FAQ-3_ _The Great Magnet, The Earth

8/22/2019 FAQ-3_ _The Great Magnet, The Earth

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7/21/13 FAQ-3: "The Great Magnet, the Earth"

www-spof.gsfc.nasa.gov/stargaze/magnQ&A3.htm#q46

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Get a Straight Answer

Please note!

Listed below are questions submitted by e-mail to the author of "The Great Magnet,

the Earth." Some of them (marked ***) came in response to an earlier site "The

Exploration of the Earth's Magnetosphere" and are also found there in the question-

and-answer section. Only some of the questions that arrive are listed, eitherbecause they keep coming up again and again--on the reversal of the Earth's

magnetic field, for instance--or because the answers add extra details, which might

interest other users.

Index of Questions arranged by Subject

Items covered:

1. What is "Magnetic Flux" and what are "Flux Lines"?

2. Is the surface of the Earth expanding?

3. Will a Compass work inside a Car?

4. Pole shifts? What Pole Shifts?

5. What was it that Ned Benton did?

6. Reversals of the Earth's field (4 queries)

7. Can Magnetism propel Spaceships?

8. Reversal of the Sun's Magnetic Poles9. Measuring Earth's magnetic field

10. The strength of the Earth's mgnetic field

11. Magnetic Shielding

12. Building an electromagnet

13. How do Magnetic Reversals affect Animal Migrations?

14. Which is the "True" North Magnetic Pole?

15. Magnetic intensity at Singapore

16. Inner Core Rotation

17. How does the Earth's field vary with location?
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www-spof.gsfc.nasa.gov/stargaze/magnQ&A3.htm#q46 2

18. Effect of magnetism on water

19. "Why does this happen?" (electromagnetic induction)

20. What would a Compass on the Moon point to?

21. Why do iron filings outline magnetic field lines?

22. Is Earth held in its orbit by magnetic forces?

23. All magnetism due to different arrangements of magnetic poles?

24. Magnetism to replace gravity in a space station?

25. Magnetic reversal due soon? And are volcanoes a factor?

26. Can magnetic reversals affect the human mind?

27. When and where can I see "Northern Lights"?

28. Magnetic reversals due to comet impact?

29. Space Radiation and our weakening magnetic field

30. Can the Sun trigger magnetic reversals?

31. What is the smallest magnet?

32. Isn't the Sun too hot to be magnetic?

33. "Artificial magnetic shields" for astronauts?34. The movie "The Core"

35. Can we tell if a symmetric magnetic field rotates around its axis?

36. What causes permanent magnetism?

37. What types of metal are attracted to magnets?

38. "If the earth is a giant magnet, why doesn't all iron stick to it?"

39. Risks from stormy "Space Weather"

40. Does our magnetic field stop the atmosphere from getting blown away?

41. Dynamos triggered by the sun?

42. Could generated electricity affect Earth's magnetic field?

43. "Magneto-therapy"

44. Curie Point

45. Blocking of magnetic fields

46. Earth magnetism from rotating electric charges?

47. Teacher seeks easy experiments

48. Local field does not always decrease!

49. Loss of magnetic energy from Earth

50. Tesla's patents, and ball lightning

51. Can electricity be generated from the Earth's magnetic field?

52. Decay of magnetism in a magnet

53. Magnetizing glass by a radio wave?

54. Magnetization of materials

55. Induction by non-fluctuating magnetic fields?

56. Good "magnetic insulators"

57. Creating magnetic pottery

58. Shielding magnetic fields (2 messages)

59. Conductivity and Transparency

60. Heat sources inside the Earth
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61. Geomancy

62. Are we approaching a polarity reversal?

63. Magnetic Levitation

64. Why does the magnetic field stop particles but not EM radiation?

65. Earth's rotation and magnetism

66. A career in geomagnetism?

67. The movie "The Core"

68. Telling the 6th grade about polarity reversals

69. Magnetic Flux

70. Why do moving electric charges create a magnetic field?

71. Weakening of the Earth's Field (2 questions)

72. Focusing magnetic fields

73. Is gravity related to magnetism?

74. Observing Magnetic Planets

75. How does magnetism spin aluminum disks in power meters?

76. Magnetic Poles in Druid times?

77. Magnetism linked to Global Warming?78. Uses of Magnetic Energy

79. Can sparks generate magnetic fields

80. Can a magnetometer detect cracks in an oil well?

If you have a relevant question of your own, you can send it to

earthmag("at" symbol)phy6.org

Before you do, though, please read the instructions

29. Space Radiation and our weakening Magnetic Field

Hi Dr. Stern:

I hope you can help me. I was just checking out your webpage and a

question regarding the earth's Van Allen belts and solar flares/solar winds. I

read that the earth's magnetic field has actually weakened by about 7% and

field's actual total energy measured is less by 14% (since 1829). What is

the impact of this weakening on the Van Allen Belts and the earth's

Magnetosphere?

If solar flare activity increases (e.g. second-biggest geomagnetic storm

ever measured hit the earth about a week ago) and the earth's magnetic

field weakens, what impacts would we observe inside the atmosphere?

Higher radiation exposure for folks on planes? Greater disruptions with
http://www-spof.gsfc.nasa.gov/stargaze/FAQinst.htmhttp://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q80http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q79http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q78http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q77http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q76http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q75http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q74http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q73http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q72http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q71http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q70http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A5.htm%20#q69http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q68http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q67http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q66http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q65http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q64http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q63http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q62http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A4.htm#q61


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electrical grids and radio transmissions? What's projected in the long term?

Can you recommend any websites that "a non-scientist lay person" might

be able to read up on this. I guess the late August solar flare activity had

nothing to do with the New York blackout (it occurred 2 weeks earlier in

August).

REPLY

When discussing risks and dangers from radiation in space, you should

really distinguish two kinds of radiation:

(1) Trapped radiation, e.g. Van Allen Belt

(2) Energetic ions emitted by solar flares.

(1) Trapped radiation is governed by the geomagnetic field. If you are

below the belt (as in the international space station) or elsewhere outside itsintense part, you should have nothing to worry about. It could well be that

the belt is now 7% weaker than in the time of Gauss, 160 years ago, but

that does not really change the preceding statement. These ions have about

50 MeV.

(2) Solar flares release unpredictable blasts of particles of higher energy,

often 500 MeV and up to 10 GeV. In this case, people on the ground are

still safe, because the atmosphere has enough thickness to stop the

particles, equivalent to something like 4 meters of concrete. See the end of

http://www.phy6.org/Education/wsolpart.htm If you are in a spacecraft onyour way to Mars, that can be dangerous. In Ben Bova's book "Mars" this

does happen, and astronauts have to hide in a protected area--behind fuel

tanks, probably.

On Earth, we have an additional shield, the Earth's magnetism, which will

deflect all but the highest energies from regions at equatorial and middle

latitudes. Jetliners crossing the polar region may perhaps find it useful to fly

a little deeper in the atmosphere, maybe, and I heard the Concorde carried

a radiation alarm.

The magnetic field would have completely protected the space station in

its originally planned orbit, inclined 29 degrees to the equator (latitude of

Cape Canaveral). As it happened, this was later increased to about twice

as much, to enable Russian launch sites to resupply the station (which

turned out quite important after the "Columbia" disaster). Twice each orbit,

therefore, the station has relatively weak magnetic protection, near its

closest approach to the magnetic poles. I heard a rumor that during the 3

big flare events at the end of October the astronauts did in fact hide, but

that is strictly hearsay which I cannot confirm. The even bigger flare on


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November 4 did not produce such a radiation surge.

I am not sure about disruption of power grids, but I think it arises when

the auroral electrojets shift to lower latitudes during storms. There are two

large electric currents flowing along the auroral zone towards midnight,

associated with the polar aurora (or more precisely, with the electric

currents which produce big aurora; see in "Exploration of the Earth's

Magnetosphere.") Like any electric currents, they produce a magnetic field

which can be observed on the ground, and which changes fairly irregularly.

When they move equatorwards, into more inhabited regions (and out of

them again), the changing magnetic field induces electric currents in the high

voltage networks there. The induction is slow, so the transformers of the

grid, configured to impede currents of 60 or 50 cycles/second, see

essentially a DC current, to which they offer it no significant impedance,

allowing it to grow big. Such a current can burn out transformers, unless

appropriate circuit breakers are tripped in time. I don't know how serious

that is: burn-outs happened in 1989, but as far as I know, not recently.

I am not an expert in disruption of radio. Flares emit X-rays, which

modify the ionosphere, adding ionization deeper down. It then can absorb

certain frequencies, but I am not sure whether, say, cell phones are

affected, or ships and airplanes. I think the frequencies used by

communication satellites are high enough to be immune, and of course a lot

of land traffic these days uses optical cable. I am not sure about GPS.

30. Can the Sun trigger magnetic reversals?

(shortened) Current thinking suggests that the dynamo effect runs the

earth's magnetic field. Computer models have been run which suggest that

simply applying he rules of interaction of fluid dynamics and magnetism can

create a stable and reversing polarity field of magnetism. But we are

troubled to explain why the field does not run down, and we really can't

model accurately the fluid mechanics of the outer core.

This can be probably be better understood by the picture of manydifferent dynamic movements creating magnetic fields, of a multitude of mini

dynamos operating within the earth about areas of upwelling and vortices.

The earth travels in the magnetic field of the sun and interacts with solar

wind and radiation in the magnetosphere, and this will excite fields which

support the current flowing in a particular direction. Hence the north-south

orientation of the current field, slowly precessing but stable.

My theory is this, that a hitherto unknown solar eruption on a grand scale

changes the exiting fields and as a result, the sum of dynamo fields is altered


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and could lead to a pole reversal. This would allow rapid pole reversals and

does not require wholesale restructuring of the outer core.

I am alas a poor student of extraterrestrial physics and do not have the

math, facilities or background to explore my theory further. I would like to

discuss this with someone, and ask your advice as to who to approach for

assistance.

REPLY

Your concern seems to be with the way the magnetic field in space affects

that of the core, and whether it can trigger reversals. Actually the effect is

very small and thus probably not significant.

As I type this (4 November 2003), a big magnetic storm is in progress,

and after dinner my wife and I will drive out of town to see if aurora is

visible. According to the web, data from Kyoto on

http://www.antarctica.ac.uk/SatelliteRisks/lastweek.htmlthe average magnetic intensity at the equator has dropped by some 350 nT

(nano-Tesla), in a region where the total field is about 30,000 nT. This

seems to be the largest storm of the year so far, and the change is a little

over 1% or 0.01 . That ratio also turns out to be of the order of the ratio

between the energy of the disturbance and the magnetic energy of the core

outside the surface of Earth (theorem of Dessler, Parker and Sckopke).

Thus the internal energy is still much larger, even in a large disturbance.

You write "what would happen if, say, a pressure wave moved the so

called 'bow shock' boundary say half the distance towards the earth". Itdoes happen in magnetic storms--may even have happened today. When

this happens, the result is in the opposite direction from that of trapped ions

and electrons added by the magnetic storm. The 1% cited here is the net

sum, and the sign (direction of the added field, today southward) suggests

the added ions and electrons have a dominating effect.

And that is just at the surface of the Earth. Because of conductivity of the

core, any disturbance is very severely attenuated inside it. A highly

conducting material shields out external magnetic disturbances.

One thing about reversals. They seem to happen rapidly, but theory

suggests (at least considering just the resistive nature of the fluid) that the

magnetic energy of the core can only change very slowly. What it might be

doing instead is redistribute itself--less in the main "dipole" part and more in

the complex components ("higher harmonics") which diminish steeply with

distance and therefore contribute less to the field observed on the surface.

In recent years, I have read (work of Ned Benton) that the dipole field has

weakened steadily, but the complex part has grown stronger, and the sum-
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total of their energy is roughly constant.

So during a reversal, complex magnetic fields are expected to persist and

contain most of the energy. Since these fields are much more intense than

anything created by electric currents in space (certainly in the core, but even

on the surface), I do not expect external sources to significantly affect the

production of the new dynamo field.

31. What is the smallest magnet?

I read with great interest you clear and concise description of magnets and

magnetism and was hoping you could answer a question for me.

What is the smallest magnet that is possible ?

If I have read your page correctly there can be no magnetism without an

electric current. If this is correct where does the electric current come from

within the Earth ?

REPLY

What is the smallest magnet possible? Maybe the electron. Imagine it (as

people around 1900 imagined it) as a tiny sphere loaded with negative

electric charge. If you make that charge rotate around some axis, its

different parts will move in circles, each acting like a small current, and the

result would be that the electron is magnetized along its rotation axis--"has amagnetic moment" in sciencespeak.

Something like that was discovered in 1925 by Uhlenbeck and

Goudsmit, the so-called electorn spin. They deduced it while trying to

explain the spectral lines of atoms--see

http://www.phy6.org/stargaze/Sun4spec.htm

These are phenomena of individual atoms, and at that scale, physics laws

change to different laws, so-called quantum physics. What on our scale issmooth and continuous (e.g. the range of orbits allowed for a satellite)

becomes choppy and discrete (e.g. range of orbits allowed to an electron in

an atom). By those laws, even the picture of an electron as a rotating

charged sphere, or of an electron orbiting inside an atom, are not really

right. But they help our imagination get the main points right--such that

electrons are magnetized.

Protons and even neutrons are also magnetized, and much more weakly.

This is used in MRI magnetic imaging--see "optional excursion" for the


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teacher.

http://www.phy6.org/stargaze/Lprecess.htm

32. Isn't the Sun too hot to be magnetic?

Hello Sir,

A magnet loses its properties at a particular temperature, but we know

that there is a very strong magnetic field around the sun where the

temperature is way beyond the Curie`s Temperature. So what is the reason

behind suns magnetism ? Thank you.

REPLY

Your question shows an understanding of physics... but also, that you have

not read my web pages, where this is discussed in detail.

The magnetism of the Sun indeed used to be a great puzzle: not only was

the Sun extremely hot, much hotter than any Curie temperature, but it was

also a gas. Yet sunspots were intensely magnetic.

Sir Joseph Larmor therefore proposed in 1919 that perhaps sunspot

magnetism came from electric currents, driven by a "dynamo process" by

flows on the Sun (which is hot enough to conduct electricity). Later the

same idea was extended to the liquid core of the Earth, which is also hotter

than any Curie temperature, but again, probably contains molten iron whichconducts electricity.

For more, see the sections on the dynamo process in "The Great

Magnet, the Earth", home page

http://www.phy6.org/earthmag/dynamos.htm

http://www.phy6.org/earthmag/dynamos2.htm

They cover the dynamo process at an elementary level, and more details

are in "A Millennium of Geomagnetism" linked from the home page of that

web collection. As you will read there, the process for the Earth has nowbeen successfully simulated on a computer, including polarity reversals.

(The polarity of the Sun's magnetism also reverses with the 11-year cycle.)

33. "Artificial magnetic shields" for astronauts?

Could you please tell me if you have ever heard of a supposed

phenomenon called "Magnetic Deficiency Syndrome" that affected early
http://www-spof.gsfc.nasa.gov/stargaze/dynamos2.htmhttp://www-spof.gsfc.nasa.gov/stargaze/dynamos.htmhttp://www.phy6.org/stargaze/Lprecess.htm


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Russian and American Astronauts?

Did N.A.S.A. install "Artificial magnetic shields" to overcome the

supposed condition ( Which caused bone density loss)?

The answers to these questions trouble me. I thought it was zero gravity

that caused bone density loss.

REPLY

Yes, I have heard about it, but only from letters like yours. Whichever way

the story got started, it is false: I know of no magnetic problems in orbit,

and of no artificial magnetic shields.

The magnetic field sensed in Earth orbit is very weak, and I know of no

magnetic effects. Have you ever undergone an MRI scan--a medical scan

using a magnetic resonance imaging (MRI) machine? You lie on a narrow

pallet and are wheeled into the middle of a large magnet, with very intensefield. It's a noisy procedure, but you can sense no effect due to magnetism,

because to the best of my knowledge, there is nothing in the human body

affected by magnetism.

Loss of bone density is still ascribed to weightlessness, and is

counteracted by exercise machines. See also my web page

http://www.phy6.org/stargaze/Sskylab.htm

Concerning various medical problems or cures ascribed to magnetism,

and other unusual claims for magnetism, please look uphttp://www.chem1.com/CQ/magscams.html

34. The movie "The Core"

Can the Earth's magnetic field just "dwindle away," as a recent movie "The

Core" proposes? And if this were somehow to happen--what dire

consequences (also described in the film) could we expect?

REPLY

Sleep soundly: the premise is far fetched, and even if it did somehow

happen, you would probably not notice any difference.

Could it happen? The magnetization of the ocean floor (among others)

shows that the north-south "main magnetic field" of the Earth does

occasionally reverse north-south polarity, at irregular intervals averaging

about half a million years. Right now the intensity of this field is decreasing
http://www.chem1.com/CQ/magscams.html


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at about 7% per century. That is a typical rate of variation, suggesting that if

a reversal happens, we will have ample notice.

However, at the reversal itself the field is not necessarily zero. Other,

more complex parts of the field exist, and right now it looks as if these are

soaking up magnetic energy lost from the main north-south field. At the time

of reversal, the Earth may have for a while 4, 6 or more magnetic poles,

and a somewhat weaker field--but it is not expected to lose its magnetism

altogether.

And yet, if it ever did... would we be exposed to radiation bursts from

the Sun--the kind which erupt of the order of once a year (or less) and can

imperil future astronauts on their way to Mars? No, because we are

shielded by the atmosphere, an absorber comparable to 10 feet of

concrete. Solar bursts cannot penetrate that thickness. It is true that the

magnetic field of Earth deflects the fast protons of those bursts even before

they reach the top of the atmosphere--but that magnetic shield fails near the

magnetic poles, yet no extra radiation is detected there at ground level.

Without magnetic protection, the solar wind emitted by the Sun would

also reach the atmosphere. Could it perhaps strip our atmosphere away?

Maybe, given a few billion years, but not quickly. Venus lacks a magnetic

field and experiences a stronger solar wind, being closer to the Sun, yet

retains a very dense atmosphere. Mars, without a global-size magnetic field,

has only a thin one--but the gravity holding down its atmosphere is only 1/3

of ours.

So sleep soundly, even after you may have watched the movie.

35. Can we tell if a symmetric magnetic field rotates

around its axis?

(shortened)

Question that puzzles me for a long time is basically very simple. Does

earth's magnetic field rotate around it's magnetic poles axis Well, looking at

the rotation of magnetic anomalies, and rotation of magnetic poles, this is

true. But that cannot be, and should not be considered as rotation of

magnetic field on it's magnetic axis. The experiments can show us that the

rotation of any magnetic field on it's magnetic axis is impossible and

contrary to the very laws of nature. That should be viable even for complex

magnetic structures as earth's magnetic field is. Yet, it is obvious that

majority of scientific community is even unaware of Faraday's experiments

with rotating magnets..


11/26



REPLY

Your question brings up something which has confused many people (even

me, when I was younger).

Basically, the rotation of axially symmetric magnetic fields in a vacuum

around their axis of symmetry is NOT observable. If you have a bar magnet

and attach it to a shaft which rotates it around its symmetry axis (the lineconnecting its poles) you will not find any difference whether it rotates or

not. The outside magnetic field--and the electric field, too--is not changed

by the rotation, and the equations which determine these fields do not

reflect rotation of the source.

However, that is in a vacuum (and to all practical purposes, also in air).

When matter is present--especially, electrically conducting matter--rotation

may make a difference. Take for instance Faraday's disk dynamo, where a

conducting disk rotates in a magnetic field (see illustration in

http://www.phy6.org/earthmag/dynamos.htm ). The magnetic field may beaxially symmetric, and the disk and its motion have the same symmetry, but

it makes a difference, because a moving CONDUCTOR in a magnetic field

B, at a point moving with velocity V, experiences an electric field E = VB in

a direction perpendicular to both B and V (mathematically you need use

here a "vector product", but let me not go into that detail).

If instead the magnet rotates around its axis and the disk is at rest,

nothing happens to the disk, which shows that it is the motion of the

CONDUCTOR that matters, not that of the magnetic source. Except of

course in non-symmetric sources, where the motion causes observablechanges in B--these do matter, and such irregular components clearly rotate

with the Earth.

If the disk is not connected, the only effect of this E is to move electric

charges across the disk, until they create an opposite field which cancels E,

and nothing more happens. However, if electrical contacts from the outside

touch the disk as in the drawing, connecting it to a circuit which does NOT

rotate, then the electrical charges which try to neutralize E are carried away

to the outer circuit, and the device works as an electric generator.

Just for your interest: at one time it was suggested that any spinning

matter, conducting or not, produced a magnetic field, but experiments

showed that was untrue. See 2nd paragraph in section 14 on web page

http://www.phy6.org/earthmag/ /mill_5.htm.

--------------------------

There exists another level of this discussion, but if you find it confusing,

you may stop here. Suppose you have a fluid which conducts electricity
http://www-spof.gsfc.nasa.gov/stargaze/mill_5.htmhttp://www-spof.gsfc.nasa.gov/stargaze/dynamos.htm


12/26



very well--such as the metal mercury, or liquid sodium, or the molten iron in

the core of the Earth, or even the ionized gas ("plasma") which surrounds

the Earth in space (it may not conduct as well as mercury, but the

dimensions of many thousands of kilometers help create the same result).

Assume that it contains a magnetic field, as is certainly true for the Earth in

space.

If this conducting fluid moves through the magnetic field, its motion

generates electric currents, like the motion of the wheel in a Faraday

dynamo. Those currents, in turn, create magnetic fields of their own, and

modify the original magnetic field.

In the general case, finding the modified magnetic field is a complicated

mathematical problem, requiring that one also calculates electric fields and

electric currents. However, if the conductivity is very, very good, the

equations show that the solution simplifies. Namely, it then turns out that

FIELD LINES SEEM TO MOVE with the material. Let a field line be

drawn at some specific time, and imagine you could mark all the portions ofthe fluid (all the atoms, if you wish) through which is passes at that time. If

you then let some time pass, find where these atoms are now and draw a

line through them, the mathematics of the problem tells you that they are

ALSO connected by the same field line.

Physicists like to say that this is THE SAME field line, traveling with the

fluid as if it were "frozen" to it. In this way we can say that magnetic field

lines "move." This is a very convenient was of avoiding the calculation of

electric fields and currents, although it is strictly true only for "infinite

conductivity" limit. But one must always remember--this is not somethinghappening in a vacuum, but in a very good electrical conductor

A study project involving this "freezing" is described in

http://www.phy6.org/Education/wimfproj.html

36. What causes permanent magnetism?

I realized a couple of days ago that I don't know the answer to this question

and was hoping that you would answer it for me. Surprisingly, no one here

at work knows the answer either! We are a bunch of engineers doing

software, some people have EE backgrounds, some physics. I am

embarrassed! I understand the business about electric currents being the

real reason for magnetism (hence sunspots, etc.), and the loop of wire

resulting in transformers. I just don't understand a permanent magnet or

what is so special about iron that an electric field induces magnetism in a

piece of iron. It doesn't happen in too many other materials. Why is

stainless steel different (most of it is NOT magnetic)?


13/26



REPLY

Yes, magnetism requires currents going around in loops (not electric fields

but electric currents). However, a spinning electric charge also fills the bill.

A few days ago someone sent an e-mail question "what is the smallest

magnet?" and my answerwas, a spinning electron.

The trouble is, by the time you get down to the scale of electrons, therules of physics change to so-called "quantum physics." Electrons turn out

to have a natural spin and associated magnetic properties, but the direction

of the spin/magnetic axis is severely constrained, and the relation between

the two is not what you expect from a rotating charge.

Iron and other "ferromagnetic" substances get their magnetization from

spinning electrons. In other substances, neighboring spins arrange to cancel

each other--the way two neighboring bar magnets do (N of one is next to S

of the other). Iron atoms are not permitted to do so, because of properties

of quantum physics. Sorry I cannot say more--it isn't my field--but look uphttp://en.wikipedia.org/wiki/Ferromagnetism .

37. What types of metal are attracted to magnets?

We are students working on a science project involving magnetism. We are

investigating what types of metals are attracted to magnets. Could you

please send us your opinion on this subject along with any other information

you may have.

REPLY

(see also previous question and its answer)

Iron is attracted to magnets, but why? Because near a magnet, in a

"magnetic field", ordinary iron turns into a temporary magnet. See web page

http://www.phy6.org/earthmag/inducemg.htm

on "Performing Gilbert's Experiment on Induced Magnetism."

Iron and some alloys (and I am not sure, but also maybe nickel) turn into

fairly strong temporary magnets. These are "ferromagnetic" materials--look

up ferromagnetism in an encyclopaedia. Some very strong magnets contain

no iron but have compounds of rare earth elements.

Many other materials are "paramagnetic" and while they too turn into

temporary magnets, these are very feeble, and are only weakly attracted.

"Diamagnetic" materials also turn into feeble magnets, but of opposite

polarity, so these are slightly repelled.
http://www-spof.gsfc.nasa.gov/stargaze/inducemg.htmhttp://en.wikipedia.org/wiki/Ferromagnetismhttp://www-spof.gsfc.nasa.gov/stargaze/magnQ&A3.htm#31


14/26



Now go do your work!

38. "If the earth is a giant magnet, why doesn't all iron

stick to it?"

I am a second grade teacher in Massachusetts. One of my students, a little

boy named Seamus, has really stumped me with a question while studying

the make up of the earth. He asked;

"If the earth is a giant magnet, why doesn't everything made of

iron stick to it, especially at the north and south poles??"

I have done some research, but am having a hard time putting it in terms

REPLY

This is not an easy question to answer at the second-grade level, but I will

try. The answer has two parts: (1) The force of the Earth's magnetism is notall that great. It takes a delicately balanced magnetic needle (known as a

magnetic compass!) to show its effect. (2) The magnetic force on a

magnetic needle consists of two effects: (a) it tries to TURN the needle (b)

it tries to MOVE the needle, for example to attract it. The turning effect is

MUCH stronger than any attraction. As noted under (1), we need a

delicately balanced needle to detect the magnetically produced turning, but

we would need an INCREDIBLY sensitive instrument to measure any

attraction.

Here is the reason why. Suppose you have a pivoted magnetic needle or

bar magnet, with "N" and "S" poles which, as in any magnet, have an equal

strength. (At this point you might want to make a drawing). The N pole will

be attracted by the north magnetic pole of the Earth and the S pole will be

repelled from it, so the needle will rotate until the "N" pole is as close to the

north magnetic pole as it can go, and the "S" pole as far from it. BOTH

forces here help produce the same rotation.

But what would be the forces MOVING the magnet? The N pole is

attracted, the S pole repelled, and both forces are ALMOST the same. If

they were EXACTLY the same, they would cancel and the result would be

zero--no force at all. As it is, since the needle has already rotated, the N

end is a TINY bit closer to the north magnetic pole (say two inches, the

length of the needle), and the force on it is a TEENY bit stronger. But that

teeny difference is not nearly enough to move the needle, even if the pivot

did not hold it back.

So far we have talked about magnetized needles, not plain iron.

However, plain iron near a magnet itself becomes a temporary magnet--see


15/26




So all what was said about magnetized iron holds in principle for iron

(though in the weak field of the Earth, an iron nail is magnetized much more

weakly than, say, a compass needle).

And because the attraction results from the cancellation of opposing

forces, you now understand why an iron nail (say) is attracted to a magnet

only when it is VERY close to the magnet's pole--when the magnetic pole

at the attracted end of the nail is MUCH closer than the repelled end.

39. Risks from stormy "Space Weather"

Hi Dr. Stern:

I hope you can help me. I was just checking out your webpage and a

question regarding the earth's Van Allen belts and solar flares/solar winds. I

read that the earth's magnetic field has actually weakened by about 7% andfield's actual total energy measured is less by 14% (since 1829). What is

the impact of this weakening on the Van Allen Belts and the earth's

Magnetosphere?

If solar flare activity increases (e.g. second-biggest geomagnetic storm

ever measured hit the earth about a week ago) and the earth's magnetic

field weakens, what impacts would we observe inside the atmosphere?

Higher radiation exposure for folks on planes? Greater disruptions with

electrical grids and radio transmissions? What's projected in the long term?

Can you recommend any websites that "a non-scientist lay person" might

be able to read up on this. I guess the late August solar flare activity had

nothing to do with the New York blackout (it occurred 2 weeks earlier in

August).

Reply

When discussing risks and dangers from radiation in space, you should

really distinguish two kinds of radiation:

(1) Trapped radiation, e.g. Van Allen Belt

(2) Energetic ions emitted by solar flares.

(1) Trapped radiation is governed by the geomagnetic field. If you are

below the belt (as in the international space station) or elsewhere outside its

intense part, you should have nothing to worry about. It could well be that

the belt is now weaker than in the time of Gauss, 160 years ago, but that

does not really change the preceding statement. These ions have about 50

MeV.
http://www-spof.gsfc.nasa.gov/stargaze/inducemg.htm


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(2) Solar flares release unpredictable blasts of particles of higher

energy, often 500 MeV and up to 10 GeV. In this case, people on the

ground are still safe, because the atmosphere has enough thickness to stop

the particles, equivalent to something like 4 meters of concrete. See the end

of

http://www.phy6.org/Education/wsolpart.html

If you are in a spacecraft on your way to Mars, that can be dangerous. In

Ben Bova's book "Mars" this does happen, and astronauts have to hide in aprotected area--behind fuel tanks, probably.

On Earth, we have an additional shield, the Earth's magnetism, which will

deflect all but the highest energies from regions at equatorial and middle

latitudes. Jetliners crossing the polar region may perhaps find it useful to fly

a little deeper in the atmosphere when the sun emits high-energy particles,

and I heard the Concorde carried a radiation alarm.

The magnetic field would have completely protected the space station in

its originally planned orbit, inclined 29 degrees to the equator (latitude ofCape Canaveral). As it happened, this was later increased to about twice

as much, to enable Russian launch sites to resupply the station (which

turned out quite important after the "Columbia" disaster). Twice each orbit,

therefore, the station has relatively weak magnetic protection, near its

closest approach to the magnetic poles. I heard a rumor that during the 3

big flare events at the end of October 2003 the astronauts did in fact hide,

but that is strictly hearsay which I cannot confirm. The even bigger flare on

November 4 did not produce such a radiation surge.

I am not sure about disruption of power grids, but I think it arises whenthe auroral electrojets shift to lower latitudes during storms. There are two

large electric currents flowing along the auroral zone towards midnight,

associated with the polar aurora (or more precisely, with the electric

currents which produce big aurora; see in "Exploration of the Earth's

Magnetosphere.") Like any electric currents, they produce a magnetic

field which can be observed on the ground, and which changes fairly

irregularly.

When they move equatorwards, into more inhabited regions (and out of

them again), the changing magnetic field induces electric currents in the high

voltage networks there. The induction is slow, so the transformers of the

grid, configured to impede currents of 60 or 50 cycles/second, see

essentially a DC current, to which they offer it no significant impedance,

allowing it to grow big. Such a current can burn out transformers, unless

appropriate circuit breakers are tripped in time. I don't know how serious

that is: burn-outs happened in 1989, but as far as I know, not recently.

I am not an expert in disruption of radio. Flares emit X-rays, which
http://www.phy6.org/Education/wsolpart.html


17/26



modify the ionosphere, adding ionization deeper down. It then can absorb

certain frequencies, but I am not sure whether, say, cell phones are

affected, or ships and airplanes. I think the frequencies used by

communication satellites are high enough to be immune, and of course a lot

of land traffic these days uses optical cable. I am not sure about GPS.

That's about all I know on this subject. Let me know if you find anything

more, or anything contrary to what I know.

40. Does our magnetic field stop the atmosphere from

getting blown away?

Thank you for such an in depth and informative Web Site. I have a

question about the force of the solar wind against the magnetosphere. If the

Earth's magnetosphere turned off (magnetic fields no longer existed on

Earth), how long could life on the Earth survive? Eventually the solar wind

would blow the atmosphere away.

Reply

I don't have an exact answer, and it all depends on what you mean by

"eventually." If the process happens it is probably too slow to make much

difference.

Venus has no magnetic field, its gravity is less than ours and being closer

to the Sun, it experiences a much stronger solar wind, yet it retains a dense

atmosphere. True, because its atmosphere is so dense, it can suffer

appreciable loss without much change.

I don't know what the loss rate is, but it could be calculated from

observations downwind from Venus, and maybe someone has done so. I

have found a long article (below) but it does not seem to give an answer

http://www-

ssc.igpp.ucla.edu/personnel/russell/papers/interact_solwind/

Another web page suggests little change in the atmosphere:

http://pauldunn.dynip.com/solarsystem/Venus_B.html

41. Dynamos triggered by the sun?

(from new Zealand)

The dynamo effect is has a solid background, but we are troubled to

explain why the field does not run down, and we really can't model

accurately the fluid mechanics of the outer core.

Exciting an electrical field or a magnetic field is essential to provide a


18/26



strong dynamo effect as with any typical rotating field generator, and in

getting it to run in a particular direction. If the multitude of mini dynamos

were operating within the earth about areas of upwelling, and rotational

vortices, the fact that the earth travels in the magnetic field of the sun and

interacts with solar wind and radiation in the magnetosphere, will excite

those fields which support the current flowing in a particular direction,

hence the slowly processing but stably north south orientation of the current

field. My theory is this, that a hitherto unknown solar eruption on a grandscale changes the exciting fields and as a result the sum of dynamo fields is

altered and could lead to a pole reversal. This would allow rapid pole

reversals and does not require wholesale restructuring of the outer core.

I am alas a poor student of extraterrestrial physics and do not have the

math, facilities or background to explore my theory further. I would like to

discuss this with someone, and ask your advice as to who to approach for

assistance.

Reply

Explaining the details of geomagnetic dynamos can't be done briefly, also

it's not my field really, and very mathematical. Still, I'll try.

Two things to note.

First, a magnetic dynamo, like almost any process in nature, needs

energy (in that respect, energy is like money). Geomagnetic dynamos are

believed to be driven by flows in the liquid part of the Earth's core, and the

flows are driven by heat generated there.

In one simple view, the interior of the Earth is heated by long-lived

radioactive elements (uranium, thorium and potassium) in the crust, which

keeps it at a temperature sufficient to keep iron fluid. If that alone

happened, no flow would be needed (and hence, no dynamo would arise).

However, some extra heat is generated--perhaps by a slight amount of

radioactive elements left in the core, perhaps by very slow solidification of

fluid iron onto the inner core (no one really knows). If the amount of heat is

small, it may just be conducted away to the mantle and beyond. But if there

is too much heat for this process to do the job, the fluid starts circulating

and convecting it away, like boiling water in a pot. The atmosphere gets rid

of heat by a similar convection process, see

http://www.phy6.org/stargaze/Sweather1.htm

As long as energy is supplied, the convection will continue, and if

conditions are right for a dynamo, it will not run down. Instead it will settle

down within some comfortable limits. It can't grow too large and become

"runaway" unless more energy is made available somehow.
http://www.phy6.org/stargaze/Sweather1.htm%22


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Secondly, you may indeed say there exists a "multitude of mini

dynamos," not just a single "strong dynamo effect as with any typical

rotating field generator." If you look at a magnetic map of Earth, you will

note that although the field has a two-pole structure, it also contains many

bumps. This "bumpiness" reflects a complex flow and field in the core. This

is essential: Thomas Cowling in 1933 proved a dynamo cannot be

symmetric around some axis.

The core has about half the radius of Earth, and it turns out that the

distance filters the field. The 2-pole part (dipole) goes down like the 3rd

power of distance, so at the surface of the core it is 8 times stronger. More

complex parts, however (there is a mathematical technique for isolating

them) go down like 4th, 5th, 6th... power of distance, which means that at

the surface of the core they are 16, 32 and 64 times stronger than they

seem at the surface. The dipole is still dominant there, but by a much

smaller margin. The complicated parts are quite big there.

One may thus look at the flow as a collection of circulating eddies. Acrude model was proposed by Rikitake (1971?) with two eddies--call

them A and B. Each of them may be thought of as a Faraday disk dynamo-

-see http://www.phy6.org/earthmag/dynamos.htm

The motion of disk A creates an electric current which produces a

magnetic field, and that field is sensed by B. Then the motion of B through

this magnetic field generates a current, which creates a magnetic field... and

that is the field sensed by A, the one which allows it to generate a current.

Each disk creates the magnetic field used by the other. It turns out such a

model can reverse, and oscillate.

All this sounds a bit like the chicken-and-egg paradox: you need some

magnetic field to start either dynamo! Actually, if conditions are right, even

a tiny field gets amplified more and more, and the process only saturates

when the limited energy available won't support further growth. So you do

not need events on the Sun, etc, whose magnetic influence is always very

weak.

[By the way, this resembles somewhat the classical model of arms

race, proposed by Lewis Fry Richardson(1881-1953). There, the

arms production of country A is proportional to the arms country B

is known to have, and vice versa. It can get out of hand. See

http://shakti.trincoll.edu/~pbrown/armsrace.html where the

following can be found:

"The Richardson Arms Race model was developed by English

physicist Lewis Fry Richardson(1881-1953), who was
http://www-spof.gsfc.nasa.gov/stargaze/dynamos.htm


20/26



troubled by WWI and WWII because of his Quaker beliefs.

Based on the assumption that having a large available arsenal

makes a given nation more likely to engage in conflicts,

Richardson conjectured that an arms race was often a prelude

to war. The ultimate goal of his model is to examine the

stability (or lack thereof) of an arms race between two nations

in order to predict whether a small incident could potentially

start a large conflict."]

You may find more details and references on dynamos in my review

article "A Millennium of Geomagnetism," starting at

http://www.phy6.org/earthmag/mill_1.htm

I would not however recommend the "Nova" program "Magnetic

Storms" shown here last night on public TV; it will probably reach New

Zealand in due time. It supposedly discusses the Earth's dynamo and field

reversals, but does so in a confused and confusing way. Even though some

of its participants are top scientists, the overall narration and editing were ofpoor quality and often in error.

42. Could generated electricity affect Earth's magnetic

field?

att: Dr.David P Stern

Earths magnetic field is weakening, leading to a pole shift (question #6d).

I would like to know if the effect of all the electricity generated by power

plants etc. on the Earth's magnetic field would also contribute to this

problem.

Reply

A quick answer is no, for several reasons. The world uses alternating

current with 50 or 60 reversal cycles per second. You can pick up this

field almost anywhere--just tie a loose wire to an oscilloscope and you will

see the waveform--but this does not affect the averaged magnetic field.

In addition, to create a widespread magnetic field, you need the current

to flow around a large loop. Electric currents of the power grid do not do

that.

Take for example the power cord of any electric applicance you have. It

hardly produces any magnetic effect, because it has two parallel wires close
http://www-spof.gsfc.nasa.gov/stargaze/magnQ&A1.htm#q6http://www-spof.gsfc.nasa.gov/stargaze/mill_1.htm


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to each other carrying current in opposite directions. (The third wire,

connected to the ground, is just for safety.) Because the electric currents in

the wires are equal and opposite, their distant magnetic fields cancel each

other almost perfectly. Only in the small space between the wires does a

sizable magnetic field exist. Power grid currents also come in pairs that

cancel, even if the return flow is through the ground.

Furthermore, I am not sure power grid currents are strong enough. Given

a choice to transmit energy using a large current at low voltage or a small

current at high voltage, power companies choose the latter, because the

power loss caused by resistance is proportional to the current. However,

the magnetic field produced is proportional to that current, too.

43. "Magneto-therapy"

(from France)

Dear Sir,

I am in the search of documentation on magneto therapy. certain

apparatuses, very expensive, are on sale by canvassers in residence and

appear me to be swindle.

Can - you to inform me?

Reply

Your guess seems correct. There exist many magnetic devices on themarket (bracelets, mattress pads etc.), and as far as I know, they are all

useless.

Occasionally letters about this arrive, and one of them I put on the web.

See

http://www.py6.org/Education/FAQs4.html#52

Concerning various medical problems or cures ascribed to magnetism,

and other unusual claims for magnetism, please look uphttp://www.chem1.com/CQ/magscams.html

44. Curie Point

Dear Dr. Stern:

I am sending this message on behalf of my 8-year-old son. Jacob is

preparing a project on magnetism for his third-grade science fair. Jacob
http://www.chem1.com/CQ/magscams.htmlhttp://www.phy6.org/Education/FAQs4.html#52


22/26



notes that iron magnets lose their ability to attract when heated sufficiently.

Jacob's question, in his words:

Do you have information about why magnets lose their force when

heated? Everyone can tell me that it happens, and I even did it

myself, but no one can tell me WHY.

I know that Jacob will be very grateful for any explanation you can provide,

or any child-accessible sources you could suggest.

Reply

The effect you are studying is called the Curie Point, after the French

physicist Pierre Curie who discovered it in 1895. He went on to marry a

young Polish chemist named Maria Sklodowska, who as Maria Curie went

on with Pierre to discover radium and earn the Nobel Prize.

Magnets are a very special kind of material with strong magneticproperties--much stronger than those of other substances. Such materials

are called "ferromagnetic" because iron is the best known one and "ferro"

refers to iron, from its Latin name (e.g. the family name "Ferraro" means

"Smith", someone who works with iron).

All matter consists of atoms, and atoms are made of nuclei and of

electrons. Both are magnetic. The magnetism of protons (hydrogen nuclei)

is what makes MRI scanners in medicine possible ("nuclear magnetic

resonance") but electrons are much more strongly magnetized, and

therefore they are the one that count in most magnetic properties of matter.Their magnetism is related to "electron spin," with the electrons behaving

as if they were also spinning around the direction in which they are

magnetized. An electron carries a negative electric charge, and a charge

spinning around an axis indeed should indeed make it act like a small bar

magnet (although the numbers do not fit exactly, for reasons related to

quantum theory, the physics of atomic dimensions).

In iron and ferromagnetic materials, spins can line up inside the crystal

structure and create small "domains," blocks in which all electrons are lined

up. Obviously, each domain is a strong magnet. In a permanent magnet,many of these domains are also lined up (in an electromagnet they only do

so temporarily), giving the strong magnets we know. By the way, there

exists a limit to the strength of such magnets ("saturation")--if all domains

line up, the magnetism is as strong as it can get, it cannot grow any more.

Some of the strongest magnets in the world therefore rely just on electric

currents.

Heat creates disorder. Heat an ice cube and at a certain temperature, the

forces that make water molecules stick to each other give way. That would


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be the melting point. Heat a magnet and at a certain temperature the orderly

arrangement of electron spins falls apart, too. That would be the Curie

point.

I looked on the web for "Curie point". Some sites are:

http://www.exploratorium.edu/snacks/curie_point.html

http://en.wikipedia.org/wiki/Curie_point http://physics.ucsd.edu/was-

sdphul/labs/demos/modern/curie.html demo

You will also find some facts about magnets, and their history, on "The

Great Magnet, the Earth"

http://www.phy6.org/earthmag/demagint.htm.

45. Blocking of magnetic fields

Silly question? Is there anything on the planet I could put between twomagnets to completely block magnetism? I would call it a magnetic blocker.

Is there such a thing? I'm sure some materials could weaken it, but I am not

sure anything blocks it. I would be very grateful for a reply whether you

know the answer or not. The internet is a vast ocean of @#$%&! to me,

but when I find someone who knows what they are talking about it's much

more tolerable.

Reply

Nothing can block magnetic fields, the way a slab of wood can blocksunlight from going past it. The equations don't allow that. However, you

can divert a magnetic field from the region where you don't want it to be,

and that's often just as good. Example: in old days, TV picture tubes had a

shield of soft iron around their necks. (Maybe they still do: haven't looked

inside a TV for decades). The idea was to prevent stray magnetic fields

from reaching the electron beam and jiggle or defocus it. Magnetic field

lines directed towards the neck of the tube hit the shield and are channeled

into it--they go around the glass tube and then come out of the other side of

the shield and continue.

A question similar to yours was asked before--see

http://www.phy6.org/earthmag/magnQ&A1.htm#q11

An interesting application of magnetic shielding is the experiment on

cigarette smoking by Dr. David Cohen of MIT. See:

http://www.phy6.org/earthmag/magmeter.htm

46. Earth magnetism from rotating electric charges?
http://www-spof.gsfc.nasa.gov/stargaze/magmeter.htmhttp://www-spof.gsfc.nasa.gov/stargaze/magnQ&A1.htm#q11http://www-spof.gsfc.nasa.gov/stargaze/demagint.htm


24/26



I have always wondered whether the magnetic field of the Earth is

produced by electric charges rotating with it. It is a thought that has been

puzzling me for many, many years.

Reply

A rotating electric charge could create a magnetic field, but Earth does

not carry free charges--if it did, electrons or ions from space would beattracted and would quickly cancel them. Also, the magnetic axis of Earth is

not its rotation axis, plus the field has complex parts with more than 2

poles--and of course, evidence of old lavas tells us the field reverses

directions now and then.

There do exist electric currents in space, whose energy is supplied by the

solar wind; their magnetic fields cover huge regions, but they are rather

weak. The analysis method of Gauss allows one to tell how much of the

Earth's field originates above us and how much below us. The result is that

less than 0.5% comes from the outside.

47. Teacher seeks easy experiments

(From a letter by a high-school teacher)

... Also, does anyone have nice labs or demos they could share for

magnetism/EM induction?

Reply

Quick demos in high school:

(1) Magnetize a sewing needle, then float it in a Petri dish filled

with water, on top of a vu-graph projector, for the entire class to

see. Kids will learn not juts about geomagnetism but also about

surface tension.

(2) Magnetic induction can be demonstrated on top of a

projector, in a magnetic analog of the electroscope. See


(3) Oersted's experiment can also be demonstrated on the top of

a projector. See end ofhttp://www.phy6.org/earthmag/oersted.htm

All three are quickies with rather little preparation. Kids can also run them

by themselves.

48. Local field does not always decrease!
http://www-spof.gsfc.nasa.gov/stargaze/oersted.htmhttp://www-spof.gsfc.nasa.gov/stargaze/inducemg.htmhttp://www-spof.gsfc.nasa.gov/stargaze/gauss.htm


25/26



Respected sir,

I am an undergraduate BSc (Hons) Physics student at the University of

Mauritius doing my final year project entitled "Geomagnetism studies

over the Indian ocean.". I have provided the computer program

calculating the local magnetic field intensity F with my location--latitude

20.17 S, longitude 57.33 E and elevation (highest point) 828m. The

program gave me values of the total field F (=magnitude of the magnetic

vectorB) for 1900-2004.

The value of the total field is found to be decreasing during the interval

1900-1997 (from 39834 nT to 36884 nT), but from 1998-2004, there is

an increase! (From 36985 nT to 37420 nT). I have read that at present the

magnetic field continues to weaken. Then how is it possible that here from

1998 to 2004 we are having an increase? Should there not be a decrease?

I am really stuck at this point and do not know how to explain this. I

have applied the program to another location ( 39.25 N, 105.28 Welevation 735m) and there I get a continuous decrease in F for 1900-2004,

from 59288 nT to 53390 nT. This suggests a decrease exists over the

entire interval. But if so, how can the other result, at my location, be

explained?

I would be very grateful to you if you could give an answer to my question.

Reply

I do not have the codes which you use and can only guess. What isdecreasing all these years is the dipole component of the field. That is the

biggest contribution to F and over a long time (such as 1900-1997, almost

a century) usually dominates the local trend.

However there exist other terms, such as quadrupole (n=2) and higher.

They seem to be increasing (if the total energy of the field is almost

constant, as Ned Benton found) and more important, they are not axially

symmetric, and slowly migrate. I suggest that they are the cause.

The trouble with F is that it is non-linear, involving the square of thevector field B. I do not know if you can modify your code . If you can,

have it calculate separately B1, the dipole (vector) field and B2, the non-

dipole field. Then (* is scalar multiplication)

F*F = (B1*B1 + 2 *B1*B2 + B2*B2)

Now track over the same years B1*B1 , which is the contribution to F*F

from the dipole alone, and of 2*B1*B2 + B2*B2, roughly the contribution

of the higher harmonics (B2*B2 is small, and you can perhaps neglect it).


26/26


My guess is that the first term declines steadily over 1900-2004, but the

second may grow. It may perhaps overtake the decline in 1997, but is

probably present even before.

You may also discuss it with your professor.

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Author and Curator: Dr. David P. Stern

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Last updated 6 June 2002

Re-formatted 9-27-2004
http://www.phy6.org/stargaze/Sstern.htm

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FAQ-3_ _The Great Magnet, The Earth