Donald Savage
Headquarters, Washington, DC                   March 9, 1999
(Phone:  202/358-1547)

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

Annette Trinity Stevens
Montana State University, Bozeman
(Phone:  406/994-5607)

RELEASE:  99-35

SOLAR STRUCTURES CAN HELP FORECAST LARGEST SOLAR BLASTS

     "S" marks the spot for scientists trying to forecast solar 
eruptions that can damage satellites, disrupt communications 
networks and cause power outages.

     Using the Japanese Yohkoh spacecraft, NASA-sponsored 
scientists have discovered that an S-shaped structure often 
appears on the Sun in advance of a violent eruption, called a 
coronal mass ejection, that is as powerful as billions of nuclear 
explosions.

     "Early warnings of approaching solar storms could prove 
useful to power companies, the communications industry and 
organizations that operate spacecraft, including NASA," said Dr. 
George Withbroe, science director for Sun-Earth Connection 
research at NASA Headquarters.  "This is a major step forward in 
understanding these tremendous storms."

     "S marks the spot," said Dr. Alphonse Sterling of 
Computational Physics, Inc., Fairfax, VA, detailed to the 
Institute of Space and Astronautical Science (ISAS), Japan.  "We 
have found a strong correlation between an S-shaped pattern on the 
Sun, called a sigmoid, and the likelihood that an ejection will 
occur from that region within days.  Each sigmoid is like a loaded 
gun that we now know has a high probability of going off."

     "The S-shaped regions are the dangerous ones," said Dr. 
Richard Canfield, a research professor of physics at Montana State 
University-Bozeman, and lead author on a paper to be published in 
the March 15 issue of Geophysical Research Letters.  "As soon as 
we can recognize an S-shaped region, we know that it is more 
likely to erupt.  Other common structures look like a butterfly, 
quite symmetric, and these rarely erupt."

     The sigmoid structures are likely the result of twisted solar 
magnetic fields, said Dr. Sarah Gibson of the University of 
Cambridge, UK.  "The key to the coronal mass ejection is its 
magnetic field, which can structure and propel the mass outward," 
said Gibson.

     Coronal mass ejections are violent discharges of electrically 
charged gas from the Sun's corona, or outer atmosphere.  The 
largest explosions in the solar system, they hurl up to 10 billion 
tons of gas into space at speeds of one to two million miles an 
hour.  The outbursts occur several times a day, but not all are 
hurled toward Earth.

     Images from various spacecraft have provided often 
spectacular images and information after a coronal mass ejection 
had already erupted, but scientists have been trying for some time 
to identify a precursor for these events.  Sterling and Dr. Hugh 
Hudson of the Solar Physics Research Corporation, Tucson, AZ, 
working at ISAS, first observed a relationship between a sigmoid 
shape before a coronal mass ejection, and an arch-shape 
afterwards.  Later, Hudson and others found the same pattern in 
several other ejections.

     That finding prompted Canfield, Hudson and Dr. David 
McKenzie, a research scientist at Montana State University, to 
look for a statistical correlation between the sigmoid shape and 
subsequent eruptions.  They viewed a total of two years of daily 
X-ray images from the Japanese/US/UK Soft X-ray Telescope on 
Yohkoh.  The composite pictures -- 50 images each day -- were made 
into movies for analysis.

     "We need to get past simple classifications such as, 'Is it 
sigmoidal or not, is the sunspot big or small,' and get to 
quantitative measurements that answer, 'how twisted are the 
magnetic fields, how big is the spot'," Canfield said.  "As well, 
we want to know in which direction the ejection is going to go and 
how many regions are likely to erupt."

     Ultimately, Canfield continued, the National Oceanic and 
Atmospheric Administration (NOAA) may be able to include warnings 
of coronal mass ejections in its space weather forecasts.  NOAA is 
building a Solar X-ray Imager similar to that on Yohkoh, scheduled 
for launch next year, he said.

                              - end -

NOTE TO EDITORS: Images and supporting material can be found on 
the Internet at:

        http://solar.physics.montana.edu/press/
         FTP://PAO.GSFC.NASA.GOV/newsmedia/CME
      http://www.isas.ac.jp/info/sat/yohkoh-e.html#Tag:0
            http://solar.physics.montana.edu/YPOP/