Cyclicity of Solar Activity

Figure 1
[7]  It is accepted to call solar activity the entire set of phenomena in the solar atmosphere that change its radiation in various ranges of electromagnetic waves and various-energy particle fluxes. In the optical range these changes are exhibited basically in the change of the number of various solar structures; they are almost invisible in the optical radiation (~0.1%). However, in soft X rays these changes are observable both in the number of structures and in radiation: the difference in the "background'' radiation level in the 1-8 Å range (1-12.5 keV) at the solar activity maximum and minimum exceeds two orders of magnitude (more than 100 times). The solar activity state is characterized by some observational indices; of these, the longest time series exists for the relative sunspot number ( W ) introduced for the first time by R. Wolf. This index was determined on a regular basis at first in Zürich and since 1849 until now in Brussels. This year may be considered as the beginning of scientific observations of the Sun. In addition, Wolf restored monthly average values of the given index since 1749 and annual averages since 1700 using rather fragmentary data of individual European observers. Using literary data of occasional telescopic observations, modern explorers have managed to qualitatively prolong this series to 1611. The reliability of all retrieved data is low; they enable us only to see a hint that the cyclic solar activity existed also at that time. One of the most remarkable features of the Sun are nearly-periodic changes of intensity or number of different manifestations of solar activity (SA)--solar activity cycles. For the first one, the cycle that began in March 1755 is conventionally adopted. Figure 1 shows the entire known series of relative sunspot numbers since 1610 until present; the confidence of the observational data is shown graphically; crosses: isolated observations (qualitative estimate), light-gray curve: low veracity; darker curve: reliable data. It should be noted that the analysis and comparison of Wolf number series for the periods 1749-2006 (numbered series) and 1849-2006 (reliable series) has shown obvious differences in the positions and magnitudes of the fundamental harmonics and spectral parameters of these series. In addition, the comparison of the series infers:

[8]  All this puts in question the correctness of using the retrieved part of the series in the majority of applications. In other words, to study the effect of solar activity on various long-term processes, one can use only the reliable series of Wolf numbers (1849-2006), from the middle of cycle 9 to cycle 23 of solar activity. The small statistics of reliable solar cycles (14) and absence of a physical model of a solar cycle development puts so far insuperable barriers to the reliability of solar cycle prediction prior to its beginning. However, the situation changes with the beginning of a new cycle: after 18-24 months of its development, it is already possible to determine its height, the epoch of its maximum, and probable duration of the current solar cycle. For the last two cycles the most successful prediction of the solar cycle development its beginning was done by the Waldmeier method and by the method of solar cycle sets similarity proposed by the author [Ishkov, 2003, 2005]. Table 1 lists the characteristics of all "numbered'' solar cycles.

Figure 2
[9]  Almost eleven years of the development of the current cycle 23 (Figure 2) have completely uncovered its characteristics and the majority of features of its evolution. The current cycle is the second component of the physical 22-year solar cycle, and the greatest surprise was that, contrary to the Gnevyshev-Ol' rule, the trailing odd cycle 23, for the first time in the entire realistic (since 1849) history of the research of solar cycles, has become smaller than the leading even cycle 22. The main stages of the current solar cycle development [Ishkov, 2005] are as follows:


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