Since the launch of the Solar and
Heliospheric Observatory (SOHO) in 1996, scientists have used its
Extreme-Ultraviolet Imaging Telescope (EIT) to study flares, filaments and
coronal mass ejections. The telescope has also discovered solar tsunamis
(also called “EIT waves” by solar scientists), huge propagating waves that
are triggered along with coronal mass ejections and can travel the entire
diameter of the sun. Researchers at Southwest Research Institute (SwRI) are
applying this unusual phenomenon for the first time to new studies of the
solar corona.
The Transition Region and Coronal Explorer (TRACE) spacecraft, launched in
1998, has provided new data complementing SOHO observations. Its higher
resolution and faster cadence give solar physicists the tools to study
hitherto unseen details. Dr. Meredith Wills-Davey, a post-doctoral
researcher in the SwRI Space Studies Department, uses TRACE data to better
understand the nature of solar tsunamis and the structure of the corona
through which they travel. Her work is being presented June 16 at the Solar
Physics Division Meeting of the American Astronomical Society in Laurel, Md.
“Just as geologists can learn about material in the ground by studying the
waves generated by earthquakes,” she says, “solar physicists can use these
solar tsunamis to learn more about the structure of the solar corona.”
TRACE observations of a well-observed event on June 13, 1998, are
sufficiently detailed that it is possible to show, through morphology alone,
that the propagation must be a “fast-mode magnetoacoustic wave.” Analysis of
the amplitude and the energy flux of the wave front shows that it actually
increases through much of its lifetime. This suggests that, rather than
being a single impulse, the wave driver may exist for an extended period.
Because this particular event was associated with a coronal mass ejection,
it is possible the wave is somehow part of the coronal mass ejection
formation, says Wills-Davey.
Comparison between current observations at different coronal temperatures
also offers insight into the wave’s altitude of propagation. Evidence
suggests that the tsunami is skimming along the base of the corona. This
idea is also consistent with the lack of measurable dispersion in the wave,
a circumstance more easily explained if the front travels at a constant
height. Existing models and theories suggest that propagating waves in the
corona should be trapped in “wave guides,” but this appears to be the first
observational evidence.
“These pulse waves serve as ‘sonar pulses’ that will let us probe the local
conditions in up to 30 percent of the sun’s atmosphere at once,” says Dr.
Craig DeForest, a senior research scientist at SwRI. “In addition, they help
us study the unknown processes at play in solar flares, the largest
explosions in our solar system.”
“The study of waves in the corona is a new venture with an exciting future,
and the benefits to our understanding of the sun should be substantial,”
adds Wills-Davey, who recently received NASA funding to continue this work.
The research to date has been funded by NASA and the American Association of
University Women Educational Foundation.
EDITORS: An image of an EIT wave is available for download at
www.swri.org/press/cme.htm.
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SwRI is an independent, nonprofit, applied research and development
organization based in San Antonio, Texas, with more than 2,800 employees and
an annual research volume of more than $339 million.
