Tidal Forcing on the Sun and the 11-Year Solar-Activity Cycle

The hypothesis that tidal forces on the Sun are related to the modulations of the solar-activity cycle has gained increasing attention. The studies proposing physical mechanisms of planetary action via tidal forcing have in common that quasi-alignments between Venus, Earth, and Jupiter (V–E–J configurations) would provide a basic periodicity of ≈ 11.0 years able to synchronize the operation of the solar dynamo with these planetary configurations. Nevertheless, the evidence behind this particular tidal forcing is still controversial. In this context we develop, for the first time, the complete Sun’s tide-generating potential (STGP) in terms of a harmonic series, where the effects of different planets on the STGP are clearly separated and identified. We use a modification of the spectral-analysis method devised by Kudryavtsev ( J. Geod. 77 , 829, 2004 ; Astron. Astrophys. 471 , 1069, 2007b ) that permits us to expand any function of planetary coordinates in a harmonic series over long time intervals. We build a catalog of 713 harmonic terms able to represent the STGP with a high degree of precision. We look for tidal forcings related to V–E–J configurations and specifically the existence of periodicities around 11.0 years. Although the obtained tidal periods range from ≈ 1000 years to 1 week, we do not find any ≈ 11.0-year period. The V–E–J configurations do not produce any significant tidal term at this or other periods. The Venus tidal interaction is absent in the 11-year spectral band, which is dominated by Jupiter’s orbital motion. The planet that contributes the most to the STGP in three-planet configurations, along with Venus and Earth, is Saturn. An ≈ 11.0-year tidal period with a direct physical relevance on the 11-year-like solar-activity cycle is highly improbable.