Earth's magnetic field fading :: POLE SHIFT

[iyah360]

http://www.cnn.com/2003/TECH/science/12/12/magnetic.poles.ap/index.html

Report: Earth's magnetic field fading
Slight chance of flipping magnetic poles
Friday, December 12, 2003 Posted: 9:45 AM EST (1445 GMT)


SAN FRANCISCO (AP) -- The strength of the Earth's magnetic field has decreased 10 percent over the past 150 years, raising the remote possibility that it may collapse and later reverse, flipping the planet's poles for the first time in nearly a million years, scientists said.

At that rate of decline, the field could vanish altogether in 1,500 to 2,000 years, said Jeremy Bloxham of Harvard University.

Hundreds of years could pass before a flip-flopped field returned to where it was 780,000 years ago. But scientists at a meeting of the American Geophysical Union cautioned that scenario is an unlikely one.

"The chances are it will not," Bloxham said Thursday. "Reversals are a rare event."

Instead, the weakening, measured since 1845, could represent little more than an "excursion," or lull, which can last for hundreds of years, said John Tarduno of the University of Rochester.

Such a lull could still have significant effects, especially in regions where the weakening is most pronounced.

Over the southern Atlantic Ocean, a continued weakening of the magnetic field has diminished the shielding effect it has locally in protecting the Earth from the natural radiation that bombards our planet from space, scientists said.

As a result, satellites in low-Earth orbit are left vulnerable to that radiation as they pass over the region, known as the South Atlantic anomaly.

Among the satellites that have fallen prey to the harmful effects was a Danish satellite designed, ironically, to measure the Earth's magnetic field, Bloxham said.

The weakening -- if coupled with a subsequently large influx of radiation in the form of protons streaming from the sun -- can also affect the chemistry of the atmosphere, said Charles Jackman of NASA's Goddard Space Flight Center.

That can lead to significant but temporary losses of atmospheric ozone, he said.

[iyah360]

http://www.pbs.org/wgbh/nova/magnetic/reversals.html

Most of us like stability in our lives, especially when it comes to planet-wide phenomena, such as the daily appearance of the sun or the periodic change of season. So it can be unsettling to learn of global phenomena that are inherently unstable, unpredictable. Such is the case with the Earth's magnetic field. Every so often, our planet's magnetic poles reverse polarity (see When Compasses Point South). Compass needles have always pointed north; in a reversal, they would point south.

You could perhaps take comfort in the knowledge that these reversals happen infrequently -- on average every 250,000 years -- but maybe not when you consider that it's been over 700,000 years since the last reversal, and the next one may be currently underway.

The Earth's magnetic field is created deep within our planet's outer core through a complex, self-sustaining interaction known as the "geomagnetic dynamo" (see What Drives Earth's Magnetic Field?). In the 1980s, Gary Glatzmaier, now at the University of California, Santa Cruz, and Paul Roberts of the University of California, Los Angeles, began work on a computer model that simulates this interaction. By 1995, they had created a model that not only created a self-sustaining magnetic field (the first to do so), but after simulating the passage of 36,000 years, the field it generated spontaneously flipped.

Here, view the animation generated by the Glatzmaier-Roberts computer model and see what happens during a reversal. --Rick Groleau