科研之友
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摘要
We have surveyed the heavy ion composition of corotating interaction regions (CIRs) over the recent solar minimum and combined this with our earlier survey to cover the 1998-2011 period encompassing a full solar cycle and onset of the new cycle. We find that the solar minimum CIR intensities and spectral forms are similar to those in active periods, indicating that the basic acceleration mechanism does not vary with solar activity for energies below a few MeV nucleon(-1). However, the heavy ion abundances show a clear correlation with sunspot number, where heavy ions are more enhanced during active periods. Over the mass range He-Fe, the enhancement is organized by a power law in Q/M with exponent - 1.9, with Fe/O varying by a factor of similar to 6. During solar minimum CIR Fe/O was similar to 0.05, well below the corresponding solar wind ratio. Previous studies have shown that rare ions (He+, He-3) enhanced in CIRs come from the suprathermal ion pool. The observations presented here extend this evidence, indicating that in addition to rare He+ and He-3 the CIR major heavy ion species are accelerated out of the suprathermal ion pool, not the bulk solar wind.
- 出版日期2012-4-1
