Extreme Ionospheric Storm Effects at Mid-latitudes During May 2024 Geomagnetic Storm

The May 2024 geomagnetic superstorm (Gannon storm) was the most intense in the past 30 years, which produced major disturbances in the coupled ionosphere-thermosphere (IT) system. In this study, we investigate the large-scale ionospheric storm effects at low and mid-latitudes using a combination of satellite observations, ground-based measurements, and model outputs. Analysis of DMSP F16–F18 data shows significant increases in the topside ionospheric density at mid-latitudes during storm growth phase, followed by a decrease below quiet-time levels in late recovery phase. These ion density variations along DMSP orbits are used to identify the positive and negative phases of the ionospheric storm. At low latitudes, strong occurrences of plasma bubbles were observed in the pre-sunrise sector. The upward TEC measurements from GRACE-FO and SWARM satellites, along with ionograms from the Jicamarca station, indicate an extreme uplift of the ionospheric F-region during the positive phase. Ground-based TEC data in the American sector show substantial TEC enhancement at mid-latitudes during the positive phase, followed by significant depletion during the negative phase. To investigate the drivers behind these extreme ionospheric responses, we further analyze neutral winds, composition (O/N₂ ratio), NO cooling, and Poynting flux using data from satellites (DMSP, GRACE-FO, TIMED-GUVI) as well as atmospheric models (GITM, TIEGCM).