Tornadoes are one of those amazing, awesome acts of nature that simply leave you dumbfounded. How can nature be so powerful and destructive? And how can nature be so weird? There is nothing that would cause you to imagine a huge, swirling, 200 MPH beast of a storm that appears to have a mind of its own. You have to actually seen one with your own eyes to believe it. Yet in certain places, tornadoes appear with amazing regularity! That's why we see them in the news all the time.

In this edition of How Stuff Works we will take a look at tornadoes to learn about how they work!

Tornadoes and Your Bathtub
If you have ever seen a whirlpool form in your bathtub, sink or toilet when the water is draining, you have seen the fundamentals of a tornado at work. A drain's whirlpool, also known as a vortex, forms because of the downdraft that the drain creates in the body of water. The downward flow of the water into the drain begins to rotate, and as the rotation speeds up the vortex forms.

Why should the water start rotating? There are lots of explanations, but here is one way to think about it (and this way happens to apply to black holes as well as it does to drains). Imagine you are a particle in the water, and you are being pulled toward the suction that the drain creates. You are accelerating toward the point of suction. However, because of your previous momentum, the number of other particles getting sucked toward the point, etc., chances are that you are going to be off to one side of the point of suction when you arrive. That deflection sets you up on a spiraling path into the point of suction, like a moth spiraling in toward a light. Once the spiral has started in one direction, it tends to influence all of the other particles as they arrive. A very strong spiraling tendency is created. Eventually there is enough spiraling energy to create a vortex.

Given that you see vortexes all the time in tubs and sinks, it is obviously a fairly common phenomenon! In a tornado, the same sort of thing happens with air.

Tornadoes and Thunderstorms
With a tornado there is no drain. Instead, there is a thunderstorm cloud. A typical thunderstorm cloud can accumulate a huge amount of energy. If the conditions are right, this energy creates a huge updraft into the cloud. According to Encyclopedia Britannica:

"The energy to drive thunderstorms is supplied by a variety of sources, but most of it comes from the heat released when water vapour condenses to form cloud droplets. For every gram of water condensed, about 600 calories of heat are made available. When the water freezes in the upper parts of the cloud, another 80 calories of heat per gram of water are released. This energy goes to increase the temperature of the updraft and, in part, is converted to kinetic energy of upward and downward air movement. If the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours, which is equivalent to a 20-kiloton nuclear warhead. A large, severe thunderstorm might be 10 to 100 times more energetic."

The tornado snakes down out of a thundercloud as a huge, swirling rope of air. Wind speeds in the 200 to 300 MPH range are not uncommon. If the vortex touches ground, the speed of the whirling wind (as well as the updraft and the pressure differences) can cause tremendous damage. The tornado follows a path that is controlled by the path of its parent thundercloud, and it will often hop. The hops occur when the vortex is disturbed. You have probably seen that it is easy to disturb a vortex in the tub, but then it will reform. The same thing can happen to a tornado's vortex, causing it to form and collapse along its path.

A tornado snakes down out of the thundercloud and eventually
touches ground. When it does it picks up a swirling cloud of
dust and debris.

Tornado Ratings
Tornadoes are rated on what is called the Fujita scale, named for the inventor. On this scale there are seven levels:

Links

• Tornado FAQ - answers to many questions from USA Today
• Tornado Safety
• Turn! Turn! Turn! - nice intro from SciAm
• Tornadoes.... Nature's Most Violent Storms - NOAA site
• The Tornado Project Online
• Online Guide to Meteorology - Very cool video on Coriolis force ("rotating merry-go-round")
• Which way will my bathtub drain?
• Vortex and Vortex