JoNova » Giant double whirlpools in the ocean and the DIY ones you can make in your pool

How much don’t we know?

Giant pairs of whirlpools travel across the ocean for months in a bizarre pair.

These large paired whirlpools, hundreds of kilometers across, travel eastward at something like 10-20cm per second. This is one pair crossing from Tasmania to NewZealand. This was there in our satellite data but “invisible” til recently. As David Evans says “I wonder what else we are observing but not seeing?”

Modon E, Twin Whirlpool, Tasmania to NZ. Map.

The pair of whirlpools called Modon E travelling eastward from Tasmania to NZ.

Modon-E, whirlpools, travelling, Graphic.

The ocean becomes connected at two distant points as the Modon-E whirlpool pair travels from Tasmania to NZ in 2010-2011

In the mini-pool version, these rolling whirlpools are connected in a U shape under water.

Wow. PhysicsGirl shows how to make these by pushing a plate through the water, and adding food coloring. Switch on your science nerd, show the kids! (send me your photos :- ))

The two vortexes spin in opposite directions but are connected as a pair underwater. This was created by PhysicsGirl using a plate in a pool and two different food colorings.

Twin giant ocean whirlpools travel for months winding their way across oceans

Peter Dockrill reports on an interview published in Popular Science

For the first time, scientists have recorded a bizarre phenomenon in fluid dynamics, which up until now had only ever been theoretically predicted, but never observed in the wild.

“Ocean eddies almost always head to the west, but by pairing up they can move to the east and travel ten times as fast as a normal eddy, so they carry water in unusual directions across the ocean,” explains oceanographer Chris Hughes from the University of Liverpool in the UK.

“What we found was a pair of eddies spinning in opposite directions and linked to each other so that they travel together all the way across the Tasman Sea, taking six months to do it.”

Since 1993, satellites have recorded nine of these pairs (called Modons). Eight of nine that have been found were around Australia. (Perhaps Australian-NZ oceanography is special, but I suspect other modons just haven’t been identified yet). From the paper:

The nine modons we have identified are probably the clearest. There is no sharp cutoff to what could be considered a modon, and there are many other temporary associations of pairs of vortices, particularly to the southwest and south of Australia, and in the region of formation of Agulhas ring eddies. There are hints of acomplex eddy regime in the Pacific off the southern tip of South America, but the relatively small amplitudes and length scales here make interpretation ambiguous. There may also be brief pairings in the Gulf of Alaska and eddies shed from the southern tip of Madagascar certainly interact (de Ruijter et al., 2005, 2004), but clear evidence of modons is not seen. Movies showing modon propagation are given in the supporting information of this paper.

h/t to David E

Watch Physics Girl do some extremely cool pool tricks.

I’ve seen 99% of the hands-on science tricks out there but this was totally new to me. Oogle away. The twin vortices leave pairs of shadows on the pool floor. They travel right across the pool, but vanish sometimes unpredictably, or are destroyed easily by any interference.

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Notice the red ink whirlpool reaches over and envelops the blue one. The colors stay separate.

Twin whirlpools under water, pool.

BGR reports on the phenomena:

Mike Wehner:

You can think of an ocean eddy as something like an underwater tornado with two ends. The swirling water is sped along the twisting vortex, pushing it from one spot in the ocean to another. They’re a well documented natural phenomenon, and serve to regulate temperatures and transport nutrients over large distances, but fast-moving twin eddies put a new spin on what scientists thought they already knew.

Researchers were able to observe the odd ocean behavior using satellite data to measure the depth at which the eddies took shape as well as the speed of the water within them. The flowing water acts like a two-lane highway, moving in both directions simultaneously.

For any small sea creatures not capable of escaping the vortex, the ride can be a long one.

Double Whirlpools in the Ocean, Graphic path.

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We’re not sure how they are formed. From the paper:

From our data it is difficult to determine the formation mechanism. Precursor eddies are rarely distinguishable, though for the Tasman Sea modons the anticyclonic vortex can sometimes be seen propagating down theAustralian coast for some time before pairing up with an opposite vortex in the vicinity of Tasmania, which is reminiscent of the Southwick et al. (2015) mechanism, though it should be noted that there is significant variation in the position at which pairing occurs. It is quite striking in the animations how rapid the initial propagation can be after pairing, giving the appearance of a jet squirting out from the coast before settling into a modon form. For the open ocean cases it is even less common to see precursor eddies, but the many monopolar eddies in these regions suggest that a chance pairing of two complementary vortices is likely in these regions. If anything, it is surprising that we only have one example in the Atlantic sector, given how

energetic the Agulhas region is.

Never too old to get excited. :- )

REFERENCE

Hughes, C and Miller, P (2017) Rapid Water Transport by Long-Lasting Modon Eddy Pairs in the Southern Midlatitude Oceans, Geographical Research Letters, 44, PDF in full

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