Particle transport and energization associated with substorms

Energetic particle flux enhancement events observed by satellites during su bstorms are studied by considering the interaction of particles with earthw ard propagating electromagnetic pulses of westward electric field and consi stent magnetic field of localized radial and azimuthal extent in a backgrou nd magnetic field. The energetic particle flux enhancement is mainly due to the betatron acceleration process: particles are swept by the earth-ward p ropagating electric field pulses via the E x B drift toward the Earth to hi gher magnetic field locations and are energized because of magnetic moment conservation. The most energized particles are those which stay in the puls e for the longest time and are swept the longest radial distance toward the Earth. Assuming a constant propagating velocity of the pulse, we obtain an alytical solutions of particle orbits. We closely examine substorm energeti c particle injection by computing the particle flux and comparing with geos ynchronous satellite observations. Our results show that for pulse paramete rs leading to consistency with observed flux values, the bulk of the inject ed particles arrive fi om distances of less than 9 R-E, which is closer to the Earth than the values obtained Ly the previous model (Li et al., 1998).