Origin and Dynamics of Solar Magnetism (eBook)

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 115
Setup and Parameters for Geodynamo Models 115
Classes of Dynamo Solutions 117
Flow Structure and Field Generation Mechanism 119
Comparison of Geodynamo Models with Earth's Field 120
Scaling of Dynamo Properties 121
Specific Models for Various Planets Other than Earth 125
Mercury 126
Saturn 127
Uranus and Neptune 127
Discussion 128
Acknowledgements 128
References 128
Observations of Photospheric Dynamics and Magnetic Fields: From Large-Scale to Small-Scale Flows 130
Introduction 130
The Spatial and Temporal Scales 131
Overview of Different Scales 131
Coupling between Different Scales 132
Multi-Scale Analysis 132
Small-Scale Flows and Magnetic Fields 135
Introduction 135
Observational Techniques 136
Supergranulation 137
Flows around Active Regions 140
Global-Scale Flows and Magnetic Fields 140
Introduction 140
Observational Techniques 141
Differential Rotation 141
Torsional Oscillation 142
Poleward Meridional Flow 142
Solar Cycle Variations of the Flows 143
Search for Return Meridional Flows 144
Solar Irradiance Variations 146
Stellar Activity 147
Conclusion 148
References 149
Large Scale Flows in the Solar Convection Zone 153
Introduction 153
Modelling Approach 154
2-D Axisymmetric Mean Field Models 154
3-D Global MHD Simulations 154
Solar Convection 155
Maintenance of Large Scale Flows 158
Differential Rotation 160
Results from Mean Field Models 160
Angular Velocity and Momentum Redistribution in 3-D Global Models 161
Meridional Flow 164
Results from Mean Field Models 164
Amplitude and Profile of Meridional Circulation in 3-D Models 164
Variability of Meridional Circulation and Observational Constraints 165
Magnetic Feedback on Mean Flows 165
The Influence of a Dynamo Induced Magnetic Field on the Mean Flows 165
Results from Mean Field Models Possessing a Cyclic Magnetic Field 169
Conclusions 172
Acknowledgements 173
References 174
Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux 176
Introduction 176
Observations of Emerging Magnetic Flux in the Photosphere 179
Joy's Law and Magnetic Flux Transport 179
Mass Flows 182
Investigations of Emerging Flux by Helioseismology 184
Method of Time-Distance Helioseismology 184
Tomographic Imaging of Wave-Speed Perturbations 186
Subsurface Flows 190
Comparison with Theoretical Models 192
Discussion and Future Perspectives 194
Acknowledgements 195
References 195
The Topology and Behavior of Magnetic Fields Emerging at the Solar Photosphere 197
Introduction 197
Emergence of Twisted Magnetic Flux and the Formation of Filament Channels 198
Hinode Observations of Filament Channel Formation/Destruction 200
The Occurrence of a ``Naked Bald Patch'' 202
Emerging, Twisted Flux or Shear-Generated Flux Ropes? 202
The Small-Scale Topology of Magnetic Fields at the Site of Emergence 204
Hinode SP Observations of Emerging Flux 205
Fine-Scale Properties of Emerging Flux 206
The Role of Small Scale Processes in Flux Emergence 208
Acknowledgements 210
References 210
Sunspots: From Small-Scale Inhomogeneities Towards a Global Theory 213
Introduction 214
Time Scales: 214
Energy Transport in Umbra and Penumbra 214
Jelly Fish and Field-Free Gaps: 214
Stability of Sunspots and Monolithic Models: 215
Inhomogeneities in Umbra and Penumbra 215
Umbral Dots 215
The Physics of Umbral Dots: 215
Penumbral Inhomogeneities 216
Morphological Description 216
Evershed Flow, Uncombed Magnetic Field, and NCP 217
The Flow Field: 218
The Magnetic Field: 218
The Magnetic Canopy: 219
The Net Circular Polarization (NCP): 219
Magnetized or Non-magnetized Flow: 219
Penumbral Models 219
Convective Models 220
Ideal Magneto-Convection 221
Weak Magnetic Field at Footpoint: 221
Magneto-Convective Overshoot: 222
Serpentine Flow: 222
Siphon Flows: 222
Heat Transport: 222
Non-ideal Magneto-Hydrodynamics 223
Radiative Magneto-Convection 223
Conclusions 224
Acknowledgements 225
References 225
Recent Evidence for Convection in Sunspot Penumbrae 229
Introduction 229
Overview of Established Models 230
Embedded Flux Tubes 230
Siphon Flow and Dynamic Flux Tube Models 231
Convection and Downward Pumping of Magnetic Flux 232
Limitations and Problems of Flux Tube Interpretations 233
Ambiguities of Interpretations Based on Inversions 234
Convective Origin of Penumbral Filaments 235
Limitations of the Convective Gap Model 239
Support From Observations 239
Support from 3D MHD Simulations 240
Connections to Flux Tube Models 242
Conclusions 244
Acknowledgements 246
References 246
Helioseismology of Sunspots: A Case Study of NOAA Region 9787 248
Introduction 249
Observations of NOAA Region 9787 250
MDI/SOHO Observations 250
Oscillatory Power and Acoustic Halos 253
Wave Absorption 254
Travel Time Measurements 255
Phase-Speed Filtering versus Ridge Filtering 255
Ridge and Off-Ridge Filtering 258
Moat Flow Inversion (Ridge Filters) 260
Sound Speed versus Wave Speed 261
Wave-Speed Inversion (Phase-Speed Filters) 263
Ring-Diagram Analysis 265
Numerical Forward Modeling 266
Discussion: The Elusive Structure of Sunspots 268
Problematic Travel Times 268
Conflicting Wave-Speed Profiles 269
Conclusion 270
Acknowledgements 271
References 271
Small-Scale Solar Magnetic Fields 273
Introduction 273
Quiet Sun Magnetic Fields 274
Magnetic Flux in the Quiet Sun 275
Methods 275
Measurements of Magnetic Flux in the Quiet Sun 276
Magnetic Field Strength of Quiet Sun Fields 278
Horizontal Fields in the Internetwork 282
Source of Internetwork Fields 282
Transient Horizontal Magnetic Field 285
Properties of Horizontal Magnetic Field 285
THMF and Local Dynamo Process 288
Polar Field 289
The Polar Magnetic Landscape 289
Total Magnetic Flux 290
Bright Points and Magnetic Elements 291
Observations of Small-Scale Field Concentrations 292
Field Concentrations in Internetwork Areas 295
Magnetic Element Dynamics 296
Formation of Bright Points 297
Formation of Magnetic Elements 298
Unresolved Magnetic Fields 299
Range of the Unresolved Scales 299
Role of the Smallest Scales for the Global Dynamo 300
Scaling Behavior of the Magnetic Field Pattern 302
Field Diagnostics Beyond the Spatial Resolution Limit 303
Zeeman Diagnostics and the Line-Ratio Technique 304
Hanle Diagnostics 306
Unified Zeeman-Hanle Diagnostics with Distribution Functions 308
Conclusion 309
References 310
Coupling from the Photosphere to the Chromosphere and the Corona 314
Introduction 315
The Sun-A Multi-Scale Object 315
Observations-Measuring the Magnetic Field in the Solar Atmosphere 320
Improving Magnetic Field Extrapolations 322
Direct Measurements of the Chromospheric Magnetic Fields 323
Spicules 324
Prominences and Filaments 324
Canopy 326
Numerical Simulations of the Quiet Sun 328
Internetwork Photosphere 328
Internetwork Chromosphere 329
Large-Scale Simulations 334
An Updated Picture of the Quiet Sun Atmosphere 334
The Large-Scale Magnetic Field 334
The Canopy Domain 336
The Sub-Canopy Domain 337
The Lower and Middle Photosphere 337
The Upper Photosphere 338
The Fluctosphere 338
Shock Waves Meet the ``Canopy'' 339
Probing the Upper Atmosphere 340
Conclusions 340
Acknowledgements 341
References 341
Magnetic Flux Emergence, Activity, Eruptions and Magnetic Clouds: Following Magnetic Field from the Sun to the Heliosphere 348
Introduction 348
Flux Emergence 349
The Three Main Rules of Magnetic Flux Emergence 349
Additional Characteristics: Asymmetries and Tilt 350
Inherent Twist and Its Implications 350
Magnetic Helicity 352
Nesting Tendency of Flux Emergence 353
Decay of Active Regions 353
The Effect of Magnetic Evolution on Activity 354
Relationship of Magnetic Properties to Activity 356
Magnetic Parametric Studies and Short-Term Activity Forecast 357
Metrics and Effects of Magnetic Complexity 358
Photospheric Fields Are Relevant, but Are They Sufficient? 359
Helicity Injection, Content and Eruptive Activity 359
Eruptions 360
Interplanetary Coronal Mass Ejections and Magnetic Cloud Characteristics 364
Coronal Mass Ejections: From Sun to Earth 369
Conclusions 373
Acknowledgements 375
References 375
Coronal Holes and Open Magnetic Flux 379
Basic Concepts 379
Solar Cycle Variation of the Open Flux 381
Flux Transport and the Formation of the Polar Coronal Holes 384
Solar Wind Speed, Coronal Heating, and Flux-Tube Expansion 385
Magnetic Reconnection and the Rotation of Coronal Holes 389
Coronal Holes, Jets, and 3He-Rich Particle Events 391
Concluding Remarks 391
Acknowledgements 394
References 394
Solar Cycle Forecasting 396
Introduction 396
Ongoing Cycle Predictions 398
Upcoming Cycle Predictions with Precursors 400
Upcoming Cycle Predictions with Dynamo Models 404
Conclusions 406
References 406
Coronal Magnetism: Difficulties and Prospects 408
Introduction 408
Approaches Based on ``Direct'' Measurement 410
Using the Zeeman Effect 410
Using Gyroresonance Emission 411
Estimates Based on Theory 411
Coronal Seismology 411
Large-Scale Modelling and Coronal Geometry 413
Summary 414
Acknowledgements 415
References 415
ISSI Workshop on Solar Magnetism: Concluding Remarks 417
Introduction 417
Mean Field Dynamo 418
Dynamo Action at Multiple Scales? 419
Global Simulations 420
The Key: Comparing the Sun with Other Stars 421
Acknowledgements 422
References 422