Download Lithosphere Calculated magnetic field from the model of sea

ENTRY QUIZ
1. What elements do we know?
2. What are they, name them?
3. Which are metals, gases, nonmetals?
4. What is next?
1
8th element
Oxygen
Atomic symbol O
Atomic number 8
Atomic weight 15.999
Gas, nonmetal
Atomic, diatomic, ozone
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Earth’s Magnetic Field
•
Introduction
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Observations
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Magnetic observatories
Satellites
Dedicated field campaigns
The external field
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•
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Earth’s structure
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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•
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Paleomagnetic observations
Secular variations
Satellite observations
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Earth’s Magnetic Field
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The Geodynamo
– Governing equations
– Approximations
– Simulations
4
Earth’s Magnetic Field
•
Crustal sources for the magnetic field
– Remanent magnetization
– Induced magnetization
– Relation to past and ongoing processes
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Magnetic Pattern of the Oceans
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Magnetic Lineations. Mars
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P-wave Velocity Perturbation
Mid-Mantle
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Shear Wave Velocity
Perturbation. Base of Mantle
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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.
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The Geomagnetic Earth
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Sources of the
Geomagnetic Field
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MAGSAT (left) and
Oersted (right) Satellites
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Magnetic lab activity 3
1.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
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German CHAMP satellite
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Örsted Satellite Orbit
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Spherical Harmonic Representation
of Magnetic Field
External source region
Source free region
”Region of observations”
Internal source
region
n = degree
V  V   V   r n S n ( ,  )  r  n 1S n ( ,  )
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Geomagnetic Spectrum
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Crustal Magnetic Fields
From Maus (2007)
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n = 100
Curie Depth Antarctica
Crustal Mag
Field
Curie Depth
Crustal
Thickness
Heat Flow
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Geomagnetic Jargong
Frontiers
Is Earth's magnetic field reversing?
Catherine Constable & Monika Korte
Earth and Planetary Science Letters 246
(2006) 1–16
Page 2
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 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.
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Variations in the magnetic field over a midocean ridge
4 3 2 1
0 1 2 3
4
Age
[My]
Normal
polarity
Calculated magnetic field
from the model of sea-floor
spreading
Reverse
polarity
Measured magnetic field
across a mid-ocean ridge
Lithosphere
Molten magma fills the gap, solidifies, cools below the Curie temperature
(560oC) and becomes magnetized in the direction of the prevalent magnetic field
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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
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the direction of the Earth magnetic field on their way through the water column
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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.
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Difference between Örsted (2000) och Magsat
(1980) measurements
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Tangential flow pattern in the outer core at
the CM transition
Anticyclonic patches
transporting oppositely
directed magnetic flux,
i.e. negative feedback.
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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
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Important Constraints on
Models of the Geodynamo
•Westward drift of non-dipolar field
•Excursions
– Frequency
– Strength distribution
•Reversals
– Frequency
– Duration
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Aborted Reversal Simulation
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Spectra of characteristic length and timescales
in core dynamics.
MAC – Magnetic, Archimedean, Coriolis waves
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Snapshot of Magnetic Field
The field is sheared
around the ‘tangent
cylinder to the
inner-core equator
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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.
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Dynamo Simulations.
Varying Heat Flow at CMB
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More Snapshots
Surface
CMB
Poloidal
Toroidal
Fields
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EXIT QUIZ
1. What 8 elements do you know?
2. What are gases, metals, nonmetals?
3. What is the next?
37