科研之友
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摘要
We have analyzed the similar to 20-320 keV nucleon-1 suprathermal (ST) heavy ion abundances in 41 corotating interaction regions (CIRs) observed by the Wind spacecraft from 1995 January to 2008 December. Our results are: (1) the CIR Fe/CNO and NeS/CNO ratios vary with the sunspot number, with values being closer to average solar energetic particle event values during solar maxima and lower than nominal solar wind values during solar minima. The physical mechanism responsible for the depleted abundances during solar minimum remains an open question. (2) The Fe/CNO increases with energy in the 6 events that occurred during solar maximum, while no such trends are observed for the 35 events during solar minimum. (3) The Fe/CNO shows no correlation with the average solar wind speed. (4) The Fe/CNO is well correlated with the corresponding upstream similar to 20-320 keV nucleon-1 Fe/CNO and not with the solar wind Fe/O measured by ACE in 31 events. Using the correlations between the upstream similar to 20-40 keV nucleon-1 Fe/CNO and the similar to 20-320 keV nucleon-1 Fe/CNO in CIRs, we estimate that, on average, the ST particles traveled similar to 2 au along the nominal Parker spiral field line, which corresponds to upper limits for the radial distance of the source or acceleration location of similar to 1 au beyond Earth orbit. Our results are consistent with those obtained from recent surveys, and confirm that CIR ST heavy ions are accelerated more locally, and are at odds with the traditional viewpoint that CIR ions seen at 1 au are bulk solar wind ions accelerated between 3 and 5 au.
- 出版日期2017-3-20
