1 Earth’s Magnetic Field Introduction –Earth’s structure Observations –Magnetic observatories –Satellites –Dedicated field campaigns The external field –Source field for studies of the electrical conductivity at crustal and mantle levels The crustal field The core field Time variations Paleomagnetic observations Secular variations Satellite observations

2 Earth’s Magnetic Field The Geodynamo –Governing equations –Approximations –Simulations

3 Earth’s Magnetic Field Crustal sources for the magnetic field –Remanent magnetization –Induced magnetization –Relation to past and ongoing processes

4 Volume 5: Geomagnetism 5.01 Geomagnetism in Perspective, Pages 1-31, M. Kono SummaryPlus | Chapter | PDF (2904 K) | View Related Articles 5.02 The Present Field, Pages 33-75, N. Olsen, G. Hulot and T.J. Sabaka SummaryPlus | Chapter | PDF (14345 K) | View Related Articles 5.03 Magnetospheric Contributions to the Terrestrial Magnetic Field, Pages 77-92, W. Baumjohann and R. Nakamura SummaryPlus | Chapter | PDF (684 K) | View Related Articles 5.04 Observation and Measurement Techniques, Pages , G.M. Turner, J.L. Rasson and C.V. Reeves SummaryPlus | Chapter | PDF (2319 K) | View Related Articles 5.05 Geomagnetic Secular Variation and Its Applications to the Core, Pages , A. Jackson and C.C. Finlay SummaryPlus | Chapter | PDF (7793 K) | View Related Articles 5.06 Crustal Magnetism, Pages , M.E. Purucker and K.A. Whaler SummaryPlus | Chapter | PDF (4208 K) | View Related Articles 5.07 Geomagnetism, Pages , S. Constable SummaryPlus | Chapter | PDF (1692 K) | View Related Articles 5.08 Magnetizations in Rocks and Minerals, Pages , D.J. Dunlop and Ö. Özdemir SummaryPlus | Chapter | PDF (3105 K) | View Related Articles 5.09 Centennial- to Millennial-Scale Geomagnetic Field Variations, Pages , C. Constable SummaryPlus | Chapter | PDF (3744 K) | View Related Articles 5.10 Geomagnetic Excursions, Pages , C. Laj and J.E.T. Channell SummaryPlus | Chapter | PDF (1692 K) | View Related Articles 5.11 Time-Averaged Field and Paleosecular Variation, Pages , C.L. Johnson and P. McFadden SummaryPlus | Chapter | PDF (3723 K) | View Related Articles 5.12 Source of Oceanic Magnetic Anomalies and the Geomagnetic Polarity Timescale, Pages , J.S. Gee and D.V. Kent SummaryPlus | Chapter | PDF (3684 K) | View Related Articles 5.13 Paleointensities, Pages , L. Tauxe and T. Yamazaki SummaryPlus | Chapter | PDF (2882 K) | View Related Articles 5.14 True Polar Wander: Linking Deep and Shallow Geodynamics to Hydro- and Bio-Spheric Hypotheses, Pages , T.D. Raub, J.L. Kirschvink and D.A.D. Evans SummaryPlus | Chapter | PDF (1558 K) | View Related Articles SummaryPlusChapterPDF (2904 K)View Related Articles SummaryPlusChapterPDF (14345 K)View Related Articles SummaryPlusChapterPDF (684 K)View Related Articles SummaryPlusChapterPDF (2319 K)View Related Articles SummaryPlusChapterPDF (7793 K)View Related Articles SummaryPlusChapterPDF (4208 K)View Related Articles SummaryPlusChapterPDF (1692 K)View Related Articles SummaryPlusChapterPDF (3105 K)View Related Articles SummaryPlusChapterPDF (3744 K)View Related Articles SummaryPlusChapterPDF (1692 K)View Related Articles SummaryPlusChapterPDF (3723 K)View Related Articles SummaryPlusChapterPDF (3684 K)View Related Articles SummaryPlusChapterPDF (2882 K)View Related Articles SummaryPlusChapterPDF (1558 K)View Related Articles

5 Volume 8: Core Dynamics 8.01 Overview, Pages 1-30, P. Olson SummaryPlus | Chapter | PDF (1025 K) | View Related Articles 8.02 Energetics of the Core, Pages 31-65, F. Nimmo SummaryPlus | Chapter | PDF (842 K) | View Related Articles 8.03 Theory of the Geodynamo, Pages , P.H. Roberts SummaryPlus | Chapter | PDF (945 K) | View Related Articles 8.04 Large-Scale Flow in the Core, Pages , R. Holme SummaryPlus | Chapter | PDF (2755 K) | View Related Articles 8.05 Thermal and Compositional Convection in the Outer Core, Pages , C.A. Jones SummaryPlus | Chapter | PDF (1763 K) | View Related Articles 8.06 Turbulence and Small-Scale Dynamics in the Core, Pages , D.E. Loper SummaryPlus | Chapter | PDF (365 K) | View Related Articles 8.07 Rotational Dynamics of the Core, Pages , A. Tilgner SummaryPlus | Chapter | PDF (2784 K) | View Related Articles 8.08 Numerical Dynamo Simulations, Pages , U.R. Christensen and J. Wicht SummaryPlus | Chapter | PDF (1868 K) | View Related Articles 8.09 Magnetic Polarity Reversals in the Core, Pages , G.A. Glatzmaier and R.S. Coe SummaryPlus | Chapter | PDF (2692 K) | View Related Articles 8.10 Inner-Core Dynamics, Pages , I. Sumita and M.I. Bergman SummaryPlus | Chapter | PDF (453 K) | View Related Articles 8.11 Experiments on Core Dynamics, Pages , P. Cardin and P. Olson SummaryPlus | Chapter | PDF (1731 K) | View Related Articles 8.12 Core–Mantle Interactions, Pages , B.A. Buffett SummaryPlusChapterPDF (1025 K)View Related Articles SummaryPlusChapterPDF (842 K)View Related Articles SummaryPlusChapterPDF (945 K)View Related Articles SummaryPlusChapterPDF (2755 K)View Related Articles SummaryPlusChapterPDF (1763 K)View Related Articles SummaryPlusChapterPDF (365 K)View Related Articles SummaryPlusChapterPDF (2784 K)View Related Articles SummaryPlusChapterPDF (1868 K)View Related Articles SummaryPlusChapterPDF (2692 K)View Related Articles SummaryPlusChapterPDF (453 K)View Related Articles SummaryPlusChapterPDF (1731 K)View Related Articles

6 Magnetic Pattern of the Oceans

7 Magnetic Lineations. Mars

8 P-wave Velocity Perturbation Mid-Mantle

9 Shear Wave Velocity Perturbation. Base of Mantle

10 Importance of Earth’s Magnetic Field Earth’s magnetic field is necessary for life on Earth. The magnetic field protects us against the flow of charged particles from the sun and acts a kind of shield. Some researchers believe that evolution of life is accelerated during periods of weak magnetic fields, because this would enhance genetic changes – mutations. The magnetic field on the continents and their shelves is used for prospecting after oil, gas and mineral deposits. The interpretation of the magnetic field on the oceans had a major impact on the development of plate tectonics.

11 The Geomagnetic Earth

12 Sources of the Geomagnetic Field

13 MAGSAT (left) and Oersted (right) Satellites

14 German CHAMP satellite

15 Örsted Satellite Orbit

16 Magnetic Field Satellites

17 Spherical Harmonic Representation of Magnetic Field Internal source region External source region Source free region ”Region of observations” n = degree

18 Geomagnetic Spectrum

19 Crustal Magnetic Fields From Maus (2007) n = 100

20 Curie Depth Antarctica Crustal Mag Field Crustal Thickness Curie Depth Heat Flow

21 Geomagnetic Jargong Frontiers Is Earth's magnetic field reversing? Catherine Constable & Monika Korte Earth and Planetary Science Letters 246 (2006) 1–16 Page 2

22  Reversals are documented in the oceanic crust 170 My back.  Reversals have taken place on the average everty year during the past 20 My.  On the average the rotation poles and the magnetic poles coincide.

23 Normal polarity Reverse polarity Age [My] Variations in the magnetic field over a mid- ocean ridge Lithosphere Calculated magnetic field from the model of sea-floor spreading Measured magnetic field across a mid-ocean ridge Molten magma fills the gap, solidifies, cools below the Curie temperature (560 o C) and becomes magnetized in the direction of the prevalent magnetic field

24 The magnetization along a 42 m long core from the Pacific at 4415 m water depth Inklination close to zero at the equator The sedimentation varies between 1-5 cm/1000 år. The sediments contain small amounts of magnetite which constitute small magnets that direct themselves into the direction of the Earth magnetic field on their way through the water column

25

26 The Gauss–Matuyama (2.58 Ma) reversal record of VGPs recorded in sediments deposited in Searles Lake, California (Glen et al., 1999b). Note the highly complex VGP path, with initial and final excursions in orange, multiple rapid oscillations in black, and main reversing phase including two large swings from high to equatorial latitudes in red.

27 Difference between Örsted (2000) och Magsat (1980) measurements

28 Tangential flow pattern in the outer core at the CM transition Anticyclonic patches transporting oppositely directed magnetic flux, i.e. negative feedback.

29  The Earth’s magnetic field is generated by electric currents in the outer liquid core, which mainly consists of iron  The iron in the core moves turbulently at speeds of about 20 km/y (i.e. 1 million times faster than the movements in the Earth’s mantle)  When the electrically conductive metal moves in the magnetic field, a new magnetic field is generated which may amplify the existing field  This self-amplifying effect is called the Geo-dynamo GEO-DYNAMO

30 Important Constraints on Models of the Geodynamo Westward drift of non-dipolar field Excursions –Frequency –Strength distribution Reversals –Frequency –Duration

31 Aborted Reversal Simulation

32 Spectra of characteristic length and timescales in core dynamics. MAC – Magnetic, Archimedean, Coriolis waves

33 Snapshot of Magnetic Field The field is sheared around the ‘tangent cylinder to the inner-core equator

34 Snapshots of a reversal Three snapshots of a simulated magnetic field at 500 years before the mid-point in the dipole reversal, at the mid-point and at 500 years after the mid-point.

35 Dynamo Simulations. Varying Heat Flow at CMB

36 More Snapshots Surface CMB Poloidal Toroidal Fields