The role of inductive electric fields in shaping and stabilizing the ring current

A comprehensive understanding of particle acceleration and transport throughout the terrestrial magnetosphere hinges on accurate characterization of the governing electromagnetic fields. While the configuration of the magnetic field controls particle drift motions, the electric field determines the large-scale transport, energization, and particle access to different magnetospheric regions.

Although a wide range of magnetic field models exists, from idealized analytical descriptions to empirical reconstructions and self-consistent numerical simulations, representations of the magnetospheric electric field remain comparatively underdeveloped. Most commonly used electric field models are empirical and assume quasi-static conditions, often derived by mapping the solar wind dawn–dusk electric field into the polar ionosphere. Such formulations, however, omit the inductive electric field produced by the omnipresent temporal variations in the magnetic field. These inductive fields are inherently dynamic and pervasive throughout the magnetosphere, and their omission from regional and global magnetospheric models limits the model performance and misrepresents the modeled particle dynamics.

In this study, we assess the influence of inductive electric fields on particle acceleration and transport using test-particle simulations within a global MHD framework that enables decomposition of the electric field into distinct source contributions (potential and inductive sources). Simulations excluding the inductive component exhibit enhanced inward penetration of energetic particles, deformation of the Alfvén layer, and efficient particle loss along open drift trajectories toward the dayside. Conversely, inclusion of both inductive and electrostatic electric fields results in stronger particle confinement and a more stable ring current. Together, these results underscore the essential role of inductive electric fields in shaping inner magnetospheric dynamics and sustaining energetic particle populations in the region.