Power Law Distributions of Suprathermal Ions in the Quiet Solar Wind

At energies above the bulk solar wind and pick-up ion cutoff, observations reveal an interplanetary suprathermal ion population extending to ∼1 MeV/nucleon and even higher energies. These suprathermal ions are found under a wide variety of conditions including periods when there are no obvious nearby accelerating shocks. We review the observational properties of these ions in quiet solar wind periods near 1 AU, including transient Corotating Interaction Region (CIR) events, and other, quieter periods in between transient enhancements. The particle energy spectra are power laws close to E−1.5 in the range above the solar wind, rolling over at energies of a few hundred keV/nucleon to a few MeV/nucleon. Although the C/O and Fe/O ratios of the tails is close to that of the solar wind, pickup ions and 3He found in the tails indicate sources distinct from the solar wind. We briefly review several mechanisms that have been proposed to explain these ions.

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