Atmospheric conditions typical during tornado formation
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A tornado begins in a severe thunderstorm called a
supercell. Scientists aren't exactly sure why, but air coming into the
storm begins to swirl and forms a funnel. The air inside the funnel spins
so fast it pulls in more air--and objects! The funnel is kind of like a
big vacuum cleaner.
The air pressure is very low inside the funnel, just like pressure is low
inside the eye of a
hurricane. Only in a tornado, the pressure is a lot lower--lower than any
other place on earth.
Tornadoes can form when the atmosphere is unstable. One other
thing that's needed is a front, a place where warm moist
air meets cold dry air. This happens a lot in the Great Plains of the
United States which is why it's called Tornado Alley.
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Where else in the world do tornadoes frequently occur?
How a Tornado Forms
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Atmospheric conditions typical during tornado formation
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A tornado begins in a severe thunderstorm called a supercell. A supercell
can last longer than a regular thunderstorm. The same property that keeps
the storm going also produces most tornadoes. The wind coming into the
storm starts to swirl and forms a funnel. The air in the funnel spins
faster and faster and creates a very low pressure area which sucks more
air (and possibly objects) into it.
The severe thunderstorms which produce tornadoes form where cold dry polar
air meets warm moist tropical air. This is most common in a section of
the United States called Tornado Alley. Also, the
atmosphere needs to be very unstable.
Tornadoes can form any time during the year, but most form in May. But,
more severe ones form earlier because the most damge is caused in April.
The more north you go, the later the peak tornado season is. This is
because it takes longer to warm the northern parts of the plains so
tornadoes form later.
Most tornadoes spin cyclonically but a few spin
anticyclonically.
Because there are records of anticyclonic tornadoes, scientists don't
think that the Coriolis Effect causes the rotations.
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Where else in the world do tornadoes frequently occur?
How a Tornado Forms
|
Atmospheric conditions typical during tornado formation
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Most tornadoes form in a part of a supercell thunderstorm called a
mesocyclone. The mesocyclone draws energy into
the storm so it can last for hours. Scientists aren't sure why, but some
can create tornadoes. Mesocyclones can be detected by conventional radar as a hook echo (example--28K JPEG). In the
mesocyclone, air is drawn into the storm. Scientists believe a vertical
wind sheer (wind that changes direction with height) causes the tornado to
begin spinning. Most tornadoes spin cyclonically but a few spin
anticyclonically.
Most tornadoes in the United States form in a section of the Great Plains
know as Tornado
Alley. Strong fronts develop between cold polar air and warm
tropical air and when the atmosphere is unstable tornadoes can
form.
Tornadoes form throught the year but most occur in May. Though, the most
damage is usually caused in April which means that the more dangerous
tornadoes form then. The more north you go, the later the main tornado
season becomes. The atmosphere in the norther plains is cooler and more
stable earlier in the year; it takes longer for the sunlight to heat it
up.
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Where else in the world do tornadoes frequently occur?
Last modified prior to September, 2000 by the Windows Team
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