Monster Waves on the Sun are Real
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November 24, 2009: Sometimes you really can believe your eyes. That's what NASA's STEREO (Solar Terrestrial Relations Observatory) spacecraft are telling researchers about a controversial phenomenon on the sun known as the "solar tsunami."
Years ago, when solar physicists first witnessed a towering wave of hot plasma racing along the sun's surface, they doubted their senses. The scale of the thing was staggering. It rose up higher than Earth itself and rippled out from a central point in a circular pattern millions of kilometers in circumference. Skeptical observers suggested it might be a shadow of some kind—a trick of the eye—but surely not a real wave.
"Now we know," says Joe Gurman of the Solar Physics Lab at the Goddard Space Flight Center. "Solar tsunamis are real."
The twin STEREO spacecraft confirmed their reality in February 2009 when sunspot 11012 unexpectedly erupted. The blast hurled a billion-ton cloud of gas (a "CME") into space and sent a tsunami racing along the sun's surface. STEREO recorded the wave from two positions separated by 90o, giving researchers an unprecedented view of the event:
Above: A solar tsunami seen by the STEREO spacecraft from orthogonal points of view. The gray part of the animation has been contrast-enhanced by subtracting successive pairs of images, resulting in a "difference movie." [larger movie] [more information]
"It was definitely a wave," says Spiros Patsourakos of George Mason University, lead author of a paper reporting the finding in the Astrophysical Journal Letters. "Not a wave of water," he adds, "but a giant wave of hot plasma and magnetism."
The technical name is "fast-mode magnetohydrodynamical wave"—or "MHD wave" for short. The one STEREO saw reared up about 100,000 km high, and raced outward at 250 km/s (560,000 mph) packing as much energy as 2.4 million megatons of TNT (1029 ergs).