Dynamics of Equatorial and Low-Latitude TEC Fluctuations during the April 2023 Geomagnetic Storm

This study investigates the ionospheric response to the April 2023 geomagnetic superstorm by analyzing Total Electron Content (TEC) variations over equatorial and low-latitude regions. TEC data derived from GNSS were processed and compared with estimates from the NeQuick model. Geomagnetic indices (Dst, AE, Kp), magnetometer data, and thermospheric $${{\text{O}} \mathord{\left/ {\vphantom {{\text{O}} {{{{\text{N}}}_{2}}}}} \right. \kern-0em} {{{{\text{N}}}_{2}}}}$$ ratios from GUVI/TIMED observations were used to track storm-time ionospheric changes. TEC was computed from dual-frequency GNSS signals, corrected for biases, and validated using statistical metrics such as RMSE and the Pearson correlation coefficient (R), which ranged from 0.66 to 0.96 across stations and storm phases. The study found both positive and negative storm-time ionospheric effects, with significant regional differences. A notable depletion in the $${{\text{O}} \mathord{\left/ {\vphantom {{\text{O}} {{{{\text{N}}}_{2}}}}} \right. \kern-0em} {{{{\text{N}}}_{2}}}}$$ ratio corresponded with TEC decreases, emphasizing thermosphere-ionosphere coupling during disturbed periods. This integrated observational and model-based approach highlights complex ionospheric dynamics triggered by geomagnetic superstorms and the value of multi-instrument analysis in space weather research.