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New research uses "solar tsunamis" to study the solar corona
Southwest Research Institute (SwRI)
June 16, 2003

Boulder, Colo. - 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.

For more information, contact Maria Martinez, Communications
Department, Southwest Research Institute, P.O. Drawer 28510, San
Antonio, Texas, 78228-0510, Phone (210) 522-3305, Fax
(210) 522-3547.

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