sábado, 13 de julio de 2013

Dramatic solar tsunamis reveal magnetic secrets in sun's corona

By Amina Khan
July 12, 2013

This image from the Solar Dynamics Observatory shows the "quiet corona" and upper transition region of the sun. A study tracking solar tsunamis through the sun's plasma shows that the quiet corona may not be so quiet after all. (Solar Dynamics Observatory / NASA)

If tsunamis on Earth don’t seem terrifying enough, imagine the power of such a monstrous wave on the sun -- bigger, faster and made of searing plasma. Scientists have spotted two solar tsunamis that have allowed them to accurately measure the sun's magnetic field. The results, published by the journal Solar Physics, should help researchers better understand the makeup of the sun’s "quiet corona" and help predict when coronal mass ejections threaten Earth.

Solar tsunamis, spotted initially in 1997, are caused when a coronal mass ejection is hurled from the sun out into space. The eruption of charged matter pushes the surrounding plasma outward, sending out a circular wave that can travel 620 miles per second and cover half the sun’s surface in an hour, said study lead author David Long, a solar physicist at University College London.

Using NASA’s Solar Dynamics Observatory and the Japanese Hinode spacecraft, the researchers managed to capture two solar tsunamis in action, rising about 43,500 miles high and speeding along at roughly 250 miles per second. Having data from both spacecraft was key. Using NASA’s spacecraft, they tracked the tsunami by watching the ultraviolet light given off as the wave progressed. Using data from the Japanese spacecraft, they determined the density of the matter it was traveling through.

In both of these events we were just in the right place — wasn’t too close, wasn’t too far away,” Long said.

That’s because as the tsunami spreads outward somewhat like a ripple, it gets distorted by the material it passes through. It will travel faster in denser areas and slower in less dense ones, Long said, because in dense areas the molecules are tightly packed together and can quickly relay the wave along. In sparser areas there might be a slight delay before one molecule runs into the next. The resulting raggedy circles showed that the wave was running through patchy star stuff rather than a smooth, homogeneous medium.

Together, this information allowed the scientists to determine what the density, and the magnetic field, looked like in the less active areas of the sun’s atmosphere known as the quiet corona.

"The fact that it gets deformed means that there are variations in the magnetic field of the solar atmosphere, which was very interesting," Long said. "There’s a lot more going on there than we originally thought."

Understanding a solar tsunami could also help scientists better predict the arrival of a coronal mass ejection. If such a burst of charged particles reaches Earth, it can wreak havoc on the globe’s power, electronics and navigation systems.

"If a coronal mass ejection is coming straight at you, it’s very difficult to measure its speed; it’s very difficult to measure how powerful it is," Long said. "So we are hoping that by looking at these waves, we’d be able to tell something about coronal mass ejections, which would be very useful for space weather forecasting."


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