ON THE PERIODICITIES IN THE SOLAR-CYCLE

The existence of a periodic variation in the sunspot number has been recognized for many years, but other periodicies than the 11.1 years one is still an open question. The power spectrum of the International sunspot number is compared with the power spectra for the same period in which the values have been taken randomly inside the error bars. More than fifty artificial sunspot cycles over a 241 years period were thus calculated. The major fact is that only a few periodicities (other than the 11 years) peak noticeably. The consequences for the future or for the reconstruction of past solar cycles are presented including the Maunder Minimum - Little Ice Age correlation. It is concluded that Fourier analysis allows the construction of a model of the Sun activity (80% can be modelled with about 8 lines), but, whatever the technique used, it is not suitable for accurate short term predictions. For long term, the models failed which is probably due to an amplitude-modulation of the sine waves.