Characteristics of the Changes in the Induced Geoelectric Field Observed by the China Geoelectric Network During the Sudden Commencement of the Geomagnetic Storm on 10 May 2024

Geomagnetically induced geoelectric fields can exhibit substantial spatial variability because regional subsurface electrical structures affect surface electromagnetic responses. This study characterized the induced geoelectric field across mainland China during the extreme geomagnetic storm of 10 May 2024, using observations from the China Geoelectric Network. We evaluated changes in field intensity, ratios between collinear short- and long-dipole measurements, and regional variations in polarization direction, with particular emphasis on the onset of the storm. The geoelectric response showed pronounced spatial heterogeneity, with substantial differences among stations during storm onset. At most stations, measurements from collinear short and long dipoles maintained consistent ratios, indicating stable local scaling between the two electrode configurations. In contrast, polarization directions inferred from the long-dipole measurements showed no uniform relationship with local land–sea orientations. High-density electrical exploration data further supported this interpretation. These findings indicate that local subsurface electrical structures play an important role in controlling geoelectric field measurements and their responses to geomagnetic disturbances. This study provides a quantitative assessment of storm-time geoelectric field variations across mainland China and establishes a basis for investigating regional electromagnetic phenomena associated with induced geoelectric fields.