Possible evidence of the resonant influence of solar forcing on the climate system

► The long-term SSN and rainfall variations were bound through a casual mathematical equation. ► Simultaneous presence of both external forcing and natural oscillations is a necessary condition. ► The yearly rainfall data for Fortaleza (Brazil) from 1849 up to 2010 were used for the analysis. ► Phase inversion in the interdecadal rainfall component is due to a period increase in SSN after 1950. ► Irregular phase shift in the decadal rainfall component is due to anharmonic character of SSN.