Shifts in Earth’s Magnetic Field Happening (Science article)

SLOSHING INSIDE EARTH CHANGES PROTECTIVE MAGNETIC FIELD
By Jeremy Hsu
Live Science
August 18, 2008

http://www.livescience.com/space/080818-mm-earth-core.html

Something beneath the surface is changing Earth’s protective magnetic field,
which may leave satellites and other space assets vulnerable to high-energy
radiation.

The gradual weakening of the overall magnetic field can take hundreds and
even thousands of years. But smaller, more rapid fluctuations within months
may leave satellites unprotected and catch scientists off guard, new
research finds.

A new model uses satellite data from the past nine years to show how sudden
fluid motions within the Earth’s core can alter the magnetic envelope around
our planet. This represents the first time that researchers have been able
to detect such rapid magnetic field changes taking place over just a few
months.

“There are these changes in the South Atlantic, an area where the magnetic
field has the smallest envelope at one third [of what is] normal,” said
Mioara Mandea, a geophysicist at the GFZ German Research Center for
Geosciences in Potsdam, Germany.

Even before the newly detected changes, the South Atlantic Anomaly
represented a weak spot in the magnetic field — a dent in Earth’s
protective bubble.

Bubble bobble

The Earth’s magnetic field extends about 36,000 miles (58,000 km) into
space, generated from the spinning effect of the electrically-conductive
core that acts something like a giant electromagnet. The field creates a
tear-drop shaped bubble that has constantly shielded life on Earth against
much of the high-energy radiation flowing from the sun.

The last major change in the field took place some 780,000 years ago during
a magnetic reversal, although such reversals seem to occur more often on
average. A flip in the north and south poles typically involves a weakening
in the magnetic field, followed by a period of rapid recovery and
reorganization of opposite polarity.

Some studies in recent years have suggested the next reversal might be
imminent, but the jury is out on that question.

Measuring interactions between the magnetic field and the molten iron core
1,864 miles (3,000 km) down has proven difficult in the past, but the
constant observations of satellites such as CHAMP and Orsted have begun to
bring the picture into focus.

Electric storm

Mandea worked with Nils Olsen, a geophysicist at the University of
Copenhagen in Denmark, to create a model of the fluid core that fits with
the magnetic field changes detected by the satellites.

However, the rapid weakening of the magnetic field in the South Atlantic
Anomaly region could signal future troubles for such satellites. Radiation
storms from the sun could fry electronic equipment on satellites that
suddenly lacked the protective cover of a rapidly changing magnetic field.

“For satellites, this could be a problem,” Mandea told SPACE.com. “If there
are magnetic storms and high-energy particles coming from the sun, the
satellites could be affected and their connections could be lost.”

The constant radiation bombardment from the sun blows with the solar wind to
Earth, where it flows against and around the magnetic field. The effect
creates the tear-drop shaped magnetosphere bubble, but even the powerful
field cannot keep out all the high-energy particles.

Topsy-turvy history

A large sunspot set off a major radiation storm in 2006 that temporarily
blinded some sun-watching satellites. Astronauts on the International Space
Station retreated to a protected area as a precaution to avoid unnecessary
radiation exposure.

The Earth’s overall magnetic field has weakened at least 10 percent over the
past 150 years, which could also point to an upcoming field reversal.

Mandea and Olsen hope to continue refining their model with updated
observations, and perhaps to eventually help predict future changes in the
Earth’s magnetic field.

The study was detailed in the May online edition of the journal Nature
Geoscience.