Simultaneous occurrence of midlatitude plasma bubbles and LSTIDs during the 10 October 2024 geomagnetic storm

In this study, we present a multi-instrumental analysis of the extreme geomagnetic storm of October 10, 2024, focusing on the inter- action between Equatorial Plasma Bubbles (EPBs) and Large-Scale Traveling Ionospheric Disturbances (LSTIDs) over the American sector. Using Rate of Total Electron Content Index (ROTI), Total Electron Content (TEC), and Detrended Total Electron Content (DTEC) maps derived from Global Navigation Satellite System (GNSS) data, we investigated the ionospheric response to the geomag- netic storm. This analysis was complemented by far-ultraviolet airglow observations from the Global-scale Observations of the Limb and Disk (GOLD) mission, in situ electron density profiles from the Swarm satellite constellation, and ground-based ionosonde measure- ments. These multi-instrumental datasets revealed a sequence of coupled processes responsible for the generation, expansion, and mor- phological deformation of EPBs, extending well beyond their typical equatorial domain. Prompt Penetration Electric Fields (PPEFs), which led to an enhanced pre-reversal enhancement (PRE) over western South America, drove a substantial uplift of the ionospheric F-region, exceeding 700 km, and favored the development of large-scale EPBs. These structures manifested as a reversed-C-shaped plasma depletion band, confirmed by both ROTI and GOLD observations. Simultaneously, DTEC maps and keograms revealed the equatorward propagation of storm-time LSTIDs. A pronounced spatial and temporal overlap between EPB and LSTID signatures was observed at midlatitudes, especially across the western South American longitudinal sector. This interaction appears to have mod- ulated the outer structure of the EPBs, leading to asymmetric deformation and enhanced latitudinal expansion. Finally, our findings highlight the role of multiscale coupling between high-latitude and equatorial processes during geomagnetic storms and emphasize the need for integrated observations to fully characterize the dynamics of storm-induced ionospheric disturbances.