A calculation of energetic proton spectra producedat substorm onset in the fields of the explosive reconnection model

Impulsive bursts are observed throughout the magnetosphere at the onset of the expansive phase of geomagnetic storms are sudden enhancements of the energetic particle flux. The model fields of the explosive reconnection model (Coroniti, 1985) is used to calculate impulsive burst particle spectra from an observing satellite's perspective. The explosive reconnection model evolves toward a steady state reconnection, determining the maximum particle energy gain. A satellite detector's location and time with reference to, respectively, the x-lines's location and temporal evolution, are important factors determining the characteristics of the observed burst spectrum. Therefore burst spectra are computed by approximating the averaging in energy and solid angle of an actual detector. The most energetic spectra are calculated after reconnection has reached a steady rate at onset. Plasma in the diffusion layer is heated by the current sheet acceleration mechanism. This heated plasma is not observed outside the diffussion region, near the separatrix, where only the most energetic particles have had time to reach after current sheet ejection. Particles gaining the most energy are accelerated in the diffusion region where the components of the magnetic field normal to the neutral sheet is small, allowing particles to stay in the region for relatively long periods of time. The particles are eventually turned perpendicular to the x-line by the normal component. These resonant particles originate in denser phase space volumes than unaccelerated particles and, hence, can enhance the distribution junction at the satellite. Energetic particle fluxes at the satellite are enhanced only if adequate numbers of the incident particles were accelerated along the x-line. It is found that spectra consistent with observations are obtained for a model detector positioned far enough from the x-line that the impinging resonant particle flux is aligned along the magnetic field.