Richard Barth
Fri, 19 Mar 1999 11:22:50 -0500

Some stuff from NASA


>FYI DX'ers:
>de K3LOW
>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
>     "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," 
>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:
>         FTP://PAO.GSFC.NASA.GOV/newsmedia/CME
Richard Barth *** W3HWN@AMRAD.ORG *** Silver Spring MD