On External Drivers of Sudden Increases of Energetic Electrons in the Quasi-Trapped Zone During Superstorms

A sudden increase in the flux of quasi-trapped energetic electrons in the forbidden zone is known as the phenomenon of forbidden energetic electrons. The Energies characteristic of the enhanced electron fluxes are tens and hundreds of keV. The flux in the forbidden zone exceeds the background values of ~10 (cm s sr) by several orders of magnitude and can reach 10 (sm s sr) during powerful storms. The mechanism of increases in quasi-trapped electron fluxes is still not entirely clear. The probability of flux enhancements displays an ambiguous dependence on the level of geomagnetic activity. However, during extremely powerful magnetic storms with |Dst| ≥ 400 nT, this phenomenon is always observed. In this paper, we check the hypothesis of earthward fast transport of particles associated with the electrical drift. The flux enhancements during five superstorms in the period from 2000 to 2025 (March 31, 2001; October 29–31, 2003; November 20, 2003; November 7–10, 2004; and May 10–13, 2024) were selected for the analysis. The solar wind and interplanetary magnetic field parameters during superstorms were analyzed to determine the most probable external drivers of the ejection of electrons with energies of 30–300 keV. Strong increases of electron flux can be caused by sudden jumps (positive and/or negative) in the total plasma pressure, as well as by inhomogeneous magnetic structures with sharp boundaries (bends or rotations of the magnetic field vector, MHD discontinuities). The intervals of near-radial field can also be considered as suitable conditions for the flux enhancement events. The time of the electric drift and the electric field intensity required for a rapid particle transport into the quasi-trapped zone are estimated.