Can Stochastic Resonance Explain Recurrence of Grand Minima?

• Published in: Astrophysical journal. Letters Vol. 916; no. 2; p. L9
• Main Authors: Albert, Carlo, Ferriz-Mas, Antonio, Gaia, Filippo, Ulzega, Simone
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01.08.2021; IOP Publishing
• Subjects: Dynamo theory; Magnetic fields; Meridional circulation; Minima; Modulation; Periodicities; Resonance; Solar activity; Solar cycle; Solar dynamo; Stochastic resonance; Sunspots
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/ac0fd6

The amplitude of the 11 yr solar cycle is well known to be subject to long-term modulation, including sustained periods of very low activity known as Grand Minima. Stable long-period cycles found in proxies of solar activity have given new momentum to the debate about a possible influence of the tiny planetary tidal forcing. Here, we study the solar cycle by means of a simple zero-dimensional dynamo model, which includes a delay caused by meridional circulation as well as a quenching of the α -effect at toroidal magnetic fields exceeding an upper threshold. Fitting this model to the sunspot record, we find a set of parameters close to the bifurcation point at which two stable oscillatory modes emerge. One mode is a limit cycle resembling normal solar activity including a characteristic kink in the decaying limb of the cycle. The other mode is a weak sub-threshold cycle that could be interpreted as Grand Minimum activity. Adding noise to the model, we show that it exhibits Stochastic Resonance, which means that a weak external modulation can toss the dynamo back and forth between these two modes, whereby the periodicities of the modulation get strongly amplified.