Earth Radiation Belts Spectacular Following Halloween Solar Storm

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."