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NSF PR 00-08 - March 9, 2000
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Scientists "See" Through the Sun to Find Stormy Regions
on the Other Side
A week's warning of potential bad weather in space
is now possible thanks to a new use of the Solar and
Heliospheric Observatory (SOHO) spacecraft. Two astrophysicists
supported by the National Science Foundation (NSF)
have developed a technique to image explosive regions
on the far side of the sun, using ripples on the sun's
surface to probe its interior.
"This is a major breakthrough in our ability to forecast
solar storms that can affect us on earth," said Morris
Aizenman of NSF's Astronomical Sciences Division.
Explosive regions on the sun are hidden until they
rotate to the side of the sun visible from earth,
giving little advance warning. The new imaging technique
uses computer modeling developed since the early 1990s
with support from NSF and observations taken with
the Michelson Doppler Imager (MDI) on NASA's SOHO
satellite to detect and locate these hidden solar
"We've known for 10 years that in theory we could make
the sun transparent all the way to the far side,"
said Charles Lindsey of Solar Physics Research Corp.
in Tucson, Ariz. "But we needed observations of exceptional
quality. In the end we got them, from MDI on SOHO."
Lindsey and his colleague Douglas Braun of NorthWest
Research Associates, Boulder, Colo., describe the
research in the March 10 edition of Science.
Active regions on the sun are often the sites of spectacular
explosive events, called solar flares, which are associated
with eruptions of plasma (hot, electrically charged
gas). The radiation and plasma from these events sweep
past the earth and can disrupt spacecraft, radio communications
and power systems. Scientists watch closely for these
eruptions because modern systems are increasingly
sensitive to solar disturbances. But experts can still
be taken by surprise as the sun rotates, bringing
hidden active regions into view.
To locate these regions in advance, the scientists
developed a technique of using ripples on the sun's
surface to image the interior. The ripples are caused
by sound waves reverberating through the sun. Analysis
of these solar sound waves, a science known as helioseismology,
has opened the sun's gaseous interior to investigation
in much the same way as seismologists learned to explore
the earth's rocky interior through the analysis of
Lindsey and Braun's technique examines sound waves
that emanate from the far side of the sun and reach
the near side by rebounding internally from the solar
surface. They used observations from MDI taken on
March 28-29, 1998, to detect a group of sunspots on
the far side of the sun that was not visible on the
near side until 10 days later.
SOHO is a cooperative project between the European
Space Agency and NASA. The far-side helioseismology
research was funded by NSF and NASA.
Editors: Images are available at: http://umbra.nascom.nasa.gov/soho/ssu/rightthrough.html
Contact at NASA is Dolores Beasley, (202) email@example.com