What are Tornadoes?

  

With wind speeds of more than 300 mph (483 km/h), tornadoes are one of the most destructive natural forces on Earth.

Though scientists don't entirely understand how tornadoes form, they do have a good idea about the conditions that cause tornadoes to develop.

Twisters have touched down on all continents except Antarctica, but certain locations on the planet are more likely to experience tornadoes than others. Most tornadoes occur in the so-called Tornado Alley— the tornado-prone region of the United States, from Texas north into Kansas and the surrounding states of the Great Plains region.

This area often has the three ingredients necessary for tornadoes to form: a lot of warm, moist air close to the ground; atmospheric instability, a condition that promotes the vertical movement of air; and clashing air fronts that act to propel moist air upward.

In Tornado Alley, warm, moist, low-elevation wind from the Gulf of Mexico collides with cool, dry, higher-elevation wind coming over the Rocky Mountains. This unstable interaction causes lots of warm air to quickly rise and cool air to fall, which leads to the formation of a supercell, a type of thunderstorm with a long-lived, swirling updraft of air.

But not all supercells result in tornadoes.

Scientists believe that if the two opposing winds move at different speeds, the air in between them will rotate around a horizontal axis. If one end of the horizontal air column gets caught in the supercell's updraft, it will tilt vertically, forming a funnel cloud.

The continuous upward energy of the supercell elongates the funnel cloud, and causes its spin to tighten and speed up — similar to the way ice skaters spin faster when their arms are pulled close to their bodies.

Rain and hail from the thunderstorm push down on the tail end of the funnel cloud. When the bottom of the funnel cloud finally touches the ground, it becomes a tornado.

Source:http://www.livescience.com