Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Magnetic Field from Core?

  1. Jun 5, 2015 #1
    1) Is there any evidence that the Earth's magnetic field originates in the core rather than elsewhere?

    2) Is there a compelling physical model?
     
  2. jcsd
  3. Jun 6, 2015 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

  4. Jun 6, 2015 #3
  5. Jun 6, 2015 #4

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    If you don't want to read the links, no one can help you.
     
  6. Jun 7, 2015 #5
    I got the impression he was asking "where" Cincinatti was, as a humorous riposte to that portion of Steam King's post.
     
  7. Jun 7, 2015 #6

    davenn

    User Avatar
    Science Advisor
    Gold Member

    LOL
    No, I took it the same way Steamking did ... suspecting that the OP didn't see or understand the clickable link
     
  8. Jun 7, 2015 #7
  9. Jun 8, 2015 #8
    The parent Wikipedia article on the predominant theory on the origin of the Earth’s magnetic field is http://en.wikipedia.org/wiki/Dynamo_theory cut-and-paste, in part, into the Wikipedia article on the Earth’s Magnetic Field.


    Upwelling matter from the core is (quazi-) organized into rotating structures called Tylor Columns due to coriolis force.

    1)Presumably, these structures are a source or electrical current loops generating a magnetic field. Perhaps this is enough explanation for most.

    2)The means by which some mechanism could be responsible for separation of charge carriers in relative motion is not addressed. Take a cylinder of iron and spin it about its axis and it does not generate a magnetic field, obviously. Can anyone supply an explanation?

    3) In combination, The Maxwell-Faraday law of induction and the Lorentz force obtain [itex]\nabla \times v \times B = -\frac{dB}{dt}[/itex]. This doesn’t match the equation given by Wikipedia where there is an extra term. Where does it come from?

    And I don't appreciate the indirect insults by the intellectual pretenders as a means to elevate their self esteem.

    Anyone else without an axe to grind?
     
    Last edited: Jun 8, 2015
  10. Jun 8, 2015 #9
    Here I am! :wink:

    But seriously stedwards, perhaps the misunderstanding could have been avoided if you had indicated in your OP that you were knowledgeable about the topic and had some specific reservations you wanted to discuss. As it was, others - myself included, thought the post was from a neophyte who was either too lazy, or too unskilled to do some basic searches.

    In the light of your actual position and before we address shortfalls of current theory, it seems you have a notion the field originates somewhere other than the core. Is that correct, and if so where? And how? And are we allowed to discuss alternative theories inside the main fora?
     
  11. Jun 10, 2015 #10
    I am new to this topic. This was the first I hear of Dynamo Theory as a serious concept. It's actually a bunch of contending models with various degrees of fitness to the geological record and projected properties of the outer core material at high pressure.

    This supplies the best introduction to the basic idea that I've found. http://abyss.uoregon.edu/~js/glossary/dynamo_effect.html
     
    Last edited: Jun 10, 2015
  12. Jul 21, 2015 #11

    Dotini

    User Avatar
    Gold Member

  13. Apr 29, 2016 #12

    Dotini

    User Avatar
    Gold Member

    https://cosmosmagazine.com/earth-sciences/rocks-hold-records-earths-ancient-magnetic-history
    The history of the Earth’s magnetic field is indelibly written in vortex-like structures inside grains of the iron oxide magnetite, a new study has shown. ....a detailed picture of the evolution of the Earth's magnetic field could improve our understanding of the planet’s core and plate tectonics.

    https://static1.cosmosmagazine.com/sites/default/files/styles/cosmos_body_full/public/280416_magnetichistory_1.jpg?itok=ZzBwsywQ [Broken]A visualisation of the thermomagnetic behaviour of a small grain of magnetite. Image A shows an electron microscopic image of the grain, while the other images are Magnetic induction maps reconstructed from holograms taken at various temperatures.
     
    Last edited by a moderator: May 7, 2017
  14. May 12, 2016 #13

    Dotini

    User Avatar
    Gold Member

    From today's edition of spaceweather.com:

    European Space Agency's constellation of Swarm satellites reveals that changes may be happening even faster than previously thought. In this map, blue depicts where Earth's magnetic field is weak and red shows regions where it is strong:

    swarm_strip2.png

    Data from Swarm, combined with observations from the CHAMP and Ørsted satellites, show clearly that the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened about 2% over Asia. The region where the field is at its weakest – the South Atlantic Anomaly – has moved steadily westward and weakened further by about 2%. These changes have occured over the relatively brief period between 1999 and mid-2016.

    http://www.esa.int/Our_Activities/Observing_the_Earth/Swarm/Earth_s_magnetic_heartbeat
    The magnetic field is thought to be produced largely by an ocean of molten, swirling liquid iron that makes up our planet’s outer core, 3000 km under our feet. Acting like the spinning conductor in a bicycle dynamo, it generates electrical currents and thus the continuously changing electromagnetic field.

    It is thought that accelerations in field strength are related to changes in how this liquid iron flows and oscillates in the outer core.

    Chris Finlay, senior scientist at DTU Space in Denmark, said, “Swarm data are now enabling us to map detailed changes in Earth's magnetic field, not just at Earth's surface but also down at the edge of its source region in the core.

    “Unexpectedly, we are finding rapid localised field changes that seem to be a result of accelerations of liquid metal flowing within the core.”
     
  15. May 13, 2016 #14
  16. May 17, 2016 #15

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    If one takes a thin spherical shell of charge and sets it into rotation
    does a magnetic field result ?
    Apparently it does
    http://www.physics.princeton.edu/~mcdonald/examples/rotatingshell.pdf
    gives equations for it
    and so do these
    http://www.physicspages.com/2013/04/07/magnetic-field-of-rotating-sphere-of-charge/
    www.physicspages.com/2013/04/11/magnetic-dipole-moment-of-spinning-spherical-shell/

    What happens if, as in a simplified earth's atmosphere
    two concentric spherical shells of charge are separated by 50 km
    and there's an E-field between the shells , earth's is a few hundred volts per meter
    and the shells rotate rotate in lockstep

    1. Does a magnetic field result?

    2. Is it in same direction as Earth's?

    might there be more going on up there than we think?
     
    Last edited: May 18, 2016
  17. May 18, 2016 #16
    Very Interesting.
     
  18. May 18, 2016 #17
    Really nice post Jim.
    I had a look at those links you posted and pretty quickly found myself out of my depth.... but as you're a smart cookie and appear to have time on your hands enough to post here I thought I'd ask...

    If angular momentum changes then the intensity of the magnetic field would change? ...and if there were precessional changes which alter angular momentum would this cause a pole excursion in the field?
    For example, if the surface of the sphere was heavier on one part of its surface and this caused a "blip" in rotation. Imagine an LP rotating on a record player and the label is off centre and transpose in to 3D.

    The reason I ask is that I read further up the thread..
    In the case of the earth's magnetic field would variations in the earth's orbital characteristics and its wobble on its axis have any effect on the magnetic field orientation and intensity?

    Apologies if any of this is badly written, ill explained or confusing... I love science but I'm not very clever, and if you have to ask a good question to get a good answer then I'm under no illusions about how this may be received.

    My next question, depending on any answers which may be coming, would be regarding how a mass transfer of weight (ice) from the Arctic to the Antarctic might affect the earth's orientation in space.... does it wobble more or differently?
     
  19. May 18, 2016 #18
    I'd say that the effects of doing this on the Earth's rotation would be minimal as the arctic ice cover is really quite a thin layer compared to the bulk of most of the Earth's radius.
    Maybe if you moved the landmasses of Canada, Greenland, Scandinavia, and parts of Siberia along with the ice, well maybe.
     
  20. May 18, 2016 #19
    Food for thought...

    Are there connections between the Earth's magnetic field and climate? https://www.researchgate.net/publication/222817231_Are_there_connections_between_the_Earth's_magnetic_field_and_climate [Broken]
     
    Last edited by a moderator: May 7, 2017
  21. May 18, 2016 #20

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2016 Award

    Thanks for the kind words Alisdair
    but
    i too was quickly out of my depth
    So in this thread i'm a noob .

    i posted the question just to explore the concept

    I've always (since high school) been suspect of the "Earth as a Dynamo" article from 1958
    homecover.gif


    Elsasser developed his dynamo theory in 1920's . I've never heard an alternative, and perhaps for good reason.
    What will those satellites find ?

    I am no geophysicist, but
    i think the iron and nickel in earth's mantle is hotter than its Curie temperature. That means it's effectively not ferromagnetic. Not magnetic at all, in fact.
    If that's so, it seems natural that earth's driving mmf likely originates someplace else.

    No personal theories on pf, so i'll tinker with that spherical shell calculation next insomnia attack.
    Here's a history of the ideas about earth's field
    http://www.phy6.org/earthmag/dynamos2.htm
    everybody seems to look inside not outside.

    Well, i just finished a fascinating book "The Sun Kings", history of solar astronomy and our observations of earth's magnetic field.
    https://www.amazon.com/Sun-Kings-Unexpected-Carrington-Astronomy/dp/0691141266
    It tells how we have slowly come to appreciate the weather links between sun and earth and magnetism's role.
    Last chapter explains how sun's magnetic field affects earth weather through cloud formation,
    The researchers cited say sun's magnetic field modulates cosmic rays by ~12% which modulates earth's cloud cover by 4 or 5 percent . Interestingly, they tied that to Maunder and Sporer and i think Oort minima by tree rings and ice core samples..

    Cloud cover obviously affects albedo.
    I'd say it's logical to think maybe earth's own field does some modulating too.

    Check out Nasa's SOHO page
    http://sohowww.nascom.nasa.gov/

    if you find a page for those satellites watching earth's magnetic field please post link.

    old jim
     
    Last edited by a moderator: May 7, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Magnetic Field from Core?
Loading...