Statistical Properties of Extreme Solar Activity Intervals

A study of long-term solar variability reflected in indirect indices of past solar activity leads to stimulating results. We compare the statistics of intervals of very low and very high solar activity derived from two cosmogenic radionuclide records and look for consistency in their timing and physical interpretation. According to the applied criteria, the numbers of minima and of maxima are 61 and 68, respectively, from the ¹⁰Be record, and 42 and 46 from the ¹⁴C record. The difference between the enhanced and depressed states of solar activity becomes apparent in the difference in their statistical distributions. We find no correlation between the level or type (minimum or maximum) of an extremum and the level or type of the predecessor. The hypothesis of solar activity as a periodic process on the millennial time scale is not supported by the existing proxies. A new homogeneous series of ¹⁰Be measurements in polar ice covering the Holocene would be of great value for eliminating the existing discrepancy in the available solar activity reconstructions.