Geomagnetic Observations and Models (eBook)

Foreword by the Series Editor 5
Contents 6
Introduction 8
Contributors 11
1 The Global Geomagnetic Observatory Network 14
1.1 The Network at the Time of the Sopron IAGA Assembly (August 2009) 14
1.1.1 Introduction 14
1.1.2 Highlights from the Sopron IAGA Assembly in 2009 15
1.1.3 The Network 15
1.1.4 INDIGO: Better Geomagnetic Observatories at the Right Place 16
1.2 Advances in a Newly Upgraded Network: The China Earthquake Administration (CEA) Effort 19
1.2.1 Observatories in China: Short History Up to Twentieth Century 19
1.2.2 Planning the Major Upgrade: Towards INTERMAGNET Standards 19
1.2.2.1 Description of Present and Future Network 20
1.2.2.2 Criteria for Geographical Distribution 21
1.2.2.3 Instrumentation 21
1.2.2.4 Buildings: Describing the Way the Buildings are Designed and How Many Per Observatory [China Earthquake Administration, 2004 ] 21
1.2.2.5 Staff: Training Level, Quantity 23
1.2.3 Modern Centralized Data Processing 24
1.2.3.1 A Centralized Approach 24
1.2.3.2 Data Quality Assessment: How-to 24
1.3 Filling the Gaps: Sea-Bottom Observatories 27
1.3.1 Rationale 27
1.3.2 Where to Deploy? 28
1.3.3 Seafloor Environments 29
1.3.4 Specific Solutions for Seafloor Geomagnetic Instrumentation 31
1.3.4.1 Underwater Housing of the Observatory 31
1.3.4.2 Total Field Measurement 33
1.3.4.3 Component Measurements 33
1.3.4.4 Orientation at the Seafloor 33
1.3.5 Shortcomings Still Preventing the Full Absolute Accuracy: How to Eliminate Them? 35
1.3.6 The Future of Seafloor Observatories: Where Do We Head from Here? 37
References 37
2 Magnetic Satellite Missions and Data 39
2.1 Introduction 39
2.1.1 Basic Equations 39
2.1.2 Magnetic vs. Gravity Field 40
2.2 Characteristics of Magnetic Satellite Data 41
2.2.1 Orbit, Time and Position 41
2.2.2 Calibration and Alignment of Satellite Data 42
2.3 A parade of Magnetic Satellite Missions 44
2.3.1 POGO (OGO-2, OGO-4, OGO-6) 44
2.3.2 Magsat 45
2.3.3 Ørsted 45
2.3.4 SAC-C/Ørsted-2 48
2.3.5 CHAMP 48
2.3.6 Swarm 48
2.4 The Years After Swarm 48
2.5 Outlook: Space Magnetic Gradiometry 50
2.5.1 General Case: B as a Solenoid Vector Field 51
2.5.2 Toroidal-Poloidal Decomposition 52
2.5.3 Laplacian Potential Approximation 52
2.5.4 Magnetic Field Gradient Tensor Visualization 53
2.6 Summary 55
References 56
3 Repeat Station Activities 57
3.1 Introduction 57
3.2 History of Repeat Stations 57
3.3 Instruments and Procedures 59
3.3.1 Establishing the Position of a Station 59
3.3.2 Establishing the Direction of True North 60
3.3.3 Measuring the Magnetic Field 61
3.3.4 Data Reduction 62
3.4 Uses of Repeat Station Data 64
3.5 State of the Art of Repeat Station Activities 65
3.6 Conclusions 66
References 66
4 Aeromagnetic and Marine Measurements 68
4.1 General Introduction 68
4.2 Introduction to Aeromagnetics 69
4.3 History of Aeromagnetics 71
4.4 Data Acquisition and Reduction 74
4.4.1 Instrumentation 74
4.4.2 Fluxgate Magnetometers 74
4.4.3 Nuclear Precession Magnetometers 75
4.4.3.1 Proton Precession Magnetometers 75
4.4.3.2 Overhauser Effect Magnetometers 76
4.4.3.3 Optical Pumping Alkali Vapor Magnetometers 76
4.5 Survey Design 76
4.5.1 Flight Direction and Line Spacing 77
4.5.2 Survey Flight Height 78
4.6 Data Acquisition 78
4.6.1 Magnetic Compensation of Aircraft 79
4.7 Data Checking and Reduction 83
4.7.1 In-Flight Data Checking 84
4.7.2 Post-Flight Checking 84
4.8 Data Processing 85
4.8.1 Magnetic Anomaly Field Determination 85
4.8.2 Temporal Reductions/Corrections 86
4.8.3 Magnetic Leveling 88
4.9 Lithospheric Field Mapping Reference Field Correction 89
4.10 Further Processing: Micro-leveling 92
4.11 Interpolating, Contouring and Gridding 93
4.12 Conclusions for Aeromagnetics 94
4.13 Introduction to Marine Magnetics 94
4.14 History of Marine Magnetics 95
4.14.1 The First Attempts 95
4.14.2 Evolution of the Global Dataset 96
4.14.3 Storage and Accessibility 98
4.14.4 Scientific Objectives 98
4.15 Sources of Error, Evolution and Correction for Scalar Sea-Surface Measurements 100
4.15.1 Magnetic Observation Accuracy 100
4.15.1.1 Definitions 100
4.15.1.2 Fluxgate Magnetometers 101
4.15.1.3 Proton Precession Magnetometers 101
4.15.1.4 Optically-Pumped or Alkali-Vapor Sensors 101
4.15.1.5 Overhauser Effect Sensors 101
4.15.2 Ship Noise 101
4.15.3 Position of the Ship 102
4.15.4 Date and Time of the Measurement 102
4.15.5 Transcription Errors 102
4.15.6 Estimation of the External Magnetic Field 103
4.15.7 Estimation of the Core Magnetic Field 103
4.15.8 Summary of Marine Magnetic Observation Errors 103
4.16 Unusual Instruments and Processing Approaches 103
4.16.1 Vector Marine Magnetic Observations 104
4.16.2 Deep-Sea Magnetic Observations 105
4.16.2.1 Procedures 106
4.16.2.2 Some Applications 107
4.17 Conclusions for Marine Magnetics 108
4.18 General Conclusion 108
References 108
5 Instruments and Methodologies for Measurement of the Earth's Magnetic Field 115
5.1 Introduction 116
5.2 Fluxgate Magnetometer 116
5.2.1 Instrument Standards and Sources of Error 117
5.2.2 Fluxgate Mechanism 118
5.2.3 Data Collection and Telemetry 120
5.3 Declination-Inclination Fluxgate Magnetometer 121
5.3.1 Observing Procedure 122
5.3.2 Instrumental Accuracy and Sources of Error 123
5.4 Scalar (Quantum) Magnetometers 125
5.4.1 Background Physics 126
5.4.1.1 Polarization 126
5.4.2 Proton Precession Magnetometer 127
5.4.3 Overhauser Magnetometers 128
5.4.4 Time of Reading 128
5.4.5 Optically Pumped Magnetometers 129
5.5 Use of Scalar Magnetometers for Component Determination 129
5.6 Automated Absolute Observations 130
5.7 Other Magnetometers 131
5.7.1 Declinometer 131
5.7.2 Quartz Horizontal Magnetometer 131
5.7.3 Torsion Photoelectric Magnetometer 132
5.7.4 Kakioka KASMMER System 132
5.8 Looking Forward 132
Appendix 1: Accuracy and Baselines 133
Appendix 2: Absolute Accuracy of Scalar Magnetometers 134
References 134
6 Improvements in Geomagnetic Observatory Data Quality 137
6.1 Introduction 137
6.2 Quality of Recording of Geomagnetic Variations 138
6.2.1 Physical Principles of Variometers 138
6.2.1.1 Fluxgate Magnetometers 138
6.2.1.2 Photoelectric Feed-Back Magnetometers 139
6.2.1.3 Vector Variometers Based on Scalar Magnetometers 139
6.2.2 Practical Aspects of Variometer Operation 140
6.2.3 Quality Detection of Variometers 141
6.2.3.1 Base Line Behaviour 141
6.2.3.2 Delta-F Check 142
6.2.3.3 Inter-Comparison with Other Magnetometers 143
6.3 Quality of Secular Variation Observations 146
6.4 External Factors Disturbing Observations of the Geomagnetic Field 148
6.5 Inspection of Reported and Final Geomagnetic Data, Aims of Verification of Data 150
6.6 Metadata and Data Quality 155
6.6.1 What is Metadata? 155
6.6.2 Metadata in Geomagnetism 155
6.6.3 Geomagnetic Metadata Standards 156
References 157
7 Magnetic Observatory Data and Metadata: Types and Availability 159
7.1 Introduction 159
7.2 Data Types 160
7.2.1 Printed Media 160
7.2.1.1 Eye-Observations 160
7.2.1.2 Magnetograms 162
7.2.1.3 Calibration Data 162
7.2.1.4 Hourly Values 162
7.2.1.5 Magnetic Activity Indices 162
7.2.1.6 Yearbooks 164
7.2.1.7 Conservation and Conversion of Printed Media 165
7.2.2 Electronic Media 167
7.2.2.1 Minute Means 167
7.2.2.2 Hourly, Daily, Monthly, Annual Means 168
7.2.2.3 Digital Magnetic Activity Indices 169
7.2.2.4 One-Second Data 169
7.2.2.5 Quasi-Definitive Data 170
7.3 Data Availability 171
7.3.1 World Data Centres for Geomagnetism 171
7.3.1.1 World Data Centre for Geomagnetism, Edinburgh 171
7.3.1.2 World Data Center for Geomagnetism, Kyoto 172
7.3.1.3 World Data Center for Geomagnetism, Copenhagen 174
7.3.1.4 World Data Centre for Geomagnetism, Mumbai 174
7.3.1.5 World Data Center for Solar-Terrestrial Physics, Moscow 174
7.3.1.6 World Data Center for Solar-Terrestrial Physics, Boulder 175
7.3.1.7 World Data Centre for Solar-Terrestrial Science, Sydney 175
7.3.1.8 World Data Center for Geophysics, Beijing 175
7.3.2 INTERMAGNET 175
7.3.3 World Data System 176
7.3.4 The International Service of Geomagnetic Indices 177
7.3.4.1 LATMOS, France 177
7.3.4.2 GeoForschungsZentrum, Germany 177
7.3.4.3 Observatorio del Ebro, Spain 177
7.3.5 Other Data Resources 178
7.3.5.1 Space Physics Interactive Data Resource 178
7.3.5.2 Observatory Operator's Websites 178
7.3.5.3 Variometer Networks 178
7.4 Metadata and Metadata Standards 178
7.4.1 Magnetic Observatory Metadata 179
7.4.1.1 Yearbooks 179
7.4.1.2 INTERMAGNET 180
7.4.1.3 Metadata Standards 180
7.4.2 FGDC Standard 180
7.4.3 ISO-19115 Standard 181
7.4.4 SPASE Data Model 181
7.4.5 XML 182
7.4.6 Databases 182
7.5 Metadata Distribution 182
7.5.1 SPIDR VO (USA) 183
7.5.2 GeoMIND (Europe) 183
7.5.3 GEOMET (Australia) 183
7.5.4 IUGONET (Japan) 183
7.5.5 GeoNetwork (Open Source) 184
7.6 Conclusion 185
Appendix 1: Data File Formats 187
World Data Centre Exchange Format 187
INTERMAGNET GIN Dissemination Formats 187
IAGA-2002 Format 187
Appendix 2: Internet Links 188
References 188
8 Geomagnetic Indices 192
8.1 Introduction 193
8.2 Physical Background 194
8.2.1 Basics 194
8.2.2 Electric Currents in the Magnetosphere-Ionosphere System 195
8.3 Polar and Auroral Indices 199
8.3.1 PC Index 199
8.3.1.1 History 199
8.3.1.2 Definition of the PC Index 202
8.3.1.3 Correlation with Interplanetary and Magnetosphere Quantities 203
8.3.1.4 Use and Misuse of PC Index 205
8.3.2 Auroral-Electrojet (AE) Indices 205
8.3.2.1 History 206
8.3.2.2 Definition of the AE Indices 206
8.3.2.3 Basic Characteristics of AE Indices 206
8.3.2.4 Relation with Magnetospheric and Ionospheric Physical Quantities 208
8.3.2.5 Use and Misuse of the AE Indices 208
8.3.2.6 What Next for the AE Indices 209
8.4 K Index 209
8.4.1 History 209
8.4.2 Definition of the K Index 210
8.4.3 The Irregular Activity as Described by the K Indices 210
8.4.4 Physical Meaning of K Indices 211
8.4.5 Use and Misuse of K Indices 212
8.5 K-Derived Geomagnetic Indices 212
8.5.1 History 212
8.5.2 Definition of the K-Derived Geomagnetic Indices 212
8.5.2.1 Kp (ap) Indices 213
8.5.2.2 am, an, and as Indices 214
8.5.2.3 a Longitude Sector Index 217
8.5.2.4 aa Index 217
8.5.3 Comparison Between ap, am, and aa 219
8.5.4 Classification of Days 221
8.5.4.1 Classification of Days as Deduced from Kp Indices 221
8.5.4.2 Classification of Days as Deduced from aa Indices 221
8.5.5 Relation with Solar Wind Parameters 221
8.5.6 Secular Variation of Geomagnetic Activity 222
8.5.7 Annual and Diurnal Modulations 223
8.5.8 Use and Misuse of K-Derived Planetary Indices 224
8.5.9 What Next? 224
8.6 Storm Indices 224
8.6.1 Dst Index 225
8.6.1.1 Definition and Method of Derivation of the Dst Index 225
8.6.1.2 Basic Characteristics of the Dst Index 226
8.6.1.3 Relationship with Magnetospheric, Ionospheric and Induced Currents 226
8.6.1.4 Use and Misuse of the Dst Index 227
8.6.2 ASY and SYM Indices 227
8.6.2.1 Definition and Method of Derivation of the ASY and SYM Indices 228
8.6.2.2 Basic Characteristics of the ASY and SYM Indices 229
8.6.2.3 Relationship of the ASY Indices with Magnetospheric and Ionospheric Currents 229
8.6.2.4 Use and Misuse of ASY and SYM Indices 230
8.6.3 Storm Sudden Commencements (ssc) 230
8.6.4 What Next? 230
8.7 Some Other Indices 231
8.7.1 IHV and IDV Indices 231
8.7.2 Pulsations Indices 231
8.7.2.1 The Wp Index 231
8.7.2.2 ULF Indices 232
8.7.2.3 Localised PC3 Indices 232
8.8 Concluding Remarks 232
References 233
9 Modelling the Earth's Magnetic Field from Global to Regional Scales 238
9.1 Introduction 238
9.2 Global Modelling With Spherical Harmonics in a Shell 240
9.2.1 Resolution of Laplace Equation by the Fourier Decomposition Method 240
9.2.2 Orthogonality and Completeness Properties 242
9.2.3 Spherical Harmonic Expansion and Convergence Properties 243
9.3 Other Modelling at a Global Scale 244
9.3.1 Wavelets 245
9.3.1.1 Poisson Wavelets 246
9.3.1.2 Multi-scale Modelling 248
9.3.2 Localized Harmonic Functions 250
9.4 Modelling the Field Regionally 252
9.4.1 Review of Modelling in the Flat Earth Approximation 252
9.4.1.1 Rectangular Harmonic Analysis 253
9.4.1.2 Cylindrical Harmonic Analysis 255
9.4.2 SCHA and R-SCHA 256
9.4.2.1 Definition of the Domain 257
9.4.2.2 Resolution of Laplace Equation in SCHA by the Fourier Decomposition Method 257
9.4.2.3 R-SCHA as a Boundary Value Problem 259
9.4.2.4 Orthogonality Properties, Uniqueness and Completeness 261
9.4.3 Boundary Effects 263
9.4.4 Infinite Conical Domain 263
9.4.5 Slepian Functions 265
9.4.5.1 Slepian Functions in KL (R) 266
9.4.5.2 Slepian Functions in KL (r) 267
9.4.5.3 Potential Field Estimation On r 268
9.5 Conclusions 269
References 270
10 The International Geomagnetic Reference Field 274
10.1 Introduction 274
10.2 Scope of the IGRF 274
10.3 Inception and Development 274
10.4 Applications and Availability 275
10.5 Geomagnetic Field Components 275
10.6 Mathematical Representation 277
10.7 IGRF 11th Generation (Revised 2009) 278
10.8 Global Magnetic Field Patterns 281
10.9 Limitations 281
10.10 Future 284
References 285
11 Geomagnetic Core Field Models in the Satellite Era 286
11.1 Introduction 286
11.2 Overview and Theory 287
11.3 Detailed Description 289
11.3.1 CHAOS Model Series 289
11.3.1.1 Aims 289
11.3.1.2 Technique 290
11.3.1.3 Results and Discussion 292
11.3.2 GRIMM Models 292
11.3.2.1 Aims 292
11.3.2.2 Techniques 294
11.3.2.3 Results and Discussion 295
11.3.3 BGS Models 297
11.3.3.1 Aims 297
11.3.3.2 Techniques 297
11.3.3.3 Results and Discussion 299
11.4 Conclusion 301
References 302
12 Interpretation of Core Field Models 304
12.1 Introduction 304
12.2 Core Dynamics and Geodynamo 305
12.3 Core Flow and High Frequency SV 306
12.3.1 Core Flow Inferred from Satellite Magnetic Data 307
12.3.2 Torsional Oscillations in the Core 308
12.4 Prediction of Geomagnetic Secular Variation 311
12.4.1 Mathematical Fundamentals of Data Assimilation 311
12.4.2 Application of Core Flow Models in SV Forecast 312
12.4.3 Assimilation with Simple Dynamical Models 313
12.4.4 Data Assimilation with Full Geodynamo Models 314
12.5 Discussion 315
References 316
13 Mapping and Interpretation of the Lithospheric MagneticINTbreak Field
13.1 Introduction 319
13.2 World Digital Magnetic Anomaly Map 320
13.3 Impacts 321
13.4 Tectonics 325
13.5 Resource Exploration 328
13.6 Interpretation of Lower Crustal Processes 340
13.7 Summary 340
References 341
Index 346