Tornadoes
Created | Updated May 27, 2003
A tornado is a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes have rotating winds of 250 miles per hour or more. They are capable of causing extreme destruction, including uprooting trees and well-made structures, and turning normally harmless objects into deadly missiles. Most tornadoes are just a few dozen yards wide and only briefly touch down, but highly destructive violent tornadoes may carve out paths over a mile wide and more than 50 miles long.
Most common in Spring and Summer, they can happen any time of the year.
Most common in the afternoon and evening, they can happen any time of day.
Although more famous in the US “Mid West” they are most common in the UK but are a world wide phenomenon. The United States reports over 1000 annually over a wide variety of geographical features from Alaska to Texas.
Pay attention to weather clues around you.
The wind may die down and the air may become very still.
Dark, often greenish sky. Thunder is associated with “greenish” clouds (a phenomenon caused by hail).
Wall cloud, an isolated lowering of the base of a thunderstorm is particularly suspect if it is rotating.
Large hail-stones.
Funnel cloud. A visible rotating extension of the cloud base is a sign that a tornado may develop.
Cloud of debris. An approaching cloud of debris can mark the location of a tornado even if a funnel is not visible.
Roaring noise . The high winds of a tornado can roar like a train.
Tornadoes may occur near the trailing edge of a thunderstorm and be quite visible. It is not uncommon to see clear, sunlit skies behind a tornado. They may also be embedded in rain and not visible at all.
Waterspouts are weak tornadoes that form over water. They are common in winter and can move inland being reclassified as tornadoes. Hurricanes also generate tornadoes when they come ashore. The position they develop is interesting -to the right and ahead of the storm. In 1967, Hurricane Beulah produced 148 tornadoes as it made landfall in south Texas.
Although tornadoes form along the dry fronts of storms they do not necessarily travel in straight lines and you can’t always tell the direction the storm is coming from. If caught out driving during one remember the road you are on may curve into the storm. Also there may be more than one, hidden by heavy rain and wind-blown debris. Until they pick up debris they may be almost transparent -although, on the Great Plains and other semi arid regions they usually occur without rain.
Tornado winds can toss large objects such as vehicles, hundreds of feet. (Mobile homes are particularly vulnerable.) Dangerous flying debris can be blown under highway overpasses and bridges, or weaker overpasses and bridges could be destroyed. You will be safer lying flat in a low-lying area where wind and debris will blow above you. Tornadoes come from severe thunderstorms, which can produce a lot of rain. If you see quickly rising water or flood water coming towards you, move to another spot. Avoid places with wide-span roofs, such as auditoriums, cafeterias, large hallways, or shopping malls.
If you are in a high-rise building, pick a place in a hallway in the centre of the building, they are often the most reinforced part of structure. If you live in a mobile home make sure it has a designated shelter. Mobile homes are much more vulnerable to strong winds than bricks and mortar. Every building has different “safe” places. If you live in a danger zone it might be an idea to know where they are and how to get there in an emergency. The same is true for fires and other emergencies. Of course a safe place in a tornado is not the same as a safe place in a fire.
The Fujita - Pearson Tornado Scale:
F-0: 40-72 mph, chimney damage, tree branches broken.
F-1: 73-112 mph, mobile homes pushed off foundation or overturned.
F-2: 113-157 mph, considerable damage, mobile homes demolished, trees uprooted.
F-3: 158-205 mph, roofs and walls torn down, trains overturned, cars thrown.
F-4: 207-260 mph, well-constructed walls levelled.
F-5: 261-318 mph, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters.
Advance planning and quick response are the keys to surviving tornadoes. You want, for example, to be able to get to an uncluttered spot where flying glass is not going to be a problem. Can’t get under the bed for old socks? Why not have that clean out now? Seriously though, modern homes are designed with acres of windows, so tipping a sofa up and sliding underneath may save you. Keep an hold of it too as it might get blown away from you. (Go with it right to the edge of the runway.)
Less than 2% of all tornadoes are powerful enough to destroy a building. If one is imminent, strong close walls are likely to provide the best protection get to the lowest level and away from windows, preferably in a small room. Closer walls will help provide more support to the roof and the more walls between you and the outside the better. That violent 2% account for some 70% of fatalities as they generate large hail stones and hurl debris. Major outbreaks occur with persistent storm systems. In the US, the government works with radio and television to give as much warning as possible (their National Oceanic & Atmospheric Administration even supplying a special Weather Radio.)
Foresite is a great thing. And if you are in the wrong place at the wrong time it is good to be prepared. The fact is that the majority of these events come out of the blue and will strike you when there is almost nothing that you can do about it.
You can't live your life thinking "today there may be an earthquake, storm or flood." no more than you can be prepaed not to get caught in a riot or have a burglar break into your home. You just do your best with the daily priorities of life.
Emergency kits are a good idea for all those special little occasions you might wish to experience next time from a greater distance:
Flashlight and extra batteries.
Portable, battery-operated radio and extra batteries.
First aid kit and manual.
Emergency food and water.
Can opener.
Essential medicines.
Cash and credit cards.
Sturdy shoes and/or boots and other clothing needs.
Spades, pry-bars and hammers along with various other tools and fixings. I’d put a coil of rope in there too but it wouldn’t be long enough by about 2 feet. How does that work|?
Knowing what weather could happen helps.
After an emergency is generally considered a good time to have had some emergency training by. If you still have one:
Return home only when authorities say it is safe.
Use the telephone only for emergency calls.
Clean up spilled medicines, bleaches, or petrol or other flammable liquids immediately.
Leave the buildings if you smell gas or chemical fumes.
Remember to help your neighbours who may require special assistance. (Library books and etc.)
If the electric goes of get your freezers contents to someone who has not been affected.
Take pictures of the damage (believe it or not, you will forget the best bits.) (It will bore your friends and family after their initial interest but you never know how interested the insurance people will be.) Photograph house and contents and don’t trust anyone that is called an insurance assessor. They are criminals.
If you smell gas or hear a blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main if you can and call the emergency services from a safe place. (If you turn off the gas for any reason, it must be turned back on by a professional. Don’t forget the special key for that in the emergency tool kit.)
Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice.
Check for sewage and water lines damage. If you suspect sewage lines are damaged, avoid using toilets until they’ve been checked. If water pipes are damaged, contact the water company and avoid using water from the tap. You can obtain safe water by melting ice cubes.
Don’t get caught out in a storm, check local building codes and stuff like that for any work you are going to have done. And to rectify potential hazards that you are already saddled with. I bet you don’t know how to unravel who is responsible for what since the utilities were privatised do you?
Have fun.
Just a little codicil:
http://www.astrogeo.va.it/immagini/cielo/giudici.htm
I came across the following theory in Google groups. I have tried to contact the author but to no avail. Here is an edited piece of the theory that appears on his site. My words are in brackets = ().
There are a number of good references (Snow 1984, and Davies-Jones 1995) that describe the meteorology leading up to the development of the tornado but....a void in explanations for the fully developed tornado.
The tornado, in essence, is a very strong vortex with one end attached to the ground and the other end extending upward to a varying or undefined height. This configuration suggests to the aerodynamicist that there are vortex lines concentrated in the core of the tornado, that are splayed out radially in all directions on the ground. The vortex lines are diffused upward into the clouds only to turn downward and connect up with the vortex lines on the ground at some remote distance from the tornado. The whole vortex field appears to be toroidal in shape with one end flattened by the ground. This picture is based on the aerodynamic theory that vortex lines must close on themselves and cannot be unconnected.
The generation of a strong vortex requires strong velocity gradients and most strong vortices are usually created by the interaction between an established fluid flow and a solid surface. On a wing, for example, there is an array of vortex lines of one polarity generated by the boundary layer on the upper surface and another array of opposite polarity generated by the boundary layer on the lower surface.
(On an airplane’s wing the two different strengths of vortex lines combine to give the plane lift and leave a rotating eddy in its wake. The lift and the eddy are not self generating; the wind is totally dependent on the engine or some other outside source.)
Somewhere along the closed loop of vortex lines of the tornado there is an energy source. (Contemporary theory is in error because with) normal aerodynamic principles there cannot be strong velocity gradients in free air, because there is no mechanism to support them.
Energy density decreases with distance from the source. This is decreed by the second law of thermodynamics. Since the most energetic location of the rotational kinetic energy of the tornado is at its base, this is the location of the source of this energy.
(The forces driving and holding together a tornado must be equal and opposite or it would just fly apart.)
If we know the velocity profile, we can calculate the shear or retarding force. In the air, the shear force is very weak because the air viscosity is very small. Calculations show that the power for a tornado in air with a simple velocity profile with a maximum velocity of 90 meters/sec (295 ft/sec) and a radius of 30.5 meters (100 ft) and a height of 305 meters (1000 ft) is of the order of 1 horsepower.
However, calculations of the drag horsepower of a turbulent boundary layer of the same velocity profile (as described above) when the tornado is on the ground, yields tens of thousands of horsepower.
What is the driving force at the air/ground interface? One element of the tornado that has been considered in the past is the considerable electrical activity associated with the storm that generates the tornado [Vonnegut 1960, Whiting 1964, and Davies- Jones 1975]. The driving source of the tornado is a toroidal electric current field.
Air conductivity increases as the air pressure falls. The inflow (or outflow) of current, in air, to the base of the tornado core is almost at right angles to the earth's magnetic field and the interaction of the two provides a tangential J x B force. This is the same force that drives electric motors and would imply that the tornado is a "natural" electric motor. This force is composed of an electric current density: J and a magnetic field: B.
One difference between the toroidal vorticity field (the theory currently accepted by meteorologists) and the toroidal current field (the theory being proposed by the author: Wallace Luchuk) is that at the ground/air interface, the vorticity lines cannot penetrate the earth, while the electric current lines can.
One other difference that must be mentioned here is that the subsonic aerodynamic field adjusts itself to meteorological perturbations at the speed of sound, while the electric field adjusts itself to electrical field perturbations at close to the speed of light.
Satellite data has revealed that lightning in the vicinity of a tornado mysteriously ceases when the tornado is being spawned. If the toroidal current stays in the air a nascent tornado may appear, because it does not require much power to sustain a tornado in air. However when the tornado touches down, the tornado becomes very powerful. Air conductivity is about 6 x 10-14 mhos/meter (Nat. Acad. Press. 1986) while the ground conductivity is about 10 x 10-3 mhos/meter (Weeks. 1964).
(However there is always a snag isn’t there:)
If the proposed theory is true, it should be possible to detect and determine the tornado strength by measuring ground currents over an area surrounding the tornado. The ground current around a tornado should be in a radial or a partially radial pattern. The center of this radial pattern should locate the tornado and the direction of the current (inward or outward) should reveal the direction of rotation of the tornado.
(If they could be predicted in the time required for that experiment, they wouldn’t be the problem they are.)
One other implication of the theory is that if the earth’s magnetic field is a requirement, then there should be no tornadoes (or waterspouts) along the earth's magnetic equator, because the earth's magnetic field (being a dipole) would be horizontal there. Also if the tornado strength is a function of magnetic field strength and current density, there should be a correlation between areas with the strongest magnetic field strengths and ground conductivities and the strongest tornadoes. (The full theory along with diagrammes and equations can be found at www.cafes.net/wallytul/ )
Most common in Spring and Summer, they can happen any time of the year.
Most common in the afternoon and evening, they can happen any time of day.
Although more famous in the US “Mid West” they are most common in the UK but are a world wide phenomenon. The United States reports over 1000 annually over a wide variety of geographical features from Alaska to Texas.
Pay attention to weather clues around you.
The wind may die down and the air may become very still.
Dark, often greenish sky. Thunder is associated with “greenish” clouds (a phenomenon caused by hail).
Wall cloud, an isolated lowering of the base of a thunderstorm is particularly suspect if it is rotating.
Large hail-stones.
Funnel cloud. A visible rotating extension of the cloud base is a sign that a tornado may develop.
Cloud of debris. An approaching cloud of debris can mark the location of a tornado even if a funnel is not visible.
Roaring noise . The high winds of a tornado can roar like a train.
Tornadoes may occur near the trailing edge of a thunderstorm and be quite visible. It is not uncommon to see clear, sunlit skies behind a tornado. They may also be embedded in rain and not visible at all.
Waterspouts are weak tornadoes that form over water. They are common in winter and can move inland being reclassified as tornadoes. Hurricanes also generate tornadoes when they come ashore. The position they develop is interesting -to the right and ahead of the storm. In 1967, Hurricane Beulah produced 148 tornadoes as it made landfall in south Texas.
Although tornadoes form along the dry fronts of storms they do not necessarily travel in straight lines and you can’t always tell the direction the storm is coming from. If caught out driving during one remember the road you are on may curve into the storm. Also there may be more than one, hidden by heavy rain and wind-blown debris. Until they pick up debris they may be almost transparent -although, on the Great Plains and other semi arid regions they usually occur without rain.
Tornado winds can toss large objects such as vehicles, hundreds of feet. (Mobile homes are particularly vulnerable.) Dangerous flying debris can be blown under highway overpasses and bridges, or weaker overpasses and bridges could be destroyed. You will be safer lying flat in a low-lying area where wind and debris will blow above you. Tornadoes come from severe thunderstorms, which can produce a lot of rain. If you see quickly rising water or flood water coming towards you, move to another spot. Avoid places with wide-span roofs, such as auditoriums, cafeterias, large hallways, or shopping malls.
If you are in a high-rise building, pick a place in a hallway in the centre of the building, they are often the most reinforced part of structure. If you live in a mobile home make sure it has a designated shelter. Mobile homes are much more vulnerable to strong winds than bricks and mortar. Every building has different “safe” places. If you live in a danger zone it might be an idea to know where they are and how to get there in an emergency. The same is true for fires and other emergencies. Of course a safe place in a tornado is not the same as a safe place in a fire.
The Fujita - Pearson Tornado Scale:
F-0: 40-72 mph, chimney damage, tree branches broken.
F-1: 73-112 mph, mobile homes pushed off foundation or overturned.
F-2: 113-157 mph, considerable damage, mobile homes demolished, trees uprooted.
F-3: 158-205 mph, roofs and walls torn down, trains overturned, cars thrown.
F-4: 207-260 mph, well-constructed walls levelled.
F-5: 261-318 mph, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters.
Advance planning and quick response are the keys to surviving tornadoes. You want, for example, to be able to get to an uncluttered spot where flying glass is not going to be a problem. Can’t get under the bed for old socks? Why not have that clean out now? Seriously though, modern homes are designed with acres of windows, so tipping a sofa up and sliding underneath may save you. Keep an hold of it too as it might get blown away from you. (Go with it right to the edge of the runway.)
Less than 2% of all tornadoes are powerful enough to destroy a building. If one is imminent, strong close walls are likely to provide the best protection get to the lowest level and away from windows, preferably in a small room. Closer walls will help provide more support to the roof and the more walls between you and the outside the better. That violent 2% account for some 70% of fatalities as they generate large hail stones and hurl debris. Major outbreaks occur with persistent storm systems. In the US, the government works with radio and television to give as much warning as possible (their National Oceanic & Atmospheric Administration even supplying a special Weather Radio.)
Foresite is a great thing. And if you are in the wrong place at the wrong time it is good to be prepared. The fact is that the majority of these events come out of the blue and will strike you when there is almost nothing that you can do about it.
You can't live your life thinking "today there may be an earthquake, storm or flood." no more than you can be prepaed not to get caught in a riot or have a burglar break into your home. You just do your best with the daily priorities of life.
Emergency kits are a good idea for all those special little occasions you might wish to experience next time from a greater distance:
Flashlight and extra batteries.
Portable, battery-operated radio and extra batteries.
First aid kit and manual.
Emergency food and water.
Can opener.
Essential medicines.
Cash and credit cards.
Sturdy shoes and/or boots and other clothing needs.
Spades, pry-bars and hammers along with various other tools and fixings. I’d put a coil of rope in there too but it wouldn’t be long enough by about 2 feet. How does that work|?
Knowing what weather could happen helps.
After an emergency is generally considered a good time to have had some emergency training by. If you still have one:
Return home only when authorities say it is safe.
Use the telephone only for emergency calls.
Clean up spilled medicines, bleaches, or petrol or other flammable liquids immediately.
Leave the buildings if you smell gas or chemical fumes.
Remember to help your neighbours who may require special assistance. (Library books and etc.)
If the electric goes of get your freezers contents to someone who has not been affected.
Take pictures of the damage (believe it or not, you will forget the best bits.) (It will bore your friends and family after their initial interest but you never know how interested the insurance people will be.) Photograph house and contents and don’t trust anyone that is called an insurance assessor. They are criminals.
If you smell gas or hear a blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main if you can and call the emergency services from a safe place. (If you turn off the gas for any reason, it must be turned back on by a professional. Don’t forget the special key for that in the emergency tool kit.)
Look for electrical system damage. If you see sparks or broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice.
Check for sewage and water lines damage. If you suspect sewage lines are damaged, avoid using toilets until they’ve been checked. If water pipes are damaged, contact the water company and avoid using water from the tap. You can obtain safe water by melting ice cubes.
Don’t get caught out in a storm, check local building codes and stuff like that for any work you are going to have done. And to rectify potential hazards that you are already saddled with. I bet you don’t know how to unravel who is responsible for what since the utilities were privatised do you?
Have fun.
Just a little codicil:
http://www.astrogeo.va.it/immagini/cielo/giudici.htm
I came across the following theory in Google groups. I have tried to contact the author but to no avail. Here is an edited piece of the theory that appears on his site. My words are in brackets = ().
There are a number of good references (Snow 1984, and Davies-Jones 1995) that describe the meteorology leading up to the development of the tornado but....a void in explanations for the fully developed tornado.
The tornado, in essence, is a very strong vortex with one end attached to the ground and the other end extending upward to a varying or undefined height. This configuration suggests to the aerodynamicist that there are vortex lines concentrated in the core of the tornado, that are splayed out radially in all directions on the ground. The vortex lines are diffused upward into the clouds only to turn downward and connect up with the vortex lines on the ground at some remote distance from the tornado. The whole vortex field appears to be toroidal in shape with one end flattened by the ground. This picture is based on the aerodynamic theory that vortex lines must close on themselves and cannot be unconnected.
The generation of a strong vortex requires strong velocity gradients and most strong vortices are usually created by the interaction between an established fluid flow and a solid surface. On a wing, for example, there is an array of vortex lines of one polarity generated by the boundary layer on the upper surface and another array of opposite polarity generated by the boundary layer on the lower surface.
(On an airplane’s wing the two different strengths of vortex lines combine to give the plane lift and leave a rotating eddy in its wake. The lift and the eddy are not self generating; the wind is totally dependent on the engine or some other outside source.)
Somewhere along the closed loop of vortex lines of the tornado there is an energy source. (Contemporary theory is in error because with) normal aerodynamic principles there cannot be strong velocity gradients in free air, because there is no mechanism to support them.
Energy density decreases with distance from the source. This is decreed by the second law of thermodynamics. Since the most energetic location of the rotational kinetic energy of the tornado is at its base, this is the location of the source of this energy.
(The forces driving and holding together a tornado must be equal and opposite or it would just fly apart.)
If we know the velocity profile, we can calculate the shear or retarding force. In the air, the shear force is very weak because the air viscosity is very small. Calculations show that the power for a tornado in air with a simple velocity profile with a maximum velocity of 90 meters/sec (295 ft/sec) and a radius of 30.5 meters (100 ft) and a height of 305 meters (1000 ft) is of the order of 1 horsepower.
However, calculations of the drag horsepower of a turbulent boundary layer of the same velocity profile (as described above) when the tornado is on the ground, yields tens of thousands of horsepower.
What is the driving force at the air/ground interface? One element of the tornado that has been considered in the past is the considerable electrical activity associated with the storm that generates the tornado [Vonnegut 1960, Whiting 1964, and Davies- Jones 1975]. The driving source of the tornado is a toroidal electric current field.
Air conductivity increases as the air pressure falls. The inflow (or outflow) of current, in air, to the base of the tornado core is almost at right angles to the earth's magnetic field and the interaction of the two provides a tangential J x B force. This is the same force that drives electric motors and would imply that the tornado is a "natural" electric motor. This force is composed of an electric current density: J and a magnetic field: B.
One difference between the toroidal vorticity field (the theory currently accepted by meteorologists) and the toroidal current field (the theory being proposed by the author: Wallace Luchuk) is that at the ground/air interface, the vorticity lines cannot penetrate the earth, while the electric current lines can.
One other difference that must be mentioned here is that the subsonic aerodynamic field adjusts itself to meteorological perturbations at the speed of sound, while the electric field adjusts itself to electrical field perturbations at close to the speed of light.
Satellite data has revealed that lightning in the vicinity of a tornado mysteriously ceases when the tornado is being spawned. If the toroidal current stays in the air a nascent tornado may appear, because it does not require much power to sustain a tornado in air. However when the tornado touches down, the tornado becomes very powerful. Air conductivity is about 6 x 10-14 mhos/meter (Nat. Acad. Press. 1986) while the ground conductivity is about 10 x 10-3 mhos/meter (Weeks. 1964).
(However there is always a snag isn’t there:)
If the proposed theory is true, it should be possible to detect and determine the tornado strength by measuring ground currents over an area surrounding the tornado. The ground current around a tornado should be in a radial or a partially radial pattern. The center of this radial pattern should locate the tornado and the direction of the current (inward or outward) should reveal the direction of rotation of the tornado.
(If they could be predicted in the time required for that experiment, they wouldn’t be the problem they are.)
One other implication of the theory is that if the earth’s magnetic field is a requirement, then there should be no tornadoes (or waterspouts) along the earth's magnetic equator, because the earth's magnetic field (being a dipole) would be horizontal there. Also if the tornado strength is a function of magnetic field strength and current density, there should be a correlation between areas with the strongest magnetic field strengths and ground conductivities and the strongest tornadoes. (The full theory along with diagrammes and equations can be found at www.cafes.net/wallytul/ )
