Impact of the October 2024 G4 geomagnetic storm on GNSS performance: observations and physical mechanisms

Based on kinematic precise point positioning (PPP) and three-dimensional ionospheric tomography (3D-CIT) techniques, this study systematically analyzes the spatiotemporal characteristics of positioning performance degradation across approximately 520 global GNSS stations during the severe G4-level geomagnetic storm of 10–11 October 2024, and further investigates the underlying physical driving mechanisms in the American sector. The analysis of global positioning performance reveals that degradation is most pronounced at high geomagnetic latitudes, where the peak values of three-dimensional root-mean-square error (3D-RMS), rate of TEC index (ROTI), and cycle slips reach 27.5 cm, 0.75 TECU/min, and 6.3 occurrences, respectively. Further investigation of physical processes in the American sector identifies two major types of ionospheric disturbances. During the middle stage of the main phase, 3D-CIT reconstructs the three-dimensional structure of a storm-enhanced density (SED) plume over North America, formed by the rapid sunward transport of high-density mid-latitude plasma. During the late main phase, multi-source observations integrating ROTI, ionosonde, and magnetometer data reveal equatorial plasma bubbles (EPBs) and associated small-scale irregularities near the low-latitude magnetic equator in the Central American region, triggered by a post-sunset prompt penetration electric field (PPEF) on the low-latitude nightside. These disturbances significantly exacerbate localized positioning performance degradation in the American sector. Their impacts are mainly manifested as plasma irregularities induced by strong electron density gradients and boundary instabilities during SED plasma transport, as well as EPB-related irregularities generated by the Rayleigh–Taylor instability, triggered by enhanced E×B vertical drift under the influence of the low-latitude nightside PPEF.