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The Sun’s magnetic (Hale) cycle and 27 day recurrences in the aa geomagnetic index
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Chapman, Sandra C., McIntosh, S. W., Leamon, R. J. and Watkins, Nicholas W. (2021) The Sun’s magnetic (Hale) cycle and 27 day recurrences in the aa geomagnetic index. Astrophysical Journal, 917 (2). 54. doi:10.3847/1538-4357/ac069e ISSN 0004-637X.
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Official URL: https://doi.org/10.3847/1538-4357/ac069e
Abstract
We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 yr Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSNs) since 1818. The occurrences of solar maxima show almost no discernible Hale cycle dependence, consistent with the clock being synchronized to polarity reversals. We reengineer the Sargent R27 index and combine it with our epoch analysis to obtain a high time resolution parameter for 27 day recurrence in aa, 〈acv(27)〉. This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high-speed streams, is fast, with an upper bound of a few solar rotations. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd. Galactic cosmic ray flux rises in step with 〈acv(27)〉 but then stays high. Our analysis also identifies a slow-timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow-timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.
| Item Type: | Journal Article | ||||||
|---|---|---|---|---|---|---|---|
| Subjects: | Q Science > QB Astronomy | ||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||
| Library of Congress Subject Headings (LCSH): | Solar cycle, Solar magnetic fields , Hilbert transform | ||||||
| Journal or Publication Title: | Astrophysical Journal | ||||||
| Publisher: | IOP Publishing | ||||||
| ISSN: | 0004-637X | ||||||
| Official Date: | 17 August 2021 | ||||||
| Dates: |
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| Volume: | 917 | ||||||
| Number: | 2 | ||||||
| Article Number: | 54 | ||||||
| DOI: | 10.3847/1538-4357/ac069e | ||||||
| Status: | Peer Reviewed | ||||||
| Publication Status: | Published | ||||||
| Reuse Statement (publisher, data, author rights): | This is an author-created, un-copyedited version of an article accepted for publication/published in Astrophysical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.3847/1538-4357/ac069e | ||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||
| Date of first compliant deposit: | 8 July 2021 | ||||||
| Date of first compliant Open Access: | 17 August 2022 |
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