ENTRY QUIZ 1 1. What elements do we know? 2. What are they, name them? 3. Which are metals, gases, nonmetals? 4. What is next? 8 th element 2 Oxygen Atomic symbol O Atomic number 8 Atomic weight Gas, nonmetal Atomic, diatomic, ozone 3 Earths Magnetic Field Introduction Earths 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 4 Earths Magnetic Field The Geodynamo Governing equations Approximations Simulations 5 Earths Magnetic Field Crustal sources for the magnetic field Remanent magnetization Induced magnetization Relation to past and ongoing processes 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 Earths Magnetic Field Earths 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 Magnetic lab activity Place close to permanent magnet various objects 2.Place these objects 5 cm close to compass 3. Move those objects in clock wise direction 4.Observe and record results 5.Make reasonable conlusions 15 German CHAMP satellite 16 rsted Satellite Orbit 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) 116 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 r. 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 GaussMatuyama (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 rsted (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 Earths 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 Earths 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 EXIT QUIZ What 8 elements do you know? 2. What are gases, metals, nonmetals? 3. What is the next?