May 31, 2000
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Three-dimensional images of
magnetic storms from the Sun,
developed by physicists at the
University of California, San
Diego and Japan's Nagoya
University, are allowing
space-weather forecasters to
improve their predictions of
solar disruptions. |
These large magnetic storms
are produced by energetic
solar eruptions known as
"coronal mass ejections".
They consist of giant clouds
of energetic electrons and
strong magnetic fields,
traveling from the Sun at up
to 2 million miles an hour.
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When they reach Earth, the coronal mass ejections and the storms
they cause can interrupt satellite communications, produce
destructive surges in power grids and even increase radiation
exposure to people flying in airplanes.
Space-weather forecasters have for years issued warnings of
these storms whenever they detected a coronal mass ejection,
or solar flare, near the Sun. But, because they could not see
the mass ejection traveling through space, they could not tell
with any certainty whether it would affect Earth when it arrived
four days later or whether it would totally bypass the planet.
Using a network of four radio telescopes in Japan, UCSD and
Nagoya University physicists have improved those predictions
dramatically by developing a method of detecting and predicting
the movements of these geomagnetic storms in the vast region of
space between the Sun and Earth. By focusing the telescopes on
powerful sources of natural radio emissions in the universe, the
physicists infer the location of these storms by the intensity
fluctuations, or "scintillation", they produce in these radio
sources.
"Basically, the more scintillation there is, the more material
there is along the line of sight", says Bernard V. Jackson, a
solar physicist at UCSD's Center for Astrophysics and Space
Sciences who developed the detection technique with Masayoshi
Kojima of Nagoya University's Solar-Terrestrial Environment
Laboratory. " It's the same reason stars twinkle. In the case
of the twinkling stars, the fluctuations are caused by changes
in the atmosphere, which cause scintillation of the starlight."
The scientists are able to detect the direction and velocity of
the storms by precisely measuring when a particular fluctuation,
or "twinkle" reaches each of the four radio telescopes. The
telescopes are separated from one another in four Japanese radio
observatories. "If you have four radio telescopes not too far apart,
then you can correlate the time the scintillation pattern goes from
one telescope to the other", says Jackson. "That allows you to say
how fast the material is moving." Combining all of the information
in a computer program, the scientists produce a three-dimensional
picture of the region between the Sun and Earth, a view Jackson
says is similar to "a CAT-scan of the solar wind".
That information is then sent to the National Oceanic and
Atmospheric Administration's Space Environment Center in
Boulder, Colo., which provides forecasts and warnings of
space-weather disturbances. The center is now closely watching
for coronal mass ejections, which become more frequent as the
Sun approaches the peak of its 11-year cycle. Because the
scientists' technique, known as three-dimensional tomography,
was not available the last time the Sun reached its peak period
of activity, forecasters at the center will be able to make much
more accurate predictions of any geomagnetic storms that affect
Earth than they did during the last solar maximum.
Jackson estimates that the accuracy of the forecasts will be
improved dramatically once again, when a U.S. Air Force satellite
is launched in December, 2001. It will carry an instrument that
will take direct pictures of the mass ejections between the Sun
and Earth by detecting the sunlight that is reflected from the
clouds of electrons, a process known as Thomson scattering.
Called the Solar Mass Ejection Imager, the instrument, which
is being built with Air Force and NASA financing, eliminates
stray sunlight and precisely removes the effects of starlight
from one image to the next to detect the faint Thomson scattering
of sunlight from the electrons. It was designed by a team of
scientists that includes Jackson, UCSD physicists Andrew
Buffington and P. Paul Hick, and colleagues at the Air Force
Research Laboratory, University of Birmingham in the U.K., Boston
College, Boston University,the Johns Hopkins University's Applied
Physics Laboratory and the Naval Research Laboratory.
"We'll get a thousand times more data from the Solar Mass
Ejection Imager and we'll be able to resolve these things by an
order of magnitude better", says Jackson. "We know coronal mass
ejections are important and we know they cause effects on Earth.
But until now we didn't have a way to view them very well."
"We are now at the stage where weather forecasting on global
scales was 30 years ago, when satellites first became available",
he adds. "We discovered then that we could see hurricanes really
well from a satellite, could tell what direction they were going in,
and could watch them over time to predict where they were going
to make landfall. We're now at the same point with coronal mass ejections".
Bernard Jackson will be at the Spring Meeting of the American
Geophysical Union in Washington, D.C., from May 31 to June 2,
and can be reached during that time through the AGU pressroom
at 202-371-5087 or at bvjackson@ucsd.edu. He will
present a
paper and co-chair a session on June 2 at 8:30 a.m. on The Sun,
Corona, and Heliosphere at Mid to High Latitudes During Solar Maximum.
CASS/UCSD
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