Tuesday, August 10, 2010

Solar tsunami

A solar tsunami has been caught in the act of rolling across the face of the sun. The unusual shock wave, clocked at about 700,000 miles per hour, was triggered by a huge Dec. 6 flare that erupted from a rowdy Earth-sized sunspot during what is otherwise a relatively quiet time for the sun.

"This is clearly a unique event," said Alexei Pevtsov, a solar physicist at NASA headquarters. "I don't think we've ever seen a wave of that magnitude."

Normally when shock waves are seen on the sun, they tend to be short-lived, narrowly directed and seen in the super hot outer "corona" of the sun's atmosphere, he said.

This tsunami, however, was seen expanding through the much less hot chromosphere, just below the outer corona, with an almost perfectly circular wave front — like that of a stone dropped in a pond.

"In this case there was this humongous explosion that cased the waves," said solar researcher K. S. Balasubramaniam of the National Solar Observatory in Sunspot, New Mexico, where the solar tsunami was witnessed and photographed. "It took about 30 or 40 minutes to cover the Sun."

The tsunami itself was seen as a brightening caused by the squeezing, and therefore heating of hydrogen gas. The flare itself ignited at 1:28 pm EST and gave off a powerful burst of X-rays.

For a few minutes a small corner of the responsible sunspot brightened in white light to about 100 times the average brightness of any other similar sized patch on the sun.

To see the sun-enveloping tsunami in the chromosphere the researchers watched the sun in the same band of deep red light that comes from that layer — a color called H-alpha. The telescope they used, which is the prototype telescope for the new Optical Solar Patrol Network, monitors the sun in that particular color of light, as well as near-infrared.

Along its way the solar tsunami was seen shutting down magnetic fountains from the sun called filaments. These are areas where less-hot hydrogen gas rides magnetic fields lines in high, graceful loops. They look dark in the solar tsunami images because they suck up H-alpha light.

Interestingly, the filaments started up again after the wave passed, albeit less vigorously, Balasubramaniam told Discovery News. That means the tsunami tinkered with the filaments in a way that might be reproduced on a computer model — which could reveal more about how the sun works.

"We're just beginning to model them," Balasubramaniam said. And he hopes there are more such tsunamis on the sun so he and other scientists can gather as much information from them as possible.

"It gives us a new tool to measure conditions in the sun's atmosphere," agreed Pevtsov.