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Solar cycle

On July 1st, 2015, the World Data Centre for Sunspot Index and Long-term Solar Observations (WDC-SILSO) service operated by the Royal Observatory of Belgium released a new series of monthly sunspot numbers dating back to the year 1749. Inhomogeneities in earlier versions of the data are corrected in this new release (version Nb.2.0). The data are publicly and freely available from the WDC-SILSO website http://sidc.be/silso/datafiles.


This series is analyzed using circular analysis to determine the periodicity of the occurrence of solar maxima. The circular analysis is combined with spiral graphs to provide a single visualization, simultaneously showing the periodicity of the series, the degree to which individual cycle lengths deviate from the average period, and differences in levels reached during the different maxima.

The methods and results are discussed in :
Buelens, B. (2016). Visual circular analysis of 266 years of sunspot counts. Big Data, 4(2): 89-96. DOI: 10.1089/big.2015.0055

Code to compute the spiral visualization is available on github.