<p>Using multi-source observational data from GPS receivers, magnetometers, Swarm satellites, and the GUVI/TIMED satellite, this study analyzed the ionospheric total electron content (TEC) response to a G5 geomagnetic storm of October 2024 across the American, European–African, and East Asian–Australian longitudinal sectors. The results reveal significant longitudinal-sector differences and north–south asymmetry in the global ionospheric response. Positive storms predominated in the American sector, associated with strong eastward prompt penetration electric field (PPEF), whereas the European–African and East Asian–Australian sectors were characterized primarily by negative storms driven by thermospheric O/N₂ depletion. The irregularity activity exhibited a clear latitudinal dependence: at high latitudes, the Rate of TEC Index (ROTI) reached values 5–6 times those of quiet periods, with the occurrence rate of ROTI &gt; 0.5 exceeding 70%. Combined analysis of GUVI/TIMED satellite and geomagnetic observation data indicated that the PPEF was the key driver of the initial TEC enhancement in the equatorial anomaly region. In contrast, thermospheric composition changes, specifically a decrease in the O/N₂ ratio, were the primary cause of the subsequent negative storms at middle and high latitudes. Thus, the spatiotemporal evolution of the ionospheric storm is attributed to the nonlinear coupling of multiple processes, including the global ring current, regional current systems, and background thermospheric circulation, which collectively produce pronounced longitudinal-sector variability.</p>