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Solar surface magnetism: selected topics
Thaler, I.
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Citation for published version (APA):
Thaler, I. (2014). Solar surface magnetism: selected topics
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Download date: 19 Jun 2017
Contents
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Introduction
1.1 Magnetic Field Generation on the Sun . . . . . . . . . . . . . . . . .
1.1.1 Global dynamo action- The solar cycle . . . . . . . . . . . .
1.2 Local Dynamo Action on the Solar Surface? . . . . . . . . . . . . . .
1.3 The Total Solar Irradiance Variation due to Magnetic Structures on Solar Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Sunspots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.4.1 Life time of a sunspot? . . . . . . . . . . . . . . . . . . . . .
1.4.2 What causes a sunspot to have a penumbra? . . . . . . . . . .
1.5 Summary of main results . . . . . . . . . . . . . . . . . . . . . . . .
Brightness of the Sun’s small scale magnetic field: proximity effects
2.1 Brightness variation of the Sun . . . . . . . . . . . . . . . . . .
2.2 Causes of brightness variation . . . . . . . . . . . . . . . . . . .
2.2.1 Observations . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2 Simulations . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Brightness of magnetic structures and their environment . . . . .
2.3.1 Origin of magnetic brightenings . . . . . . . . . . . . . .
2.3.2 Dark rings and dark lanes . . . . . . . . . . . . . . . . .
2.4 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4.1 Numerical methods . . . . . . . . . . . . . . . . . . . . .
2.4.2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5.1 Sources of darkening . . . . . . . . . . . . . . . . . . . .
2.5.2 Resolution dependence . . . . . . . . . . . . . . . . . . .
2.5.3 Vertical velocities . . . . . . . . . . . . . . . . . . . . . .
2.6 Discussion and conclusions . . . . . . . . . . . . . . . . . . . . .
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Flux canceling in 3D radiative MHD simulations
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Three-dimensional magnetic fields . . . . . . . . . . . . . . . . . . .
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Solar Surface Magnetism
3.3
3.4
3.5
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3.2.1 ‘flux canceling’ . . . . . . . . . . . . . . . . . . . .
3.2.2 Simulations . . . . . . . . . . . . . . . . . . . . . . .
Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.1 Numerical methods . . . . . . . . . . . . . . . . . . .
3.3.2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.3 Analysis . . . . . . . . . . . . . . . . . . . . . . . .
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1 Initial vertical magnetic field with uniform |Bz | = 50 G
3.4.2 Initial magnetic field fragmented into kG flux tubes . .
3.4.3 Dependence on initial field strength . . . . . . . . . .
Discussion and conclusions . . . . . . . . . . . . . . . . . . .
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Small Scale dynamos on the solar surface: dependence on magnetic Prandtl
number
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Dynamos, fluctuating and non-, at low Prm . . . . . . . . . . . . . . .
4.2.1 Transient behavior . . . . . . . . . . . . . . . . . . . . . . .
4.2.2 Experimental evidence . . . . . . . . . . . . . . . . . . . . .
4.2.3 Indications of solar small-scale dynamo action . . . . . . . .
4.3 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.1 Numerical methods . . . . . . . . . . . . . . . . . . . . . . .
4.3.2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.3 Implementation of the magnetic Prandtl parameter in the STAGGER code . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.5 Discussion and Conclusions . . . . . . . . . . . . . . . . . . . . . .
4.5.1 Relation between intrinsically weak and strong surface fields .
4.5.2 Role of an imposed weak net flux . . . . . . . . . . . . . . .
Sunspots
5.1 Why sunspots are interesting? . . . . . . . . . . . . . . . . . .
5.2 How do sunspots look below the surface- the anchoring problem
5.2.1 How do sunspots appear at the photosphere? . . . . . .
5.2.2 Sunspot modeling . . . . . . . . . . . . . . . . . . . .
5.2.3 Life time of a sunspot in simulations . . . . . . . . . . .
5.3 Additional boundary force increases stability of a sunspot? . . .
5.3.1 Numerical Methods . . . . . . . . . . . . . . . . . . . .
5.3.2 Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3.3 Results and Discussion . . . . . . . . . . . . . . . . . .
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Contents
5.4
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What causes a sunspot to have a penumbra? . . . . . . . . . . .
5.4.1 Does a perturbation of the magnetic field in convection
trigger the formation of a penumbra in the photosphere?
5.4.2 Perturbation force description . . . . . . . . . . . . . .
5.4.3 Results and Discussion . . . . . . . . . . . . . . . . . .
Nederlandse Samenvatting
Acknowledgments
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