- Introduction



Stability - I

Stability - II





                                                  - an overview


A tornado is a type of intense rotary storm. According to the Glossary of Meteorology, a tornado is-   "a violently rotating column of air, in contact with the ground, either pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud."

The image “http://www.cimms.ou.edu/~doswell/a_tornado/Laverne.JPG” cannot be displayed, because it contains errors.  A funnel cloud, which
 is a type of
 condensation cloud, is
 funnel-shaped in
 structure and extends
 down from a cumuliform
 cloud by a rotating
 column of air towards
 the ground. It may or
 may not touch the
 ground. If it touches
 the ground it is called
                       rotating column of air
http://www.cimms.ou.edu             is a ‘vortex’.
This diagram shows a funnel 
cloud that does not touch
the ground.

Tornadoes are much stronger than dust devils, hurricanes or mid-latitude cyclonic storms. Practically it is the most violent of all the vortex storms we see in nature. Storms are marked by disturbance and strong wind in the atmosphere. When the storm accompanies thunder and lightning, it is called thunderstorm.

In a tornado, a strong up drift of air exists and  the pressure remains very low at the core. So, if it is strong enough, it can suck in (up) almost everything that comes into it’s path. The tornado is not always visible but the circulation of debris around the funnel makes it visible.

                                         A funnel cloud that is
                                         almost invisible.                

In a small scale, tornado is the most violent atmospheric phenomenon. The vortex of a tornado is only a few hundred meters wide on an average. The wind speed inside a tornado normally ranges from 40 mph to as high as 300 mph. Speeds higher than this are actually rare. Depending on its speed, tornadoes are  rated using F-scale.

Tornadoes may rotate both cyclonically or anti-cyclonically, but cyclonic rotation is most common. It can be mentioned here that if a wind swirl is counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere, it is called cyclonic.  But contrary to a common belief, coriolis force or earth’s rotation has no role in the direction of rotation of  a tornado.


Tapas Bhattacharya
Web-project :  Phys-645, Fall-2007, UAF. 
Animation for 'Home'  - taken from

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