December 6, 2012

What is a Tornado?

Hi, I’m Emerald Robinson, and in this What Is video we’re going to talk about nature’s most violent storm: the tornado.

A tornado, or “twister,” is a storm made of a quickly rotating air column that stretches between the clouds and the earth.

Tornadoes usually form from a specific type of a thunderstorm called a “supercell.” Supercells are characterized by an updraft, a mass of warm air that rises from the Earth. Sometimes when winds high above the earth and winds close to the ground blow at different speeds and in different directions, they form a horizontal tube of rotating air. When this tube becomes tipped vertically by a supercell updraft, it becomes a “mesocyclone.”

As the supercell’s rain falls, the air around the mesocyclone cools, causing it to sink. When this cool downward moving air meets the warm air rising from the earth inside the spinning mesocyclone, the mesocyclone’s rotation speeds up and forms a swirling wall of clouds. When this wall touches the ground, bits of dirt and debris get caught in it, causing it to darken, and making the familiar funnel cloud that we associate with tornadoes.

A tornado’s lifespan can be anywhere from a few seconds to several hours.  Typical wind speeds are about one hundred miles per hour, but can be much, much faster.

Tornado intensity is rated on what’s called the Fujita, or “F” Scale. Where a tornado falls on the F Scale depends on two things: wind speed and amount of damage. A F1 tornado has a wind speed of about one hundred miles per hour, and may push cars along the ground or damage small homes; a F5 tornado may have wind speeds of over three hundred miles per hour and toss cars into the air or completely destroy houses.

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