What Are Tornadoes?

Tornado at Union City, Oklahoma Credit: NOAA Photo Library
Tornado at Union City, Oklahoma Credit: NOAA Photo Library

Also known as a twister, a tornado is a rotating column of air that can cause a tremendous amount of damage on the ground. Tornadoes can very in size from harmless dust devils to devastating twisters with wind speeds greater than 450 km/h.

A tornado looks like a swirling funnel of cloud that stretches from bottom of the clouds down to the ground. Depending on the power of the tornado, there might be a swirling cloud of debris down at the ground, where it’s tearing stuff up. Some tornadoes can look like thin white ropes that stretch from the sky down to the ground, and only destroy a thin patch of ground. Others can be very wide, as much as 4 km across, and leave a trail of destruction for hundreds of kilometers.

Tornadoes appear out of special thunderstorms known as supercells. They contain a region of organized rotation in the atmosphere a few kilometers across. Rainfall within the storm can drag down an area of this rotating atmosphere, to bring it closer to the ground. As it approaches the ground, conservation of momentum causes the wind speed to increase until it’s rotating quickly – this is when tornadoes cause the most damage. After a while the tornado’s source of warm air is choked off, and it dissipates.

When a tornado forms over water, it’s called a waterspout. These can be quite common in the Florida Keys and the northern Adriatic Sea. Most are harmless, like dust devils, but powerful waterspouts can be driven by thunderstorms and be quite dangerous.

Scientists have several scales for measuring the strength and speed of tornadoes. The most well known is the Fujita scale, which ranks tornadoes by the amount of damage they do. A F0 tornado damages trees, but that’s about it, while the most powerful F5 tornado can tear buildings off their foundations. Another scale is known as the TORRO scale, which ranges from T0 to T11. In the United States, 80% of tornadoes are F0, and only 1% are the more violent F4 or F5 twisters.

Although they can form anywhere in the world, tornadoes are mostly found in North America, in a region called Tornado Alley. The United States has the most tornadoes of any country in the world; 4 times as many as the entire continent of Europe. The country gets about 1,200 tornadoes a year.

We have written many articles about the tornado for Universe Today. Here’s an article about the biggest tornado, and here’s an article about how tornadoes are formed.

If you’d like more info on tornadoes, check out the National Oceanic & Atmospheric Administration (NOAA) Homepage. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

What was the Largest Tornado Ever Recorded?

Determining the biggest tornado can be a tricky endeavor. First of all, there is no direct absolute way to measure the width of a tornado. There is also the fact that a tornado can be ranked by many factors such as wind speed, level of destruction caused, drop in barometric pressure, or the length of travel path. Each of these play a role in determining the overall power of a tornado.

Another problem is that in many cases like in the Tornado Alley of the Midwestern United States, a storm system often produces multiple tornadoes. This can make it difficult to measure an individual tornado since it destructive force is combined with that of other tornadoes spawned by the same storm system.

While there is no definitive method there are some records that can give us a general idea about some of the greatest tornadoes in recorded history. The most powerful tornadoes tend to be in the United States, but there are others that can compete in other parts of the world.

The title of most devastating tornado goes to the Tri-State tornado of 1925. The twister traveled through three states and killed 698 people. This makes it the deadliest tornado in US history. It also had the longest track and duration traveling a distance of over 200 miles and lasting 3.5 hours. Even then this is just for the United States. The deadliest tornado in the world occurred in 1989 in Bangladesh taking over 1300 lives.

The closest measure to the Biggest tornado would be the widest damage path. This the with of the destruction a tornado causes not it actual size. This measure is a good estimate for the actual width of the tornado’s funnel cloud. The storm that holds the record occurred in Wilber-Halland Nebraska. The tornado had a destruction path with a width of over two miles. The tornado destroyed most of the buildings in the area.

As you can see you define the largest tornado by many factors. This just shows the various ways in which we as casual observers can measure and determine the power of a tornado. This provides an interesting insight into what makes a tornado so destructive and hard to predict. It is also important to remember once again that tornadoes rarely occur as singular phenomenons. A group of smaller tornadoes in an outbreak can be as effectively powerful and destructive as one major tornado.

If you enjoyed this article there are other pieces on Universe Today that you will loved to read. There is an interesting article about the winds on Venus. There is also another interesting article on Global warming.

You can also check out resources online. There is a great article about Tornadoes on National Oceanic and Atmospheric Administration website There is another interesting piece on tornadoes on the University Corporation for Atmospheric Research website.

You can also check out Astronomy Cast. Episode 151 talks about atmospheres.