Date: Tue, 16 Aug 2005 17:28:59 -0700 (PDT)
From: Ron Baalke <baalke@zagami.jpl.nasa.gov>
Subject: NASA Scientists Closer to Timely Space Weather Forecasts

Erica Hupp
Headquarters, Washington August 16, 2005
(Phone: 202/358-1237)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-5017)

Buddy Nelson
Lockheed Martin, Palo Alto, Calif.
(Phone: 510/797-0349)

RELEASE: 05-226

NASA SCIENTISTS CLOSER TO TIMELY SPACE WEATHER FORECASTS

Scientists funded by NASA have made big strides in
learning how to forecast "all clear" periods, when severe
space weather is unlikely. The forecasts are important
because radiation from particles from the sun associated
with large solar flares can be hazardous to unprotected
astronauts, airplane occupants and satellites.

"We have a much better insight into what causes the
strongest, most dangerous solar flares, and how to
develop forecasts that can predict an 'all clear' for
significant space weather, for longer periods," said
Dr. Karel Schrijver of the Lockheed Martin Advanced
Technology Center (ATC), Palo Alto, Calif. He is lead
author of a paper about the research published in the
Astrophysical Journal.

Solar flares are violent explosions in the atmosphere of
the sun caused by the sudden release of magnetic energy.
Like a rubber band twisted too tightly, stressed magnetic
fields in the sun's atmosphere (corona) can suddenly
snap to a new shape. They can release as much energy as
one, 10 billion megaton nuclear bomb.

Predicting space weather is a complicated problem. Solar
forecasters focus principally on the complexity of solar
magnetic field patterns to predict solar storms. This
method is not always reliable, because solar storms
require additional ingredients to occur. It has long been
known large electrical currents must be present to power
flares.

Insight into the causes of the largest solar flares came
in two steps. "First, we discovered characteristic patterns
of magnetic field evolution associated with strong
electrical currents in the solar atmosphere," said ATC's
Dr. Marc DeRosa, co-author of the paper. "It is these
strong electrical currents that drive solar flares."

Subsequently, the authors discovered the regions most
likely to flare had new magnetic fields merge into them
that were clearly out of alignment with the existing field.
This emerging field from the solar interior appears to
induce even more current as it interacts with the existing
field.

The team also found flares do not necessarily occur
immediately upon the emergence of a new magnetic field.
Apparently the electrical currents must build up over
several hours before the fireworks start. Predicting
exactly when a flare will happen is like studying
avalanches. They occur only after enough snow built up.
Once the threshold is reached, the avalanche can happen
anytime by processes not yet completely understood.

"We found the current-carrying regions flare two to three
times more often than the regions without large currents,"
Schrijver said. "Also, the average flare magnitude is
three times greater for the group of active regions with
large current systems than for the other group."

The researchers made the discovery by comparing data about
magnetic fields on the sun's surface to the sharpest
extreme-ultraviolet images of the solar corona. The
magnetic maps were from the Michelson Doppler Imager (MDI)
instrument on board Solar and Heliospheric Observatory
(SOHO) spacecraft. SOHO is operated under a cooperative
mission between the European Space Agency and NASA.

The corona images were from the NASA Transition Region and
Coronal Explorer spacecraft (TRACE). The team also used
computer models of a three-dimensional solar magnetic
field without electrical currents based on SOHO images.
Differences between images and models indicated the
presence of large electrical currents.

"This is a result that is more than the sum of two
individual missions," said Dr. Dick Fisher, Director of
NASA's Sun-Solar System Connection Division. "It's not
only interesting scientifically, but has broad
implications for society."

For imagery about the research on the Web, visit:

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

For information about NASA and agency programs on the Web,
visit:

http://www.nasa.gov/home/index.html

-end-