Balogh / Nordlund / Zahn. The Origin and Dynamics of Solar Magnetism

1. Auflage 2009
ISBN: 978-1-4419-0239-9
Verlag: Springer-Verlag
Format: PDF
Kopierschutz: Wasserzeichen (»Systemvoraussetzungen)

E-Book, Englisch, 432 Seiten

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).

Autoren/Hrsg.

Balogh, A.

Nordlund, Å.

Zahn., J.-P.

Thompson, M.J.

Balogh, Andre

Solanki, S.K.

Zahn, J.-P.

Inhaltsverzeichnis

1;Contents;4
2;Introduction to Solar Magnetism: The Early Years;6
2.1;Sunspots as Indicators of Solar Variability;6
2.2;George Ellery Hale and the Discovery of Solar Magnetism;10
2.3;Toward Today's Research in Solar Magnetism: Eugene Parker;13
2.4;Solar Magnetism: The Current Status;15
2.5;Acknowledgements;17
2.6;References;17
3;Solar Magnetism: The State of Our Knowledge and Ignorance;20
3.1;Introduction;20
3.2;Solar Magnetic Fields;21
3.3;Thoughts on the Solar Dynamo;24
3.4;Discussion;26
3.5;References;28
4;Chaos and Intermittency in the Solar Cycle;30
4.1;Sensitive Systems;30
4.2;Examples of Sensitivity;31
4.2.1;An Illustration from Bifurcation Theory;31
4.2.2;A Chaotic System;33
4.2.3;Qualitative Considerations;34
4.3;Quantifying Chaotic Behavior ;37
4.3.1;Studying Empirical Attractors;37
4.3.2;An Illustrative Example;39
4.3.3;A Solar Attractor ;40
4.4;Dimensional Reduction;42
4.4.1;Linear Theory;44
4.4.2;Weakly Nonlinear Theory;45
4.4.3;Amplitude Equations;46
4.5;Grand Minima;47
4.5.1;A Solar Oscillator;48
4.5.2;On-Off Intermittency;49
4.6;Ruminations;51
4.6.1;Simple Oscillators;51
4.6.2;Spatio-Temporal Aspects;53
4.6.3;The End;54
4.7;Acknowledgements;55
4.8;References;55
5;The Solar Dynamo;57
5.1;Introduction;57
5.2;Magnetic Activity on the Sun;58
5.3;Helioseismology and Internal Properties of the Sun;60
5.4;Dynamo Theory;63
5.5;Solar Dynamo Models;64
5.6;Beyond Mean-Field Dynamos;65
5.7;Predicting the Future;68
5.8;References;68
6;Flux-Transport Solar Dynamos;71
6.1;What Is a Flux-Transport Dynamo;71
6.2;A Brief History of Development of Flux-Transport Dynamos;72
6.3;Existence of Meridional Circulation;72
6.4;Flux-Transport Dynamo Solutions;74
6.5;Some Unique Properties of a Flux-Transport Dynamo;75
6.6;Discussion and Future Prospects;77
6.7;Acknowledgements;78
6.8;References;78
7;The Solar Dynamo: The Role of Penetration, Rotation and Shear on Convective Dynamos;80
7.1;Introduction: Models of Solar Cycle;80
7.2;The Physical Effects That May Play a Role in Dynamo Action;82
7.3;The Role of Penetration on Compressible Dynamos;85
7.4;Turbulent Boussinesq Dynamos with Penetration, Rotation and Shear;86
7.5;Discussion;87
7.6;Acknowledgements;88
7.7;References;88
8;Advances in Theory and Simulations of Large-Scale Dynamos;90
8.1;Introduction;90
8.2;Saturation Phenomenology in a Periodic Box;92
8.3;Mean-Field Theory and Transport Coefficients;94
8.4;The Test-Field Method;95
8.4.1;The Essence of the Test-Field Method;96
8.4.2;Rm-Dependence of the Kinematic Values of alpha and etat;96
8.4.3;Scale-Dependence of alpha and etat;97
8.4.4;Quenching for Equipartition-Strength Fields;98
8.5;Three Paradigm Shifts Revisited;99
8.5.1;Magnetic Buoyancy: from Distributed Dynamos to the Overshoot Layer;99
8.5.2;Helioseismology: Overshoot Layer and Flux-Transport Dynamos;99
8.5.3;Catastrophic Quenching: Interface and Flux-Transport Dynamos;100
8.6;Implications and Open Problems;100
8.7;Conclusions;103
8.8;Acknowledgements;104
8.9;References;104
9;Planetary Dynamos from a Solar Perspective;108
9.1;Introduction;109
9.2;Planetary Magnetic Fields;109
9.2.1;Geomagnetic Field;109
9.2.2;Other Planets;111
9.3;Solar Versus Planetary Dynamos;113
9.3.1;Energetics;113
9.3.2;Magnetic Turbulence;114
9.3.3;Stratification;114
9.3.4;Inertial Forces;115
9.4;Setup and Parameters for Geodynamo Models;115
9.5;Classes of Dynamo Solutions;117
9.6;Flow Structure and Field Generation Mechanism;119
9.7;Comparison of Geodynamo Models with Earth's Field;120
9.8;Scaling of Dynamo Properties;121
9.9;Specific Models for Various Planets Other than Earth;125
9.9.1;Mercury;126
9.9.2;Saturn;127
9.9.3;Uranus and Neptune;127
9.10;Discussion;128
9.11;Acknowledgements;128
9.12;References;128
10;Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows;130
10.1;Introduction;130
10.2;The Spatial and Temporal Scales;131
10.2.1;Overview of Different Scales;131
10.2.2;Coupling between Different Scales;132
10.2.3;Multi-Scale Analysis;132
10.3;Small-Scale Flows and Magnetic Fields;135
10.3.1;Introduction;135
10.3.2;Observational Techniques;136
10.3.3;Supergranulation;137
10.3.4;Flows around Active Regions;140
10.4;Global-Scale Flows and Magnetic Fields;140
10.4.1;Introduction;140
10.4.2;Observational Techniques;141
10.4.3;Differential Rotation;141
10.4.4;Torsional Oscillation;142
10.4.5;Poleward Meridional Flow;142
10.4.6;Solar Cycle Variations of the Flows;143
10.4.7;Search for Return Meridional Flows;144
10.4.8;Solar Irradiance Variations;146
10.5;Stellar Activity;147
10.6;Conclusion;148
10.7;References;149
11;Large Scale Flows in the Solar Convection Zone;153
11.1;Introduction;153
11.2;Modelling Approach;154
11.2.1;2-D Axisymmetric Mean Field Models;154
11.2.2;3-D Global MHD Simulations;154
11.3;Solar Convection;155
11.4;Maintenance of Large Scale Flows;158
11.5;Differential Rotation;160
11.5.1;Results from Mean Field Models;160
11.5.2;Angular Velocity and Momentum Redistribution in 3-D Global Models;161
11.6;Meridional Flow;164
11.6.1;Results from Mean Field Models;164
11.6.2;Amplitude and Profile of Meridional Circulation in 3-D Models;164
11.6.3;Variability of Meridional Circulation and Observational Constraints;165
11.7;Magnetic Feedback on Mean Flows;165
11.7.1;The Influence of a Dynamo Induced Magnetic Field on the Mean Flows;165
11.7.2;Results from Mean Field Models Possessing a Cyclic Magnetic Field;169
11.8;Conclusions;172
11.9;Acknowledgements;173
11.10;References;174
12;Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux;176
12.1;Introduction;176
12.2;Observations of Emerging Magnetic Flux in the Photosphere;179
12.2.1;Joy's Law and Magnetic Flux Transport;179
12.2.2;Mass Flows;182
12.3;Investigations of Emerging Flux by Helioseismology;184
12.3.1;Method of Time-Distance Helioseismology;184
12.3.2;Tomographic Imaging of Wave-Speed Perturbations;186
12.3.3;Subsurface Flows;190
12.4;Comparison with Theoretical Models;192
12.5;Discussion and Future Perspectives;194
12.6;Acknowledgements;195
12.7;References;195
13;The Topology and Behavior of Magnetic Fields Emerging at the Solar Photosphere;197
13.1;Introduction;197
13.2;Emergence of Twisted Magnetic Flux and the Formation of Filament Channels;198
13.2.1;Hinode Observations of Filament Channel Formation/Destruction;200
13.2.2;The Occurrence of a ``Naked Bald Patch'';202
13.2.3;Emerging, Twisted Flux or Shear-Generated Flux Ropes?;202
13.3;The Small-Scale Topology of Magnetic Fields at the Site of Emergence;204
13.3.1;Hinode SP Observations of Emerging Flux;205
13.3.2;Fine-Scale Properties of Emerging Flux;206
13.3.3;The Role of Small Scale Processes in Flux Emergence;208
13.4;Acknowledgements;210
13.5;References;210
14;Sunspots: From Small-Scale Inhomogeneities Towards a Global Theory;213
14.1;Introduction;214
14.1.1;Time Scales:;214
14.2;Energy Transport in Umbra and Penumbra;214
14.2.1;Jelly Fish and Field-Free Gaps:;214
14.2.2;Stability of Sunspots and Monolithic Models:;215
14.3;Inhomogeneities in Umbra and Penumbra;215
14.3.1;Umbral Dots;215
14.3.1.1;The Physics of Umbral Dots:;215
14.3.2;Penumbral Inhomogeneities;216
14.3.2.1;Morphological Description;216
14.3.2.2;Evershed Flow, Uncombed Magnetic Field, and NCP;217
14.3.2.2.1;The Flow Field:;218
14.3.2.2.2;The Magnetic Field:;218
14.3.2.2.3;The Magnetic Canopy:;219
14.3.2.2.4;The Net Circular Polarization (NCP):;219
14.3.2.2.5;Magnetized or Non-magnetized Flow:;219
14.4;Penumbral Models;219
14.4.1;Convective Models;220
14.4.2;Ideal Magneto-Convection;221
14.4.2.1;Weak Magnetic Field at Footpoint:;221
14.4.2.2;Magneto-Convective Overshoot:;222
14.4.2.3;Serpentine Flow:;222
14.4.2.4;Siphon Flows:;222
14.4.2.5;Heat Transport:;222
14.4.3;Non-ideal Magneto-Hydrodynamics;223
14.4.4;Radiative Magneto-Convection;223
14.5;Conclusions;224
14.6;Acknowledgements;225
14.7;References;225
15;Recent Evidence for Convection in Sunspot Penumbrae;229
15.1;Introduction;229
15.2;Overview of Established Models;230
15.2.1;Embedded Flux Tubes;230
15.2.2;Siphon Flow and Dynamic Flux Tube Models;231
15.2.3;Convection and Downward Pumping of Magnetic Flux;232
15.3;Limitations and Problems of Flux Tube Interpretations;233
15.3.1;Ambiguities of Interpretations Based on Inversions;234
15.4;Convective Origin of Penumbral Filaments;235
15.4.1;Limitations of the Convective Gap Model;239
15.4.2;Support From Observations;239
15.4.3;Support from 3D MHD Simulations;240
15.4.4;Connections to Flux Tube Models;242
15.5;Conclusions;244
15.6;Acknowledgements;246
15.7;References;246
16;Helioseismology of Sunspots: A Case Study of NOAA Region 9787;248
16.1;Introduction;249
16.2;Observations of NOAA Region 9787;250
16.2.1;MDI/SOHO Observations;250
16.2.2;Oscillatory Power and Acoustic Halos;253
16.2.3;Wave Absorption;254
16.3;Travel Time Measurements;255
16.3.1;Phase-Speed Filtering versus Ridge Filtering;255
16.3.2;Ridge and Off-Ridge Filtering;258
16.4;Moat Flow Inversion (Ridge Filters);260
16.5;Sound Speed versus Wave Speed;261
16.6;Wave-Speed Inversion (Phase-Speed Filters);263
16.7;Ring-Diagram Analysis;265
16.8;Numerical Forward Modeling;266
16.9;Discussion: The Elusive Structure of Sunspots;268
16.9.1;Problematic Travel Times;268
16.9.2;Conflicting Wave-Speed Profiles;269
16.10;Conclusion;270
16.11;Acknowledgements;271
16.12;References;271
17;Small-Scale Solar Magnetic Fields;273
17.1;Introduction;273
17.2;Quiet Sun Magnetic Fields;274
17.2.1;Magnetic Flux in the Quiet Sun;275
17.2.1.1;Methods;275
17.2.1.2;Measurements of Magnetic Flux in the Quiet Sun;276
17.2.2;Magnetic Field Strength of Quiet Sun Fields;278
17.2.3;Horizontal Fields in the Internetwork;282
17.2.4;Source of Internetwork Fields;282
17.3;Transient Horizontal Magnetic Field;285
17.3.1;Properties of Horizontal Magnetic Field;285
17.3.2;THMF and Local Dynamo Process;288
17.4;Polar Field;289
17.4.1;The Polar Magnetic Landscape;289
17.4.2;Total Magnetic Flux;290
17.5;Bright Points and Magnetic Elements;291
17.5.1;Observations of Small-Scale Field Concentrations;292
17.5.2;Field Concentrations in Internetwork Areas;295
17.5.3;Magnetic Element Dynamics;296
17.5.4;Formation of Bright Points;297
17.5.5;Formation of Magnetic Elements;298
17.6;Unresolved Magnetic Fields;299
17.6.1;Range of the Unresolved Scales;299
17.6.2;Role of the Smallest Scales for the Global Dynamo;300
17.6.3;Scaling Behavior of the Magnetic Field Pattern;302
17.6.4;Field Diagnostics Beyond the Spatial Resolution Limit;303
17.6.4.1;Zeeman Diagnostics and the Line-Ratio Technique;304
17.6.4.2;Hanle Diagnostics;306
17.6.4.3;Unified Zeeman-Hanle Diagnostics with Distribution Functions;308
17.7;Conclusion;309
17.8;References;310
18;Coupling from the Photosphere to the Chromosphere and the Corona;314
18.1;Introduction;315
18.2;The Sun-A Multi-Scale Object;315
18.3;Observations-Measuring the Magnetic Field in the Solar Atmosphere;320
18.3.1;Improving Magnetic Field Extrapolations;322
18.3.2;Direct Measurements of the Chromospheric Magnetic Fields;323
18.3.2.1;Spicules;324
18.3.2.2;Prominences and Filaments;324
18.3.2.3;Canopy;326
18.4;Numerical Simulations of the Quiet Sun;328
18.4.1;Internetwork Photosphere;328
18.4.2;Internetwork Chromosphere;329
18.4.3;Large-Scale Simulations;334
18.5;An Updated Picture of the Quiet Sun Atmosphere;334
18.5.1;The Large-Scale Magnetic Field;334
18.5.2;The Canopy Domain;336
18.5.3;The Sub-Canopy Domain;337
18.5.3.1;The Lower and Middle Photosphere;337
18.5.3.2;The Upper Photosphere;338
18.5.3.3;The Fluctosphere;338
18.5.4;Shock Waves Meet the ``Canopy'';339
18.5.5;Probing the Upper Atmosphere;340
18.6;Conclusions;340
18.7;Acknowledgements;341
18.8;References;341
19;Magnetic Flux Emergence, Activity, Eruptions and Magnetic Clouds: Following Magnetic Field from the Sun to the Heliosphere;348
19.1;Introduction;348
19.2;Flux Emergence;349
19.2.1;The Three Main Rules of Magnetic Flux Emergence;349
19.2.2;Additional Characteristics: Asymmetries and Tilt;350
19.2.3;Inherent Twist and Its Implications;350
19.2.4;Magnetic Helicity;352
19.2.5;Nesting Tendency of Flux Emergence;353
19.3;Decay of Active Regions;353
19.3.1;The Effect of Magnetic Evolution on Activity;354
19.4;Relationship of Magnetic Properties to Activity;356
19.4.1;Magnetic Parametric Studies and Short-Term Activity Forecast;357
19.4.2;Metrics and Effects of Magnetic Complexity;358
19.4.3;Photospheric Fields Are Relevant, but Are They Sufficient?;359
19.4.4;Helicity Injection, Content and Eruptive Activity;359
19.5;Eruptions;360
19.6;Interplanetary Coronal Mass Ejections and Magnetic Cloud Characteristics;364
19.7;Coronal Mass Ejections: From Sun to Earth;369
19.8;Conclusions;373
19.9;Acknowledgements;375
19.10;References;375
20;Coronal Holes and Open Magnetic Flux;379
20.1;Basic Concepts;379
20.2;Solar Cycle Variation of the Open Flux;381
20.3;Flux Transport and the Formation of the Polar Coronal Holes;384
20.4;Solar Wind Speed, Coronal Heating, and Flux-Tube Expansion;385
20.5;Magnetic Reconnection and the Rotation of Coronal Holes;389
20.6;Coronal Holes, Jets, and 3He-Rich Particle Events;391
20.7;Concluding Remarks;391
20.8;Acknowledgements;394
20.9;References;394
21;Solar Cycle Forecasting;396
21.1;Introduction;396
21.2;Ongoing Cycle Predictions;398
21.3;Upcoming Cycle Predictions with Precursors;400
21.4;Upcoming Cycle Predictions with Dynamo Models;404
21.5;Conclusions;406
21.6;References;406
22;Coronal Magnetism: Difficulties and Prospects;408
22.1;Introduction;408
22.2;Approaches Based on ``Direct'' Measurement;410
22.2.1;Using the Zeeman Effect;410
22.2.2;Using Gyroresonance Emission;411
22.3;Estimates Based on Theory;411
22.3.1;Coronal Seismology;411
22.3.2;Large-Scale Modelling and Coronal Geometry;413
22.4;Summary;414
22.5;Acknowledgements;415
22.6;References;415
23;ISSI Workshop on Solar Magnetism: Concluding Remarks;417
23.1;Introduction;417
23.2;Mean Field Dynamo;418
23.3;Dynamo Action at Multiple Scales?;419
23.4;Global Simulations;420
23.5;The Key: Comparing the Sun with Other Stars;421
23.6;Acknowledgements;422
23.7;References;422