Press Release

New Explanation of Solar Eruptions Ignites Debate

By SpaceRef Editor
November 15, 1999
Filed under

Scientists Present New Theory on the Origin of Inclement “Space Weather” that Disrupts Satellites, Cell Phones, Electric Power

College Park, MD (November 15, 1999)–Increased danger to satellites, the threat of power outages,
and a greater risk of cell phone disruptions are being forecast for early next year. That’s when the Sun
will experience the most active part of its 11-year cycle with a heightened burst of energy. At a
meeting in Seattle this week, researchers from the Naval Research Laboratory in Washington, D.C. will
present a controversial new explanation for the origin of the violent solar eruptions which can trigger
these disturbances. While some scientists say their theory is premature and hard to test, others applaud
it as an intriguing new idea.

“The degree to which the data agrees with the new theory is unprecedented,” says Jonathan Krall of the
Naval Research Laboratory. Team leader James Chen of the Naval Research Lab will present the theory
at the American Physical Society Division of Plasma Physics Meeting in Seattle on November 16.

Everyone agrees that this is an important question to pursue.

“There is a compelling national interest in predicting and understanding these eruptions, because they
can affect electronic communications and electric power transmission here on Earth,” according to Joe
Gurman of the NASA Goddard Space Flight Center in Greenbelt, Maryland. “The question of where these
eruptions really originate is a very important one,” he says. Answering this question, scientists
believe, will ultimately improve efforts to forecast and prepare for electrical and communications
disruptions on our planet.

Earth is affected by the Sun in more ways than one. In addition to shining light on our planet, the Sun
erupts regularly, sending forth streams of charged particles that can pass by the Earth. These particles
can disrupt the magnetic field of the Earth, creating disturbances to cell-phone communications and
even knocking out power grids in extreme cases.

The prevailing theory says that the energy responsible for these eruptions, called “coronal mass
ejections,” comes from the corona, the Sun’s outermost atmosphere. “But these theories have not been
shown to reproduce observations,” says Krall.

In contrast, Krall and Chen argue that the energy responsible for these eruptions is stored below the
photosphere, the visible solar surface underneath the corona.

To bolster their theory, the scientists have examined a wealth of data recently collected from the LASCO
(Large Angle and Spectrometric Coronagraph Experiment) instrument on the SOHO spacecraft launched
in 1995. “With observations extending out to an unprecedented 30 solar radii [where one solar radius
is the distance between the Sun’s center and its visible surface], we were able to compare theory to
observation in great detail,” Krall says.

Their explanation involves the concept of “solar flux ropes,” giant magnetic field loops rooted below the
photosphere. According to the theory, electrical current increases along a flux rope prior to solar
eruption. As the current flows, the rope’s magnetic field is increased in what’s called a “flux injection.”

Flux injection causes the rope to expand, taking electrically charged particles (mostly protons and
electrons) with it and ejecting them into interplanetary space. Each such eruption can eject up to 100
trillion grams of matter at speeds of up to 1000 kilometers per second. According to Krall, a significant
fraction of all solar eruptions–more than 30%–are caused by flux ropes.

“We have evaluated several different mechanisms of eruption. The purpose of doing so was to compare
our model with traditional ones,” Krall says. We have found that our proposed scenario provides the best
description of observed solar eruptions, as well as the properties of observed ?magnetic clouds,'” says
Krall.

“Magnetic clouds” are collections of charged particles in interplanetary space. They originate from the
solar wind, streams of charged particles emitted regularly by the Sun. Believed to be associated with the
solar eruptions, these clouds have distinctive magnetic fields that have been observed by spacecraft.

However, solar astrophysicists have mixed reactions to this new proposal. Here are a few:

“I believe the new model raises more problems than it solves,” says Leon Golub of the
Harvard-Smithsonian Center for Astrophysics. “There have been some problems with the ?old
paradigm,’ but they are rapidly disappearing as the result of more recent work,” he said.

“It is a well accepted observation that the photosphere remains very passive during an eruption,” says
Terry Forbes of the University of New Hampshire. “Although the researchers claim that flux can be
injected without disturbing the surface enough to be noticeable, they have yet to provide a convincing
demonstration of why this is so.”

“This theory reflects the authors’ support of what is an emerging paradigm in solar physics,” says
Richard Canfield of Montana State University. “There is certainly evidence that it may be correct,
though there is much work to be done before the case is proven.”

And according to Joe Gurman of NASA-Goddard, “We are at least 5 or 10 years away from the time in
which we can definitively test this model and the others, using local helioseismology,” in which
scientists measure vibrations on the surface of the Sun. “In fact, it’s only been very recently that
researchers have obtained good magnetic field measurements in the corona,” he says. “We need to rule
out the possibility that the eruptions originate in the corona, and this will be hard to do.”

“At first sight, the Chen and Krall model is as credible as any of the other explanations that are on the
table, and it is certainly a new and interesting idea,” says Craig DeForest of NASA-Goddard. “I’m
certainly interested to see how it develops and whether it agrees with observations.”

# # #

CONTACTS: Ben Stein, Inside Science News Service, 301-209-3091,
[email protected]
Randy Atkins, Inside Science News Service, 301-209-3238, [email protected]
Jonathan Krall, Naval Research Laboratory, 202-404-7719,
[email protected]

SpaceRef staff editor.