observations from ACE, TIMED, and SOHO. An empirical model by Scherliess and Fejer (1999) was used to estimate equatorial plasma drifts and assess disturbed electric fields. Results show a ∼120 km uplift in hmF2 due to PPEF, expanding the Equatorial Ionization Anomaly (EIA) crest beyond 20° dip latitude. DDEF effects during HILDCAA induced sustained F-region oscillations (∼100 km). The storm also altered thermospheric composition, with [[O]/[N2] enhancements coinciding with TEC increases. Plasma irregularities, inferred from the Rate of TEC Index (ROTI 0.5–1 TECU/min), extended from equatorial to South Atlantic Magnetic Anomaly (SAMA) latitudes. These results demonstrate prolonged ionospheric disturbances under CIR/HSS forcing and highlight the relevance of such events for understanding extended storm-time electrodynamics at low latitudes.