# Effects of the October 2024 Storm over the Global Ionosphere
## 4 Results
### Large-Scale Travelling Ionospheric Disturbances  
LSTIDs are manifestations of GWs and are frequently observed across the global ionosphere. During geomagnetic storms, the probability of LSTID formation and propagation increases significantly due to intensified energy input into the upper atmosphere [5; 7]. TEC perturbations are commonly used to detect and analyze TID behaviour in space weather studies. [PERSON] et al. (2010) [24] reported such storm-time LSTID signatures in the European sector. In this study, we examined LSTID activity during the main phase of the October 2024 geomagnetic storm, particularly from 15:00 UT on 10 October to 02:30 UT on 11 October--a period considered optimal for LSTID generation [24]. To do so, we analyzed global dTEC maps, as described in Section 2. While we were limited to visual identification of propagation direction due to the data format, which precludes estimation of LSTID periodicity, wavelength, or speed, the methodology for generating and interpreting these maps is well established in [PERSON] et al. (2002) [20]. Given the spatial density of GNSS stations, this analysis focuses on the Northern Hemisphere, particularly Europe, Japan, and North America. Figures 12-17 present the evolution of LSTID activity across the Northern Hemisphere during the storm's main phase. Following the SSC at 15:16 UT, initial LSTID signatures were detected over both the European (marked by the red circle) and Japanese (blue circle) sectors, as shown in Figure 12a--d. During the 15:20--15:50 UT interval, dTEC fluctuations reached --4 TECU over Europe and --5 TECU over Japan. LSTID propagation directions suggested southwestward movement over Europe and possible equatorward expansion of the polar ionosphere, consistent with findings by [PERSON] et al. (2025) [18]. Figure 14: (**a–d**) LSTIDs detected in the global dTEC map over the Northern Hemisphere on 10 October during **(a)** 19:10 UT, **(b)** 19:20 UT, **(c)** 19:40 UT, and **(d)** 19:50 UT. Figure 12: (**a–d**) LSTIDs detected in the global dTEC map over the Northern Hemisphere on 10 October during **(a)** 15:20 UT, **(b)** 15:30 UT, **(c)** 15:40 UT, and **(d)** 15:50 UT. As the storm intensified, LSTID activity became more widespread. Figure 13a-d displays dTEC patterns from 17:00 to 17:40 UT. LSTID signatures extended to the North American sector, marked by the green circle. In Europe, LSTIDs were evident over the polar latitudes (60-70\({}^{\circ}\)N) propagating northeastward, while midlatitude LSTIDs appeared to move from southeast to northwest. In Japan, southward-propagating LSTIDs were detected, especially during 17:00-17:10 UT. The North American region also showed signs of poleward EIA expansion, particularly between 17:00 and 17:20 UT. During 19:10-19:50 UT (Figure 14a-d), LSTIDs intensified further. The European polar region exhibited an east--west structured plasma pattern, while Japan showed southwest-to-northeastward-propagating LSTIDs that intensified toward the end of the interval. In North America, a dTEC depletion at 19:10 UT shifted northeastward with decreasing fluctuation magnitude--again suggesting poleward EIA expansion. At the storm's peak, Figure 15a-d shows clearer LSTID patterns, particularly over North America, where northeast-to-southwest-propagating LSTIDs dominated. The European polar region recorded high dTEC fluctuations, while the western midlatitude sector experienced sharp depletions. [PERSON] et al. (2025) [PERSON] et al. (2025) linked these ionization changes to intense F-region perturbations, amplified by the plasmaspheric effect on VTEC. Figure 16: (**a**–**h**) LSTIDs detected in the global dTEC map over the Northern Hemisphere on 10 October during (**a**) 22:10 UT, (**b**) 22:30 UT, (**c**) 22:50 UT, (**d**) 23:00 UT, (**e**) 23:10 UT, (**f**) 23:20 UT, (**g**) 23:30 UT, and (**h**) 23:40 UT. Figure 15: (**a**–**d**) LSTIDs detected in the global dTEC map over the Northern Hemisphere on 10 October (**a**) 20:50 UT, (**b**) 21:10 UT, (**c**) 21:30 UT, and (**d**) 21:40 UT.