DS899: 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.
Figure DS899-F1. 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].
Figure DS899-F2. 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.
Figure DS899-F3. 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.
Figure DS899-F4. 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. The maximum, at the outside, was about 950 millibars, the minimum, at the centre, about 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).
Figure DS899-F5. Measured and theoretical pressures in a tornado. From [5]
Disrupting a 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 some sort of 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].
Figure DS899-F6. 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.
Lifting a Twister
Most of the damage occurring with tornados happens at its base, where it is in contact with the ground. Structures and objects on the ground may be picked up and hurled great distances, and suffer damage when brought to a halt.
If a way could be found to lift a twister, so its base was no longer in contact with surface objects, its destructive power might be minimized. While having a sheet of metal over a building should work to divert a tornado over the building, this would not be practicable, but maybe a similar effect could come from some sort of mesh. Not directly applicable, but perhaps with the germ of a treatment, is the "vortex destroyer", a wire gridwork with square holes about 2.5 cm across, laid proud on the surface where a vortex can attach itself on an aeroplane engine [9].
A treatment which would suck the energy from the tornado might be possible. Arrester beds, which can suck the energy from a runaway vehicle running downhill, are made of a thick bed of loose pebbles. While it would not be acceptable to have a treatment which involved loose pebbles flying around in a tornado, maybe a treatment could be designed which allowed energy extraction but constrained any loose pebbles from getting loose.
How tornados travel
The behaviour of tornados travelling over an undulating or otherwise varying terrain has been studied, with results not always clearcut. According to [8], tornadoes can be influenced by varying ground elevations, although it's a complex interaction and not always straightforward. Here's a breakdown of what research suggests.
Tornadoes can ascend and descend terrain: Tornadoes do not avoid mountains or hilly areas. There have been documented cases of tornadoes, like the 1987 Teton-Yellowstone tornado, climbing to over 3,000 metres above sea level.
The effect of elevation on tornado strength can vary. Some studies suggest that tornadoes can lose strength as they ascend mountainous terrain due to colder, more stable air, which is less conducive to sustaining their power. Other research indicated that tornadoes can cause greater damage when travelling uphill or on high ground or ridges.
There's also research indicating that tornadoes might be stronger in localized valleys than on top of nearby hills, and that convergence of winds tends to occur at lower elevations. Conversely, some studies have shown tornadoes "skipping" over valleys and concentrating damage on hilltops.
Tornadoes tend to curve to the left when going uphill and to the right when going downhill. While tornadoes are less common in mountainous areas due to colder, more stable air, certain topographical features like valleys can sometimes "channel" inflow into a supercell thunderstorm, potentially enhancing or even initiating tornado genesis.
Beyond elevation, surface roughness (like forested areas versus open fields) can also influence tornado characteristics. It's important to note that the exact mechanisms of how topography influences tornadoes are still being studied [8], and there can be conflicting findings depending on the specific tornado, terrain, and methodology used in the research. However, it's clear that varying ground elevations can play a role in a tornado's behaviour, including its intensity and path.
Synthetic tornados as power sources or to cancel natural tornados
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 anticlockwise 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 .
[8]. Bard AI. Do tornados rise and fall with varying ground elevations?
https://www.aoi.com.au/Data/Tornados & Bard.pdf .
[9]. Dave Gutz. How do you stop a vortex once it is formed? https://www.quora.com/How-do-you-stop-a-vortex-once-it-is-formed .
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