Magnetospheric effects on high-energy solar particles during the 2012 May 17th event measured with the PAMELA experiment

The great challenge in constraining scenarios for solar energetic particle (SEP) acceleration is due to the fact that the signatures of acceleration itself are heavily modified by transport within interplanetary space. During transport, SEPs are subject to pitch angle scattering by the turbulent magnetic field, adiabatic focusing, or reflecting magnetic structures. Ground Level Enhancements (GLEs) provide an ideal way to study acceleration with minimal transport. In this work, we present a unique high-energy SEP observation from PAMELA of the 2012 May 17 GLE and interpret the observed pitch angle distributions as a result of local scattering (1 AU) by the Earth's magnetosheath.