Dynamics of the EIA–Auroral Oval Convergence over South America during the 10–12 May 2024 Superstorm

The extreme geomagnetic storm of 10–12 May 2024 provides a unique opportunity to investigate large-scale ionospheric dynamics and coupling processes between low- and high-latitude regions. In this study, we perform a detailed spatio-temporal analysis of the southern crest of the Equatorial Ionization Anomaly (EIA) and the auroral oval, with particular emphasis on the processes leading to their apparent overlap during the storm.
To track the evolution of these two regions, we combine ground-based and space-borne observations. Ionospheric parameters (foF2 and hmF2) from the Tucumán (low-latitude) and Bahía Blanca (mid-latitude) ionosondes in Argentina are analyzed together with Total Electron Content (TEC) maps derived from the RAMSAC and IGS GNSS networks, electron density profiles from COSMIC-2 radio occultations, maximum ionospheric electron density (NMAX) observations from GOLD, auroral particle precipitation measurements from DMSP/SSUSI, and all-sky optical observations from Río Grande.
In addition, preliminary observations reveal a pronounced positive ionospheric storm over South America, characterized by enhanced TEC and a substantial increase in plasma density. During the storm main phase, an intense optical emission feature observed from an all-sky imager in southern South America exhibited an equatorward evolution, coincident with the expansion of auroral precipitation detected by DMSP/SSUSI and with a strong regional enhancement of NMAX observed by GOLD. Concurrently, ionosonde measurements show an abrupt decrease in foF2 and a marked increase in hmF2, indicating significant uplift of the F-region ionosphere. Following the peak disturbance interval, Spread F developed at both Tucumán and Bahía Blanca, suggesting the generation of ionospheric irregularities under highly disturbed conditions.
The combined dataset enables continuous monitoring of ionospheric density structures across a broad latitudinal range, allowing us to investigate the temporal and spatial evolution of the EIA–auroral interaction during one of the most intense geomagnetic storms of Solar Cycle 25.