Killing Tornados --
How To Stop A Twister
David Noel
<davidn@aoi.com.au>
Ben Franklin Centre for Theoretical Research
PO Box 27, Subiaco, WA 6008, Australia.
About Tornados
Tornados (or whirlwinds, or twisters) have a record of inflicting enormous damage to property and life, wherever they occur. The prime area is "Tornado Alley", an area of the Great Plains north of the Gulf of Mexico, but other parts of the World may be affected at times.
Tornado Alley. From [4]
Scientists and others have devoted a great deal of study to observing and measuring tornados -- what the weather conditions are like when they form, where they originate, and how they travel. Perhaps the leading researcher has been Tim Samares of Applied Research Associates Inc, killed, together with two colleagues, by an Oklahoma tornado on 2013 May 31. A good video program on their work is at [3].
Tim Samares. From [1]
The surprising thing, amid the widespread concern about damage by tornados, is that virtually no research has been done on how to stop them. This article is intended to promote such research, to find out how to stop tornados in their tracks.
Killing Tornados
To work out how we might kill a tornado, we need to know about its structure and the forces that hold it together.
Tornados are a type of vortex -- a swirling mass of matter created and maintained by the steady inflow of energy from outside. Other types of vortex include whirlpools in the sea, the gravity wells around planets, even the swirling of water as it goes down the plughole.
Cross-section of Tornado. From [2]
In essence, a tornado is a spinning mass of air, cylindrical or conical in shape, with its mass concentrated at its rim, held there by centrifugal forces. At the centre of the cylinder the air pressure is much less, because the centrifugal forces have moved the air particles out towards the rim.
Tornados contain enormous amounts of energy, and this energy is continuously being added to by conditions just outside its base. If this inflow of energy was disrupted, the tornado would collapse. Energy is streamed rapidly upwards in the tornado, at height its structure may loosen and a top may be formed.
Of course this is a simplification, in practice other factors, such as water being drawn in and forming a water-vapour loading in the swirling air, can be important.
Of vital importance is the fact that air pressure at the centre of a tornado is much lower than at its rim or in the outside air. Tim Samaras was able to set up pressure recorders over which the centre of a tornado passed.
Measured pressures across the base of a tornado. From [5]
This difference in pressure between the centre and the outside was, in practical terms, enormous, falling from about 950 to 850 millibars. These are the sort of pressure figures shown on weather charts, where a fall of 20 millibars between Area A and Area B would imply a strong wind flowing from A to B to fill the pressure deficiency. But where A and B might be hundreds of kilometres apart, parts of the tornado only metres apart may have five times this deficit. Here, then, is the source of the enormous destructive force of some tornados.
There is a theoretical backing to this tornado picture. The pressure measurements made by Tim Samaras fit in fairly well with a mathematical model called a Rankine Vortex (this could apply to any form of vortex).
Measured and theoretical pressures in a tornado. From [5]
Killing the Twister
In principle, to kill a twister you need only disrupt its heart, the point of low pressure at the centre of its base.
Since tornados continually move (usually at about 40-70 km/hr [6]), to hit the heart, you need to move the disruption platform to cross the tornado's path. This platform could vary in sophistication from a toy remote-control car to an advanced rover like those deployed by NASA [7].
NASA Innovation Rover platform. From [7]
The disruption device needs to break the pattern of energy flow into the base of the tornado. A small amount of explosive is the obvious choice, though other methods, such as a high-voltage arc discharge, might also work.
Synthetic tornados as power sources
Clearly, tornados are able to extract enormous amounts of energy from the environment. In theory, it should be possible to make controlled artificial tornados, perhaps in tall columns, from which energy could be extracted.
If this technique could be mastered, it should also be possible to create artificial tornados which rotate in the opposite direction to the norm. In the northern hemisphere, tornados rotate anticlockwise when viewed from above (due to a phenomenon called the Coriolis Force), so an anti-tornado would rotate clockwise. Merging a synthetic clockwise anti-tornado with a natural one would be another way in which the natural one could be killed.
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References and Links
1. Storm chaser Tim Samaras among those killed by Oklahoma City tornado. http://www.abc.net.au/news/2013-06-03/stormchasers-among-those-klled-by-oklahoma-tornado/4728306.
2. Cross-section of Tornado - Illustration. http://www.fotolibra.com/gallery/49774/cross-section-of-tornado-illustration/.
3. Video -- Storm Chasers: Inside the Tornado -- National Geographic. http://video.nationalgeographic.com.au/video/environment/environment-natural-disasters/tornadoes/inside-the-tornado/ .
4. Tornado Alley. http://www.cbsnews.com/htdocs/natural_disasters/tornado/framesource_map.html .
5. Lee, J. J., T. M. Samaras, and C. R. Young, 2004. Pressure measurements at the ground in an F-4 tornado.. 22nd Conf. on Severe Local Storms, Hyannis, MA. Amer, Meteor. Soc., CD_ROM, 15.3. http://ams.confex.com/ams/pdfpapers/81700.pdf .
6. How Fast do Tornadoes Move? http://answers.ask.com/Science/Nature/how_fast_do_tornadoes_move .
7. NASA Innovation Rover. http://www.rccoh.com/IMG/land/off-road/killer.krawler/rover.plate.jpg .
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