Tornadoes – What They Are, How They Form, And Their Main Characteristics
Tornadoes – What They Are, How They Form, And Their Main Characteristics
Most readers will never see one, while others experience multiple events in a single year. Most people, though, know the term “tornado” very well. We examine this extreme meteorological phenomenon.
Not only are they famous (or rather infamous) for their dramatic appearance and destructive power, but they have also been further “glorified” by Hollywood in more than a few of its disaster movies.
Although they can occur anywhere across the world, the central plains of the United States experience an unusually high concentration of tornadoes every year in a region commonly known as Tornado Alley.
This article examines what exactly a tornado is and how it forms. It also looks at its characteristics and where it typically occurs.
What Is A Tornado?
Before we take a more in-depth look at how they form and their defining characteristics, we first need a clear and concise definition of what exactly a tornado is:
Tornado Definition
A tornado is defined as a funnel-shaped, fast-rotating column of air that forms at the base of a storm cloud and extends to the ground. It is characterized by a strong low-pressure center surrounded by rotating high-velocity winds. It typically forms in a supercell with strong up- and downdrafts.
How A Tornado Is Formed
The majority of tornadoes form in violent thunderstorms, especially in what are 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. This means a tornado needs a supercell to develop, but not all supercells can produce tornadoes.
The specific conditions needed for the formation of a tornado involve a combination of wind movements. Both downdrafts (sinking air) and updrafts (rising air) are required for tornado development.
Diagram illustrating the formation of a tornado. Click on the image for a larger view.
Warm, moist air near the surface of the ground starts to rise, creating an area of lower pressure. As it continues to rise, it is hit by winds moving at different speeds and in different directions. It is these winds that allow the air 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 force the rotating updraft into a narrower space. This increases the wind speed within the rotating column of air.
The wind speed is further increased as the rotating air moves closer to the axis of the low-pressure area. (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). This is similar to 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 momentum).
The supercell starts acting like 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 one has a better understanding of how tornadoes are formed, it is easier to understand 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 Gulf of Mexico over this region.
Here, the Great Plains further contribute to creating this ideal environment, as the relatively flat landscape allows these two air masses to collide and form supercells. The resulting thunderstorms and unstable atmosphere are the perfect recipe for tornadoes to develop.
Characteristics Of A Tornado
Many readers, especially from the Central United States, will already be very familiar with the characteristics of a tornado, especially its almost unmistakable shape.
A tornado is characterized by the very recognizable funnel-shaped, fast-rotating column of air, with its narrow base touching the ground and then broadening out as it reaches up to the base of a cumulonimbus cloud.
Not all tornadoes conform to this familiar image. There are also a few characteristics of tornadoes that are not that well-known but still very relevant and important to those potentially affected. We 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 air, it is not naturally visible by itself. What makes it visible is the objects on the ground it crosses and picks up.
I already mentioned that dust and debris are some of the common objects that are sucked up and give them their familiar grey-brown color. 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 a waterspout.)
A big danger and concern for meteorologists occurs when a tornado is not visible, or when objects or terrain mask its visibility. In a heavily wooded region with large trees, for example, it is tough to spot and identify an approaching tornado.
Two other factors that can completely mask a tornado are heavy rain and the cover of darkness. When a tornado occurs during heavy rainfall, the rain-wrapped funnel can be completely invisible until it is too late.
Also, 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 that many people have compared to freight trains or airplanes taking off, it may be masked if it occurs during a heavy thunderstorm.
These are some of the 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 has greatly improved over the last few decades.)
2) The Unpredictable Path Of A Tornado
People, even experienced observers, still look at an approaching tornado and the path it is following to make a judgment call to flee/take shelter or stay put. This is a terrible mistake.
One of the most dangerous aspects of a tornado is the unpredictability of the path it is following. There is a common perception that a tornado follows the path of the storm system it travels in, or that the majority of tornadoes move from southwest to northeast.
Although there is some truth in these perceptions, tornadoes can veer off-course or completely change direction within the larger storm system 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, tornadoes can also suddenly appear from almost 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 color, depending on the surface it covers and the types of debris it picks up.)
In general, the average tornado is about 200 meters (660 feet) wide. Wind speeds vary considerably depending on the tornado’s strength, while most tornadoes travel less than 10 kilometers (6 miles) before dissipating.
These are averages, however. Some tornadoes are so small and weak that they are almost unnoticeable. On the other side of the spectrum, some tornadoes are 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 traveled continuously through parts of Missouri, Illinois, and Indiana for a distance of approximately 362 kilometers (219 miles).
4) Funnel Clouds Creating False Assumptions About Tornadoes
Funnel clouds can be a clear indication of the presence of a tornado. Many observers mistakenly use the size of the funnel cloud to try to 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, a tornado’s true size 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 an 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 Enhanced Fujita Scale. Tornado strength is categorized from EF0 to EF5.
(EF0 indicates light damage to vegetation and little or no structural damage, while EF5 indicates the strongest form of a tornado, which has the ability to rip buildings off their foundations and cause major structural damage to skyscrapers.)
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 broad term coined by the media, and the region can be found in the Great Plains of the Central United States. It is not an official scientific term & meteorologists have not clearly defined the area, but the highest concentration of tornadoes occurs here.)
Outside of North America, two of the highest concentrations of tornadoes can be found in Argentina and Bangladesh.
Conclusion
This article provided a clear description of how tornadoes are formed, how they work, as well as their most important characteristics. In the process, some misconceptions, dangers, and myths were highlighted.
It also clearly highlighted the destructive nature and dangers of these meteorological phenomena and focused on their impact on the areas they encounter.
Until next time, keep your eye on the weather!