The asymmetry of the solar cycle: A result of non-linearity

The paper presents a numerical analysis of Wolf sunspot numbers, with emphasis being laid on the asymmetry of the cyclic variation. To that purpose we have used the standard tables of monthly numbers and, in addition to the Fourier transform, we have done an overall analysis of the trend around each maximum. Many of these maxima present an asymmetry, and sometimes the presence of two maxima is evident. The non-linear RLC van der Pol model suggested by Polygiannakis and Moussas [Polygiannakis, J.M., Moussas, X. A nonlinear RLC solar cycle model. Solar Physics 163, 193–203, 1996] can explain many features of the observed asymmetries. Our analysis shows that a consistent deconvolution in two Gaussian curves is possible for each maximum. We may presume that the observed sunspot time series includes a hidden complex structure. This could give some hints of a behavior typical for coupled non-linear oscillators. It is a matter of further interpretations. whether such “oscillators” are just a simple approximation of a much complex phenomenon, or are a sign of another more physically based model like the dynamo model (or other models).