A small soap bubble can contain swirling patterns that mimic Jupiter's Great Red Spot and hurricanes on Earth, according to a new study.
Soap films have been used before to model planetary atmospheres, because both systems are very thin compared with their extent, behaving almost as if they are 2-dimensional.
Turbulent motion in a flat soap film can develop into pairs of vortices, like twin hurricanes rotating in opposite directions. It doesn't produce the single swirling storms seen in nature, however.
So Hamid Kellay and his team at the University of Bordeaux 1 in France made a more realistic mini-planet. Or rather, half of one. They created a hemispherical soap bubble, resting in a circular groove 10 centimetres across, blown through a straw using human lung power.
"We use a tube of rubber connected to a pipette, so it's a sophisticated straw. That way we can blow the bubbles very slowly, or suck a little out to adjust the volume," Kellay told New Scientist.
The bubble is heated from below, causing plumes of warmer soap solution rise up and tangle at higher latitudes. The team recorded dozens of their "soapstorms", and then Kellay's student Fanny Seychelles tracked their motion on digitised recordings.
Like Earth and Jupiter, Kellay's bubble-world develops single, isolated vortices. "They look like hurricanes," he says.
Kellay suggests that flat films previously failed to reproduce realistic single storms because they have side walls to confine the soap solution, and those walls interrupt the turbulent flow, unlike in free-flowing atmospheres.
Buffeted by more plumes rising from the warm equator, the storms stagger about randomly, moving on average at about 1 cm/sec.
At first sight that's unlike real hurricanes, which usually follow fairly straight paths, determined by other factors - such as the Coriolis force - that are absent from the Bordeaux bubbles.
But hurricanes do also display a small amount of random motion, which turns out to have the same statistical properties as the motion of the mini-storms. Small-scale jitters are interrupted quite often by larger jolts.
It should be possible to make your own little semi-world of storm at home, using a straw and a dish of warm soapy water. Kellay suggests that a temperature of around 50 °Celsius ought to be warm enough to produce convection.
Journal reference: Physical Review Letters (vol 100, p 144501)
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