# Effects of the October 2024 Storm over the Global Ionosphere
## 4 Results
### Storm Effects on Swarm Observation  
In the previous section, the analysis of storm-induced changes in foF2 and hmF2 was limited to \(\pm\)45\({}^{\circ}\) geographic latitude due to the restricted latitudinal coverage of COSMIC-2. To expand this latitude scope and gain a more complete picture of the global ionospheric response, the current section examines in situ Ne measurements from Swarm satellites A and B during the October 2024 geomagnetic storm. While Swarm data have been extensively used to study the May 2024 Mother's Day superstorm, a detailed global study of Swarm Ne response to the October event has not yet been reported. [PERSON] et al. (2025) [PERSON] et al. (2025) investigated field-aligned currents (FACs) and polar electrojet (PEJ) activity during this storm, but their analysis was confined to the polar ionosphere. To address this gap, we analyzed Swarm A and B Ne data for the interval from 15:00 UT on 10 October to 21:00 UT on 11 October. This time frame was selected based on both the SYM-H index (Figure 2) and foF2/hmF2 variation (Figures 3 and 4), which indicate that significant storm activity diminished after \(\sim\)21:00 UT on 11 October. The comparison was based on data from 5,6 October, which represents geomagnetically quiet conditions. The results are presented in Figures 10a-t and 11a-t, where each set of four panels per time window displays (1) Swarm Ne for quiet conditions, (2) storm-time Ne, (3) Madrigal global TEC maps under quiet conditions, and (4) corresponding storm-time TEC maps. Figure 9: (**a–d**) Global variation in [O/N\({}_{2}\)] ratio on (**a**) 9 October, (**b**) 10 October, (**c**) 11 October, and (**d**) 12 October. To assess storm-induced global ionospheric variations, it is essential to first characterize the typical behaviour of the ionosphere under geomagnetically quiet conditions. For this purpose, we analyze ionospheric observations from 15:00 UT on 5 October to 21:00 UT on 6 October, as illustrated in Figures 10 and 11. This study primarily aims to examine the potential poleward expansion of the EIA and the equatorward extension of the polar ionosphere, with particular focus on the EIA dynamics and polar ionospheric responses. Swarm A, orbiting at a lower altitude than Swarm B, exhibits more pronounced EIA features along its trajectory. Between 15:00 and 18:00 UT on 5 October, well-defined EIA crests are observed within \(\pm 15^{\circ}\) magnetic latitude across the European-African sector, where the geographic and geomagnetic equators are closely aligned. In the South American sector, Swarm B also detects a significant crest near \(-15^{\circ}\)N, indicative of enhanced equatorial fountain effects. As the observation period progresses, both Swarm A and B detect EIA signatures over western longitudes. Over South America, EIA crests recorded by Swarm A between 21:00 UT on 5 October and 03:00 UT on 6 October extend from \(5^{\circ}\)N to \(-30^{\circ}\)N following the geomagnetic equator. During the same interval, Swarm B observes increased perturbations across equatorial regions (\(\pm 15^{\circ}\) latitude), particularly over the Pacific sector. Between 03:00 and 06:00 UT, Swarm A continues to record westward EIA development confined within \(\pm 15^{\circ}\) latitude, while Swarm B detects heightened ionospheric disturbances over the Asian region, suggesting intensified fountain effects at higher altitudes. From  
Figure 10: (**a–t**) Three-hour global tracks of Swarm Ne (Swarm A represented by brown tracks and Swarm B represented by blue tracks). The leftmost column represents the Swarm tracks from 15:00 UT on 5 October to 06:00 UT on 6 October, a geomagnetically quiet period for reference. The second column depicts the storm-time Swarm tracks from 15:00 UT on 10 October to 06:00 UT on 11 October. The third and fourth columns represent the madrigal global TEC maps during the geomagnetically quiet and disturbed periods.