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B. Bonev (Ritter Astrophysical Research Center, Univ. of Toledo)
A cycle search technique, called T-R Periodgram Analysis, is applied to two basic time series for solar activity: the Zurich series (International Sunspot Number) and the Schove series (after 296 AD). A criterion, based on Monte-Carlo procedure, for the statistical reliability of the quasi-periodicities is developed. The stability of the identified cycles is examined by testing different fractions from the time interval covered by the series. All observed cycles, except those with 11-year, quasi-century, and quasi-two century periods, turn out to be highly questionable. The interpretation of the long-term solar variability is far from simple. A 100-year cycle which satisfies the Monte-Carlo criterion is present only in the Zurich series data. The Schove series highlights the generally accepted quasi-two century cycle that is well defined and determines the long-term solar activity behavior after about 1000 AD. On the other hand, between 296 AD and 1000 AD stable and statistically reliable cycles are not identified and the variations are irregular rather than cyclic. Weak periodicities are present but well bellow the noise level. This modulation in the features of the solar variability indicated in the Schove series might be connected with the influence of a much longer periodicity than than those discussed here, in particular the possible 2400-year cycle.
The author(s) of this abstract have provided an email address for comments about the abstract: bbonev@astro1.panet.utoledo.edu