Impact of Induced Electric Fields Inside the Magnetopause on Magnetopause Shadowing of Radiation Belt Electrons

Abstract Loss of relativistic electrons with energies above 0.5 MeV through the magnetopause, commonly referred to as magnetopause shadowing, has been extensively investigated using both simulations and observations. However, direct and systematic observational evidence remains limited. In this study, we extend a previously developed magnetopause model by incorporating inward magnetopause motion, which generates induced electric fields within the boundary layer. These fields are amplified during compression and further enhanced by magnetic field strengthening on the magnetospheric side. Relativistic electrons (0.5–a few MeV) are influenced by the induced fields primarily through gyroradius reduction caused by energy loss and through drift toward the magnetosphere, both of which inhibit escape. Stronger electric fields extend the energy range of confined electrons toward higher energies. Depending on the local field geometry, the induced electric field can either accelerate or decelerate electrons. In contrast, ultra‐relativistic electrons (several MeV), with gyroradii comparable to the magnetopause thickness, are less affected and more likely to escape directly. When a finite magnetic field component normal to the magnetopause is present, electrons across a broad energy range (0.5–10 MeV) can escape efficiently, as this component guides their motion across the boundary and reduces sensitivity to the induced field. In such cases, energy variations still occur but become less significant with increasing normal component strength, owing to shorter residence times within the magnetopause.