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Evolution of the 155 day periodicity in sunspot areas during solar cycles 12 to 21
Lean, Judith
AA(U.S. Navy, E. O. Hulburt Center for Space Research, Washington, DC)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 363, Nov. 10, 1990, p. 718-727. (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Solar Cycles, Sunspots, Evolution (Development), H Alpha Line, Solar Flares, Time Series Analysis
Bibliographic Code:


Sunspot area data during solar cycles 12-21 are examined with both periodogram and evolutionary spectral analysis techniques for evidence of a periodicity near 155 days. This periodicity is found to be present only during epochs of maxium activity, when it modulates the sunspot areas by as much as 15-20 percent of the amplitude of the 11 yr cycle. The 155 day periodicity typically occurs in episodes of from 1 to 3 yr, with sequential episodes often in opposite solar hemispheres; the strengths of these episodes appear to track the general level of solar activity. Comparing the phases of sinusoids fitted to the sunspot area data within individual solar cycles provides evidence for coherency within + or - 8 days of a period at 155 days between solar cycles 19, 20, and 21. However, within any one episode the actual period of the 155 day cycle may drift from 130 to 185 days.

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Database: Astronomy
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