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The Origin and Dynamics of Solar Magnetism

:	M. J. Thompson, A. Balogh, J. L. Culhane, Å. Nordlund, S. K. Solanki, J.-P. Zahn.
:	M.J. Thompson, Andre Balogh, J. Len Culhane, Å. Nordlund, S.K. Solanki, J.-P. Zahn
:	The Origin and Dynamics of Solar Magnetism
:	Springer-Verlag
:	9781441902399
:	1
:	CHF 86.90
:

:	Astronomie
:	English

:	432
:	Wasserzeichen
:	PC/MAC/eReader/Tablet
:	PDF

Starting in 1995 numerical modeling of the Earth's dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).

	Contents	4
	Introduction to Solar Magnetism: The Early Years	6
	Sunspots as Indicators of Solar Variability	6
	George Ellery Hale and the Discovery of Solar Magnetism	10
	Toward Today's Research in Solar Magnetism: Eugene Parker	13
	Solar Magnetism: The Current Status	15
	Acknowledgements	17
	References	17
	Solar Magnetism: The State of Our Knowledge and Ignorance	20
	Introduction	20
	Solar Magnetic Fields	21
	Thoughts on the Solar Dynamo	24
	Discussion	26
	References	28
	Chaos and Intermittency in the Solar Cycle	30
	Sensitive Systems	30
	Examples of Sensitivity	31
	An Illustration from Bifurcation Theory	31
	A Chaotic System	33
	Qualitative Considerations	34
	Quantifying Chaotic Behavior	37
	Studying Empirical Attractors	37
	An Illustrative Example	39
	A Solar Attractor	40
	Dimensional Reduction	42
	Linear Theory	44
	Weakly Nonlinear Theory	45
	Amplitude Equations	46
	Grand Minima	47
	A Solar Oscillator	48
	On-Off Intermittency	49
	Ruminations	51
	Simple Oscillators	51
	Spatio-Temporal Aspects	53
	The End	54
	Acknowledgements	55
	References	55
	The Solar Dynamo	57
	Introduction	57
	Magnetic Activity on the Sun	58
	Helioseismology and Internal Properties of the Sun	60
	Dynamo Theory	63
	Solar Dynamo Models	64
	Beyond Mean-Field Dynamos	65
	Predicting the Future	68
	References	68
	Flux-Transport Solar Dynamos	71
	What Is a Flux-Transport Dynamo	71
	A Brief History of Development of Flux-Transport Dynamos	72
	Existence of Meridional Circulation	72
	Flux-Transport Dynamo Solutions	74
	Some Unique Properties of a Flux-Transport Dynamo	75
	Discussion and Future Prospects	77
	Acknowledgements	78
	References	78
	The Solar Dynamo: The Role of Penetration, Rotation and Shear on Convective Dynamos	80
	Introduction: Models of Solar Cycle	80
	The Physical Effects That May Play a Role in Dynamo Action	82
	The Role of Penetration on Compressible Dynamos	85
	Turbulent Boussinesq Dynamos with Penetration, Rotation and Shear	86
	Discussion	87
	Acknowledgements	88
	References	88
	Advances in Theory and Simulations of Large-Scale Dynamos	90
	Introduction	90
	Saturation Phenomenology in a Periodic Box	92
	Mean-Field Theory and Transport Coefficients	94
	The Test-Field Method	95
	The Essence of the Test-Field Method	96
	Rm-Dependence of the Kinematic Values of alpha and etat	96
	Scale-Dependence of alpha and etat	97
	Quenching for Equipartition-Strength Fields	98
	Three Paradigm Shifts Revisited	99
	Magnetic Buoyancy: from Distributed Dynamos to the Overshoot Layer	99
	Helioseismology: Overshoot Layer and Flux-Transport Dynamos	99
	Catastrophic Quenching: Interface and Flux-Transport Dynamos	100
	Implications and Open Problems	100
	Conclusions	103
	Acknowledgements	104
	References	104
	Planetary Dynamos from a Solar Perspective	108
	Introduction	109
	Planetary Magnetic Fields	109
	Geomagnetic Field	109
	Other Planets	111
	Solar Versus Planetary Dynamos	113
	Energetics	113
	Magnetic Turbulence	114
	Stratification	114
	Inertial Forces	11