Stephen Salter, the man who was on the forefront of wave energy technology during the 1973 Oil Crisis, has been working on a new idea over the past few years — a device made from old tires and plastic tubes that could prevent hurricanes from developing. He calls it the 'Salter Sink'.
A 'Salter Sink' consists of a large floating ring — anywhere from 10 to 100 metres across — made of recycled tires, with a 50-200 metre-long tapered plastic tube hanging below it. As waves of warm surface water top the edges of the ring, some of that water is trapped in the middle of the ring. Since the edges of the ring are above the ocean level, the surface of the trapped water is also above the ocean level, and gravity acts to pull the water inside of the ring down. The continued action of waves adding more water into the ring and that water being pull downward by gravity acts as a continuous pump to push the warm surface water downward, with no moving parts, and completely powered by wave-action.
When the water is pushed out the bottom of the tube, it mixes into the colder water that is below the surface layer, and this has the overall effect of cooling the surface water over time. The Sink would only need to cool the surface water to below 26.5 degrees C, which is the critical temperature for maintaining most tropical cyclones (tropical storms or hurricanes).
The Salter Sink was developed in connection with Intellectual Ventures Lab. Intellectual Ventures is a company founded in 2000 by Nathan Myhrvold, former Chief Technology Officer at Microsoft, with the support of Bill Gates. Other projects in development there are a deep brain surgery tool, a super-thermos for transporting vaccines, and a death-ray for killing mosquitoes.
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Although the Salter Sink appears to be quite effective, is low-cost and low-maintenance, and it would be fairly easy to deploy a network of them simply by dropping them off the back of a ship, I'm not sure of the wisdom behind preventing tropical cyclones.
Tropical storms and hurricanes are an important way that the Earth uses to transport heat from the equator towards the poles. Preventing these storms from forming would cause the sea surface temperatures at the equator to climb until they reached a point where they overwhelmed the prevention system, and generated a storm of cataclysmic proportions.
Even limiting the system so that it only lowers the sea surface temperature by a small amount — enough that it prevents the strongest of hurricanes from forming, but not so much that it prevents all tropical cyclones — may backfire, causing the strength of tropical cyclones to simply be split between mild-to-moderate storms and truly cataclysmic.
Additionally, tropical cyclones have been known to generate and sustain over colder waters. It all depends on the difference between the sea surface temperatures and the temperature of the air at around 5km above the surface. If the temperature at that level (where the air pressure is about half what it is at the surface) is low enough, storms can maintain their strength over much cooler ocean temperatures. For example, Hurricane Epsilon, in 2005, was able to maintain strength over water that was only 21 degrees C.
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This is certainly and interesting idea, though. Perhaps if these were deployed specifically to weaken or divert storms as they approached land, rather than attempting to prevent them from forming, that would be preferable. However, I think there would still be the worry of unwanted or unanticipated side-effects, and I would live in dread of the day that this inadvertently caused a storm that went completely off the scale.