what is geomagnetic field

8/3/2019 What is Geomagnetic Field

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What is thehat is theGeomagneticGeomagnetic

FieldField?!!

What is thehat is theGeomagneticGeomagnetic

FieldField?!!

By HayanonTranslated by Y. Noda

Supervised by Y. Kamide



A Message from C. F. Gauss (1777-1855)

I was born in Germany, the son of a poor gardener.When I was a child, I often found mistakes in myfather's calculation in wages for his employees. Thatgave me more fun than in the playground. Questionedby a teacher in 1st grade about the sum of the first

100 integers, I got the answer in a few seconds. Infact, it's quite simple. Make 100 pairs of numbers,each pair summing up 101, like 1+100, 2+99, ... Thenmultiply 101 by 100. It is 10100. Divide it by 2, that's5050, the answer.

You may have noticed that some of the theorems in mathematics and physics,units, and formulas were named after me. At the age of 30, I became aprofessor at Gottingen University, where I enjoyed arithmetic theory, least-squares method, and potential theory. It's nice to meet you, readers, here inthis book about my accomplishments estimating the geomagnetic intensity ofthe Earth using my spherical harmonic analysis. The actual data I used werecollected from about 100 observatories over the world, with the support of theRoyal Astronomical Society.

By the way, I heard that the geomagnetic field has been decreasing since Imeasured its intensity. It's really worrisome.



Today we arevisiting a planetariumto see magnificentauroras.

Hi. I'm Mol and this is

my robotic dog Mirubo.My favorite subjectin elementary school is

Science!

Those auroraswere sobeautiful.

Yes, they were just like the

real ones.

I wish I couldsee real aurorasin Japan.

Huh?

I've heard that

auroras will comedown to Japansometime in thefuture.

What?!

It's notpossible!!

Yes, it is.I mean it.

Now, now.Calm downkids.

Aa r g h argh P o w

!Pow

!



What's thisall about?

J e l l o - m a g n e t .

..?

Oh, it's you.

Aurora sensei !

Let's askhim!

Can aurorasbe seen inJapan in the

future?

Definitely. What a shock!

You see,I'm alwaysright.

But it won'thappen for about1000 years.

1000 years!Why?! I can't waitthat long.

I want to see anaurora today!

Well, it isnot such asimple matterbecause

the aurorarelates to thegeomagnetic

field.

Geomagnetic,what?

B e h

a v e

Beh

ave

y o

u r s e l f .

yo

urself.

W h a a a m

Haa

haha

haa



Hmm...

I don't know.Huh, huh.

Be serious!!

The earth itselfis a

The

compass lovessomeone inthe north.

Do you have anyidea of what thisis?

Co... compass?

That'scorrect.

Why does thecompass pointto the north?

huge magnet.

Really?

What?!

Great!

I've got it! The

needle is pulled bythe magnetic forcethat comes from themagnetic north.

Still, I don't careabout the geomagneticfield. I perhaps do if powerof the magnetic field is

effective to reduce ...

What doesthat matterto us?

Of course, it doesmatter a greatdeal to us.

MagneticField Line

GeographicNorth Pole Magnetic

North Pole

Magnetic polesare differentfrom geographicpoles.

GeographicSouth Pole

MagneticSouth Pole

yea

the burden onmy shoulders.



From the galaxycome high-energyparticles calledcosmic rays, and

solar wind fromthe sun, to the

Earth ...

withterrific speed.

The Earth's magneticfield, called thegeomagnetic field,

protects the

Earth from cosmicrays and solar wind.

Just like a

barrier!!

Without the

barrier, solar windwould blow awaythe atmosphere.

And, cosmic rays

might destroy ouroptic nervesystem ...

as well as ourcells, leadingto ...

mutation orextinction of

life onthe Earth.

Thegeomagneticfield is great!!

But thatfriendlybarrier doesnot existforever.

No!!Agugh...

The geomagneticfield is alwayschanging.

W a h o o !



The geomagnetic northpole at present is here,11.5 off the north pole,at the northwest cornerof Greenland.

Surrounding itstretches the linecalled the "Auroral Belt"where auroras can befrequently seen.

The geomagneticnorth pole hasbeen moving allthrough the longhistory of the

Earth.

Movement of thegeomagnetic northpole for the past2000 years.

Not only the position ofthe magnetic pole, but

the magnetic intensityis also changing.

The geomagnetic

intensity hasdecreased by 10%during the 200 yearssince it was firstmeasured by Gauss inthe early 19thcentury.

If the geomagnetic

intensity keepsdecreasing at thecurrent pace, it willbe zero in

1200 years.

Because of this the aurora willventure ever farther south.It's expected that the auroral belt

will reach Japan in 1000 years.

Whaat?!

B a n g !

Bang!



That's why we thinkthat the auroras willbe seen in Japan in1000 years.But, ultravioletrays and cosmicrays falling ... down to the

Earth willalso increase.

We need to stayaway from them.

Wow, somany reversals!!

In the long history of

the Earth, there weremany magnetic reversalsand disappearances ofthe magnetic field.

Late CretaceousPeriodPaleogeneNeogene

Quaternary Period

Middle JurassicPeriod

Late JurassicPeriod

Early CretaceousPeriod

Late CretaceousPeriod

Mesozoic Era

ReversedPolarity

NormalPolarity

Mesozoic EraCenozoic Era

I've never

imagined thatsuch things are ...

lying aheadin ourfuture.

The most recentgeomagnetic reversalwas 700,000 yearsago.

That's along timeago.

Let'ssee ...

How did you calculatethat it occurred700,000 years

ago?

And, is it truethat reversalstook place sofrequently?

Goodquestions.

[History of Geomagnetic Reversals]



It's likea magneticdisk!Amazing!

Researchers found thatsome of the volcanic rockscollected from differentvolcanoes in the world arereversely magnetized.

I see, volcanicrocks areremaining asthey were.

The layer in ChibaPrefecture, Japan, hasa high-quality

geomagnetic record, ...

which shows that700,000 years agothe geomagneticfield disappearedand the magneticpoles were reversed.

Great!!

Fossils of

foraminifers theresuggest that 40% of them

living in the shallowsof the sea ... died out due to the

massive ultraviolet lightwhich fell down to theEarth at the geomagnetic

reversal.

40%?! Besides, organic-carbon producedfrom foraminifers'corpses contributedto global warminglobal warming.

Geomagnetic changeshave great impact onthe Earth'senvironment inthis way.

Scary ...I hate it.

When lava flows cooleddown, forming volcanicrocks after eruptingfrom a volcano, theyacquired records of the

geomagnetic field.



When the geomagnetic fieldweakens, it will be loosenedinto small bumps and stopcovering the Earth.

Then, auroraswill be seen invarious places inthe world.

There is a hypothesisthat geomagneticvariations relate to the

Dinosaur Extinctionat the end of theCretaceous period.

Gee!That'sincredible!

Now, I don't want tosee auroras inJapan ...

Changesin the Earth's

magnetic fieldcause serious

problems.

This is not just in the

past. We are still facingproblems resulting

from the

geomagnetic field status.If there were no geomagneticforce, ozone would bereduced by cosmic rays, and

ozone holes would rapidlyexpand.

Its impact on the ozone

depletion is incomparableto that of

chlorofluorocarbons.

The geomagneticfield is protectingthe ozone layer,

too.

The geomagneticfield is an invisible,mighty wall.

Yes, it's ourguardian.

That'sweird.

Huhhuhh



Aurora sensei,what creates thegeomagnetic

field then?How does ageomagneticreversaloccur?

Unfortunately we have no answersto either of yourquestions.

The inside of the Earth istoo hot for a bar magnet

to survive. So, the Earth'smagnet should be anelectromagnet,

because when itscurrents get reversed,the geomagnetic poles

could be reversed,too.

Thesehypotheses,however, are not proved

yet.

Umm, it'sa mystery. Of course,

there are many

scientists workingon this problem.

I really want to

watch aurora,but...

hope the

geomagneticreversal will

never everoccur.

Heaven,Buddha,and ...

Geomagnetism,pleasesave us.

Sorry, but it willcome someday. That's a

natural law.

You don't??

Uh ...

P l e a s e h e l p ! !

Please help!!



Whaaah!!

What shouldI do?

Don't youhave anygood ideas?

Nothing.It's a matter ofnature, and out ofour control.

I will be frighteneduntil the disaster

comes!

It's nouse to cry,anyway.

There, there.Don't worrytoo much.

Boo-hoo.

The 1200 year dateto reach zero ingeomagnetic was deduced

from data for only the past200 years. No onecan predict exactly

when.

Blow yournose.

Anyhow,

we still have1200 long years.

Yeah, that'sright.

I don't think so.1200 years goquickly.

T e e,

h e e,

h e e.

Noooo.Pleasedon't.

Joking

Relax,Mol.

W e e e eee e e e p eeep

H i c

c u p



I'm stillscared.

Don't cry,Mol.

It won't occurtoday or tomorrow.

Right.

Auroras are not at lowlatitudes. And that isevidence that thegeomagnetic field

protects the Earth.

Hurray for thegeomagneticfield !!

I hope thegeomagneticfield canhear you.

I see ...

Mol and Mirubo nowunderstand the importanceof the geomagnetic field,which is covering theEarth and protectingall life.

H a ,h a

Boohoo

Grizzlingrizzling



What is the Geomagnetic Fieldhat is the Geomagnetic Field?!!

Hello, Mol and Mirubo. Let'stalk about the Earth's

magnetic power.I understand that the Earthitself is a gigantic magnet.

Wow, I want to buy a magnetthat big! How much does itcost?

Seriously, even though theEarth possesses the magneticfield, there is no magnet

buried in the Earth interior.

What does that mean? Didsomeone dig deep into theground? Where does theEarth's magnet come from?

The higher the temperaturewhere a magnet is located,the more it loses itsintensity. Deep inside theEarth is a few thousand

degrees, too hot for a magnetto survive.

Sounds interesting! I'll do anexperiment with my magnets.

That's a good idea. Onepicture is worth a thousandwords.I'll give you a clue. Theinside of the Earth hasmolten metals which carry anelectric current.

It's an electromagnet!!

That's right. The Earth hasan electromagnet inside. Itgenerates magnetic fieldslike a bar magnet does. Whenthe intensity and direction ofthe electric currents change,magnetic poles can even be

reversed.

Oh, my. My compass can't beused anymore after the

geomagnetic poles arereversed.

Don't worry. It will be in thefar distant future, over 1000 years.

Ah, there is a long long timeleft.

In the Earth's history,however, 1000 years is rathershort.Anyhow, the geomagnetic

field is always changing. Inauroras a large amount ofelectricity is flowing. Thephenomena called "magneticstorms" cause huge electriccurrents, inducing magneticfields all over the world.

Is their intensity verystrong? Strong enough toharm me?

The maximum isapproximately 1-10 millionamperes.

Really? My house has only 30amperes!

Do you know what animals cansense the Earth's magneticfield?

I don't know. Maybe it's you.

No way, I don't have suchpower. It's pigeons, dolphins,migrating birds, etc.Various experiments arebeing conducted on theirperceptions of magnetic field.

Mirubo, I think you need toinstall a magnetic sensor in your brain. You don't have a

sense of direction at all.

No kidding, Mol !!



AuroraroraLights seen in the polar sky caused bythe solar wind, the flow of chargedparticles called plasmas. The solar windenters the Earth's magnetosphere andtravels into the nightside of the Earth,being accelerated along magnetic fieldlines, then colliding with the atmosphereover the polar regions. This collisioncreates the lights. The aurora is 100 -500 km above the Earth' surface.

Carl Friedrich Gaussarl Friedrich Gauss1777-1855Gauss was a German mathematician andphysicist. In 1839, he proved that theEarth's magnetic field originates frominside the Earth and not from outside.The unit gauss is used for measuring themagnetic intensity.

CompassompassA device for deciding directions with amagnetic needle. When two magnets are

brought together, the N-pole of onemagnet attracts the S-pole of the other,or the N-poles of two magnets repel. TheN-pole of a compass heads toward Earth'sS-pole in the north pole region, and thusinforms us which direction is north.

Cosmic Raysosmic RaysVarious types of high energy particlesfluttering in space, including galacticcosmic rays coming from outside the solarsystem and solar energetic particlesoriginating from solar flares. Most cosmic

rays are absorbed or weakened in theEarth's atmosphere at around 100-500 kmabove the Earth.

Cretaceous Periodretaceous PeriodThe period about 140-65 million yearsago, and the last section of the MesozoicEra. The climate then was mild, plantswere exuberant, and dinosaurs thrived.At the end of the Cretaceous, dinosaursand ammonites extinguished. Variouscauses are thought to be responsible forthe extinction, such as a meteorite event,drastic climate change, geomagneticreversal, etc. The Mesozoic is followed bythe Cenozoic Era, the age of mammals.

ForaminiferoraminiferForaminifers are tiny unicellular

organisms mainly found in the sea. Theyhave calcareous shells formed fromcarbon dioxide in the air.

Geomagnetic Fieldeomagnetic FieldThe Earth has the magnetic property ofa big bar magnet. There exists the N-polein the south polar region and the S-pole inthe north polar region, generating a worldof magnetic fields surrounding the Earth.

Organic Carbonrganic CarbonLiving matter is made up of organiccompounds associated with organic carbon.When plants or animals die, stored organiccarbon forms carbon dioxide.

Ozone Holezone HoleThe ozone layer exists at an altitude of

about 30 km, surrounding the Earth. In1980, it was found to be mostly depletedin the stratosphere above the Antarctic,like a hole circling around the south pole.The ozone hole is known to be largest inSeptember.

PlasmalasmaEvery substance is made up of atoms.

When atoms are striped of negativelycharged electrons, they become positivelycharged ions. A gas made up of positivelyand negatively charged particles is called aplasma. Over 99% of the Universe ismade up of plasmas, different from solid,liquid, and gas. This is the reason why

plasmas are called the fourth state ofmatters.

Solar Windolar WindFlows of charged particles, plasmas,coming out of the sun. The Earth'smagnetic field is swept into a tail-likeshape away from the sun. A comet's tailforms in the same way.

Ultraviolet Lightltraviolet Light The Sun emits various wavelengths of

light. Among them is high-energyultraviolet light with a wavelength of 400nanometers. Ultraviolet light is harmfulto our lives, causing risks of cancer orgene damage. It is mostly absorbed,however, near the ozone layer 30 kmabove the ground.



"What is the Geomagnetic Field ?!" is published with cooperation of Kodomo noKagaku, and with advice by Professors Takasi Oguti and Nobuaki Niitsuma.Mol, Mirubo, and Sensei thank Lorraine Kroehl, Lisa Kihn, Terry Onsager, and

Barbara Poppe for their help in preparing the English version of our story.

Solar-Terrestrial Environment Laboratory

(STEL), Nagoya University

STEL is operated under an inter-university cooperative systemin Japan. Its purpose is to promote "research on the structureand dynamics of the solar-terrestrial system," in collaborationwith a number of universities and institutions both in Japan andabroad. The Laboratory consists of four research Divisions: Atmospheric Environment, Ionospheric and MagnetosphericEnvironment, Heliospheric Environment, and Integrated Studies.The Center for Joint Observations and Data Processing is alsoaffiliated to the Laboratory to coordinate joint research projectsand construct data bases. At its seven Observatories/Stations,ground-based observations of various physical and chemicalentities are conducted nationwide.

http://www.stelab.nagoya-u.ac.jp/

National Geophysical Data Center (NGDC)Space Environment Center (SEC)National Oceanic and Atmospheric Administration (NOAA)

NGDC and SEC of NOAA, located in Boulder, Colorado, arepart of the US Department of Commerce. NGDC providesscientific stewardship, products and services for geophysicaldata describing the solid earth, marine, and solar-terrestrialenvironment, as well as earth observations from space.Continually monitoring Earth's space environment, SEC

provides reliable and useful solar-terrestrial information,conducts research and development programs to understandthe environment, and plays a leadership role in the spaceweather community.

http://www.ngdc.noaa.gov/ http://www.sec.noaa.gov/

NGDCGDC

HayanonGraduated from the Department of Physics of Ryukyu University, Hayanon, a writer and cartoonist,has contributed a number of serials in popular magazines on the basis of her strong background inscience and computer games. Her consistent writing style, expressing a love for science, is wellaccepted.

http://www.hayanon.jp/Kodomo no Kagaku (Science for Children)Kodomo no Kagaku, published by the Seibundo Shinkosha Publishing Co., Ltd. is a monthly magazinefor juniors. Since the inaugural issue in 1924, the magazine has continuously promoted scienceeducation by providing various facets of science, from scientific phenomena in everyday life to cuttingedge research topics.

http://www.seibundo-net.co.jp/

September 2003 All rights reserved.

Produced by the Solar-Terrestrial Environment Laboratory, Nagoya University under theauspices of the Ministry of Education, Culture, Sports, Science and Technology .

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