Sunspot Count Periodicities in Different Zurich Sunspot Group Classes Since 1986
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We used two methods to investigate the periodic behavior of sunspot counts in four categories for the time period January 1986 – October 2013. These categories include the counts from simple (A and B), medium (C), large (D, E, and F), and final (final-stage; H) sunspot groups. We used i) the multitaper method with red noise approximation, and ii) the Morlet wavelet transform for periodicity analysis. Our main findings are that 1) the solar rotation periodicity of about 25 to 37 days, which is of obvious significance, is found in all groups with at least a 95 % significance level; 2) the periodic behavior of a cycle is strongly related to its amplitude and group distribution during the cycle; 3) the appearance of periods follows the amplitude of the investigated solar cycles; and that 4) meaningful periods do not appear during the minimum phases of the investigated cycles.
We would like to underline that the cyclic behavior of all categories is not exactly the same; there are some differences between these groups. This result can provide a clue for the better understanding of solar cycles.
KeywordsFrequency analysis: multitaper method Morlet wavelet analysis Sunspots: sunspot classification Sunspots groups Sunspot counts
The authors thank the anonymous referee for his/her useful comments and suggestions. The wavelet software was provided by C. Torrence and G. Compo, and is available at http://paos.colorado.edu/research/wavelets . We acknowledge usage of sunspot data from the National Geophysical Data Center. This study was supported by the Scientific Research Projects Coordination Unit of Akdeniz University through Project of 2012.01.0115.008.
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