External Forcing of the Solar Dynamo

Abstract

In this paper I examine whether external forcing of the solar dynamo on long timescales can produce detectable signal in the form of long term modulation of the magnetic cycle. This task is motivated in part by some recent proposals (Abreu et al., 2012; Astron. Ap., 548, A88; Stefani et al., 2021; Solar Phys., 296, 88), whereby modulation of the solar activity cycle on centennial and millennial timescales, as recovered from the cosmogenic radioisotope record, is attributed to perturbation of the tachocline driven by planetary orbital motions. Working with a two-dimensional mean-field-like kinematic dynamo model of the Babcock-Leighton variety, I show that such an external forcing signal may be detectable in principle but is likely to be obliterated by other internal sources of fluctuations, in particular stochastic perturbations of the dynamo associated with convective turbulence, unless a very efficient amplification mechanism is at play. I also examine the ability of external tidal forcing to synchronize an otherwise autonomous, internal dynamo operating at a nearby frequency. Synchronization is readily achieved, and turns out to be very robust to the introduction of stochastic noise, but requires very high forcing amplitudes, again highlighting the critical need for a powerful amplification mechanism.

The Planetary Theory of Solar Activity Variability: A Review

“…This could be equivalent to having gravitational tidal amplitudes amplified from 1 mm to 1 km at the tachocline. This amplification could solve the problem of the "homeopathic" gravitational tidal energy contribution highlighted by Charbonneau (2022).…”

“…Many authors suggest that solar cycles revealed in sunspot and cosmogenic records could derive from a deterministic non-linear chaotic dynamo (Weiss and Tobias, 2016;Charbonneau, 2020Charbonneau, , 2022. However, the assumption that solar activity is only regulated by dynamical and stochastic processes inside the Sun has never been validated mainly because these models have a poor hindcasting capability.…”

“…Other authors reasonably claimed that planetary gravitational tides are too weak to modulate solar activity (Charbonneau, 2002;de Jager and Versteegh, 2005;Charbonneau, 2022); yet, several empirical evidences support the importance of their role (Wolff and Patrone, 2010;Abreu et al, 2012;Scafetta, 2012b;Stefani et al, 2016Stefani et al, , 2019. Stefani et al (2016Stefani et al ( , 2021 proposed that the Sun could be at least synchronized by the tides of Venus, Earth and Jupiter, producing an 11.07-year cycle that reasonably matches the Schwabe cycle.…”

“…This could be equivalent to having gravitational tidal amplitudes amplified from 1 mm to 1 kilometer at the tachocline. This amplification could solve the problem of the "homeopathic" gravitational tidal energy contribution highlighted by Charbonneau (2022). By using such a large amplification factor the estimated gravitational power Ωtidal dissipated inside the solar core, Scafetta (2012b) calculated the tidallyinduced TSI produced by each of the planets (Figure 9A and B), as well as that of all the planets together (Figure 9C).…”

Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing

“…A related question that presents itself concerns the possible influence of tidal forces on convective motion 30 . While, due to the huge differences between the tidal and inertial forces in the solar convection zone 22,23 , any noticeable effect in this region seems extremely unlikely, convection is at least an attractive candidate for an experiment on helicity synchronization. In view of the significant challenges in carrying out liquid metal experiments on the very TI 21 , Rayleigh-Bénard(RB) convection may provide an interesting surrogate with nearly identical topological features.…”