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Description
Geomagnetic storms disturb the near-Earth space environment and induce geoelectric fields at ground level, posing risks to critical infrastructure. This study investigates the spatial and temporal structure of the geoelectric field (E-field) in south-southeast Brazil during the May 2024 geomagnetic storm, focusing on polarization effects and regional susceptibility to geomagnetically induced currents (GICs) in an area influenced by the South Atlantic Magnetic Anomaly (SAMA). We used geomagnetic data from three ground-based stations: the principal site SJG (L-shell=1.27), its near-magnetic conjugate, SJC (L-shell=1.17) and an intermediate station EUS, (L-shell=1.09). The SJC station samples geomagnetic field variations within the SAMA region, where the unique ionospheric conductivity pattern modulates magnetosphere-ionosphere coupling and leads to distinct geomagnetic responses between conjugate points. We estimated E-fields at 63 locations across the study region, using frequency-domain transfer functions derived from a regional conductivity model. The results highlight a clear preferred polarization of the E-field within two directional sectors: 74°-94° and 235°-255°, measured clockwise from geographic East. We conclude that ground infrastructure aligned along these orientations is significantly more exposed to GIC-driving geoelectric fields. Our analysis shows that the preferred polarization of the E-field is primarily governed by the local underlying conductivity structure, while amplitude differences are modulated by ionospheric dynamics, especially under SAMA influence. Spectral decomposition reveals that lower-frequency components dominate the hazardous E-field response. This directional and frequency-dependent characterization is crucial for identifying ground-level critical infrastructure most susceptible to GICs and for guiding mitigation planning in low-latitude regions affected by complex electrodynamic environments.
