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View Full Version : Decline in Earths magnetic field and energy.



Gerald Stevens
2015-Jul-25, 02:16 AM
So its no secret that there has been around a 10% overall decrease in the earths magnetic field strength since 1845. There are published papers you can find throughout the internet making these claims but then I come across material that state things like it may be weakening but other parts are increasing as this happens due to field lines simply reshuffling themselves. That sounds logical. But specifically what I'd like to know is, since this "weakening" has taken place, has there been any data collected that tells us if in fact the magnetic fields are no longer able to stop particle energies of a certain magnitude that it was once able to? Say, as an example it was first established that the field could stop incoming particle energies at 10 GeV at equatorial regions. What would those energies look like today and what agency is responsible for keeping track of this data?

a1call
2015-Jul-25, 08:53 PM
During this change the strength of the magnetic field dropped to 5% of its present strength.


https://en.m.wikipedia.org/wiki/Geomagnetic_reversal#Effects_on_biosphere (https://en.m.wikipedia.org/wiki/Geomagnetic_reversal#Effects_on_biosphere)

https://en.m.wikipedia.org/wiki/Geomagnetic_reversal#/media/File:NASA_54559main_comparison1_strip.gif

https://en.m.wikipedia.org/wiki/Geomagnetic_excursion#Effects

Jens
2015-Jul-26, 01:30 AM
So its no secret that there has been around a 10% overall decrease in the earths magnetic field strength since 1845. There are published papers you can find throughout the internet making these claims but then I come across material that state things like it may be weakening but other parts are increasing as this happens due to field lines simply reshuffling themselves.

I've never heard that about reshuffling. But I think the initial claim is fairly well recognized, that the earth's magnetic field has been weakening. It is known to fluctuate so there is nothing really that unusual about it. About the effects, I think yes that you can check the links by a1call.

tusenfem
2015-Jul-27, 01:28 PM
I do not know anything about "field line shuffling" or what that would mean. Indeed, the field is decreasing in magnitude a bit, and it is known that when e.g. a field reversal happens, the dipole gets weaker and weaker, but the quadrupole, octupole etc. can increase a bit during this process.

tusenfem
2015-Jul-27, 05:33 PM
sorry unwillingly closed the thread
reopened again

kevin1981
2015-Jul-27, 11:57 PM
I think it would be cool if we went to sleep one day and when we woke up the poles had flipped !

What is the likelihood this could happen ?

Noclevername
2015-Jul-28, 12:28 AM
I think it would be cool if we went to sleep one day and when we woke up the poles had flipped !

What is the likelihood this could happen ?

It takes a while longer than overnight, I think. There's gaps of several thousand years in the sea-bed fossil magnetism.

tusenfem
2015-Jul-28, 06:40 AM
Just found a paper in Nonlinear Processes in Geophysics
L. K. Feschenko and G. M. Vodinchar: Reversals in the large scale αΩ-dynamo with memory (http://www.nonlin-processes-geophys.net/22/361/2015/npg-22-361-2015.html) (open access)

Gerald Stevens
2015-Jul-29, 09:19 PM
I do not know anything about "field line shuffling" or what that would mean. Indeed, the field is decreasing in magnitude a bit, and it is known that when e.g. a field reversal happens, the dipole gets weaker and weaker, but the quadrupole, octupole etc. can increase a bit during this process.

This (https://www.ngdc.noaa.gov/geomag/faqgeom.shtml#What_is_the_Main_Field)page talks about the "The Earth's magnetic field intensity is roughly between 25,000 - 65,000 nT (.25 - .65 gauss)." Is this the main field intensity or the dipole moment strength? Because it goes on to say that "However, the present dipole moment (a measure of how strong the magnetic field is) is actually higher than it has been for most of the last 50,000 years and the current decline could reverse at any time."

JohnD
2015-Jul-30, 02:06 PM
This, published two days ago in Nature (28/7/2015) shows that even faster changes in the field strength were occurring in the Southern Hemisphere in the first half of the first Millenium, Common Era.
http://www.nature.com/ncomms/2015/150728/ncomms8865/full/ncomms8865.html

Antiquity of the South Atlantic Anomaly and evidence for top-down control on the geodynamo
Tarduno JA, Watkeys MK, Huffman TN, Cottrell RD, Blackman EG, Wendt A, Scribner CA, Wagner CL.
Fires started by people in South Africa heated and 'fixed' the magnetisation of the ground beneath. Measuring this has showed that about 1300 CE the rate of fall of the Earth's magnetic flux in this region was quicker than it is today and that it fell to lower levels.
No 'flip' of the Earth's magnetic field followed.

John

tusenfem
2015-Jul-30, 03:48 PM
This (https://www.ngdc.noaa.gov/geomag/faqgeom.shtml#What_is_the_Main_Field)page talks about the "The Earth's magnetic field intensity is roughly between 25,000 - 65,000 nT (.25 - .65 gauss)." Is this the main field intensity or the dipole moment strength? Because it goes on to say that "However, the present dipole moment (a measure of how strong the magnetic field is) is actually higher than it has been for most of the last 50,000 years and the current decline could reverse at any time."

that is the field at the equator (weakest) andcat the poles (strongest) of the multipole field
the dipole component of the earth's magnetic multipole field is by far the strongest component of all
it can well be that it is higher than the last 50000 years, i would not know and have to take their word for it, noaa is a reliable source
about the reversal of the decline, yes that could happen. as the dynamo is a chaotic process it is difficult to predict what is going to happen