Imagine riding in an airplane as the plane is jolted¹ back and forth² by gusts³ of wind that you can't prove exist but are there nonetheless（尽管如此）. Similar turbulence⁴ exists in space, and a research team led by the University of Iowa reports to have directly measured it for the first time in the laboratory.

 

"Turbulence is not restricted to environments here on Earth, but also arises pervasively⁵ throughout the solar system and beyond, driving chaotic⁶ motions in the ionized gas, or plasma⁷, that fills the universe," says Gregory Howes, assistant professor of physics and astronomy at the UI and lead author of the paper to be published Dec. 17 in the online edition of Physical Review Letters, the journal of the American Physical Society. "It is thought to play a key role in heating the atmosphere of the sun, the solar corona⁸（日冕）, to temperatures of a million degrees Celsius⁹, nearly a thousand times hotter than the surface of the sun."

 

He adds: "Turbulence also regulates the formation of the stars throughout the galaxy¹⁰, determines the radiation emitted from the super massive black hole at the center of our galaxy and mediates¹¹ the effects that space weather has on the Earth."

 

One well-known source of gusty¹² space winds are the violent emissions¹³ of charged particles from the sun, known as coronal mass ejections. These solar-powered winds can adversely¹⁴ affect satellite communications, air travel and the electric power grid¹⁵. On the positive side, solar storms also can also lead to mesmerizing¹⁶ auroras at the north and south poles on Earth.

 

Howes notes that unlike gusts of wind on the surface of Earth, turbulent motions in space and astrophysical systems are governed by Alfven waves, which are traveling disturbances¹⁷ of the plasma and magnetic field. Nonlinear interactions between Alfven waves traveling up and down the magnetic field -- such as two magnetic waves colliding to create a third wave -- are a fundamental building block of plasma turbulence, and modern theories of astrophysical turbulence are based on this underlying¹⁸ concept, he says. "We have presented the first experimental measurement in a laboratory plasma of the nonlinear interaction between counter-propagating Alfven waves, the fundamental building block of astrophysical（天体物理学的） turbulence," Howes says.

 

Contributing authors on the paper are D.J. Drake, K.D. Nielson, Craig Kletzing, and Fred Skiff, all of the University of Iowa, and T.A. Carter of the University of California, Los Angeles. The research, conducted at the Large Plasma Device at UCLA, was funded by a grant from the NSF/DOE Partnership¹⁹ in Basic Plasma Science and Engineering.

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