What's behind the speedy 'smoke ring' vortices?

Typically, ocean waters flow gently westward, in part driven by the massive, slow waves generated by the Earth's spin. Even when whirlpools or eddies pop up, they tend to flow along with the rest of the water. But sometimes two eddies can combine into something called a modon, a massive vortex that can break off from the ocean's regular flow.

Nine of these modons, which were spotted around Australia between 1993 and 2016, were analyzed using satellite imagery and ocean temperature data. The modons — which can resemble massive smoke rings in the water — were found to travel several times faster than the ocean's typical currents, a new study finds.

In the study, which was published Dec. 4. in the journal Geophysical Research Letters, the scientists said they didn't see any clear evidence on how the modons formed. However, the strange swirls could result from one of two processes: two opposite-spinning eddies fusing together or one larger eddy splitting off into two pieces that spin in opposite directions, the study said. [In Photos: Travel Australia's Great Ocean Road]

Regardless of how the modon is formed, its overall structure is the same: The modon consists of two vortices spinning in opposite directions of each other, with their tails joining together beneath the surface of the water. In the paper, the scientists described the phenomenon as the bottom half of a smoke ring bisected by the surface of the water. YouTuber "Physics Girl" illustrates the half-ring well in a video where she uses food dye to show how two separate vortices interact and join together.

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These massive vortices aren't short-lived. The study found that they can last for up to six months before splitting apart, and then, those individual vortices can spin for several months beyond that. One crossed the entire Tasman Sea, the body of water between Australia and New Zealand, according to the study.

In some cases, the modons broke apart when they collided with a continental shelf; in other cases, the scientists couldn't deduce the reason from the available satellite data.

Still, what stood out about these powerful vortices is that they could travel either east or west at up to 7.9 inches (20 centimeters) per second — a speed that's several times the speed of Rossby waves, which averages 4-8 inches (1-2 cm) per second in the analyzed region. (Rossby waves are waves that naturally result from the Earth's rotation, according to the National Oceanic and Atmospheric Administration.) Sometimes the modons would pivot toward the north or south, strengthening whichever eddy was spinning in that direction and weakening the other before balancing out again, the study found.

Because these oceanic smoke rings travel independently and faster than ocean currents, the researchers suggested in the paper that the modons can rapidly transfer water, heat and minerals from one place to another, and even speculated that they could carry small organisms for great distances in their tow.

Original article on Live Science.