In addition to the 11 year sunspot cycle, there are two other short cycles that are picked up by scientific analysis. It is suggested that low solar cycle 24 is the result of being at the low end of the de Vries cycle. The last minimum of this magnitude was the Dalton minimum, and that was 205 years ago.
http://wattsupwiththat.com/2010/02/0...cle-24-update/
You can see that cycles 22 and 23 is similar to cycles 3 and 4 - just before the Dalton Minimum.
The next previous incident of the 205 de Vries cycle was at the beginning of the Maunder Minimum. The Maunder minimum must have coincided with both the de Vries cycle minimum and another longer wave cycle. What is happening now only occurs every 205 years.
In the 14C record, which extends back for 11500 years, the principal periodicity determined by frequency analysis is that of the 205-year de Vries cycle, though the 2300-year Hallstatt cycle is also present (Beer 2000). The de Vries cycle is also prominent in the 10Be record, which Clilverd et al. do not exploit. Over the last decade, 10Be abundances have been measured in ice cores from Greenland, yielding a proxy record that so far extends back for 50000 years (see figure 1b). Statistical analysis of this rich data set (Wagner et al. 2001) reveals a significant peak in the power spectrum at a 205-year period that is definitely solar in origin (see figure 2).
http://www.blackwellpublishing.com/p.../aag_45206.htm
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Originally Posted by KJ6BSO
