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Date Posted: Mon, 09/22/03 2:00am
Author: Weatherboy
Subject: Tornado spinning
In reply to: Ylva 's message, "Re: Survivors of the Storm -- HowR'Ya Doin' ??" on Sun, 09/21/03 7:55am

>Interesting and scary at the same time. How come
>tornados appear on the east coast only? And is there
>something like El Ninjo on the westcoast?
>
>Here by the sea where I live, they warn us on the
>radio if the wind blows 180 miles/hour or faster. (But
>it never spins 'round; what makes a tornado spin?)

Tornadoes are spawned from a complex weather system called a mesocyclone. This is a hugely bigly huge supercell thunderstorm that has it's own rotation, as the supercell becomes higher from anvil to base the speed of the downdrafts within the cell increases because the temperature gradient becomes more and more extreme. A wall cloud forms at the outflow boundary at the base of the rear of this mesocyclone, and if the vortex is right, a tornadoe will form from this dropping, spinning mass of downward flowing air. Because there are several pressure gradients within the spinning tornado, that spin is maintained around an innermost near vacuum. The faster the spin, the more sustainable the tornado is. Faster, bigger tornadoes get higher values on a danger rating system called the Fujita scale. This scale goes up to F5(throws houses around).
Tornadoes need a lot of heat and a fairly stable landmass platform to develope. If the temps are too low, you won't get enough cloud height to make a mesocyclone. Not enough humidity= no mesocyclone. That's why regions like OklahomaKansasIllinois make the best tornadoes. They sometimes will form over oceans if the ocean is warm and a cold front is crossing through a storm formation system.You won't see them on chilly islands... :) And there's the other ingrediant- a cold front has to be moving through a hot,humid low pressure system to build these things. Electricity plays some role, but they aren't really sure what that is, or if it's maybe only a side effect of the spinning- the mesocyclone acts as a giant magneto.
Whew. Sorry bout that. I nearly majored in agricultural meteorology. And now, so have you. Taking a semester of it this year, as a matter of fact, love the stuff.
Layterz
OnBWeatherBoy

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