The ionospheric total electron content and thermospheric winds during weak geomagnetic disturbances in January 2024

Geomagnetic activity is often ignored in understanding the ionospheric day-to-day variability during quiet times. The maximum daily mean K_p was 1.75 (maximum K_p3h = 3.3) on January 12–26, 2024. When the weak geomagnetic activities were enhanced, the ionospheric total electron content (TEC) decreased remarkably from the post-midnight to dawn sectors around the Weddell Sea Anomaly region (0°–90°W and 60°–80°S), and the disturbance amplitude attained ~20 TEC units around 4 local time. Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellite observations showed that the middle-latitude zonal winds became more westward, with the disturbance amplitude exceeding ~120 m/s in the post-midnight sector as the weak geomagnetic activity intensified. The interplanetary magnetic field B_z and B_y might jointly modulate polar convection to cause the changes in thermospheric dynamics. Zonal wind associated with the geomagnetic declination could almost account for the TEC oscillation around the Weddell Sea Anomaly. Results of this study indicate that weak geomagnetic disturbances during quiet times can cause huge ionospheric changes via dynamic processes and cannot be ignored.