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Caption for Item 1: This tsunami from 1998 was first imaged by the SOHO spacecraft with a closer shot from TRACE. Credit: NASA/ESA/LMSAL

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Caption for Items 2- 4: This animated view shows the shock wave from solar flare radiating out through the corona. Credit: NASA

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Tsunamis Sweep Through the Solar Atmosphere
What Scientists Can Learn by Watching their Wakes

 

This tsunami from 1998 was first imaged by the SOHO spacecraft with a closer shot from TRACE.

Item 1

 
Imagine being at a concert where someone on stage sets off a firecracker. Not everyone would hear the 'pop' of the firecracker at the same time - the sound travels in a wave to those in the back, right? Now imagine that you could see the sound travel - and be able to determine how many people are at the show, where they're standing in clumps, and where the T-shirt vendors are - just by seeing that sound wave.

Scientists like Dr. Meredith Wills-Davey are doing just that on the Sun thanks to 'solar tsunamis,' huge distributive waves of energy triggered by the wildly powerful solar flares and coronal mass ejections constantly occurring in the solar atmosphere, or corona. These are sound waves, yet because they're occurring on the gaseous Sun, satellites are able to see them pass through regions of varying densities, structures and magnetic fields. So far the waves observed have varied in duration from 10 minutes to an hour and travel at a speeding pace of about 300 km/second (186 miles/second). To give some perspective, asteroids or comets that collide with the Moon travel at a significantly slower rate of 20 km/second (12 mps) and the space shuttle travels at about 7 km/second (4.3 mps).

Coronalseismology - the Next Step?

 

This animated view shows the shock wave from solar flare radiating out through the corona.

Item 2

 

"Just as geologists can learn about material in the ground by studying the waves generated by earthquakes, solar physicists can use solar tsunamis to learn more about the structure of the solar corona," said Dr. Wills-Davey, a post-doctoral researcher in the Southwest Research Institute (SwRI) in Boulder, Colo. "You expect the sound wave to behave a certain way depending on what it travels through. Sound waves act as probes to tell you about the center of the Sun."

When the wave moves through the corona, it vaguely resembles a ripple sent through a pond after having a pebble thrown in. Anything from temperature fluctuations to varying regions of density can cause the tsunami waves to slow down, speed up or move in different directions. Depending on the data available, scientists can also spot changes in the tsunami wake from satellite image to image.

"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," said 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."

Influential Explosions with Many Unknowns

 

This animated view shows the shock wave from solar flare radiating out through the corona.

Item 3

 

The explosive solar flares can release as much energy as a billion one-megaton nuclear bombs. They occur in the solar atmosphere and result in the heating of solar gas and the acceleration of particles to nearly the speed of light. Coronal Mass Ejections, or 'CMEs,' are often associated with flares but release plasma into space - sometimes toward Earth - rather than being contained within the corona. Both events seem to be caused by magnetic reconnection, the twisting and snapping of magnetic field lines on the Sun. When these fields snap from the buildup of magnetic energy, the resulting explosions emit radiation ranging from radio waves to X-rays.

Scientists don't understand a lot of the processes involved in solar flares and CMEs, including the fact that flares and CMEs occur within seconds of each other, leading to mysteries regarding which comes first. Also, these flares and CMEs are often so bright that many details referring to their origins are obscured in satellite images, if they're able to catch them at all. In other words, any new insights into these solar processes will drastically improve our understanding of these powerful events and help to bolster our efforts to protect satellites, power grids and astronauts from their dangerous output.

Spotting Tsunamis Under the Radar

 

Still from animation showing the shock wave.

Item 4

 

It's only recently that satellites have improved in clarity and frequency of output to make observations of these tsunami waves possible. The SOHO spacecraft, in operation since 1995, originally spotted them, but because the imaging instrument only sends back pictures every 15 minutes, only the largest waves are spotted. The TRACE spacecraft, launched in 1998, provides a better close-up view of the region where the flare forms and takes pictures about every one to two minutes in varying wavelengths. But it also takes a dedicated scientist to track these waves - and decipher what can be gained with that information. This last element explains why research of these tsunamis has been rather slow, despite the now vast archives from TRACE.

Wills-Davey expects that there are many more forms of these tsunamis propagating on the Sun that just haven't been seen yet. She's working on writing computer programs to better identify these waves - to essentially recognize and track them from the hours of data acquired from multiple spacecraft observing the Sun. New spacecraft like the 2006 Solar-B and 2008 Solar Dynamics Observatory (SDO) missions are also expected to improve observations of these solar tsunamis.

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