Monitoring Ionospheric Changes on Horseshoe Island, Antarctica: A Case Study of the May 12, 2021 Geomagnetic Storm

The high-latitude ionosphere is one of the most susceptible regions to energetic particle precip- itation resulting from solar activities and geomagnetic storms, primarily due to open magnetic field lines. This vulnerability renders every study conducted in the region both critical and characteristic. In this context, ionospheric variations over the polar region are systematically monitored using data from the TUR1 GNSS station, operated within the Turkish Scientific Re- search Camp located on Horseshoe Island, Antarctica. This study focuses on the geomagnetic activity event recorded on May 12, 2021 (DOY 132), during the ascending phase of the onset of Solar Cycle 25. Within the scope of the study, Total Electron Content (TEC) estimations were performed using high-resolution RINEX observation data obtained from the TUR1 sta- tion, and ROTI (Rate of TEC Index) values—a key indicator of ionospheric irregularities were calculated. Through the analysis of the DOY 132 case, electron density fluctuations occurring in the ionospheric F layer due to the geomagnetic storm and the impact of these fluctuations

on GNSS signal quality were investigated. Furthermore, the hardware performance and signal tracking sensitivity of the TUR1 station were evaluated based on the variations in the Signal- to-Noise Ratio (SNR) recorded during the storm. The results demonstrate that on DOY 132, when the Kp index reached 4+, significant increases and abrupt fluctuations in TEC values were observed compared to quiet days. These findings confirm that the TUR1 station clearly captured the increase in local ionospheric electron density (positive ionospheric storm effect) at the onset of the geomagnetic disturbance and possesses sufficient sensitivity to detect micro- scale ionospheric turbulence. Consequently, it has been verified that the data provided by the TUR1 station constitutes a reliable, sustainable, and scientifically high-quality resource for space weather monitoring activities in the region.

“This study was supported by projects numbered “124G057” and “118Y322” within the scope of TÜBİTAK Kutup (Polar) 1001 program.” The authors thanks TUBITAK for their support.

Keywords: Ionosphere, Total Electron Content (TEC), Geomagnetic Storm, GNSS