Abundances and Energy Spectra of Corotating Interaction Region Heavy Ions Observed During Solar Cycle 23

Details Abundances and Energy Spectra of Corotating Interaction Region Heavy Ions Observed During Solar Cycle 23 Abundances and Energy Spectra of Corotating Interaction Region Heavy Ions Observed During Solar Cycle 23

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...678.1458m&link_type=abstract

The Astrophysical Journal, Volume 678, Issue 2, pp. 1458-1470.

Astronomy and Astrophysics

Astronomy

20

Acceleration Of Particles, Ism: Cosmic Rays, Interplanetary Medium, Shock Waves, Sun: Solar Wind, Sun: Abundances

Scientific paper

Using instruments on the ACE spacecraft, we surveyed the heavy-ion spectra and composition over the range He-Fe for 41 corotating interaction regions (CIRs) during 1998-2007. Below ~1 MeV nucleon-1 the spectra are power laws in kinetic energy nucleon-1 with an average spectral index of 2.51+/-0.10, rolling over above ~1 MeV nucleon-1 to power-law spectra with an average index of 4.47+/-0.17. The spectral shapes for different species are similar, leading to relative abundances that are constant over our energy range, even though the intensities cover up to 8 orders of magnitude. Relative to oxygen, the measured abundances at 385 keV nucleon-1 for 4He, C, N, Ne, Mg, Si, S, Ca, and Fe are 273+/-72, 0.760+/-0.023, 0.143+/-0.005, 0.206+/-0.009, 0.148+/-0.006, 0.095+/-0.005, 0.028+/-0.002, 0.007+/-0.001, and 0.088+/-0.007, respectively. Except for an overabundance of 4He and Ne, the abundances are quite close to that of the fast solar wind. We have found 3He/4He ratios to be enhanced over solar wind values in ~40% of the CIRs. The Fe/O ratio in individual CIRs is observed to vary over a factor of ~10 and is strongly correlated with the solar wind Fe/O ratio measured 2-4 days preceding each CIR. Taken together with previous studies showing the presence of pickup He+ in CIRs, the observational data provide evidence that CIR energetic particles are accelerated out of a suprathermal ion pool that includes heated solar wind ions, pickup ions, and remnant suprathermals from impulsive solar energetic particle events.

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