What Is A Tornado, How Is It Formed And What Are Its Main Characteristics?
Whether you live in an area frequently experiencing tornado activity, or halfway around the world and has never seen a tornado in your life, we all have a clear idea what a tornado looks like and how destructive it can be.
Not only are they famous (or rather infamous) for their dramatic appearance and destructive power, but they have also been made more famous and "glorified" by Hollywood in more than a few of their "disaster movies".
(I must admit, from viewing real footage of actual tornadoes and the destruction they leave in their path, this is one instance where Hollywood don't need to exaggerate for dramatic effect. They can really be as monstrous and destructive as they are being portrayed.)
But when it comes to down to the nuts & bolts, what is a tornado really?
A tornado is a funnel-shaped fast rotating column of air, which forms at the base of a cumulonimbus cloud and reach all the way to the ground. It is characterized by a low-pressure center with winds rotating around it at high velocities.
Obviously this a very a short & simplistic summary of what exactly a tornado is. Through the course of this article we will take a closer look at how they are formed and what makes them work.
Where Do Tornadoes Occur?
Tornadoes can occur all across the world, especially in the presence of thunderstorms (which create the ideal conditions for the formation of tornadoes).
The highest concentration of tornadoes, however, can be found in North America, especially in Florida and an area called Tornado Alley.
("Tornado Alley" is a very broad term coined by the media, and the region can be found in the Great Plains of the Central United States. As this is not an official scientific term, meteorologists have not clearly defined the area, but the highest concentration of tornadoes can be found in this area.)
Outside of North America, two of the highest concentrations of tornadoes can be found in Argentina and Bangladesh.
There is a reason why tornadoes can be found in bigger numbers in specific areas. The best way to understand where and why tornadoes occur, is to have a look at how they are formed in the first place.
How A Tornado Is Formed
The majority of tornadoes are formed in violent thunderstorms, especially in what is called supercells. (The most intense and violent form of a thunderstorm.)
The conditions in a supercell need to be ideal in order for a tornado to develop. Which means a tornado needs a supercell to develop, but not all supercells are able to produce tornadoes.
The specific conditions needed for the formation of a tornado is actually a specific combination of wind movements. A combination of both downdrafts (sinking air) and updrafts (rising air) is required for tornado development.
The illustration above shows you the complex interaction between cloud formation, wind speeds and direction, as well as altitude that takes place during the formation of a tornado in a supercell. In the following paragraphs I will break it down and explain it in a more simplistic and digestible form.
Warm moist air near the surface of the ground starts to rise, creating a low-pressure system. As it continues to rise, it is hit by winds with different speeds and blowing in different directions. It is these winds that allows it to start spinning.
This alone is not enough though. Air rotation near the ground is essential for the process to be completed. As the cold air from the upper atmosphere starts to descend (creating downdrafts), it comes in contact with the updraft, putting pressure on the rising air.
This pressure and friction caused by the downdraft forces the space of the rotating updraft to be condensed. This increases the wind speed within the rotating column of air.
The wind speed is further increased by the rotation towards the axis of the low-pressure system. (Remember, air always flows from an area of high to an area of low pressure).
This acceleration in wind speed towards the axis is called conservation of angular momentum (or spin). Think of a figure skater starting to spin on ice. As he/she starts pulling their arms in, they start rotating faster and faster (to conserve angular movement). This is exactly how the wind speed increase around the axis of the rotating column of air.
The supercell starts acting as a giant vacuum cleaner as the rotating column of air strengthens and sucks more air away from the surface of the ground.
If the combination of "downdraft pressure" and "updraft suction" is strong enough, the column of rotating air will reach the ground, which will complete the formation of the tornado.
As it touches the ground, debris and dirt sucked up by the tornado, will form the visible funnel formation we all know so well. (Tornadoes can actually be invisible, but more on that in the next section).
Now that you have a better understanding of how tornadoes are formed, it is easier to see why certain areas are so prone to the development of tornadoes.
And this is why the area known as Tornado Alley is such an ideal breeding ground for tornadoes. As the cold dry air from Canada moves south, it collides with the warm moist air from the Golf Of Mexico over this region...
The Great Plains in this area further contributes to the creation of this ideal environment, as the relatively flat landscape allow these two air masses to collide and form supercells. The resulting thunderstorms and unstable atmosphere is the perfect recipe for tornadoes to develop and flourish.
Characteristics Of A Tornado
Many of you already know, and I already mentioned earlier in the article, the very familiar shape of a tornado.
The funnel-shaped fast rotating column of air, with the narrow part touching the ground and then broadening out as it reaches up to the base of the (normally cumulonimbus) storm cloud, is the very recognisable image of a tornado as we know them.
It should be noted however that not all tornadoes conform to this almost stereotypical image we are so familiar with. There are also a few characteristics of tornadoes that are not that well-known, but still very relevant and important to those potentially affected. Let's take a look at a few of the most important ones:
1) Tornadoes Are Not Always Visible.
Since a tornado is essentially a fast rotating column of wind, they are not naturally visible by themselves. What makes them visible is the objects on the ground they cross and pick up.
I already mentioned dust and debris are some of the common objects that are sucked up and give them their familiar grey-brown colour. Other objects include vegetation and even water. In the latter case. (As mentioned earlier, when a tornado originates over water, it is referred to as water-sprout.)
A big danger and worry for meteorologists are when a tornado is not visible, or its visibility is masked by different factors. In a heavily wooded area with large trees, it is very difficult to spot an approaching tornado. The same applies when a tornado hasn't
Two other factors that can completely mask a tornado is heavy rain and the cover of darkness. When a tornado occurs during a heavy rainfall, the rain-wrapped funnel can be completely invisible until it is too late.
Obviously, if a tornado occurs at night, you may literally be unaware of it until it is right upon you. Although it makes a loud noise many people have compared to freight trains or airplanes taking off, even that sound may be mask if it occurs during a heavy thunderstorm.
These are one of many reasons early warning systems should be in place in areas often affected by tornadoes, and why people should always heed these warnings. (Luckily the accuracy of early warning systems have been greatly improved over the few decades.)
2) The Unpredicted Path Of A Tornado
People, even experienced observers, still look at an approaching tornado and the path it is following, to make a judgement call to flee/take shelter or stay putt. This is a terrible mistake.
One of the most dangerous aspects of a tornado, is the unpredictability of its path or direction. There is a common perception that a tornado follows the path of the storm system it is travelling in, or that the majority of tornadoes moves from southwest to northeast.
Although there is some truth in these perceptions, within in these larger movements tornadoes can veer off-course or completely change direction without any warning. (Some have even been known to stop and double back on their path.)
Apart from the unpredictable path an established tornado follows, they also have the ability to suddenly appear from literally any direction. Observers have reported tornadoes appearing out of nowhere.
In this case, ideal conditions for the creation of a tornado have been building up, invisible to most observers. Once these conditions have intensified enough, a tornado can literally form and seemingly "appear out of nowhere".
3) Speed And Size Of A Tornado
Tornadoes literally come in all shapes and sizes. (And don't forget about colour, depending on the surface it covers and types of debris it picks up.)
In general, the average tornado is about 200 meters (660 feet) wide, with wind speeds of about 50 miles (80 kilometers) per hour. As far as distance goes, they very seldom travel further than 10 kilometers (6 miles).
These are averages however. Some tornadoes are so small and weak, they are almost unnoticeable. On the other side of the spectrum you get tornadoes so big and destructive that they have the capability to destroy entire towns.
The most destructive ones can reach wind speeds of up to 300 miles (480 kilometers) per hour, and be more than 3 kilometers (2 miles) in diameter.
An example of an extreme tornado that makes your "average tornado" look like a little breeze, is the Tri-State tornado of 1925, mentioned earlier in this post. It travelled continuously through parts of Missouri, Illinois and Indiana for a distance of 362 kilometers (219 miles).
4) Funnel Clouds Creating False Assumptions About Tornadoes
Funnel clouds are a clear indication of the presence of a tornado. Many observers mistakenly use the size of the funnel cloud to try and determine its strength and size.
This is another easy mistake to make, as the funnel cloud is very often not an accurate indicator of size and strength.
In many cases, the true size of a hurricane is much larger than the funnel cloud would suggest. In recent history, a tornado near Dodge City in Kansas, was observed with the actual width of the tornado being 3 times larger than the funnel cloud.
Similarly, the size of a tornado is not a indicator of its strength. In fact, a very narrow tornado only a few dozen feet wide, can be much stronger and more destructive than one more than a mile wide.
The best way to measure the true impact of a tornado is by using proven standardized scales.
The strength of a tornado is normally measured by the Fujita scale. The tornado strength is categorized from EF0 to EF5. (With EF0 indicating light damage to vegetation and no structural damage, and EF5 indicating the strongest form of a tornado which have the ability to rip buildings off their foundation and cause major structural damage to skyscrapers.)
You now should have a much better understanding of how tornadoes are formed, what makes them work, as well as their most important characteristics.
In the process, some misconceptions, dangers and myths were highlighted. Hopefully this will also help you, especially if you live in an area affected by tornadoes but are not familiar with them, to better understand their behaviour and be a little more informed and prepared.
Feel free to leave me any comments, questions or suggestions, and I will get back to you as soon as possible.
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Until next time, keep your eye on the weather!