Cyclone on a bubble: The latest tool in hurricane intensity forecasting

Hurricane-like vortices swirl on the surface of a soap bubble. Credit: Hamid Kellay, CNRS.fr

Monday, August 25, 2014, 8:47 AM - Given their potential for disrupting our lives and causing widespread destruction, forecasting the strength and path of a tropical cyclone is very important, and scientists have turned to a few different tools to help them. One of the latest may seem unusual, but it's surprisingly effective - soap bubbles.

Scientists track tropical storms and hurricanes using stations on the ground and on the water. They take harrowing flights through them in planes that are packed with sensors and monitors, or send robot drones through them in their place. Satellites provide an outstanding views from orbit that give amazing perspective on their size, circulation and motion. All of these methods provide researchers with several real-world opportunities each year to learn more about these storms, but having a reliable and repeatable way of viewing them whenever we like would be an invaluable tool in forecasting their intensity.

Credit: NASA

A team of French scientists has developed a way to do just that, by watching swirling vortices moving through the membrane of a heated soap bubble.

If comparing a soap bubble to the Earth's atmosphere seems a bit unrealistic, the scale is actually not too far off. Just look at the thickness of the atmosphere compared to the size of the Earth - especially the troposphere (the orange/brown layer in the image to the right). While this lowest layer of the atmosphere, which is where all of our weather happens, ranges from between 9 and 17 kilometres thick, and tropical cyclones can reach up to that full height, that's only a fraction of a percent of the radius of the planet. Even the width of the storm, up to 1000 kilometres or more across, is so much bigger than the thickness of the storm that it can be considered to be a 2-dimensional object. Same goes for the membrane of a bubble.

Setting up a device that would blow a half-bubble - representing the northern hemisphere of the planet - and heating that bubble from the base and allowing it to be rotated if needed, the researchers created a system where, if you shone polarized light through the bubble membrane, they could watch tiny cyclones develop and march across the bubble. Watch this happen in the video below:

Comparing their bubble vortices to around 150 different real cyclones from both the Atlantic and Pacific oceans, the researchers found that both followed a simple relationship for their intensification, and the first 50 hours or so of development can determine just how strong a particular cyclone will become.

According to a press release from the researchers: "This study therefore provides a simple model that could help meteorologists to better predict the strength of tropical cyclones in the future."

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