SOLAR STRUCTURES CAN HELP FORECAST LARGEST SOLAR BLASTS
Fri, 19 Mar 1999 11:22:50 -0500
Some stuff from NASA
>Headquarters, Washington, DC March 9, 1999
>Goddard Space Flight Center, Greenbelt, MD
>Annette Trinity Stevens
>Montana State University, Bozeman
>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
> "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,"
> 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
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Richard Barth *** W3HWN@AMRAD.ORG *** Silver Spring MD