Magnetospheric Effects on High Energy Solar Particles: PAMELA Measurements

Abstract:

Solar Energetic Particles (SEPs) are thought to be accelerated at the Sun by solar flares or by the shocks formed by Coronal Mass Ejections (CMEs). Even more elusive is the origin of the highest energy SEPs in so-called Ground Level Enhancements (GLEs). At these energies, the effects of transport are often minimal, providing an opportunity to investigate the problem of particle acceleration. However, the effects of transport en route to Earth often obscure the acceleration process(es). The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument provides new data that aid in separating the effects of acceleration and transport. Furthermore, PAMELA bridges a critical gap in energy between the low-energy space-based and highest-energy ground-based measurements. We report on recent PAMELA observations of high-energy SEPs and illustrate some of the governing effects of acceleration and transport with the first GLE of solar cycle 24, i.e., 2012 May 17. The PAMELA data of 2012 May 17 reveal two distinct spectral components, a low-energy SEP component that exhibits significant scattering or redistribution, accompanied by a high-energy component that reaches the Earth relatively unaffected by dispersive transport effects. We postulate that the scattering or redistribution at low energies takes place locally providing one of the first opportunities to witness the effects of SEP transport in the Earth's magnetosheath.