Equatorial F‐Region Responses to the Main Phase of the 10 May 2024 Geomagnetic Storm Over the South American Sector: Observations and Model Simulations

Abstract

This study examines the equatorial ionospheric response over the South American sector during the onset of the extreme 2024 Mother's Day geomagnetic storm, which began at ∼17 UT on 10 May and reached the G5 level. Pronounced disturbances in ionospheric electrodynamics were observed under both daytime and nighttime conditions. Variations in the F2‐layer critical frequency (foF2) and peak height (hmF2) were analyzed using ionosonde observations from equatorial stations at Belém and São Luís (SL) (Brazil) and Jicamarca (Peru), together with simulations performed with the SUPIM‐INPE model. At the onset of the storm's main phase, a simultaneous and abrupt uplift of the F2 layer was observed at all three stations. Model results indicate that this enhancement was primarily driven by eastward undershielding electric fields, with meridional winds contributing to hmF2 variations over the Brazilian sector. Around 19:00 UT, a complex descent of the ionosphere was detected, which is attributed to the combined effects of westward overshielding, disturbance dynamo electric fields, meridional winds, F3‐layer disruption, and large‐scale traveling ionospheric disturbances (LSTIDs). Although the model reproduced the formation of the F3 layer over Belém and SL, its duration was overestimated compared to observations. On the other hand, its results showed a consistent trend. Near 20:00 UT, a pronounced uplift of the F layer, followed by an anomalous decrease in foF2, was observed over Brazil. In contrast, different features were observed at Jicamarca, suggesting distinct combined roles of LSTIDs and the eastward electric field in the Brazilian sector, as qualitatively confirmed by the modeling.