Observations and modeling of energetic electron dynamics during the October 2001 storm

Abstract

We examined and simulated the dynamics of energetic electrons during the October 2001 magnetic storm with the relativistic RAM electron model for a wide range of energies. The storm had a rapid main phase followed by a day of strong geomagnetic activity that produced a second Dst minimum and then a very quiet recovery phase. During the main phase and the period of intense activity, the observed hot electron flux (E = 30 keV) increased at low L while decreasing at large L and then decayed abruptly at the beginning of the recovery phase when activity subsided. The flux of subrelativistic (E = 100–300 keV) electrons also increased at low L and decreased at large L during the main phase and the period of intense activity but remained high throughout the recovery phase. In contrast, the relativistic (E = 300–1200 keV) electron flux decreased during the main phase, remained low throughout the period of intense activity, and then increased above prestorm values during the recovery phase in spite of the low activity. The highest energy electron flux (E > 1200 keV) decreased during the main phase and never recovered to prestorm levels. The numerical simulation was compared with observations. We identified the physical processes which produce the flux variations at the different energies. In the simulation, the hot electrons were convected inward during the main phase, reproducing the observed local time flux asymmetry. The higher‐energy electrons, on the other hand, were predominantly transported inward by radial diffusion and not convective motion. The simulation was not able to reproduce the subrelativistic and relativistic electron flux enhancement and spatial expansion as observed during the recovery phase. In the simulation, most of the energization occurred around the main phase and the period of intense activity with negligible transport or flux enhancement during the recovery phase. The discrepancy between the observed and simulated high energy electron flux suggests that only convective transport and radial diffusion cannot fully explain the electron dynamics. An additional mechanism may be necessary to explain enhancements of high energy electron flux during the recovery phase of the storm.