The May 2024 Geospace Superstorm and Its Impact on the Global Electric Circuit Worldwide

Abstract

In May 2024, a sequence of intense solar eruptions—including multiple M- and X-class flares and several coronal mass ejections (CMEs)—from solar active regions 3663 and 3664 triggered one of the most extreme geomagnetic storms of Solar Cycle 25. The storm produced a minimum disturbance storm-time index (Dst) of –406 nT and a peak interplanetary magnetic field (IMF) magnitude of $\sim$70 nT at the first Lagrangian point (L1). This event also generated a large Forbush Decrease (FD) in galactic cosmic rays and a Ground-Level Enhancement (GLE) of solar energetic particles, offering a unique opportunity to assess solar–terrestrial coupling through the Global Electric Circuit (GEC). %We analyzed fair-weather surface Potential Gradient (PG) data from twelve instruments distributed across seven stations worldwide, spanning different geomagnetic latitudes. The datasets were filtered for meteorological effects and normalized using standardized background values. To interpret the geomagnetic influence, we applied the Weimer empirical model to compute the ionospheric cross-polar-cap potential. Statistical analyses, including Welch’s two-sample t-tests, were performed to identify significant PG anomalies relative to quiet conditions. Our results reveal a sharp PG decrease coincident with the interplanetary shock arrival, followed by multi-day PG enhancements correlated with the FD amplitude. The PG increase magnitude scaled with cosmic-ray flux reduction, confirming the influence of reduced atmospheric conductivity on the GEC. The observed responses vary with geomagnetic latitude, suggesting a combined role of ionospheric electric field and conductivity modulation. This study provides the first global assessment of GEC perturbations during the May 2024 geospace superstorm and demonstrates that combined solar wind, geomagnetic, and cosmic-ray drivers jointly shape near-surface atmospheric electricity. We analyzed fair-weather surface Potential Gradient (PG) data from twelve instruments across seven stations worldwide, spanning a broad geomagnetic-latitude range, and air-Earth current density ($J_z$) data from one instrument. Data were screened using strict meteorological criteria, and anomalies were computed in physical units relative to station-specific non-geostorm diurnal backgrounds (all non-geostorm days in May 2024). To interpret geomagnetic forcing, we applied the Weimer empirical model to estimate ionospheric cross-polar-cap potential. Statistical inference used moving-block bootstrap tests (6 h blocks) with Holm correction for multiplicity. Results show an early PG decrease near interplanetary shock arrival, followed by day-dependent behavior during the Forbush-decrease interval, including multi-station positive phases but with heterogeneous station-level responses, with robust effects limited to a subset of station/day comparisons after multiplicity correction. Effect magnitudes and directional coherence are consistent with combined electrodynamic forcing and conductivity modulation, with sensitivity varying by location. This study provides a global assessment of GEC perturbations during the May 2024 superstorm and indicates that solar-wind, geomagnetic, and cosmic-ray variability likely jointly modulate near-surface atmospheric electricity.