Inner Magnetospheric Convection Electric Fields and Corresponding Geomagnetic Indices During High-Speed Solar Wind Streams

Enhancements of large-scale convection electric fields in the inner magnetosphere, likely linked to low-latitude penetration electric fields in the ionosphere, are key components of solar wind–magnetosphere–ionosphere coupling. These fields reflect large-scale magnetosphere  convection induced by the solar wind and are known to influence various geomagnetic indices such as Kp, AU, and Dst. In this study, we examine large-scale electric fields observed by the Van Allen Probes, along with solar wind conditions and geomagnetic indices, during 191 isolated high-speed solar wind events from October 2012 to August 2019. We find that the strength of the electric field within L-shells less than 5.5 increases with both solar wind speed and the southward component of the interplanetary magnetic field, while solar wind density has little effect. Superposed epoch analysis reveals that the penetration depth of the convection electric field increases with solar wind speed. When solar wind speed exceeds 550 km/s, significant electric fields reach L ∼ 3. Statistical analyses show that the Kp, AU, and Dst indices exhibit an approximately linear relationship with electric field strength when Ey,RMS < 1mV/m. Above this threshold, the increasing rate in these indices decreases, indicating a nonlinear response of geomagnetic indices to stronger convection electric fields. Additionally, AU correlates approximately linearly with Kp, while Kp shows a roughly logarithmic relationship with Dst. These results confirm that magnetospheric convection significantly influences Kp, AU, and Dst, particularly under high-speed solar wind conditions.