Reversal of Earth's magnetic field

  1. I understand that the sun changes magnetic polarity far more often than Earth does (correct me if I'm wrong as it's just what I read).

    Apparently it is statistically likely that the earth's magnetic field will change polarity at some time, so what sort of effects will this have in practcal terms on us and our environment, apart from ruining the betting odds of any sensible result in pigeon racing or possibly getting the auroras in odd places

    Can you think of any products which would be advantageous to have given this situation if it happened suddenly as I'd like to get in with the patents well before the event!
  2. jcsd
  3. Evo

    Staff: Mentor

    The reversal isn't sudden, it usually happens gradually over a period of 1,000-5,000 years. It's been ~780k years since the last reversal, and scientists say it may happen in another 1,000 years, or not.

    From the many articles and programs I have read, the wikipedia article actually does a fine job of briefly going over the issues.

    I can post other links later. But you should read this first.
    Last edited: Apr 28, 2014
  4. davenn

    davenn 4,346
    Science Advisor
    Gold Member
    2014 Award

    hi Evo,

    you had better correct your 780 million years to 780,000 yrs :wink:

    there's been some 20 - 21 reversals in the last 5 million years

  5. Evo

    Staff: Mentor

    LOL!! Corrected, thanks! I got it correct in other threads I've posted on this. We've had quite a few.
  6. Dotini

    Dotini 748
    Gold Member

    The South Atlantic Anomaly is a dent in Earth's shield against cosmic radiation, 124 miles above the ground (200 kilometers). It may be the most dangerous place in the Earth's sphere for satellites and spacecraft to traverse, because anything electronic traveling through it is vulnerable to strong radiation from space and tends to malfunction.

    particularly hot and dense feature in the mantle below southern Africa and the Atlantic called the Large Low Shear Velocity Province may have something to do with locally weakening the magnetic field and periodic reversals.
  7. What can be the cause of this anomaly?
    Remnant of some ancient collision of the Earth with another protoplanetary body?
    This is not wild speculation. it's pretty much accepted that an event of this kind is the reason why we have a large moon.
  8. Evo

    Staff: Mentor
  9. If the earth spinning core causes the magnetic field then wouldn't it have to be spinning the other direction for the magnetic field to change polarity ? and if the magnetic field is getting weaker does this mean it is going to stop spinning before a reversal? I would be more worried about the atmosphere being blasted into space then getting a patent in.

    You could patent compass paint but I doubt it will make you rich =)
  10. I'm not sure of the exact dynamics underlying the generating of Earths magnetic field, I don't think anyone is sure for certain.
    However there is strong evidence of geomagnetic reversal happening previously and several times.
    It's not an event which happens instantly, it can take centuries or millennia to complete, so it probably wouldn't have dramatic consequences on human timescales.
    It's also not very predictable, there having been some reversals which apparently changed back again within quite a short time geologically.
    Last edited: Aug 4, 2015
  11. From your link, Rootone:
    I actually happen to know a Geophysics PHD candidate and she assured me this convection model is the most widely accepted at this time. (So accepted that she was surprised when I mentioned there were occasional "uncertainties" about it here at PF.)
    As she explained it to me, there are masses and masses of free electrons in the molten metals of the earth's interior. The molten metal nearest the core is the hottest and it tends to rise as cooler metal from nearer the surface sinks. There results very slow convection currents full of negative charge; she said the motion was on the order of "feet per year." Very slow, but the fact there is such a massive amount of free electrons in it causes it to have a magnetic field.

    At any rate, no geophysicist thinks the core is rotating at some different rate than anything else, or that the core is inert while everything above it rotates. That's a crackpot idea that was proposed in a sci-fi film some years back.
  12. well tthat makes alot more sense when you put it that way =) thanks
  13. There's not much doubt that the generation process is comparable to a dynamo and that convection plays a part.
    What there is doubt about is the reason for anomalies and reversals
  14. The Sun changes polarity every eleven years. The mechanism is this: big tubes of magnetic flux form. The tubes have polarity. The negative end of the tube is attracted to the positive pole, and the positive end of the tube to the negative pole. The tubes move slowly, but they get there eventually, weakening the field. Eventually the field reverses polarity.

    The same would happen within the Earth but the iron core resists the reversal. According to a recent simulation, the iron core has opposite polarity than the mantle. The mantle is "trying" to reverse the polarity of the core. Every now and then it succeeds. There is nothing cyclic about it. Knowing the time of previous reversals is no use in predicting the next reversal.

    During the transition the magnetic field does not collapse. Instead the magnetic poles wander over the surface of the Earth. There could be four or more poles instead of the usual two.

    Charged particles are attracted to the poles. These poles could be over cities or whatever, so there could be severe electrical storms in such areas. Such reversals have occurred many times and haven't resulted in mass extinctions, but they would disrupt electronic communications and damage/disable satellites. Power lines would serve as antennae collecting large amounts of energy, causing destructive power surges.
  15. davenn

    davenn 4,346
    Science Advisor
    Gold Member
    2014 Award

    not quite right
    The sunspots change their magnetic polarity every ~ 11 years. The overall magnetic field of the sun changes polarity every 22 years

    The magnetic fields of the sun / sunspots is generated in the Convective Zone. This is the outer zone of the Sun from the surface down to the Radiation Zone. The radiation zone extends from the bottom of the convective zone to the core.
    Unlike the Earth, the magnetic field of the Sun is not generated in the core region

    please provide some references to that .... it sounds a little Sci Fi' ish :wink:

    This already occurs when the Earth's magnet field is subjected to large CME's ( coronal Mass Ejections) from the sun

    Last edited: Aug 10, 2015
  16. supercomputer-based simulation of the geodynamo by Gary Glatzmeier of the University of California, Santa Cruz, and his colleagues. "Our solution shows how convection in the fluid outer core is continually trying to reverse the field but that the solid inner core inhibits magnetic reversals because the field in the inner core can only change on the much longer time scale of diffusion."

    Youtube of the results:

    Correct. But there are not all that many power lines or satellites near the Earth's magnetic poles at this time. Should the poles move to populated areas there would be more damage near such poles should a CME occur.
    Last edited: Aug 11, 2015
  17. Would these floating poles move the auroras with them?
  18. Baluncore

    Baluncore 3,305
    Science Advisor

    If the magnetic field was strong enough, the aurora would be present. But if the migrating pole was weak, the aurora would not be as distinct.
  19. If all the poles are scattered it may not even be strong enough to illuminate then...
  20. The assumption that a geomagnetic field reversal takes 2000 to 5000 years has been proven to be incorrect by paleo geomagnetic analysis.

    In the last 10 years it has been found that the geomagnetic field changes rapidly and cyclically.

    What drives that change is not known.

    "Is the geodynamo process intrinsically unstable?

    Recent palaeomagnetic studies suggest that excursions of the geomagnetic field, during which the intensity drops suddenly by a factor of 5 to 10 and the local direction changes dramatically, are more common than previously expected. The `normal' state of the geomagnetic field, dominated by an axial dipole, seems to be interrupted every 30,000 to 100,000 kyr; it may not therefore be as stable as we thought.

    Recent studies suggest that the Earth's magnetic field has fallen dramatically in magnitude and changed direction repeatedly since the last reversal 700 kyr ago (Langereis et al. 1997; Lund et al. 1998). These important results paint a rather different picture of the long-term behaviour of the field from the conventional one of a steady dipole reversing at random intervals: instead, the field appears to spend up to 20 per cent of its time in a weak, non-dipole state (Lund et al. 1998). One of us (Gubbins 1999) has suggested that this is evidence of a rapid natural timescale (500 yr) in the outer core, and that the magnetic field is usually prevented from reversing completely by the longer diffusion time of the inner core (2 to 5 kyr). This raises a number of important but difficult questions for geodynamo theory. How can the geomagnetic field change so rapidly and dramatically? Can slight variations of the geomagnetic field affect the dynamics of core convection significantly? If so, is the geodynamo process intrinsically unstable?"

    "New evidence for extraordinary rapid change of geomagnetic field during a reversal

    Palaeomagnetic results from lava flows recording a geomagnetic polarity reversal at Steens Mountain, Oregon suggest the occurrence of brief episodes of astonishingly rapid field change of six degrees per day. The evidence is large, systematic variations in the direction of remanent magnetization as a function of the temperature of thermal demagnetization and of vertical position within a single flow, which are most simply explained by the hypothesis that the field was changing direction as the flow cooled."

    "The tectonic and geomagnetic significance of paleomagnetic observations from volcanic rocks from central Afar, Africa

    Reheating and partial remagnetization by the overlying flow cannot explain either of the transitional directions because both differ significantly from that of the reversely magnetized overlying flow. The high-temperature component gives a VGP in the northern Pacific, whereas the lower-temperature component gives a nearly antipodal VGP south of Cape Town, South Africa. Hence, the configuration of the geomagnetic field appears to have jumped nearly instantaneously from a northern-hemisphere transitional state to a southern-hemisphere one during this normal to reverse polarity transition."
  21. The European set of three satellites SWARM is now providing almost real time global analysis of the geomagnetic field with laboratory like precision.

    It has found that the geomagnetic is currently dropping at 5%/decade which is 10 times faster than is possible based on the current assumed model of the geomagnetic field.

    "Earth's Magnetic Field Is Weakening 10 Times Faster Now
    ...Previously, researchers estimated the field was weakening about 5 percent per century, but the new data revealed the field is actually weakening at 5 percent per decade, or 10 times faster than thought. (Betzalel: 10 times faster than physically possible if the cause of the geomagnetic field changes is changes at the liquid core/solid core boundary) As such, rather than the full flip occurring in about 2,000 years, as was predicted, the new data suggest it could happen sooner.
    Floberghagen hopes that more data from Swarm will shed light on why the field is weakening faster now."

    One of the reasons the SWARM satellites were designed was to try to understand the reasons for the sudden acceleration of the North Magnetic Pole drift.

    "What Caused Recent Acceleration of the North Magnetic Pole Drift?

    The north magnetic pole (NMP) is the point at the Earth’s surface where the geomagnetic field is directed vertically downward. It drifts in time as a result of core convection, which sustains the Earth’s main magnetic field through the geodynamo process. During the 1990s the NMP drift speed suddenly increased from 15 kilometers per year at the start of the decade to 55 kilometers per year by the decade’s end. This acceleration was all the more surprising given that the NMP drift speed had remained less than 15 kilometers per year over the previous 150 years of observation. Why did NMP drift accelerate in the 1990s?

    Answering this question may require revising a long-held assumption about processes in the core at the origin of fluctuations in the intensity and direction of the Earth’s magnetic field on decadal to secular time scales, and hints at the existence of a hidden plume rising within the core under the Arctic."
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