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What Makes a Tornado Form?

Although the specifics of tornado formation remain a mystery, current meteorology understands them to be a byproduct of atmospheric interplays found within supercells. Supercell is the term granted to thunderstorms that exhibit a deep, persistently rotating updraft. This circulating updraft is known as a mesocyclone. On occasion, the supercell’s mesocyclone can develop into a violently rotating column, which spans the earth and the clouds. Typically, these columns are pendent from cumulonimbus clouds. On rare occasions, the rotating columns can form with the base of a nimbus cloud. These rotating columns of air form the condensation funnel of the tornado. Initially, they are not visible to the naked eye. Over time, as the condensation funnel collects debris and dust, it becomes much more evident.

How Do Mesocyclones Form Tornados?

While a mesocyclone does not guarantee a tornado’s generation, tornados only form from thunderstorms demonstrating this atmospheric occurrence. Mesocyclones are not stationary, two-dimensional constructs. They have the ability to move along the third dimension’s axis. As the mesocyclone falls beneath the cloud base, it becomes manipulated by both downdrafts and updrafts. In turn, this leads to tornado generation.

Tornado Formation: a Mesocyclone Manipulation

Moist, cool air from the storm’s downdraft region interplays with warm updraft region air. The convergence of these two drafts causes a rotating wall cloud to form. Rear flank downdrafts focus the base of the mesocyclone, leading to an air siphon phenomenon. Intensifying updrafts create low-pressure areas at ground level, pulling the focused mesocyclone down, and forming the condensation funnel. The cross sectional diameter of the air siphon phenomenon narrows as it nears the ground, leading to the twister’s familiar shape: a tiny tip near the ground expanding in diameter as it stretches toward the clouds.

 

Resources

“Tornadoes:violently Rotating Columns of Air.” Tornadoes:violently Rotating Columns of Air. N.p., n.d. Web. 22 Jan. 2013. <http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/svr/torn/home.rxml>.

“NOAA National Severe Storms Laboratory.” NSSL: Severe Weather 101: Tornadoes. N.p., n.d. Web. 22 Jan. 2013. <http://www.nssl.noaa.gov/education/svrwx101/tornadoes/>.

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