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Starting a Tornado
Name: Vince
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
I have a question related to the starting of
tornadoes that I cannot find an answer to. Maybe one of your
physics wizards can point me. First, I have researched tornadoes
pretty thoroughly, and how they start is not well understood in
detail. Unlike hurricanes in the northern hemisphere that are
always counter clockwise, sometimes tornadoes are clockwise. But
that is not my question. I have observed that if you take a basin
of water and time how long it takes to drain, you get a certain
drainage time. Now if you repeat the same "experiment" but this
time start the water rotating (in either direction), the basin
empties much faster. I cannot find any references using a
"Google" search that sheds light on why the rotational motion should
cause the basin to empty faster when it is spinning in a direction
perpendicular to the direction of flow. I fear it has something to
do with some incomprehensible solution to the Navier-Stokes
equation, but I would really like to have an explanation
Replies:
The reason the swirling sink empties is lots simpler. The swirl allows
air to go down the drain at the same time as water. Otherwise, air
trapped in the pipe interferes with flow. You get the same effect with
a pair of two-liter bottles (this works best with rigid glass). Fill
two bottles, swirl the fluid in one and invert both bottles. The
swirling fluid drains much faster because air enters the bottle easily.
As for the tornadoes, they form along a "dry line" where winds travel in
opposite direction on either side of the line. For more details,
contact the Severe Storms people at the US Weather bureau in Oklahoma.
R. Avakian
Cole,
Tornados form as a result of rotation of air within
a thunderstorm. That rotation must first be present
or a tornado can not form.
Strong vertical motions in the thunderstorm are
translated into horizontal rotational motions as the storm
intensifies. This begins up in the thunderstorm a ways
and begins to move downwards until a funnel cloud can
be seen protruding from the bottom of the cloud. When it
extends all the way down to the ground, it is called a tornado.
There are many funnel clouds that do not become full-blown
tornados.
It is common for tornados to form from thunderstorms that are
themselves rotating, a clear indication of strong rotational
forces at work with the thunderstorm which could result in a
tornado.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012
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