An overview of the planetary theory of solar activity variability and its importance for understanding climate oscillations

The complex dynamics of solar activity appear to be controlled by a number of individual oscillations from the monthly to the millennial scales, the most well-known of which is the 11-year Schwabe sunspot cycle. These oscillations are important also because many of them characterize the oscillations found in the climate of the Earth and could be used for climate change forecast purposes. However, the physical cause of the solar oscillations is still debated. Commenting on the origin of the 11-year sunspot cycle, Johann Rudolf Wolf (1859, MNRAS 19, 85–86) conjectured that “the variations of spot frequency depend on the influences of Venus, Earth, Jupiter, and Saturn.” There are only two options: either the solar activity changes are solely controlled by internal solar dynamo mechanisms or the solar dynamo itself is partially synchronized by external harmonic planetary forcings. The former hypothesis is today shared by the majority of solar scientists; the latter has been recently advocated by an increasing minority of solar scientists, and the debate is still going on. Here we overview the numerous pieces of evidence supporting a planetary theory of solar activity variability by demonstrating that the many planetary harmonics and the orbital invariant inequalities that characterize the planetary motions of the solar system from the monthly to the millennial time scales are not randomly distributed but clearly tend to cluster around some specific values that also match those of the main solar activity cycles. We also show that planetary models have even been able to predict the time phase of the solar oscillations including the Schwabe 11-year sunspot cycle. Although planetary tidal forces are weak, we review a number of mechanisms that could explain how the solar structure and the solar dynamo could get tuned to the planetary motions. In particular, we discuss how the effects of the weak tidal forces could be significantly amplified in the solar core by an induced increase in the H-burning. Mechanisms modulating the electromagnetic and gravitational large-scale structure of the planetary system are also discussed.

Main Reference:

Scafetta N and Bianchini A (2022) The Planetary Theory of Solar Activity Variability: A Review. Front. Astron. Space Sci. 9:937930. doi: 10.3389/fspas.2022.937930

Scafetta, N. (2020). Solar Oscillations and the Orbital Invariant Inequalities of the Solar System. Sol. Phys. 295, 33. doi:10.1007/s11207-020-01599-y