The belt of high-energy electrons that normally cradles Earth from
afar was greatly enhanced and pushed unusually close to our
atmosphere during the violent solar activity that occurred in late
October, University of Colorado at Boulder researchers say.

The results were obtained from observations by NASA’s Solar,
Anomalous, and Magnetospheric Particle Explorer, or SAMPEX satellite,
said CU-Boulder’s Laboratory for Atmospheric and Space Physics
Director Daniel Baker. An investigator on SAMPEX, Baker will present
results from the data and the Halloween solar storm at the fall
American Geophysical Union meeting in San Francisco Dec. 8 to Dec. 12.

The radiation belts, also known as the Van Allen Belts, are named
after their discoverer, James Van Allen. “The outer Van Allen Belt
is often rather tame and is made up of modest intensities of
energetic electrons,” said Baker.

“These negatively charged elementary particles are confined like
beads on a string by the magnetic field lines that emanate from
Earth’s iron core and extend far out into space like the flux tubes
from a giant bar magnet,” he said. During the recent high-energy
solar activity of late October and early November — known by
scientists as the “Halloween storm” of 2003 — the outer Van Allen
belt was pushed and prodded to a nearly unprecedented degree.

“We have been observing the Van Allen Belts for over 11 years with
the SAMPEX spacecraft,” said Baker. “We have never seen such a
powerful enhancement and distortion of the radiation belts during the
lifetime of SAMPEX. Baker noted that the center of the outer Van
Allen belt is usually about 12,000 miles to 16,000 miles away from
Earth’s surface, as measured above the equatorial region of the Earth.

During the Halloween storm, the Van Allen radiation was greatly
increased and pushed inward toward Earth’s surface to an unusually
close degree. “From Nov. 1 to Nov.10, the outer belt had its center
only about 6,000 miles from Earth’s equatorial surface,” he said.
“This is a place where ordinarily there are almost no energetic
electrons at all.”

How the Earth’s radiation belts get so energized and distorted is
still largely an unsolved mystery, despite the fact that Van Allen
and co-workers discovered the radiation belts more than 45 years ago
at the dawn of the space age, he said.

“Researchers have learned a great deal about electron acceleration in
the belts in recent years,” said Xinlin Li, a professor and
researcher at LASP who works closely with Baker. “We are able to
understand and forecast more normal changes in the radiation belts
using our present theoretical knowledge, but extreme events such as
the Halloween storm are very hard to predict.”

Other spacecraft such as NASA’s POLAR satellite also observed the
powerful radiation belt changes. Shri Kanekal, a researcher at
Catholic University in Washington, D.C., who also is affiliated with
LASP, has studied the POLAR measurements and compared them with the
SAMPEX data. He found the POLAR data confirmed the surprising
enhancement and distortion of the Van Allen Belts.

“The changing, raging character of the radiation belts is more than a
scientific curiosity,” said Baker. “The charged particles within the
belts can have profound and deleterious effects on commercial and
operational satellites in near-Earth orbit.”

As reported in a recent paper submitted to the scientific journal,
Eos, by Ramon Lopez of the University of Texas, J. H. Allen of the
National Oceanic and Atmospheric Administration in Boulder and
CU-Boulder’s Baker, many serious spacecraft failures and “operational
anomalies” occurred during and following the Halloween storm. Many
of the problems can be directly related to the hostile radiation
environment in near-Earth space.

“We are excited to have the chance to study the most extreme events
that nature can throw at us,” he said. “We hope that in the future,
we can predict how even a storm as powerful as the Halloween storm
will affect Earth’s environment.”