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In large SEP events, ions can be accelerated at CME-driven shocks to veryhigh energies. Spectra of heavy ions in many large SEP events show featuressuch as roll-overs or spectral breaks. In some events when the spectra areplotted in energy/nucleon they can be shifted relative to each other to makethe spectral breaks align. The amount of shift is charge-to-mass ratio (Q/A)dependent and varies from event to event. This can be understood if the spectraof heavy ions are organized by the diffusion coefficients (Cohen et al., 2005).In the work of Li et al. (2009), the Q/A dependences of the scaling is relatedto shock geometry when the CME-driven shock is close to the Sun. For eventswhere multiple in-situ spacecraft observations exist, one may expect thatdifferent spacecraft are connected to different portions of the CME-drivenshock that have different shock geometries, therefore yielding different Q/Adependence. In this work, we examine one SEP event which occurred on 2013November 4. We study the Q/A dependence of the energy scaling for heavy ionspectra using Helium, oxygen, and iron ions. Observations from STEREO-A,STEREO-B and ACE are examined. We find that the scalings are different fordifferent spacecraft. We suggest that this is because ACE, STEREO-A and STEREO-B are connected to different parts of the shock that have different shockgeometries. Our analysis indicates that studying the Q/A scaling of in-situparticle spectra can serve as a powerful tool to remotely examine the shockgeometry for large SEP events.

research in astronomy and astrophysics/research in astronomy and astrophysics

Probing shock geometry via the charge to mass ratio dependence of heavy  ion spectra from multiple spacecraft observations of the 2013 November 4  event