Tornadoes 101 | National Geographic
- They begin life as ghosts, gently coursing through a solitary existence, but slowly, their gentility turns to rage. They grow larger and larger, hurling and twisting, and desperately reaching down from the sky, and what began as an invisible shade is turned into a monster. (foreboding music)
Tornadoesare powerful spinning columns of air that stretch from the ground to the clouds. Most are relatively weak, but the few that grow into large events are extremely violent and cause immense destruction.
Tornadoesoccur on six of the seven continents. The country with the most
tornadoesbased on land size is the United Kingdom with an average of about 33
tornadoesreported each year. But the country with the greatest overall number of
tornadoesand the most intense is the United States with over 1,000 reported annually.
Tornadoes, no matter where they occur, are classified as either supercell
tornadoes, which form within supercells, the most powerful class of thunderstorms, or non-supercell
tornadoes, which are smaller and weaker and form within non-supercell storms. There are many theories surrounding the formation of
tornadoes. One key component they share is the presence of both high and low pressure air in a given space. Air particles from the area of high pressure move toward an area of low pressure, a movement that creates wind. Non-supercell
tornadoes, such as waterspouts and landspouts, begin when cool high-pressure air and warm low-pressure air are present, particularly...
near ground level. As air particles move horizontally from the high pressure area to the low pressure area, wind begins to pick up. Winds blowing at different speeds and in different directions and altitudes begin to blow cyclically. In the case of non-supercell
tornadoes, they turn into an upright spinning vortex. But to create supercell
tornadoes, the circumstances are slightly different. Violent supercell storms draw warm low-pressure air up to a higher altitude, leaving behind cool high-pressure air near the ground. Air particles attempting to bring the two levels of air pressure into balance creates wind that blows vertically. The wind increases and starts to blow in a cyclical fashion, creating a pipe of wind that rolls along the ground. In both cases, an upward current of wind called an updraft provides the final ingredient for creating a tornado. In a budding non-supercell tornado, an updraft stretches its vertical vortex until it reaches the clouds. To create a supercell tornado, an updraft lifts the rolling pipe of wind upward until it stands upright. Then it pulls condensation from the skies and into the spinning vortex. As soon as the vortices, supercell or non-supercell, connect the ground to the clouds, they are officially classified as
tornadoesare rated based on a system called the Enhanced Fujita Scale. The Enhanced Fujita, or EF, Scale, classifies
tornadoesfrom a rating of EF0 to EF5. The rating is based on a number of factors, such as the...
damage a tornado causes and the Doppler radar estimates of its wind speeds. EF0