This study investigates the ionospheric response in the Southern and Northern Hemispheres over the period from 25 December 2024 to 7 January 2025. A major geomagnetic storm occurred on 1 January 2025, following the consecutive solar wind eruptions on 29–31 December 2024 and 1 January 2025. Global geomagnetic activity monitoring data showed that the Kp index surged to 8+, indicating the occurrence of this major geomagnetic storm. By analyzing the ionosonde, GNSS-TEC, and satellite in situ detection data from Learmonth, Australia (−21.8° N, 114.1° E), as well as Wake Island (19.29° N, 166.65° E), we found that the ionospheric anomalies in the two regions exhibited different patterns. The ionospheric parameters in Learmonth changed much more severely than those in Wake Island in the Pacific region. Relative to normal conditions, the disturbed ionosphere over Learmonth during 1–3 January 2025 exhibited a strong negative storm phase: foF2 decreased by 31.4%, TEC dropped by 27.17%, and M3000F2 declined by 41.2%, while hmF2 increased by 5.2%. This work provides an analysis of the differences in the ionosphere between the Northern and Southern Hemispheres affected by geomagnetic storms in late 2024. These findings highlight the need to incorporate hemispheric asymmetry into ionospheric dynamics models.
Wang et al. (Mon,) studied this question.