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ZL2VAL > PHYSIC 13.12.03 16:21l 68 Lines 2321 Bytes #999 (0) @ WW
BID : DD0341ZL2VAL
Read: GUEST
Subj: Earth's Magnetic field weakens
Path: ON0AR<ON0AR<ZL2TZE<ZL2TZE<ZL2WA<ZL2AB
Sent: 031213/0700Z @:ZL2AB.#46.NZL.OC #:31148 [New Plymouth] FBB7.00g
From: ZL2VAL@ZL2AB.#46.NZL.OC
To : PHYSIC@WW
Earth's Magnetic Field Weakens 10 Percent
By Andrew Bridges
Associated Press
posted: 03:25 pm ET
12 December 2003
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 Thursday.
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. "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.
=========================
73 de Alan
AX25:ZL2VAL@ZL2AB.#46.NZL.OC
APRS:!3903.34S/17406.45E]
IP :zl2val@qsl.net
Message timed: 21:42 on 2003-Dec-13 (NZ local)
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Points to ponder
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