Solar Energetic Particle Spectral Breaks

Details Solar Energetic Particle Spectral Breaks Solar Energetic Particle Spectral Breaks

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsh41a..10m&link_type=abstract

American Geophysical Union, Spring Meeting 2008, abstract #SH41A-10

Physics

2114 Energetic Particles (7514), 7514 Energetic Particles (2114), 7807 Charged Particle Motion And Acceleration, 7845 Particle Acceleration, 7859 Transport Processes

Scientific paper

A new generation of instruments during solar cycle 23 made it possible to measure solar energetic particle (SEP) energy spectra for many species over a broad energy interval (~0.1 to ~100 MeV/nucleon). These observations revealed that most large SEP events have power-law spectra below a few MeV/nucleon with rather hard spectral indices, followed by spectral steepening at higher energies. These spectral breaks are ordered by species - the spectra of lighter elements break at higher energy/nucleon than those for heavier species. To understand the charge-to-mass (Q/M) dependence of these spectral breaks, we have located the breaks for a range of species (e.g., H, He, C, N, O, Ne, Mg, Si, and Fe) and correlated the break locations with either measured or average Q/M ratios. As of this writing there are results for 13 large SEP events, based on data from ACE, GOES, SAMPEX, and STEREO, and charge state data from SAMPEX and ACE. We find that the location of the breaks is generally well-represented by a power-law in Q/M. This power-law fit can be related to the Q/M- dependence of the interplanetary diffusion coefficient and to the turbulence spectrum of the interplanetary magnetic field. We find that the slope of the deduced turbulence spectra are correlated with Fe/O and the proton fluence. These results support the idea that proton-amplified Alfven waves are generated in large SEP events, as expected for acceleration at parallel shocks.

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