Global ionospheric equivalent current response to a solar flare event

In this work, the low-rank approximation analysis is used to study the global ionospheric equivalent current response to a solar flare event on October 28, 2021. This study developed a method of fitting geomagnetic disturbance data with Euler potential, making the divergence of the fitted geomagnetic disturbance field as close to zero as possible. The global ionospheric equivalent current in the ionospheric E-region is decomposed into the Helmholtz components, where the divergence-free current had a greater impact on the geomagnetic field and had two current vortices flowing in opposite directions in the northern and southern hemispheres, respectively, which was similar to the characteristics of the solar quiet current studied using the spherical harmonic analysis in the past. The curl-free current had a smaller impact on the geomagnetic field and connected the two current vortices in the northern and southern ionospheric E-region. During a solar flare eruption, the overall structure of the global ionospheric equivalent current was not significantly different from that during quiet periods, but the current intensity increased significantly due to the increase in ionospheric conductivity caused by the solar flare.