Possible evidence of the resonant influence of solar forcing on the climate system
- a IKI RAS, 84/32 Profsoyuznaya Str, 117997 Moscow, Russia
- b UNITAU, 432 rua 04 de Março, 12020-270 Taubate, SP, Brazil
- Received 20 June 2011. Revised 15 January 2012. Accepted 22 January 2012. Available online 31 January 2012.
An assumption of the existence of natural climatic oscillations driven by solar activity enables an explanation of phase differences between variations in solar activity and rainfall level in Fortaleza, Brazil. Decadal and interdecadal variations in rainfall level can be reproduced using a forced oscillation equation with a driving force term that describes the variation in the sunspot number and with the assumption of the existence of 31.7-year interdecadal and 12.96-year decadal natural climatic oscillations. This equation satisfactorily reproduces the periodicity with a length of approximately 22 yr in the interdecadal rainfall variation before and up to the middle of the past century as well as the subsequent phase inversion, period and amplitude increase in the variation that followed the corresponding increases in the interdecadal sunspot number variation. The equation accurately reproduces the irregular phase shifts between decadal variations in rainfall level and in sunspot number over the entire 160 yr of recorded observations.
► The long-term SSN [sunspot number] 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.
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