Ionospheric Response to the Severe Geomagnetic Storm of 19–21 January 2026 over Almaty (Kazakhstan) According to the Digisonde and GPS Data

We present observations of the ionospheric response to the severe geomagnetic storm of 19–21 January 2026, obtained using a Digisonde DPS-4D and GPS-based vertical Total Electron Content (TEC) measurements over Almaty, Kazakhstan. Solar wind parameters, geomagnetic indices (AE and SYM-H), and Interplanetary Magnetic Field (IMF) components were analyzed to characterize the storm drivers. The ionospheric response to the geomagnetic storm of 12–13 November 2025 was additionally analyzed to provide an overall picture of the ionospheric effects within the specified latitude–longitude region. The evolution of the ionospheric disturbances revealed highly complex processes. The critical frequency and total electron content during the severe geomagnetic storms exhibited morphological similarities, reflecting a general response to geomagnetic storms, as well as notable differences in their storm-time responses and in the observed percentage deviations of foF2 and TEC relative to reference-day baselines. A combined observational approach provides a more complete picture of the ionospheric response during extreme space weather events.