Global ionospheric equivalent current response to a solar flare event.

This article focuses on analyzing the global ionospheric equivalent current response to the solar flare event on October 28, 2021, using a novel low-rank approximation analysis combined with Helmholtz decomposition. The study introduces the Euler potential method to interpolate geomagnetic disturbance data, reducing fitting errors by ensuring the divergence of the geomagnetic perturbation field is near zero. Results show that during the solar flare, the divergence-free component of the ionospheric current, primarily from the E-region, intensified significantly without major structural changes, while the curl-free component, representing F-region field-aligned currents, also increased and exhibited distinct flow patterns connecting hemispheric current vortices. This approach provides a clearer separation of ionospheric current components and their respective impacts on ground geomagnetic disturbances during solar flare events.