Acceleration mechanism responsible for the formation of the new radiation belt during the 2003 Halloween solar storm

Observations of the relativistic electron flux increases during the first days of November, 2003 are compared to model simulations of two leading mechanisms for electron acceleration. It is demonstrated that radial diffusion driven by ULF waves cannot explain the formation of the new radiation belt in the slot region and instead predicts a decay of fluxes during the recovery phase of the October 31st storm. Compression of the plasmasphere during the main phases of the storm created preferential conditions for local acceleration during interactions with VLF chorus. Local acceleration of electrons at L = 3 is modelled with a 2-D pitch-angle, energy diffusion code. We show that the energy diffusion driven by whistler mode waves can explain the gradual build up of fluxes to energies exceeding 3 MeV in a new radiation belt which is formed in the slot region normally devoid of high energy electrons