Abstract:

The rapid rise of relativistic electron fluxes inside geosynchronous orbit during the January 10-11, 1997, CME-driven magnetic cloud event has been simulated using a relativistic guiding center test particle code driven by output from a 3D global MHD simulation of the event. A comparison can be made of this event class, characterized by a moderate solar wind speed (< 600 km/s), and those commonly observed at the last solar maximum with a higher solar wind speed and shock accelerated solar energetic proton component. Relativistic electron flux increase occurred over several hours for the January event, during a period of prolonged southward IMF B_z, more rapidly than the 1-2 day delay typical of flux increases driven by solar wind high speed stream interactions. Simulations of the January event captured the flux increase around L = 4 observed by GPS satellites, following the flux decrease associated with build up of the ring current. Analysis of ULF oscillations in the simulation data shows torroidal mode structure commensurate with electron drift periods in the 0.2 - 3.2 MeV energy range between L=3-9. Oscillations in the same frequency range seen in riometer and magnetometer data suggest that resonance with ULF oscillations may play a role in energizing relativistic electrons. The radial electric field component of torriodal oscillations at the electron drift period provides a mechanism for continuous acceleration of relativisitic electrons in the absence of a large inductive electric field impulse.