May 24, 2005

Dolores Beasley 
Headquarters, Washington
(Phone: 202/358-1753)

Rachel Weintraub
Goddard Space Flight Center, Greenbelt, Md. 
(Phone: 301/286-0918) 

RELEASE: 05-132

SOLAR FIREWORKS SIGNAL NEW SPACE WEATHER MYSTERY

The most intense burst of solar radiation in five decades accompanied 
a large solar flare on January 20. It shook space weather theory and 
highlighted the need for new forecasting techniques, according to 
several presentations at the American Geophysical Union (AGU) meeting 
this week in New Orleans. 

The solar flare, which occurred at 2 a.m. EST, tripped radiation 
monitors all over the planet and scrambled detectors on spacecraft. 
The shower of energetic protons came minutes after the first sign of 
the flare. This flare was an extreme example of the type of radiation 
storm that arrives too quickly to warn interplanetary astronauts. 

"This flare produced the largest solar radiation signal on the ground 
in nearly 50 years," said Dr. Richard Mewaldt of the California 
Institute of Technology, Pasadena, Calif. He is a co-investigator on 
NASA's Advanced Composition Explorer (ACE) spacecraft. "But we were 
really surprised when we saw how fast the particles reached their 
peak intensity and arrived at Earth." 

Normally it takes two or more hours for a dangerous proton shower to 
reach maximum intensity at Earth after a solar flare. The particles 
from the January 20 flare peaked about 15 minutes after the first 
sign. 

"That's important because it's too fast to respond with much warning 
to astronauts or spacecraft that might be outside Earth's protective 
magnetosphere," Mewaldt said. "In addition to monitoring the sun, we 
need to develop the ability to predict flares in advance if we are 
going to send humans to explore our solar system."

The event shakes the theory about the origin of proton storms at 
Earth. "Since about 1990, we've believed proton storms at Earth are 
caused by shock waves in the inner solar system as coronal mass 
ejections plow through interplanetary space," said Professor Robert 
Lin of the University of California at Berkeley. He is principal 
investigator for the Reuven Ramaty High Energy Solar Spectroscopic 
Imager (RHESSI). "But the protons from this event may have come from 
the sun itself, which is very confusing."

The origin of the protons is imprinted in their energy spectrum, as 
measured by ACE and other spacecraft, which matches the energy 
spectrum of gamma-rays thrown off by the flare, as measured by 
RHESSI. "This is surprising because in the past we believed the 
protons making gamma-rays at the flare were produced locally and the 
ones at the Earth were produced instead by shock acceleration in 
interplanetary space," Lin said. "The similarity of the spectra 
suggests they are the same."

Solar flares and coronal mass ejections (CMEs), associated giant 
clouds of plasma in space, are the largest explosions in the solar 
system. They are caused by the buildup and sudden release of magnetic 
stress in the solar atmosphere above the giant magnetic poles we see 
as sunspots. The Transitional Region and Coronal Explorer (TRACE) and 
the Solar and Heliospheric Observatory (SOHO) spacecraft are devoted 
to observing the sun and identifying the root causes of flares and 
CMEs, with an eye toward forecasting them. 

"We do not know how to predict the flow of energy into and through 
these large flares", said Dr. Richard Nightingale of the Lockheed 
Martin Solar and Astrophysics Laboratory in Palo Alta, Calif. 
"Instruments like TRACE give us new clues with each event we 
observe." 

TRACE has identified a possible source of the magnetic stress that 
causes solar flares. The sunspots that give off the very largest 
(X-class) flares appear to rotate in the days around the flare. "This 
rotation stretches and twists the magnetic field lines over the 
sunspots", Nightingale said. "We have seen it before virtually every 
X-flare that TRACE has observed since it was launched and more than 
half of all flares in that time."

However, rotating sunspots are not the whole story. The unique flare 
came at the end of a string of five other very large flares from the 
same sunspot group, and no one knows why this one produced more 
sudden high energy particles than the first four.

"It means we really don't understand how the sun works," Lin said. "We 
need to continue to operate and exploit our fleet of solar-observing 
spacecraft to identify how it works."

For more information and graphics about this story on the Web, visit: 

http://www.nasa.gov/vision/universe/solarsystem/solar_fireworks.html 

	
-end-