Abstract
This paper reviews recent advances and current debates in modeling the solar cycle as a hydromagnetic dynamo process. Emphasis is placed on (relatively) simple dynamo models that are nonetheless detailed enough to be comparable to solar cycle observations. After a brief overview of the dynamo problem and of key observational constraints, we begin by reviewing the various magnetic field regeneration mechanisms that have been proposed in the solar context. We move on to a presentation and critical discussion of extant solar cycle models based on these mechanisms. We then turn to the origin and consequences of fluctuations in these models, including amplitude and parity modulation, chaotic behavior, intermittency, and predictability. The paper concludes with a discussion of our current state of ignorance regarding various key questions relating to the explanatory framework offered by dynamo models of the solar cycle.
Highlights
1.1 Scope of reviewThe cyclic regeneration of the Sun’s large-scale magnetic field is at the root of all phenomena collectively known as “solar activity”
In the solar cycle context, the dynamo problem is reformulated towards identifying the circumstances under which the flow fields observed and/or inferred in the Sun can sustain the cyclic regeneration of the magnetic field associated with the observed solar cycle
This basic model was later generalized by various authors (Tobias, 1997; Phillips et al, 2002) to include the nonlinear backreaction of the dynamo-generated magnetic field on the differential rotation; further discussion of such nonlinear models is deferred to Section 5.3.1
Summary
Besides updates relating to the literature published in the past five years (added about 60 new references), and reworking a few sections of the 2005 version, main major novelties compared to the 2005 version are: 1. Material on turbulent pumping, and its effect in various types of dynamo models (Kapyla et al, 2006; Guerrero and de Gouveia Dal Pino, 2008). 2. Besides updates relating to the literature published in the past five years (added about 60 new references), and reworking a few sections of the 2005 version, main major novelties compared to the 2005 version are: 1. Its effect in various types of dynamo models (Kapyla et al, 2006; Guerrero and de Gouveia Dal Pino, 2008). 2. Expanded Section 4.9 on MHD numerical simulations of large-scale dynamo action. 3. Added Section 5.7 on dynamo model-based cycle prediction schemes. 4. Inclusion (and discussion of) animations directly in the text, as opposed to being grouped in a ressource archive, as in my original 2005 review. By appropriate deletions elsewhere in the review, I have managed to retain its overall length at nearly the same as the 2005 version
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