Reversals of Earth's Magnetic Field Explained by Small Core Fluctuations

Apr 23, 2009 By Lisa Zyga feature
Reversals of Earth's Magnetic Field Explained by Small Core Fluctuations
According to a new model, small fluctuations in convective flow in Earth’s core can explain how the Earth’s magnetic field reverses. Image credit: Wikimedia Commons.

(PhysOrg.com) -- Based on studies of old volcanic basalt, scientists know that the Earth’s magnetic field reverses at irregular intervals, ranging from tens of thousands to millions of years. Volcanic basalt rock contains magnetite, and when the rock cools, its magnetic properties are frozen, recording the Earth's magnetic field of the time. With this data, scientists estimate that the last magnetic field reversal occurred about 780,000 years ago.

Although volcanic basalt reveals when reversals occurred, it’s much more difficult to find evidence for why or how the ’s reverses. In a recent study, scientists from the Ecole Normale Supérieure and the Institut de Physique du Globe de Paris, both in Paris, have proposed a general mechanism that provides a simple explanation for field reversals. In their model, small fluctuations in convective flow in Earth’s core can push the planet’s sensitive magnetic system away from one pole toward an intermediate state, where the system becomes attracted to the opposite pole.

“We have found a mechanism that gives simple explanations of many features of the reversals of Earth’s magnetic field,” François Pétrélis of Ecole Normale Supérieure told PhysOrg.com. “In particular, it explains the existence and the shape (slow phase followed by fast phase) of reversals, the existence and the shape of aborted reversals (‘excursions’), the statistical properties of reversals, and the possibility for very long durations without reversals (‘superchrons’).”

At present times, the Earth’s magnetic field can be described as a magnetic dipole, with the magnetic south pole currently located near the Earth’s geographic north pole, and the magnetic north pole near the geographic south pole (both magnetic poles are misaligned along the Earth’s rotational axis by about 11.3 degrees). The existence of such a long-lived magnetic field can be explained by dynamo theory, which describes how a convective, electrically conducting fluid that rotates can maintain a magnetic field.

As the scientists suggest, the reversal mechanism relies on the existence of a second magnetic mode, in addition to the dipolar field. The presence of a second mode, such as a quadrupolar field, can have significant effects on how the magnetic system reacts to changes in equatorial symmetry. As the researchers explain, the equator can be thought of as a plane of symmetry, and the convective flow in the Earth’s outer core is usually north-south symmetric. Previous studies on paleomagnetic data have proposed that reversals involve an interaction between the dipolar and quadrupolar modes, which would correlate with changes in equatorial symmetry. In support of this idea, some recent numerical simulations have shown that reversals do not occur when the convective flow remains equatorially symmetric.

“The quadrupolar field (it is likely to be a quadrupole but another structure could be possible) is also generated by the flow of the liquid core of the Earth, exactly like the dipolar field,” explained the researchers. “Most of the time, we observe a dipolar field because it is more easily generated by the flow, but in other conditions a quadrupolar field could be maintained, and this occurs in a temporary manner during a reversal.”

To further explain the dipole-quadrupole interaction, the scientists invoked a model that was recently used to describe the dynamics of a magnetic field generated in a very different system: a lab experiment involving a von Karman swirling flow of liquid sodium (which, like the Earth’s magnetic field, is generated by the dynamo effect). The scientists suggest that a general mechanism could explain both magnetic fields, independent of the different symmetries and velocities of the two systems.

“We have shown that if the dipolar field of Earth is coupled to another magnetic mode (a quadrupolar field, for instance), this coupling provides a path to flip the dipole to its opposite,” the scientists said. “If this coupling is strong enough, the magnetic field will spontaneously oscillate between the two modes and their opposite polarities. We will then observe periodic reversals of the magnetic field (this is the case of the solar magnetic field, for which the period is 22 years). In the case of Earth, the coupling is not strong enough, and oscillations are not observed. Velocity fluctuations in the liquid core are then needed to trigger a reversal.”

In the model, small fluctuations in convective flow can push the system away from one pole toward the intermediate quadrupolar state, where it becomes attracted to the opposite pole. A reversal occurs in two phases: a slow phase where the fluctuations are the motor of the evolution, and a fast phase during which the dynamics does not rely on the fluctuations. The first phase, during which the dipole amplitude decreases slowly, seems to last around 50 kiloyears (30,000-70,000 years). The second phase, which starts when the dipolar mode vanishes, is quite faster: 10,000 years are required for the dipole to recover with the opposite polarity. Sometimes, at the end of the first phase, the system may simply return to the initial pole, which is called an “excursion” when it occurs on Earth. However, if the system does reverse, the behavior happens relatively abruptly. In addition, the system usually overshoots immediately after reaching the opposite pole.

The scientists noted that the amplitude of the fluctuations does not need to be large: “Fluctuations of the flow do not switch off the magnetic field and then regenerate it with the opposite polarity,” they said. “In contrast, the dipolar field continuously changes shape during a reversal because the amplitude of the other mode (the quadrupole, for instance) continuously increases, whereas the dipole decreases. When the dipolar component vanishes, it can increase again with the opposite polarity whereas the amplitude of the other mode decreases.”

The model shows that the duration of the magnetic field in one state depends on the intensity of the convection fluctuations and also on the efficiency of the coupling between the two modes. Even a moderate change in convection can greatly affect the magnetic field polarity duration, which could account for “superchrons” - very long periods without geomagnetic reversals. Although little is known about the actual flow inside the Earth’s core, recent observations have shown that the ends of superchrons are often followed by major flood basalt eruptions, which are likely to produce equatorial symmetry breaking of convection at the core-mantle boundary, in support of the scientists’ model.

More information: Pétrélis, François; Fauve, Stéphan; Dormy, Emmanuel; and Valet, Jean-Pierre. “Simple Mechanism for Reversals of Earth’s Magnetic Field.” Physical Review Letters, 102, 144503 (2009).

Copyright 2009 PhysOrg.com.
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User comments : 24

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omatumr
2.3 / 5 (13) Apr 23, 2009
THE SUN CAUSES REVERSALS OF EARTH'S MAGNETIC FIELDS

The Sun's visible photosphere provides the illusion of a solar "surface" that separates the Earth from the Sun.

In fact, Earth moves through the outer layer of the Sun - the heliosphere - and is gravitationally, electrically and magnetically connected to it.

Solar cycles are actually cycles of deep-seated magnetic fields that periodically poke through the solar "surface" as sunspots, solar storms and violent solar eruptions.

The Standard Solar Model of a Hydrogen-Filled Sun fails to explain solar cycles, as well as many other experimental observations:

http://jenniferma...onomers/

Reversals of Earth's magnetic fields are probably caused by the same deep-seated magnetic fields that produce cycles of solar magnetic storms: The dense, energetic object at the core of our iron-rich Sun.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com/

omatumr
2.1 / 5 (10) Apr 23, 2009
PS - If the above link fails, please see the report, "Quiet Sun Shouldn’t Baffle Astronomers" posted on 23 April 2009: http://jenniferma...om/blog/
OregonWind
2.1 / 5 (10) Apr 23, 2009
Thank you, Dr Manuel. Excellent point.
E_L_Earnhardt
1.3 / 5 (11) Apr 23, 2009
If a "Scientist" begins with the "hypothetical" and finds evidence to support his "hypothosis" it is accepted. A "preacher" doesn't get the same break, but often spends about the same time in a university. I guess it's just a matter of choice!
QubitTamer
2.2 / 5 (9) Apr 23, 2009
I thought Al Gore was the only relevant force in the universe, what gives?
LucFerris
Apr 23, 2009
This comment has been removed by a moderator.
seanpu
2.7 / 5 (6) Apr 24, 2009
Although little is known about the actual flow inside the Earth%u2019s core, recent observations have shown that the ends of superchrons are often followed by major flood basalt eruptions, which are likely to produce equatorial symmetry breaking of convection at the core-mantle boundary, in support of the scientists%u2019 model.


So he's saying: in 2012 when the reserval kicks in dont be on the equator or near any fault lines or volcanoes cos they are gonna blow. in fact get out of America cos yellowstone will blow too.
aco
3.5 / 5 (4) Apr 24, 2009
At least when these fluctuations cause a reversal, the Earths poles will change to the correct magnetic name. http://en.wikiped...tic_Pole
jeffsaunders
3.8 / 5 (4) Apr 24, 2009
omatumr has given one explanation as to why we have a magnetic field at all.

And the article states that electricity flowing generates a magnetic field. Since the Earths outer core is liquid Nickel/Iron and it would rotate. However since rotating magnetic capable material does not make a magnet we still need a current to flow around. Just how much electricity has to flow through the planet to generate the magnetic field?

And since the poles do move around and sometimes swap, that would only require a change in direction of flow of the electric field. Should the solid inner core be magnetic then the entire solid inner core would have to flip, if it was a solid state magnet, and that somehow seems a lot more difficult.

My point is just that an electrically generated magnet is more easily shifted than a solid one and I have no idea just what sort of current would be required to generate the field that we actually have on Earth - does anyone know?
thales
2.6 / 5 (5) Apr 24, 2009
My point is just that an electrically generated magnet is more easily shifted than a solid one and I have no idea just what sort of current would be required to generate the field that we actually have on Earth - does anyone know?


One point twenty-one JIGAWATTS!!

Sorry, I couldn't resist :)
omatumr
2.8 / 5 (9) Apr 24, 2009
Magnetic fields on neutron stars probably span at least the range 10^{8-15} Gauss [http://arxiv.org/.../0307133].

The magnetic field of the neutron star at the core of the Sun at 1 AU from the Earth, is probably about 1,000,000,000,000 Gauss.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
dan42day
2.7 / 5 (6) Apr 25, 2009
So I assume it's safe to say that the Energizer Bunny has nothing to do with it.
omatumr
2.1 / 5 (7) Apr 26, 2009
It is safe to say that the Sun and the Earth are intimately connected in many different ways.

That was one of the main points of a paper on climate changes, "EARTH'S HEAT SOURCE - THE SUN", that was published in Energy & Environment, vol. 20 (2009) pp.131-144.

With kind regards,
Oliver K. Manuel
http://www.omatumr.com
malapropism
5 / 5 (8) Apr 26, 2009
If a "Scientist" begins with the "hypothetical" and finds evidence to support his "hypothosis" it is accepted. A "preacher" doesn't get the same break, but often spends about the same time in a university. I guess it's just a matter of choice!


While I admit that I never attend a Church or other centre for the purpose of worship, it's difficult to avoid every reference to religion due to weddings, funerals and other commemorative events that often seem to have to include it. I've yet to hear a preacher, speaking at any time about his or her religion, preface their comments by stating that their religion is a theory and their hypothesis backing this is that their God (or Gods) exists.

To be pedantic on the subject, I've also never heard any religious preacher state that they hold a null hypothesis concerning the existence of God (Gods).

Perhaps this accounts for the lack of a "break" around any assertion of a God's existence?

And what has your comment to do with the article?
malapropism
2 / 5 (4) Apr 26, 2009
My point is just that an electrically generated magnet is more easily shifted than a solid one and I have no idea just what sort of current would be required to generate the field that we actually have on Earth - does anyone know?


One point twenty-one JIGAWATTS!!

Sorry, I couldn't resist :)


Lol, excellent! It was on TV last Saturday evening where I live (NZ).

I would suggest that this indicates that lightning or a fusion-powered DeLorean is the culprit!
thales
3 / 5 (2) Apr 27, 2009
Well, happy ANZAC day Malapropism! You're right - the effects of a flux capacitor on the Earth's magnetic field could be significant.
Pumamoon
3 / 5 (2) Apr 28, 2009
thank you for your input, oliver.
do you have any thoughts about 2012? i heard there is supposed to be a big solar storm then, much less the pole reversal and it's effects.
what are your thoughts?
thank you.
RTT
not rated yet Apr 28, 2009
So if the moon revolves around the earth creating tidal motion in the molten core then wouldn't this dynamo effect keep the poles from switching?
"(which, like the Earth%u2019s magnetic field, is generated by the dynamo effect)"
omatumr
1 / 5 (3) Apr 29, 2009
Pumamoon asked, "do you have any thoughts about 2012? i heard there is supposed to be a big solar storm then"

No, I did not know about the solar storm predicted in 2012.

But that is not surprising. My areas of research expertise are a.) abundances of isotopes in various parts of the solar system and b.) energy stored in the nuclear rest masses of various types of atoms.

Here is my profile: http://myprofile....anuelo09

With kind regards,
Oliver K. Manuel
Razzbar
not rated yet Apr 29, 2009
One has to wonder what if the magnetic field is not the result of a dynamo at all. The magnetic field is the result of electrical activity so perhaps one might think of it as simply an 'energy field.' What source of electrical activity is available with which to generate this field? How is the diurnal 'wobble' of 'magnetic north' accounted for in the dynamo theory. How is the migration of the magnetic pole accounted for. Someone needs to ask what if the dynamo theory itself is in need of modification before we can understand the reversals that occur.



RB
Mercury_01
1 / 5 (2) Apr 29, 2009
I am VERY glad to hear you guys talking about this. Its a good sign that if this were to happen, at least you would not die making jokes about tinfoil hats and rolling your eyes over the prophecies. Just keep in mind that the prophecy surrounding the time on and near 2012 is the last of the legitimate prophecies we have anywhere on the planet. Some of it is also the oldest. It comes not just from the Mayans, but from all over the ancient world, and from every major religion. Do your own research. It wont hurt anyone to look into things for yourself, even if its just in passing. Ignore what you will, but keep the main point in mind. The planet may briefly become a hard place to live. If so, humans would be forced to grow up in a very real way. Its a heck of a thing to have to think about, but Id say we all have it somewhere in our minds that the proverbial feces is in close proximity to the proverbial fan. and there's not much we can do about the sun.
am_Unition
5 / 5 (3) Apr 30, 2009
...do you have any thoughts about 2012? i heard there is supposed to be a big solar storm then, much less the pole reversal and it's effects...


Alright, so I have to comment.

First of all, we can't predict solar storms. By the time we observe a solar flare, the X-ray burst has already reached Earth (obviously) and triggered a geomagnetic storm. If we observe a coronal mass ejection directed earthwards, then we have half a day to a day of warning before the particles arrive and induce a geomagnetic storm that way. So, although the solar cycle is now forecast to peak in 2012, we have no methodology of predicting a solar flare or storm or anything of that nature, especially not down to the day (like December 21st).

Also, as the article mentions, our models show that a full polar reversal takes thousands of years to fully complete. I'm not saying that our models are right, but there are many elements of dynamo theory that have proven correct.


So if the moon revolves around the earth creating tidal motion in the molten core then wouldn't this dynamo effect keep the poles from switching?

"(which, like the Earth%u2019s magnetic field, is generated by the dynamo effect)"


Not sure what you are trying to say here. Yes, tidal disturbance induced by the moon likely plays some role in turbulence created at the core-mantle boundary, where the geodynamo is thought to originate. But the moon has no dynamo, it has long since cooled off, with only remnant magnetism locked into ferromagnetic rocks.

...Just keep in mind that the prophecy surrounding the time on and near 2012 is the last of the legitimate prophecies we have anywhere on the planet...


I know many people are expecting some drastic shift in global consciousness, a "new age", etc., but I have a suspicion that this has largely already taken place... behold, the internet!


Now, all that said, I secretly hope we are indeed hit with some massive solar storm that causes a spontaneous pole-shift, forces a shift in our biological consciousness, and heralds a restructuring (for the better) of the entire global socioeconomic system. But that's just so unprofessional *YAWN* ;)
Mercury_01
1 / 5 (2) Apr 30, 2009
Word. The only thing I would add is that no prophecy ever said there was going to be a disaster on the 21st, or that the world is going to end. It simply points toward a general time when many changes will come, and that after that time, whatever methods they used to predict fail to apply.
omatumr
1 / 5 (4) May 01, 2009
True, we can't predict solar storms. In fact we understand very little about the Sun.

However, several studies have independently concluded that the solar cycles of sunspots and solar storms arise from angular momentum changes in the Sun [J. D. Jose, "Sun's motion and sunspots", Astron. J. 70 (1965) 193-200; R. W. Fairbridge and J. H. Shirley, "Prolonged minima and the 179-yr cycle of the solar inertial motion," Solar Physics 110 1987) 191-220; T. Landscheidt, "New Little Ice Age instead of Global Warming?" Energy & Environment 114 (2003) No. 2/3, pp. 327-350].

Here is a graph of the Landscheidt solar cycles: http://landscheid...m-graph/

Oliver K. Manuel
http://www.omatumr.com/




COCO
1 / 5 (1) May 01, 2009
this all was covered in an apparently (from the lack of reference to same) the HAB Theory - a wee bit more interesting than this rehash of theory. Even some sex in the novel.