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Earth’s Magnetic Field

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

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Earth’s Magnetic Field

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  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 • 5.01Geomagnetism in Perspective, Pages 1-31, M. KonoSummaryPlus | Chapter | PDF (2904 K) | View Related Articles5.02The Present Field, Pages 33-75, N. Olsen, G. Hulot and T.J. SabakaSummaryPlus | Chapter | PDF (14345 K) | View Related Articles5.03Magnetospheric Contributions to the Terrestrial Magnetic Field, Pages 77-92, W. Baumjohann and R. NakamuraSummaryPlus | Chapter | PDF (684 K) | View Related Articles5.04Observation and Measurement Techniques, Pages 93-146, G.M. Turner, J.L. Rasson and C.V. ReevesSummaryPlus | Chapter | PDF (2319 K) | View Related Articles5.05Geomagnetic Secular Variation and Its Applications to the Core, Pages 147-193, A. Jackson and C.C. FinlaySummaryPlus | Chapter | PDF (7793 K) | View Related Articles5.06Crustal Magnetism, Pages 195-235, M.E. Purucker and K.A. WhalerSummaryPlus | Chapter | PDF (4208 K) | View Related Articles5.07Geomagnetism, Pages 237-276, S. ConstableSummaryPlus | Chapter | PDF (1692 K) | View Related Articles5.08Magnetizations in Rocks and Minerals, Pages 277-336, D.J. Dunlop and Ö. ÖzdemirSummaryPlus | Chapter | PDF (3105 K) | View Related Articles5.09Centennial- to Millennial-Scale Geomagnetic Field Variations, Pages 337-372, C. ConstableSummaryPlus | Chapter | PDF (3744 K) | View Related Articles5.10Geomagnetic Excursions, Pages 373-416, C. Laj and J.E.T. ChannellSummaryPlus | Chapter | PDF (1692 K) | View Related Articles5.11Time-Averaged Field and Paleosecular Variation, Pages 417-453, C.L. Johnson and P. McFaddenSummaryPlus | Chapter | PDF (3723 K) | View Related Articles5.12Source of Oceanic Magnetic Anomalies and the Geomagnetic Polarity Timescale, Pages 455-507, J.S. Gee and D.V. KentSummaryPlus | Chapter | PDF (3684 K) | View Related Articles5.13Paleointensities, Pages 509-563, L. Tauxe and T. YamazakiSummaryPlus | Chapter | PDF (2882 K) | View Related Articles5.14True Polar Wander: Linking Deep and Shallow Geodynamics to Hydro- and Bio-Spheric Hypotheses, Pages 565-589, T.D. Raub, J.L. Kirschvink and D.A.D. EvansSummaryPlus | Chapter | PDF (1558 K) | View Related Articles

  5. Volume 8: Core Dynamics • 8.01Overview, Pages 1-30, P. OlsonSummaryPlus | Chapter | PDF (1025 K) | View Related Articles8.02Energetics of the Core, Pages 31-65, F. NimmoSummaryPlus | Chapter | PDF (842 K) | View Related Articles8.03Theory of the Geodynamo, Pages 67-105, P.H. RobertsSummaryPlus | Chapter | PDF (945 K) | View Related Articles8.04Large-Scale Flow in the Core, Pages 107-130, R. HolmeSummaryPlus | Chapter | PDF (2755 K) | View Related Articles8.05Thermal and Compositional Convection in the Outer Core, Pages 131-185, C.A. JonesSummaryPlus | Chapter | PDF (1763 K) | View Related Articles8.06Turbulence and Small-Scale Dynamics in the Core, Pages 187-206, D.E. LoperSummaryPlus | Chapter | PDF (365 K) | View Related Articles8.07Rotational Dynamics of the Core, Pages 207-243, A. TilgnerSummaryPlus | Chapter | PDF (2784 K) | View Related Articles8.08Numerical Dynamo Simulations, Pages 245-282, U.R. Christensen and J. WichtSummaryPlus | Chapter | PDF (1868 K) | View Related Articles8.09Magnetic Polarity Reversals in the Core, Pages 283-297, G.A. Glatzmaier and R.S. CoeSummaryPlus | Chapter | PDF (2692 K) | View Related Articles8.10Inner-Core Dynamics, Pages 299-318, I. Sumita and M.I. BergmanSummaryPlus | Chapter | PDF (453 K) | View Related Articles8.11Experiments on Core Dynamics, Pages 319-343, P. Cardin and P. OlsonSummaryPlus | Chapter | PDF (1731 K) | View Related Articles8.12Core–Mantle Interactions, Pages 345-358, B.A. Buffett

  6. Magnetic Pattern of the Oceans

  7. Magnetic Lineations. Mars

  8. P-wave Velocity PerturbationMid-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. External source region Source free region ”Region of observations” Internal source region Spherical Harmonic Representation of Magnetic Field n = degree

  18. Geomagnetic Spectrum

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

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

  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 250000 year during the past 20 My. • On the average the rotation poles and the magnetic poles coincide.

  23. Variations in the magnetic field over a mid-ocean ridge Age [My] 4 3 2 1 0 1 2 3 4 Calculated magnetic field from the model of sea-floor spreading Normal polarity Measured magnetic field across a mid-ocean ridge Reverse polarity Lithosphere Molten magma fills the gap, solidifies, cools below the Curie temperature (560oC) 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. 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.

  26. Difference between Örsted (2000) och Magsat (1980) measurements

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

  28. GEO-DYNAMO • 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

  29. Important Constraints on Models of the Geodynamo • Westward drift of non-dipolar field • Excursions • Frequency • Strength distribution • Reversals • Frequency • Duration

  30. Aborted Reversal Simulation

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

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

  33. 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.

  34. Dynamo Simulations. Varying Heat Flow at CMB

  35. More Snapshots Surface CMB Poloidal Toroidal Fields

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