# Effects of the October 2024 Storm over the Global Ionosphere
## 1 Introduction  
Geomagnetic storms have a profound influence on Earth's ionosphere across all latitudes, triggering intricate physical processes in equatorial, midlatitude, and polar regions. These interactions complicate our understanding of space weather dynamics [1, 2, 3, 4, 5, 6, 7]. Storm-time electricfield and energy input from the magnetosphere can induce rapid ionospheric responses, sometimes intensifying ionospheric instabilities [8; 9], while at other times suppressing them [10; 11], depending on local conditions and time scales. During Solar Cycle 25, two significant geomagnetic storms--classified as G4 and G5--occurred in 2024, coinciding with a peak in solar activity. The most intense of these was the G5-class \"Mother's Day Storm\" on 10-11 May 2024 (Kp-9), one of the strongest storms since 1957. This event generated auroras visible at midlatitudes (\(\sim\)45\({}^{\circ}\)N and \(\sim\)37\({}^{\circ}\)S) [12; 13]. [PERSON] et al. (2024) [14] reported major space weather effects over Italy, notably a substantial drop in plasma density on 11 May, resulting in a negative ionospheric storm evident in both F-layer critical frequency (foF2) and total electron content (TEC). This was linked to changes in the thermospheric composition, particularly a decrease in the [O/N2] ratio. High values of the Rate of TEC Change Index (ROTI) were also observed, associated with Stable Auroral Red (SAR) arcs and a southward shift in the ionospheric trough. The ROTI enhancement was attributed to low-latitude plasma being driven poleward by pre-reversal enhancement (PRE) after sunset, along with northward-propagating wave-like disturbances. [PERSON] et al. (2024) [13], using NASA's GOLD imager, identified a connection between the southern crest of the Equatorial Ionization Anomaly (EIA) and auroral activity near the southern tip of South America. The EIA crest shifted poleward at speeds up to 450 m/s, and auroral emission extended to midlatitudes over Southern Africa and South America, resulting in midlatitude plasma erosion. [PERSON] et al. (2024) [15] described a significant uplift in the Storm-Enhanced Density (SED) plume, with the F2-layer height (hmF2) rising by 150-300 km and GNSS scintillation observed across the auroral oval. [PERSON] et al. (2024) [16] reported Hemispheric asymmetries in the ionospheric response due to particle precipitation and thermospheric heating, along with EIA modifications and disturbance dynamo electric fields (DDEFs) at lower latitudes. [PERSON] et al. (2025) [5] investigated the ionospheric response over Europe during the Mother's Day storm using Digisonde data and Swarm satellite measurements. They found notable Ne depletion, attributed to the equatorward shift in the Midlatitude Ionospheric Trough (MIT). Large-Scale Travelling Ionospheric Disturbances (LSTIDs) and Spread F were also evident, primarily at higher midlatitudes. A broader study by [PERSON] et al. (2025) [6] showed global-scale F2-layer uplift and increased foF2 over midlatitude dayside regions, while nightside values decreased. Enhanced vertical and horizontal plasma drifts were observed, including \(\sim\)170 m/s upward drift in the Southern Hemisphere during the storm's main phase. Swarm A measurements indicated EIA expansion to 60\({}^{\circ}\)S on the dayside and 40\({}^{\circ}\)S on the nightside. The second major G4-class storm occurred on 10-11 October 2024. This event has received limited attention so far. [PERSON] et al. (2025) [17] were among the first to offer an analysis, comparing the October storm to the May G5 event. Using Vertical TEC (VTEC) and ionosonde data from Europe, the USA, and South Korea, they found that upper atmospheric ionization initially spiked after Coronal Mass Ejection (CME) arrival, followed by a prolonged depletion lasting over 24 h. Recovery began on October 12, whereas the May event showed an unusually fast rebound. These effects were attributed to intense F-layer perturbation, further amplified by plasmaspheric contribution to VTEC variation. [PERSON] et al.