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Earths magnetic field and core

  1. Jul 30, 2011 #1
    How can random electron currents in the earth's core create a ordered magnetic field?
    What makes a current in the earth be north or south what is the difference between a north current and a south one?
    How come if the magnetic field is strongest at the centre of the planet how come where it is weakest far out in space a magnetosphere is formed?
  2. jcsd
  3. Jul 30, 2011 #2


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    Not random - pretty ordered!
    See: http://en.wikipedia.org/wiki/Dynamo_theory
    or you may find it explained in many introductory textbooks on general physics (e.g Feynman's Lectures)

    There is no difference and magnetic poles of the Earth got swapped many times in (geological) history

    Oooch? Could you ask again...?
  4. Jul 30, 2011 #3
    Ok thanks

    No i mean what makes the fluid have a north magnetic field or south magnetic field sorry i cant word it very well

    Why is the magnetosphere all the way out in space where it should be the weakest if the origin is the near centre of the earth
  5. Jul 30, 2011 #4


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    That was how I understood your question ;) Nothing! It is chosen just by chance. Earth dynamo might started with south magnetic pole at Antarctida, but it might started with N-magnetic pole there. And actually, Earth swapped magnetic poles many times.

    Well - that's a definition of 'magnetosphere' - as a place, where Earth magnetic field forces ions and electrons to such and such behaviour. (See wiki: http://en.wikipedia.org/wiki/Magnetosphere) In a dense atmosphere or inside the Earth we have no free ions...
  6. Jul 30, 2011 #5
    Sorry i cant phrase it properly and thank you for your other answers. What makes some parts of fluid point north and some south? Does it have anything to do with electron spin
  7. Jul 30, 2011 #6


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    Er... I think I'd better come clean with you about this... it's... um it's not an electron spin, I'm afraid. You see, an electron is what we physicists call very very small. What we're looking for here is I think, and this is no more than an educated guess, I'd like to make that clear, is something much bigger spinning: the Earth.

    - the Earth!?!

    Could you, please, read at least Wiki article I directed you to, before asking again questions about something what is explained there pretty clearly?
    Last edited: Jul 30, 2011
  8. Jul 31, 2011 #7
    You don't understand my question but thanks for your time and answers on my other questions
  9. Aug 1, 2011 #8
    Electron spins do not play a role in the geomagnetic field generation. The temperature of the core is >5500 K, well above the ordering temperature of Fe (the primary constituent of the core). This means that thermal fluctuations are more than sufficient to destroy any ordering of the spins.

    The geomagnetic field is generated by the fluid motion of the electrically conductive fluid outer core around the solid inner core. The fluid motion of the outer core is driven by both thermal and compositional convection (as Fe freezes out of the liquid lighter elements remain creating compositional buoyancy) and is dominated by large scale flow. The Earth’s rotation also plays a big role; it produces convection columns within the outer core that align along the rotation axis. So to answer your question, thermal and compositional convection along with the Earth’s rotation control fluid flow in the outer core. Why one way or the other? The flow of fluid is approximately axial-symmetric. The thermal and compositional convection is radial and the Earth’s rotation adds a helical twist to the fluid motion.

    I guess what you are really asking is why does the geomagnetic field point north or south? First some background. As I mentioned the outer core is conductive and, in the presence of a magnetic field, electric currents will be produce inducing new magnetic. This is the basic premise of the self-sustaining dynamo, which is a big feedback system of convection to electric currents to magnetic fields, which then modify convection currents (through magnetohydrodynamics; http://en.wikipedia.org/wiki/Magnetohydrodynamics ), and so on.

    Now, imagine you have a convecting Earth-like core system in the absence of any magnetic field, i.e., convection without magnetic induction. Then a seed magnetic field was instantaneous “switched” on; the final stable configuration would depend on the interplay of the strength and direction of the seed field, the configuration of convection before the seed field (and how it changed through time, i.e., magnetohydrodynamics), magnetic diffusion through the solid inner core and its relative scale to that in the outer core (the inner core can act as a breaking system to changes in the magnetic field induced by convection in the outer core), controls on the heat flux through the core mantle boundary, and a host of other details. So those are (some of) the factors that control the orientation of the magnetic field.

    And to answer an inevitable question, no, we don’t know what the source of the geodynamo seed field was.

    I hope that goes some way to answering your question. :smile:
  10. Aug 1, 2011 #9
    yes thanks a lot ,there are so many factors contributing to the field direction it seems :smile:
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