introduction to geomagnetic fields -...

12

Click here to load reader

Upload: lamnhi

Post on 07-Apr-2019

213 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

INTRODUCTION TO GEOMAGNETIC FIELDS

Introduction to Geomagnetic Fields is a textbook for advanced undergraduateand graduate students of geophysics. It explains the natural magnetic fields inand surrounding the Earth that arise from a variety of electric currents. Suchelectric currents exist within atomic structures, in the Earth’s liquid outer core,in the ionized upper atmosphere, and in the Earth’s space environment duringsolar–terrestrial disturbances (magnetic storms).

The author clearly presents these different components of the Earth’s mag-netic field with a minimum of mathematical complexity. Variations in the geo-magnetic field over a range of time-scales are discussed, including reversalsof the Earth’s main dipolar field, disturbances of the magnetosphere caused byparticles and fields radiating from the Sun, and daily changes caused by the tidaland wind motion of the ionosphere. Readers are also introduced to the tech-niques and instrumentation for measuring geomagnetic fields, and to the rangeof applications for which these measurements are used.

This second edition has been fully revised to includemany of themost recentadvances in this subject area. It has been designed as a textbook for use withsemester courses in geomagnetism and includes student exercises at the endof each chapter. Special appendices review relevant mathematical techniquesand direct the reader to various journals, books, organizations, and websiteswhere the latest computer programs for geomagnetism may be downloaded.

wallace campbell graduated with a Ph.D. in Physics from the Universityof California, Los Angeles, in 1959. Following a year with the Geophysical In-stitute in the University of Alaska, he accepted a position for geomagnetic fieldstudies with the National Bureau of Standards Laboratory in Boulder, Colorado,that subsequently became the Environmental Research Laboratory of NOAA.He remained there until 1973 when a federal reorganization transferred hisgroup to the United States Geological Survey in Golden, Colorado, for stud-ies in geomagnetic applications. He retired from the USGS in 1996 and sincethen has worked as a Guest Scientist with the Solar–Terrestrial Physics Division,National Geophysical Data Center of NOAA. Dr Campbell is the author of 128geomagnetism publications. His research subjects include ionospheric currents,deep-Earth electrical conductivity, geomagnetic storms, geomagnetic pulsa-tions, quiet-time field variations, and geomagnetic field applications. He is alsothe coeditor (and contributing author) of the textbook Physics of GeomagneticPhenomena (1967) and the author of Earth Magnetism: a Guided Tour ThroughMagnetic Fields (2001).

Solutions to the exercises can be found at http://www.cambridge.org/9780521822060.

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 2: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 3: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

INTRODUCTION TOGEOMAGNETIC FIELDSSecond Edition

WALLACE H. CAMPBELL

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 4: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

University Printing House, Cambridge CB2 8BS, United Kingdom

Cambridge University Press is part of the University of Cambridge.

It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence.

www.cambridge.org Information on this title: www.cambridge.org/9780521822060

© Wallace H. Campbell 1997, 2003

This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press.

First published 1997Second edition 2003

A catalogue record for this publication is available from the British Library

ISBN 978-0-521-82206-0 HardbackISBN 978-0-521-52953-2 Paperback

Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 5: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

Contents

Preface page ixAcknowledgements xii1 The Earth’s main field 1

1.1 Introduction 11.2 Magnetic Components 41.3 Simple Dipole Field 81.4 Full Representation of the Main Field 151.5 Features of the Main Field 341.6 Charting the Field 411.7 Field Values for Modeling 471.8 Earth’s Interior as a Source 511.9 Paleomagnetism 581.10 Planetary Fields 621.11 Main Field Summary 631.12 Exercises 65

2 Quiet-time field variations and dynamo currents 672.1 Introduction 672.2 Quiet Geomagnetic Day 682.3 Ionosphere 742.4 Atmospheric Motions 812.5 Evidence for Ionospheric Current 862.6 Spherical Harmonic Analysis of the Quiet Field 922.7 Lunar, Flare, Eclipse, and Special Effects 1022.8 Quiet-Field Summary 1082.9 Exercises 109

3 Solar–terrestrial activity 1113.1 Introduction 1113.2 Quiet Sun 1133.3 Active Sun, Sunspots, Fields, and Coronal Holes 1163.4 Plages, Prominences, Filaments, and Flares 1223.5 Mass Ejections and Energetic Particle Events 1273.6 Interplanetary Field and Solar Wind Shocks 1283.7 Solar Wind–Magnetosphere Interaction 1353.8 Geomagnetic Storms 139

v

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 6: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

vi Contents

3.9 Substorms 1423.10 Tail, Ring, and Field-Aligned Currents 1443.11 Auroras and Ionospheric Currents 1523.12 Radiation Belts 1653.13 Geomagnetic Spectra and Pulsations 1683.14 High Frequency Natural Fields 1733.15 Geomagnetic Indices 1753.16 Solar–Terrestrial Activity Summary 1843.17 Exercises 186

4 Measurement methods 1894.1 Introduction 1894.2 Bar Magnet Compass 1904.3 Classical Variometer 1944.4 Astatic Magnetometer 1954.5 Earth-Current Probe 1964.6 Induction-Loop Magnetometer 1984.7 Spinner Magnetometer 2004.8 Fluxgate (Saturable-Core) Magnetometer 2014.9 Proton-Precession Magnetometer 2034.10 Optically Pumped Magnetometer 2054.11 Zeeman-Effect Magnetometer 2104.12 Cryogenic Superconductor Magnetometer 2124.13 Gradient Magnetometer 2134.14 Comparison of Magnetometers 2154.15 Observatories 2154.16 Location and Direction 2194.17 Field Sampling and Data Collection 2194.18 Tropospheric and Ionospheric Observations 2214.19 Magnetospheric Measurements 2224.20 Instrument Summary 2254.21 Exercises 226

5 Applications 2285.1 Introduction 2285.2 Physics of the Earth’s Space Environment 2295.3 Satellite Damage and Tracking 2305.4 Induction in Long Pipelines 2335.5 Induction in Electric Power Grids 2355.6 Communication Systems 2375.7 Disruption of GPS 2395.8 Structure of the Earth’s Crust and Mantle 239

5.8.1 Surface Area Traverses for Magnetization Fields 2415.8.2 Aeromagnetic Surveys 241

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 7: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

Contents vii

5.8.3 Conductivity Sounding of the Earth’s Crust 2465.8.4 Conductivity of the Earth’s Upper Mantle 251

5.9 Ocean Bottom Studies 2535.10 Continental Drift 2555.11 Archeomagnetism 2575.12 Magnetic Charts 2575.13 Navigation 2585.14 Geomagnetism and Weather 2595.15 Geomagnetism and Life Forms 2625.16 Solar–Terrestrial Disturbance Predictions 2695.17 Magnetic Frauds 271

5.17.1 Body Magnets 2775.17.2 Prediction of Earthquakes 277

5.18 Summary of Applications 2785.19 Exercises 279

Appendix A Mathematical topics 280A.1 Variables and Functions 280A.2 Summations, Products, and Factorials 282A.3 Scientific Notations and Names for Numbers 282A.4 Logarithms 283A.5 Trigonometry 284A.6 Complex Numbers 285A.7 Limits, Differentials, and Integrals 287A.8 Vector Notations 289A.9 Value Distributions 291A.10 Correlation of Paired Values 294

Appendix B Geomagnetic organizations, services,and bibliography 296

B.1 International Unions and Programs 296B.2 World Data Centers for Geomagnetism 298B.3 Special USGS Geomagnetics Website 303B.4 Special Geomagnetic Data Sets 304B.5 Special Organization Services 306B.6 Solar–Terrestrial Activity Forecasting Centers 309B.7 Bibliography for Geomagnetism 312B.8 Principal Scientific Journals for Geomagnetism 313

Appendix C Utility programs for geomagnetic fields 315C.1 Geomagnetic Coordinates 1940–2005 315C.2 Fields from the IGRF Model 316C.3 Quiet-Day Field Variation, Sq 316C.4 The Geomagnetic Disturbance Index, Dst 317C.5 Location of the Sun and Moon 318

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 8: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

viii Contents

C.6 Day Number 318C.7 Polynomial Fitting 319C.8 Quiet-Day Spectral Analysis 319C.9 Median of Sorted Values 319C.10 Mean, Standard Deviation, and Correlation 320C.11 Demonstration of Spherical Harmonics 320C.12 Table of All Field Models 321

References 322Index 332

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 9: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

Preface

This second edition of Introduction to Geomagnetic Fields has beenredesigned as a classroom textbook for a semester course in geomag-netism. Student exercises have been added at the end of each chapter.Outdated figures and tables are replaced with more modern equivalents.Recent discoveries, field information, and references have been addedalong with special websites and computer programs. The basic struc-ture of the original edition remains, providing a condensed and morereadable coverage of geomagnetic topics than is afforded by existingtextbooks.

My intention has been to focus upon the basic concepts and physi-cal processes necessary for understanding the Earth’s natural magneticfields. When mathematical presentation is required, I have tried to re-move the mystery of the scientists’ special jargon and to emphasize themeanings of important equations, rather than obscure the relationshipswith complex formulas. Because some formulas are needed to appreci-ate geomagnetism, I have included, in an appendix, a succinct review ofthe required mathematical definitions and facts. For those readers whoare approaching the subject of Earth magnetic fields for the very firsttime it may be helpful to start with the small layman’s presentation, de-void of all mathematical equations, that I provided as Earth Magnetism:A Guided Tour Through Magnetic Fields, Academic Press, San Diego,151 pp, 2001.

The student reader is expected to have a familiarity with the el-ementary scientific concepts identified by words of specific meaning,such as “force, velocity, energy, temperature, heat, charge, light waves,and fields of electric, magnetic, and gravitational nature”. Excellenthelp is available if you are among those readers who have somehowmissed receiving an explanation of these terms in your schooling. AlbertEinstein and Leopold Infeld realized this need back in 1938 and wrotefor you a small book, The Evolution of Physics (republished by Simonand Schuster, New York, 1961), which is as applicable today as it wasover sixty years ago. That book uses remarkable simplicity of logic andlanguage to reveal the fundamental concepts and terms now in use byphysical scientists. In particular, with no mathematical formulas, their

ix

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 10: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

x Preface

first two chapters not only provide the necessary basics for the sciencenovice but also can reawaken an appreciation of the physical world madedormant by a schooling overdose of isolated facts and mathematicalgymnastics.

To be called a proper “Introduction to Geomagnetic Fields” my bookmust contain the particular subjects that I have grouped into five chap-ters as follows. In Chapter 1 we explore the Earth’s main field, con-sider its dipole representation, examine the vast extension of the fieldsinto space, decipher the modeling methods of compact field represen-tation, locate the many magnetic poles, and discuss paleomagnetic fieldreversals due to the source currents in the deep liquid core of the Earth.In Chapter 2 we find the reasons for quiet-time regular daily and sea-sonal field variations arising as electric currents in our Earth’s upperatmosphere. We separate out the secondary currents that are inducedto flow in the Earth itself – but find application in determining Earthconductivity profiles. In Chapter 3 we consider the major disturbancesto the ordered particle and field configuration about the Earth. Thesegeomagnetic storms have their origin in solar outbursts and act as mon-itors of changes in our space environment. In Chapter 4 we discoverhow magnetic field sensors (magnetometers) function, discuss some ob-servation techniques, and look at measurement methods on the groundand in space. Finally, in Chapter 5 we consider the many useful applica-tions of our knowledge of the main geomagnetic field and its temporalchanges.

The book also contains three appendices. Appendix A is a reviewof mathematical concepts that the reader will encounter. Appendix Bprovides a guide to the major international organizations, a geomag-netism bibliography, and the useful source and website addresses forgeomagnetic information. Appendix C gives the description of free spe-cial computer programs that are designed to help the beginning studentin geomagnetism.

I have included more than the typical amount of text illustrations.Theyhave been carefully selected to clarify concepts for the reader, ratherthan to burden him with a tedious overabundance of data reproductions.A great number of significant website addresses have been included.Although I have tried to guide the reader to known non-volatile websites,neither I nor the publisher can be held responsible if a site listed in thisbook is modified or disappears. The book index has been limited to thosespecial words that I have considered to be of particular importance foran introduction to geomagnetic fields; don’t expect to find place names,etc. This is a beginning textbook about geomagnetism; for full details oneach of the chapter topics please borrow, from your library, the excellentreference books listed in Appendix B.

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 11: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

Preface xi

For the interpretation of phenomena, I have tried to stay with thecurrent scientific consensus. However, in the future, many aspects ofgeomagnetism that are still being explored will undoubtedly changesome of my viewpoints. Perhaps you can be the one to make such acontribution.

WHC

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information

Page 12: INTRODUCTION TO GEOMAGNETIC FIELDS - Assetsassets.cambridge.org/97805218/22060/frontmatter/9780521822060... · INTRODUCTION TO GEOMAGNETIC FIELDS Introduction to Geomagnetic Fields

Acknowledgments

This small book had its origin, organization, and testing in my tutoriallectures at US Geological Survey; the Space Environment Laboratory ofthe National Oceanic and Atmospheric Administration; the World DataCenter of the National Geophysical Data Center; the Australian Geologi-cal Survey Organisation (now Geoscience Australia); the Australian IPSRadio and Space Services; the Colorado School ofMines; the Universityof Colorado; the Academy of Sciences, Beijing; and the University ofCairo, Egypt.

I give special thanks for the guidance provided by researchers whoseworks are listed in the Bibliography and Reference sections, all of whomhave made important contributions to the study of geomagnetic fields.In addition I have relied heavily on my personal scientific publications;the unreferenced figures are my own.

I appreciate the help of many scientists, teachers, special friends,and excellent technical reviewers who provided suggestions and ma-terial for improving various sections of the book. In particular, forassistance in preparing this second revision, I give special thanks toJ. Quinn and D. Herzog (both at the US Geological Survey, Golden,USA), S. McLean, H. Coffey, E. Kihn, and B. Poppe (all at the NationalOceanic and Atmospheric Administration, Boulder, USA), C. Barton,P. McFadden, and P. Milligan (all at Geophysics Australia, Canberra,Australia), D. Cole (at IPSRadio and Space Services, Sydney,Australia),D. Boteler (at the Geological Survey of Canada), G. Rostoker (at theUniversity of Alberta, Canada), M. Barreto (at Observatorio Nacional,Rio de Janeiro, Brazil) and A. Adam (at the Geodetic and GeophysicalResearch Institute, Sopron, Hungary). I also thank my wife Beth, whoassisted in editing the manuscript and endured my many hours spent atthe computer.

WHC

xii

www.cambridge.org© in this web service Cambridge University Press

Cambridge University Press978-0-521-82206-0 - Introduction to Geomagnetic Fields: Second EditionWallace H. CampbellFrontmatterMore information