Video: A small soap bubble can contain swirling patterns that mimic Jupiter鈥檚 Great Red Spot and hurricanes on Earth (Courtesy of Hamid Kellay et al.)
A small soap bubble can contain swirling patterns that mimic Jupiter鈥檚 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鈥檛 produce the single swirling storms seen in nature, however.
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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.
鈥淲e use a tube of rubber connected to a pipette, so it鈥檚 a sophisticated straw. That way we can blow the bubbles very slowly, or suck a little out to adjust the volume,鈥� Kellay told 快猫短视频.
Interrupted flow
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 鈥渟oapstorms鈥�, and then Kellay鈥檚 student Fanny Seychelles tracked their motion on digitised recordings.
Like Earth and Jupiter, Kellay鈥檚 bubble-world develops single, isolated vortices. 鈥淭hey look like hurricanes,鈥� 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.
Random motion
At first sight that鈥檚 unlike real hurricanes, which usually follow fairly straight paths, determined by other factors 鈥� such as the 鈥� 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 掳Celsius ought to be warm enough to produce convection.
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