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Tornado Basics
Name: stephanie
Status: student
Grade: 9-12
Location: HI
Country: N/A
Date: 3/24/2005
Question:
What makes a tornado?
Replies:
Stephanie,
You may already find an answer to your question
on the Newton web site, but here is a brief explanation.
The initial root of a tornado is in wind shear,
where the wind speed high in the sky is much faster
in one location than it is somewhere nearby. This
is often caused by a jet stream tens of thousands
of feet up in the air, moving near an air mass that
has much less horizontal motion. Along the boundary
between the faster and slower moving air (such as a
squall line of thunderstorms or along a cold front)
the air begins to rotate tens of thousands of feet
up in the air. At the same time, a thunderstorm may
be forming in the same area. If the thunderstorm
becomes tall enough, it will grow into the area of
rotating air; the upward moving air inside the thunderstorm
can actually add to the speed of the rotation
through physical forces that can change vertical motions
into horizontal motions. Sometimes the entire
thunderstorm begins to rotate, but a much more compact
tornado vortex with very high rotation speed can form as
the rotation is carried all the way to the ground in the
form of a tornado funnel.
Dr. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory
The detailed answer is complicated, but the simple answer is that there is
the potential for a tornado arises when moist warm air (which is less
dense than cold dry air) is overrun by denser cold dry air. This is an
inversion because the less dense atmosphere is trapped under a "lid" of
much heavier air. If this inversion inverts and the temperature
differences are large enough, this re-adjustment in atmospheric densities
can occur explosively (a tornado). Keep in mind the real mechanism is much
more complicated, but the above is the simple process.
Vince Calder
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Update: June 2012
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