Space Climate 7 Meeting Abstract
Exploratory data analysis detects distinct length modes for the Schwabe cycle, in the new international sunspot number record
Jean-Guillaume RICHARD (Independent scholar)
Observed Schwabe cycle lengths are known to be poorly fitted by simple distribution models. Rudolf Wolf’s estimated range for the long-term mean of the Schwabe cycle’s length remains valid but, depending on estimates, the long-term median may have been far below or above this mean. With few observed cycles near the mean length, bimodality and multimodality are conceivable, but not proven, in cycle-length distribution. Time series analyses yield many estimates of peak frequencies in this quasi-decadal band, but the diversity of these results is difficult to interpret. Following Tukey, an exploratory data analysis approach is retained to identify the fine structure of the distribution of Schwabe cycle lengths. A simple algorithm, inspired by automated data-mining procedures, sequentially identifies distinct modes of decreasing frequency, for cycle lengths, in the new international sunspot number record’s 13-month running means series (1749-2018). The found sharp modal lengths consist in (a) the closely-packed triplet: 10.0 yr, 10.5 yr, and 11.25 yr, earlier found as peak frequencies in several time series analyses of this record, and (b) a longer isolated mode at 12.4 yr. The predominant frequency is found at 10.5 yr. The same procedure, applied to the same record smoothed otherwise, or to other records of solar activity, which either are much shorter (sunspot areas: since 1878) or exist in differing versions (sunspot groups), yields similar but less clear-cut results.
Mode of presentation: oral (Need to be confirmed by the SOC)