Introduction to Earth System

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Introduction to Earth System

• Solid Earth part
• Rocco Malservisi
• roccom_at_lmu.de
• Phone [phone]

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Elastic Waves
P waves
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Elastic Waves
S waves
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Elastic Waves
Surface waves
Surface waves front expand as a cylindrical
surface Body waves front expand as a spherical
surface Since the energy is conserved, which one
is decaying faster?
Body waves decay as inverse of square of
distance Surface waves decay as inverse of the
distance
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The same can be done with waves produced by
earthquakes that Can travel through the planet
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PREM
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Tomography
Flower, 2004 Data from Grand and Van Der Hilst
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Free oscillation Earth
http//web.ics.purdue.edu/nowack/geos557/lecture1
6-dir/lecture16.htm
Toroidal Spheroidal
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3D-MODELLE DES ERDMANTELS Kugelfunktionen
Die Eigenschwingungsmoden der Erde lassen sich
mit Hilfe von Kugelfunktionen beschreiben.
Cnm sind die Kugelkoeffizienten vom Grad n und
Ordnung m

• Zonale Komponente
• Cnm n 2, m 0
• Sektoral Komponente
• Cnm n 2, m 2
• Terrassal Komponente
• Cnm n 2, m 0

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3D-MODELLE DES ERDMANTELS Daten III.
Splitting der Eigenfrequenzen des Erdkörpers
Berechnet man die Fourier-Transformation sehr
langer Seismogramme (24 Stunden und länger) so
tauchen die Eigenfrequenzen der Erde als klare
Peaks im Spektrum auf.
Amplitudenspektrum, Irian-Java-Beben, 17. 2.
1996, Station PTGA, Brasilien
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http//earthguide.ucsd.edu/mar/dec5/earth.html
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Magnetic Field
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• We have a magnetic field that it is very similar
  to the one of a dipole.
• Well in reality this is true close to the surface
  if we go far away enough it looks more complex

Magnetopause 10Re Moon 60Re
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Magnetic Field is a vector
It has an intensity (can be measured looking At
the oscillation of a compass) And a direction The
direction change with the position
Magnetic Pole The place where the compass is
pointing Down Magnetic Equator The place where
the compass is horizontal
The Magnetic Poles are close to the
geographical Poles but do not coincide (11 off)
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The Earths Magnetic Field
B (X, Y, Z) Or B (F, I, D ) OrB
(D, H, Z)
F intensity I inclination D declination H
Horizontal component
The seven elements of the (local) magnetic
fieldin the geographic coordinate system
I. Geomagnetic field Local Geomagnetic
Field Vector
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The Earths Magnetic Field
From this Magnetic pole is the point where H0
D - 90 Magnetic Equator the point where D0
F intensity I inclination D declination H
Horizontal component
Where 3000nTltHlt6000nT erratic zone (compass work
badly) Where Hlt3000nT unusable zone (compass does
not work)
I. Geomagnetic field Local Geomagnetic
Field Vector
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Tesla (T) Magnetic flux density Wb/m2 Weber
(Wb) The weber may be defined in terms of
Faraday's law, which relates a changing magnetic
flux through a loop to the electric field around
the loop. A change in flux of one weber per
second will induce an tension of one volt.
TN/Am
V velocity m/s E electric field N/C V/m BN/Am
BiotSavart Law
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The place where the axis of the dipole intersect
the surface Of the earth are called geomagnetic
poles
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The numerical interpolation of the data is called
Geomagnetic models. Every 5 yr a new model is
released by The international community now we
have the IGRF 2005
From Press, 1992.
90 of spatial field distribution can be
explained by a simple dipolar field
I. Geomagnetic field Geocentric inclined
dipole
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Magnetic Observatory
http//www.ngdc.noaa.gov/seg/geomag/icons/Obs1999_
lg.gif
FUR http//www.geophysik.uni-muenchen.de/observato
ry/geomagnetism
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Geomagnetic models Interpolation of the
observations Using spherical harmonics. If we do
not have electrical charges and magnetic
sources We can have a potential. (otherwise it is
not conservative so no potenzial) Gauss in 1830
thought that he can divide the field in
internal And external having 2 potentials. The
internal goes as r-n the external as rn The
potential can be expressed as
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This is not only an interpolation scheme but also
the solution for the physical problem of the
magnetic field due to an internal or external
source! The coefficients are called Gauss
coefficients The internal field coef. start from
r-2 because we do not have the magnetic
monopole The internal field represent 90 of the
total field
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Table 1. Spherical Harmonic Coefficient (in nT)
of Terrestrial Magnetic Field (IGRF
1985) Coefficient Degree (m) Order (n) 1 2
3 4 ____________________________________________
__________ 4 169 gnm 3 835 -426 2
1691 1244 363 ________________________________
______________________ 1 -1903 2045 -2208
780 gno 0 -29877 -2073 1300 937 1 5497
-2191 -312 233 ________________________________
______________________ 2 -309 284 -250 hnm
3 -296 68 4 -298
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The internal field represent 90 of the total
field The coef. g with n1 m0 give the magnitude
of the dipole aligned with the rotation axis. The
coef. with n1 give the magnitude of the dipole
is the largest one 85 of the field. It is
inclinated of 11 degrees. For ngt12 the coef. are
neglegible. N2 quadrupole etc can be controlled
by regional features.
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The numerical interpolation of the data is called
Geomagnetic models. Every 5 yr a new model is
released by The international community now we
have the IGRF 2005
From Press, 1992.
90 of spatial field distribution can be
explained by a simple dipolar field
I. Geomagnetic field Geocentric inclined
dipole
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Geomagnetic Field Intensity
Other units Gauss100000nT g10000nT
I. Geomagnetic field Worldwide Variation of
F
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Geomagnetic inclination (IGRF)
I. Geomagnetic field Worldwide Variation of
I
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Worldwide Distribution of Geomagnetic Declination
according to IGRF 2000
I. Geomagnetic field Worldwide Variation of
D
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The dipolar field is called the MAIN FIELD It
changing slowly (this is why we update the model
Every 5 yr by IAGA) The external field can
change quickly. How does the field
change http//www.geophysik.uni-muenchen.de/obse
rvatory/geomagnetism
Big diurnal variation and annual variation what
can cause it?
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Temporal (diurnal and secular) variations
other secular variation reversal
From Butler, Palaeomagnetism, 1992.
Magnetic storm
Slide I. Geomagnetic field Temporal
Variations
CompareX 3 nT/km 33 km/h gt 100 nT/hY
0.3 nT/km 33 km/h gt 10 nT/h,Thus, diurnal
changes matter !
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other secular variation reversal
From Butler, Palaeomagnetism, 1992.
Slide I. Geomagnetic field Temporal
Variations
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Where the magnetic field came from?

• Dipole inside the Earth
• can not have reversal
• b-c) Uniformly magnetic mantle
• Or core, mantle of silicate
• too hot
• d) Current in the core
• Most likely

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Where the magnetic field came from?
Self Sustaining dynamo