[Yair Doza]

Yair Doza  asked the Naked Scientists:
   
Hi
 
I was wandering about the change in the magnetic pole. As I understand the core of our planet changes its rotation every ~80,000 years, causing the north and south pole to change.

For a period of time (hundred or thousands of years) there is no magnetic pole as the rotation slows down.

This raised two questions:

1 - Animals migrating that use the magnetic fields must go the wrong way after each change of the magnetic field. How do they survive? Surely the evolution to adapt to the new magnetic pole takes generations, but all the migratory organism would perish if they go north for the winter in the northern hemisphere.

2 - As I understand the magnetic field of Earth is creating Van Allen (?) belts that stop the damaging solar wind from reaching earth. What stops this wind when there is no magnetic field during the time it takes the poles to swap places?
 
Thanks

Yair Doza

What do you think?

[Bass]

Welcome to the forum Yair

Your question contains a couple of common misconceptions:

1.  The magnetic field doesn't disappear, nor does rotation of the core slow down or stop.  Physical and computer models both show that it only takes small fluctuations in convection currents in the fluid outer core to change magnetic polarity. Most likely, there are several poles (four or more) during the reversal transition.

2.  Pole reversals probably happen over a span of several thousand years, in which the poles (however many) migrate around the earth.

3.  The magnetic field still exists during the transition.

One would suspect that migratory animals may be confused during the transition period.  However, there are no indications of massive extinctions during pole reversals- so either the transition is gradual enough for animals to adapt, or they have other means of navigating.

Since the field doesn't actually disappear, solar radiation will still be deflected.

JimBob was around for the past couple of reversals- so he can relate first-hand knowledge of the process. []

[Geezer]

JimBob was around for the past couple of reversals- so he can relate first-hand knowledge of the process. []

Bass, I think that would explain why JimBob is a wee bit disoriented.

http://www.thenakedscientists.com/forum/index.php?topic=30696.msg304579#msg304579

[JimBob]

What?

Nurse please pass me my pills.

[Geezer]

I keep telling you!

Ask for the screens first (sheesh!)

[LeeE]

I believe that a small number of 'sub' magnetic poles already exist at various places around the Earth and I also seem to recall discussing these on this forum in the last year or so.  However, I've been unable to find any references to the sub-poles, or the map of them that I remember seeing, via a google search and neither could I find the forum thread via a quick search, so I might just be imagining it all.

Oh well  []

[JimBob]

I am looking for it. I have been since I saw this post without any comments on it.

[JimBob]

http://geomag.usgs.gov/charts/ig00f.pdf

The PDF file linked above will show the total magnetic intensity of the earth as it now exist.

Note that there is no magnetic intensity at the "north pole." In fact there are two areas of maximum intensity, one in Russia, the other just west of Hudson's bay in Canada.

There are also two "south poles" One near the Paraguay-Brazil-Argentina conjunction and another rather close to the present south pole.

This means that the earth's magnetic field is in a state of flux and from what we can see from history, it has always been this way.

I cannot find the "1,000 word essay" I wrote on this several years ago on this site. Oh well. One day the ghosts in the machine will deliver it to the search engines again.

[LeeE]

Hmm... I think it must have been a variation map that I remember seeing, as it's the variation centers that fit with what I recall seeing.  I believe that the 'S' intensity center located over the Paraguay-Brazil-Argentina conjunction is widely known as the SAA (South Atlantic Anomaly) despite being half over land.

Heh! - it's a bit cheeky to include the recycling symbol and "Printed on recycled paper" in a PDF []

[Geezer]

Haha! JimBob made an Electrical Engineering joke! Nice one JB.


"the earth's magnetic field is in a state of flux"

[JimBob]

Haha! JimBob made an Electrical Engineering joke! Nice one JB.


"the earth's magnetic field is in a state of flux"

(JimBob, musing to himself - "Never thought Geezer was that bright.")

[Geezer]

EE's are always bright on account of the light bulbs that are screwed into their craniums.

[Airthumbs]

Maybe the birds and fish start to die!!