Tornadoes are at once a terrible and wonderful phenomenon. Terrible, because of the death and destruction they bring. Yet, viewed from a scientific lens, they are nothing short of a wonder of nature, in all its untamed glory.
A tornado is a complex phenomenon. Questions like “What is a tornado” and “How do tornadoes form” are only natural.
What exactly is a tornado?
A tornado is a narrow, rapidly rotating column of air that extends down to the ground from a thunderstorm. Tornadoes often occur along with thunderstorms and can be the most devastating and violent phenomena of all the atmospheric storms.
8 Astounding facts about tornadoes
1. About 1200 tornadoes are reported yearly in the US, which faces the most frequent and violent of tornadoes.
2. A region in the central United States is referred to by the media as the ‘tornado alley’ because of the relatively high tornado occurrence in the region.
3. Tornadoes have been reported on all continents except Antarctica. However, violent tornadoes are not limited to the ‘tornado alley’ but have been reported in all 50 states.
4. The deadliest tornado ever recorded occurred on April 26, 1989, in the capital of Bangladesh, Dhaka. The storm killed over 1300 people and injured about 12,000 people.
5. The deadliest tornado in the history of the US is the ‘Tri-State’ tornado which resulted in the death of 695 people and left 2,027 people injured.
6. They are most frequent in the continents in mid-latitudes (between 20° and 60° N and S).
7. This violently rotating column of air has a vertical axis and it touches the ground. Because wind is invisible, many times, it is difficult to see it. However, in most cases, it is visible as a funnel cloud made up of water vapour, dust, and debris.
8. The diameter of a tornado can range from 50 to 1000 meters and these windstorms generate very strong winds with high speeds. In the case of extremely strong tornadoes, wind speeds of up to 500 km/hr have been observed.
Its lifetime is from a few seconds to more than half an hour, in some rare cases. In the northern hemisphere, the direction of rotation of a tornado is anticlockwise. This is because of the clockwise rotation of the wind in the boundary layer.
Tornadoes occur mostly in the spring and summertime, in the mid-latitudes of both the Northern and Southern Hemispheres. They can cause destruction on a great level, collapsing structures and causing deaths because of the flying debris it carries. The most intriguing question, however, is “How do tornadoes form?”
Difference between tornadoes, cyclones, typhoons, and hurricanes
Many people use the four terms synonymously, but they are very different phenomena! The answer to the question “How do cyclones form” is very different from the answer to the question “How do tornadoes form.”
- Cyclones are violent tropical storms in which wind moves around in a circle around an area of low pressure. A cyclone can move at speeds more than 118 km/hr. Typhoons and hurricanes are types of cyclones.
- Typhoons are simply violent storms with strong winds capable of uprooting many trees. A Hurricane, on the other hand, is a very large, powerful, and destructive storm with a diameter ranging from 500 to 1000 miles. It can move at a speed ranging from 80-130 miles per hour.
- The three are very similar in nature and the difference in name arises because they occur in different locations. A tornado, however, is a different kind of storm. They form spontaneously, are the hardest weather event to predict, are short-lived
How do tornadoes form?
The question, “how do tornadoes form?” has intrigued scientists for a long time. The average tornado is harmless and causes only minor damage. However, the extreme ones have proven to be the most devastating weather events in history. A wild tornado can have a diameter of several miles and can reach 480 km/hr in speed. They can also last for hours. Meteorologists have spent decades trying to understand this phenomenon. To find out the answer to the question, “How do tornadoes form,” read ahead. To answer the question, “how do tornadoes form?”, we need to understand that a tornado is usually a result of a ‘supercell thunderstorm.’
What is a supercell thunderstorm and how it may result in a tornado?
Supercell storms are the rarest of thunderstorms. A supercell storm that results in a tornado is often called a tornadic supercell. It is also the most intense thunderstorm. A supercell storm contains the most important element required for the formation of a tornado – a spinning column of air at its centre. This column of air is called a vortex.
A tornadic supercell has three defining features
- A rotating updraft (called a mesocyclone) carries warm air. (An updraft is an upward wind current).
- It has two distinct downdrafts. One is the forward flank downdraft,
- and the other is the rear-flank downdraft.
The sun heats the ground which results in the air on the ground level becoming heated as well. As this air becomes hot, it starts to rise. However, it goes up, not all at once, together, but in the form of localized packets.
This results in the formation of cumulus clouds and slowly grow and become storm clouds. When this happens in an environment where wind speeds are higher at higher altitudes (and lower at lower altitudes), the updraft begins to rotate horizontally.
The rotation causes the storm to grow. In the process, it draws warm and moist air upwards and throws out cold, dry air towards the ground and so the vortex (the spinning column of air at the centre) in the middle will begin to tilt.
The constant upward current of warm wind causes the vortex to swell with water vapour while the downdrafts (cold, denser air that is moving downwards) inside the storm contain the rotation and make it more focused and concentrated, thus creating a spiralling funnel cloud at the centre. The cold downdrafts go against the funnel cloud’s upward spiral.
In a short period, the rotation becomes so dense and strong that it results in a narrow column of violently rotating air. When this column of air reaches the ground (due to the weight and pressure from the downdraft of cool air), a tornado is formed.
The tornado is usually visible because of the funnel-shaped condensation cloud which is formed because of reduced air pressure within the vortex. It carries along with it debris and dust, which also increases its visibility.
In time, the cool downdrafts will surround and cover the tornado, cutting off the supply of warm, rising air in the process. Since it can longer grow by collecting rotating warm air from the updrafts, it slowly begins to narrow, and eventually, the vortex disappears and the tornado dissipates. Now you know the answer to the question, “How do tornadoes form?”
The strength of a tornado is usually rated based on wind speed. However, measuring the wind speed inside a tornado is a nearly impossible task, due to the sheer strength of the wind and the fact that anyone even remotely near the tornado is unlikely to make out unscathed!
However, meteorologists have devised methods to estimate wind speeds and a tornado’s strength based on the damage it leaves in its wake. To this end, Dr Ted Fujita developed a scale of tornado damage intensity in 1971. It is also called the F scale. An enhanced scale is now in use, called the Enhanced Fujita scale or the EF scale. It has 5 ratings, E0 being the lowest and E5 being the highest. The wind speed corresponding to E0 is 65-85 miles/hour. The wind speed corresponding to E5 is over 200 hundred miles per hour.
Warning signs of a tornado
Although tornadoes have been observed around the world, they are most frequent in the United States. They are difficult to predict and there are very few signs to rely upon. The funnel-shaped cloud is the most obvious and easily seen characteristic of a tornado. A rotating cloud in the shape of a funnel is, therefore, a tornado warning. Sometimes, the flying debris will be visible. A supercell thunderstorm often brings huge hailstones and flash floods along with it.
A dark sky with a greenish tint can also indicate a tornado’s presence or its formation. The green colour is visible because of the sunlight reflecting off of hailstones. If a tornado is on the way, you can also hear a loud, persistent roaring sound similar to that of a freight train.
In areas where tornadoes occur periodically, especially in the US, paying attention to watches and warnings will help you protect yourself. The National Weather Service in the US shares watches and warnings about severe weather to keep people updated.
A tornado watch
A tornado watch indicates a possibility of a tornado. In the case of a tornado watch, it is better to remain alert for approaching storms. Keep an eye on the sky, as tornados can form spontaneously, and keep yourself further updated with the help[ of radio or television. Keep a safety kit consisting of flashlights, batteries, and prescription medicines handy. Also, keep dried or canned food along with water for sustenance and a battery-powered radio to keep yourself updated.
A tornado warning
A tornado warning means that either a tornado has been sighted or detected by weather radar. In case of a warning, take shelter immediately.
If you found the article, “How do tornadoes form?” interesting and engaging, visit our website Icy Tales for similar reads.
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