Solar Energetic Particle Spectral Breaks

The five large solar particle events during October–November 2003 presented an opportunity to test shock acceleration models with in‐situ observations. We use solar particle spectra of H to Fe ions, measured by instruments on ACE, SAMPEX, and GOES‐11, to investigate the Q/M‐dependence of spectral breaks in the 28 October 2003 event. We find that the break energies scale as (Q/M)b with b ⩽ 1.56 to 1.75, somewhat less than predicted. We also conclude that SEP spectra >100 MeV/nucleon are best fit by a double power‐law shape.