Giant, energetic swirling structures—vortices—often form in situations where some fluid, whether gas or liquid, flows in an irregular or turbulent way.

But how do these things form?

Physicists have long debated it. Researchers say they can now shed new light on such structures, which include hurricanes, typhoons and Jupiter’s Red Spot.

A new study has found that the biggest vortices arise when a relatively large vortex starts to swallow energy from smaller ones nearby. The study was limited to cases where the fluid is in a thin layer, as an atmosphere is in comparison with a planet.

The physicists analyzed the process using computer simulations, experiments with a layer of water, and the power of sheer calculation.

They found that larger vortices strain and tug at the fluid directly around them, which changes the smaller vortices nearby. These start to stretch out horizontally, so they are no longer circular but more like ellipses. This forces them to slow down, draining their energy. That energy goes into the larger vortices, which become bigger and faster.

The process, known as inverse energy cascade, is “a spectacular phenomenon,” the researchers wrote in the March 3 issue of the research journal Physical Review Letters.

One theory of large-scale vortex formation has held that the mega-vortices eat small ones directly. But the researchers said their finding showed the large ones don’t engulf the small ones—they just suck up their energy.

The results will help to model and predict formation of large-scale vortices in atmospheres and oceans, said the researchers, Gregory Eyink of Johns Hopkins University in Baltimore, Md., and colleagues.


Jupiter's red spot is actually a giant, swirling storm more than twice as wide as Earth. (Credit: NASA)

ABOUT THE AUTHOR

Science writer Jack Lucentini is founder and editor of the World Science science news webzine. He has worked as a staff writer at three daily newspapers, and as a freelance science writer for a range of publications including The Washington Post, Discover magazine and The Scientist magazine. He earned his bachelor's degree at Oberlin College in Oberlin, Ohio in 1993.