Polar Opposites

Happy confluences. Tim’s post (“Earth farts”. How do you resist that?) got me thinking this morning and then the Grinch called about a hugely interesting site. During another global warming discussion, he said he’d heard something about Magnetic North moving and finally tracked down the info. And it’s moving, okay. Not at the rate New Orleans is sinking or the ice packs are melting, but at a whopping 40 clicks a YEAR.

The North Magnetic Pole is slowly drifting across the Canadian Arctic. The Geological Survey of Canada keeps track of this motion by periodically carrying out magnetic surveys to redetermine the Pole’s location. The most recent survey, completed in May, 2001, determined an updated position for the Pole and established that it is moving approximately northwest at 40 km per year.

Fascinating. Now, not being a geo/astrophysicist (or even remotely logical in any event), I was left wondering if the earth itself starts to lean a little to starboard when such things (“reversals”) occur. According to the Canadian government, it does ~ and has ~ about 400 times in the past 330 million odd years.

Reversals have been documented as far back as 330 million years. During that time more than 400 reversals have taken place, one roughly every 700,000 years on average. However, the time between reversals is not constant, varying from less than 100,000 years, to tens of millions of years. In recent geological times reversals have been occurring on average once every 200,000 years, but the last reversal occurred 780,000 years ago. At that time the magnetic field underwent a transition from a “reversed” state to its present “normal state”.

-Earth’s axis precession- MHHE

Even if a complete reversal doesn’t happen, aren’t we leaning in a smidge closer to the sun every year that the pole treks northwesterly? Won’t that make us a teensy bit warmer on it’s own? Like the stick of butter on the counter that’s moved closer to the stove, things start to heat up and soften. (And do I need to tie up the kitchen cabinets to save the dishes when we do that hard reversal jerk to the right?)
As much as I would wish it, the answer’s not as simple as too many Escalades on the I-95. Which is probably why simpletons like Al try to make it so.

38 Responses to “Polar Opposites”

  1. Ken Summers says:

    “we leaning in a smidge closer to the sun every year that the pole treks northwesterly?”
    No. The Earth still tilts in basically the same direction. The real difference is that the tropic zone (between the two belts where the sun is directly overhead at the solstices) gets a little wider or narrower. I don’t remember the exact width of the precession but I’m pretty certain those pics imply it’s much larger than it actually is.

  2. Well, that’s a 12,000 year progression,too, Ken. But it doesn’t just donk over to the right at reversal time and the ACTUAL global temperature rise is miniscule in the scheme of things, so how much does a moving pole affect a particular area’s solar exposure?

  3. And the tropics moving out would expand all the neighboring climate zones beyond their ‘normal’ ranges, right?

  4. Mike Rentner says:

    There’s been a show on cable tv about this. I can’t remember which station, probably history or A&E or Discovery.
    The coolest thing is that while the poles are in flux, magnetic north will be pretty much nowhere, there will be resultant changes to the magnetic field and the Van Allen Belt.
    So, what happens is that the aurora borealis and aurora austrialis will move close and closer to the equator, and eventually be everywhere, and brighter! There will be very pretty colors every day and more so at night.

  5. Do the magnetic poles have any effect on the earth’s axis?
    Man, the research into this stuff is 3/4’s of the fun!

    Observations Requiring Explanation
    It is of considerable significance, as I will discuss later, that the axis of the magnetic North and South Poles does not coincide with the geographical axis of the Earth’s rotation. In fact the positions of the North and South Poles upon the Earth’s surface are not even constant, being subject to apparently random drifts of hundreds of kilometers from the Geographic Poles, although roughly around them, with perhaps only the average position over many millenia approximating the positions of the Geographic Poles. At the present time there appears to be a generally westward movement, which seems to have been going on for several centuries.
    Furthermore a hypothetical line drawn from one magnetic pole to the other does not actually pass through the Earth’s center. This lack of symmetry with respect to the Earth is difficult to explain by the prevailing theories.

    Magnetic fields from past geological epochs are sometimes preserved in magnetizable strata and rocks such as lava as they cool below their Curie points, and their intensities can be measured. Variations in intensity above and below that of the present have been found.
    Many complete reversals of the Earth’s field have been documented over geological ages from studies of the movement of the sea bottom around the gigantic undersea crack that splits the globe, so clearly in fact that they are used routinely by geologists and paleontologists for relative dating of geological formations and fossilliferous strata.

    A study was made of intermittently produced Miocene lava formations at Steen’s Mountain, Oregon, USA, which gave a very detailed picture of both the intensity and directional changes which occurred during a magnetic reversal. The complete reversal took about 4500 years and the average magnetic field at the surface fell to about 20% of normal during the change. The transitional field was typically non-axisymmetric and there was much meandering, even crossing the equator three times. Three geomagnetic impulses occurred which corresponded to high rates of change of the field. The angular rates of change were approximately 50 +/- 20 degrees per year.

    On a much more rapid scale, around about 1969, a so-called ‘jerk’ occurred in the geomagnetic field, almost synchronously over the whole surface of the earth. It took place in less than 2 years and has not received a satisfactory explanation as yet.

    Wasn’t Crusader born in ’69? That might account for it.

  6. Ken Summers says:

    “Do the magnetic poles have any effect on the earth’s axis?”
    I don’t think so. The magnetic poles come from the spinning of the Earth’s iron core. I haven’t had a chance to read all the stuff you linked to but I think any connection between the magnetic poles and the axis would be a secondary effect (meaning that they both might be affected by changes in the core but are not affecting each other directly).

  7. Mike Rentner says:

    From the tv show I saw on this topic (it was very, very good, I watched it at least three times) the opposite is the case. It is the earth spinning on its axis that has an effect on the magnetic poles.
    The scientists built a metal sphere, filled it with a molten or liquid element that holds a magnetic field. Then they spun the sphere and tracked the magnetic field. It exactly paralleled observed behavior and they were able to gain new understandings of what is likely to occur that hasn’t been observed first hand (happened too long ago).
    It’s all very fascinating!

  8. Ken Summers says:

    Mike, do you remember what the show was? It sounds cool and I’d like to watch for it if it’s rebroadcast.

  9. Mr. Bingley says:

    Well, Sis, remember that Crusader is not a mere “so-called jerk”…

  10. The_Real_JeffS says:

    Which is probably why simpletons like Al try to make it so.
    Too true.
    The earth is naturally magnetic, but as Mike points out, the motion of the molten core affects it. This is similar to how a generator works, where windings are rotated through a magnetic field to produce electricity. A motor works exactly the opposite, where an electric current is through windings to spin up magnets.
    Obviously, what happens to the Earth’s natural field is not so clean and simple. It’s chaotic, and works against natural magnetism. Since magnetic polarity can change (it’s a basic physics experiment, if I recall correctly), we get the effects observed.
    But the motion of the magnetic pole is old news, THS, as fascinating as the subject. Anyone taking a basic surveying course involving the use of magnetic compasses is taught this. It’s an essential element of basic land navigation (without using a GPS, I mean) as well, but not always clearly laid out to the students. Check out this cool magnetic declination calculator.

  11. The_Real_JeffS says:

    Oh, and there’s no physical relation between the planetary axis and magnetic poles. It’s just a long standing convention to navigate by the points of a circle. Both fit within this frame of reference, and thus can be linked together for our convenience.

  12. Mr. Bingley says:

    And I thought he was born in 1970?

  13. Ken Summers says:

    “The earth is naturally magnetic, but as Mike points out, the motion of the molten core affects it”
    Jeff, are you sure about that? My recollection was that it was the core itself that generates the magnetic field from its spin. All other magnetism in the crust was caused by ferrous lava cooling in the presence of the overall magnetic field (leading to those cool phenomena like the differently polarized belts in the crust).

  14. motion of the magnetic pole is old news, THS
    Jeff, ::sigh:: you’re such a know-it-all. And forget that some of us are: a) blonde b) never have the earth’s magnetic poles enter either work or conversation in the course of the average year, less mind day c) Bingley or d) all of the above.
    And look at the lovely conversation we’re having, which your always salient facts, figures, experience and nine-hundred-pound-brain serve to augment and amplify. Plus, we learned Mike watches TV. There ya go!
    Life is good.
    And I haven’t been off my axis for quite some time.

  15. Mr. Bingley says:

    Gaia needs to get her belts checked?

  16. And, Mr. Summers, it’s simple really.

    In the absence of a diagram, this can be visualized by imagining outward bound electrons being constrained by the pattern to move from the kernel along each direction of the cartesian axis system until they reach the furthest extent of travel, namely the core/mantle boundary, where they split up in all directions to meet electrons from neighbouring cells, which forces the opposing streams into mutual descent. The descending electrons approaching the kernel are able to combine with sufficiently cooled He nuclei, finally reaching thermal equilibrium with the core temperature.
    The cycle continues at a rate set by the rate at which thermal and electrical steady state is maintained. Thermal steady state is in turn established when the rate of heat loss from the core through the mantle by conduction, and convection through the liquid layers of both the outer core and the molten magma of the mantle, balances the heat produced by radioactive decay, a process which is independent of the core temperature.
    The steady state core temperature of the Earth is far below the highest recombination temperature of Helium, hence the rate of emission of electrons gives the rate of recombination. Since the kinetic energy of the electrons emitted is known to be in the MeV range and enormous quantities of heat are liberated in maintaining the core temperature we can assume safely that the magnetic fields generated by the putative free electron current loops, where the charges are moving at such high speeds will be enormous.
    If this were all, since each cell has an equal and oppositely moving counterpart, within each of which all the electron loops are mirrored by others, all the magnetic fields generated would cancel out and no resultant field would exist.
    However additional factors now come into play. Due to the rotation of the Earth, centrifugal force causes two effects to occur. The Earth’s overall shape, and presumably that of the core also, is that of an oblate spheroid which distorts the paths that the electrons can take through the core material to favour a flattening of the cells in the axial direction.
    The second effect is the centrifugal force acting directly on the electrons themselves, flattening their orbits within the already flattened core and accentuating the effect further.
    This flattening has the overall effect of partially aligning the fields statistically along the axial direction. Even so the fields so produced would continue to add to zero because of the opposite rotations of electrons in opposing cells. However since the fields are so large in the first place, it requires only a minute asymmetry to produce a resultant which is of the correct order of magnitude to produce the observed nett field.

    Jeff doesn’t know his axis from a bore in the ground.

  17. Mr. Bingley says:

    Yeah, but you’re a pain in the axis.

  18. Mike Rentner says:

    Actually, it’s not that old. They’ve known for quite a long time that the poles move a bit, mostly from British naval studies in the 18th, 19th, and 20th centuries, but the idea that the poles vanish and then switch end is a fairly recent discovery, or so I’m led to believe.
    And yes, I watch tv! But mostly when SG-1 is on. 🙂

  19. John says:

    But I was born in 1969.

  20. Mr. Bingley says:

    Well, that explains that one, then, John. And if you throw Crusader in the pot…whoa Nelly.

  21. Mr. Bingley says:

    The russians and the germans used to make the poles move alot too, mike.

  22. mojo says:

    Uh, hello? Charged particles in motion produce a magnetic field (See Mr. Maxwell.) Molten nickel-iron (the core) is in motion (spinning) and produces a field, though not a very strong or concentrated one (try doing a cross product on the big liquid metal ball thing if you’ve got a couple of decades to spare.) But since the core is molten, it’s fluid (gee, really?) and tends to slop around a bit. The overall mag field is an average, and varys in strength and polarity.
    Clear as mud, right?

  23. Molten balls? Sloppy spinning?! I think I’ve found my life’s work.
    Saaayyyy, mojo…what year were you born???
    (And nobody axis’d you, Bingley.)

  24. The_Real_JeffS says:

    Good catch, Ken. Yeah, I goofed up there…..but the same problem occurs in that the magnetic field generation is not consistent. Thus the changing magnetic field. Guess I made an axis of myself.
    But the calculator is way cool!
    And I always thought blondes were magnetic myself………

  25. Ken Summers says:

    Jeff, blondes are moneto-magnetic: attracted to money.

  26. Ken Summers says:

    “blondes are … attracted to money”
    The reverse is also true, of course.

  27. Mr. Bingley says:

    They may not be magnetic, Jeff, but they sure charge a lot.

  28. The_Real_JeffS says:

    I was thinking that they tend to be bi-polar…….

  29. Ken Summers says:

    Gentlemen, you realize that when THS comes back we’re all dead.

  30. Kaboom says:

    Of course, the “north” magnetic pole is actually a SOUTH pole, because the “north” pole of a compass needle is attracted towards it.
    Like poles repel, so it cannot logically or factually be the “north” magnetic pole.
    Or, maybe the “north” poles on all those compass needles are wrong……

  31. John says:

    mojo – charged particles in motion are not the only things that make a magnetic field – aligned dipoles do too, as they do in permanent magnets. You can even get the randomly oriented dipoles in a piece of iron to temporarily align if you put it in a magnetic field long enough. As a kid, did you ever make an electromagnet out of a lantern battery and copper wire cioled around a nail? If you leave the circuit connected for a while and then remove the nail, the nail will remain magnetic for a few minutes.
    A similar effect is working on the ferro-magnetic elements in the Earth’s crust, dampening (a bit) the effect of the sloshing molten core.
    I’m fascinated by the fact that eventually Vega is going to be the Pole Star, as it was once in the past.

  32. Mr. Bingley says:

    Here’s to sloshing molten cores, John!

  33. Ken Summers says:

    [Heh – time to get pedantic on John] Magnetic dipoles are magnetic because of charged particles in motion (most pedantically, electrons in d-orbitals, if I recall my DGH-LOPOS correctly).

  34. mojo says:

    Anticipating the involvement of Lawyers:
    Warning: This Product Attracts Every Other Piece of Matter in the Universe, Including the Products of Other Manufacturers, with a Force Proportional to the Product of the Masses and Inversely Proportional to the Distance Between Them.

  35. mojo says:

    Saaayyyy, mojo…what year were you born???
    1954. And again in 1955. Why?

  36. We’re just performing a theoretical exercise, based on info I posted in the comments:

    On a much more rapid scale, around about 1969, a so-called ‘jerk’ occurred in the geomagnetic field, almost synchronously over the whole surface of the earth. It took place in less than 2 years and has not received a satisfactory explanation as yet.

    You’re safe, as are most of us (I’m a ’56 ~ no jerks here)…except John. And schmaybe Crusader.
    Hell, we may just lump him in with John anyway.

Image | WordPress Themes