Tornadoes: Causes, Classification, Occurrence, and Destructive Potential, 
Darrell M. Bell
Mrs. Felicia Curry
English IV
1/3/12
Tornadoes are also popularly called twisters or cyclones and are characterized by rapidly rotating columns of air hanging from cumulonimbus clouds. (1) They are generally observed as tube- or funnel-shaped clouds. At ground level they usually leave a path of destruction only about 50 m (170 ft) wide and travel an average of only about 8 to 24 km (5 to 15 mi). Contact with the ground is often of an intermittent nature lasting for a period of usually less than a couple of minutes in any particular area because the funnel tends to skip along.
Tornadoes generally exhibit a certain characteristic cycle of behavior between formation and final disappearance. The first sign of a tornado may be a strong whirlwind of dust from the ground surface, often in conjunction with the appearance of a short funnel growing from the storm cloud above it. The funnel then becomes more organized and descends further from the cloud, sometimes touching the ground. (The winds forming the funnel generally move counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, but exceptions are observed.) The funnel as a whole commonly moves forward slowly but can travel at speeds greater than 30 m (100 ft) per second. The tornado eventually becomes fragmented and dissipates.
Causes and Classification
Tornadoes are the result of great instability in the atmosphere and are often associated with severe thunderstorms. The full details of the formation of tornadoes are not known. The existence of a strong updraft, such as that generated by a severe thunderstorm, and the conservation of angular (rotational) momentum, however, are fundamental considerations. The falling of rain or hail probably drags air from aloft, and the resultant inrush of air tightens the rotational motion.
The tornado cyclone is an area of low pressure about 8 to 24 km (5 to 15 mi) in diameter, with wind speeds of approximately 240 km/h (150
Mrs. Felicia Curry
English IV
1/3/12
Tornadoes are also popularly called twisters or cyclones and are characterized by rapidly rotating columns of air hanging from cumulonimbus clouds. (1) They are generally observed as tube- or funnel-shaped clouds. At ground level they usually leave a path of destruction only about 50 m (170 ft) wide and travel an average of only about 8 to 24 km (5 to 15 mi). Contact with the ground is often of an intermittent nature lasting for a period of usually less than a couple of minutes in any particular area because the funnel tends to skip along.
Tornadoes generally exhibit a certain characteristic cycle of behavior between formation and final disappearance. The first sign of a tornado may be a strong whirlwind of dust from the ground surface, often in conjunction with the appearance of a short funnel growing from the storm cloud above it. The funnel then becomes more organized and descends further from the cloud, sometimes touching the ground. (The winds forming the funnel generally move counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, but exceptions are observed.) The funnel as a whole commonly moves forward slowly but can travel at speeds greater than 30 m (100 ft) per second. The tornado eventually becomes fragmented and dissipates.
Causes and Classification
Tornadoes are the result of great instability in the atmosphere and are often associated with severe thunderstorms. The full details of the formation of tornadoes are not known. The existence of a strong updraft, such as that generated by a severe thunderstorm, and the conservation of angular (rotational) momentum, however, are fundamental considerations. The falling of rain or hail probably drags air from aloft, and the resultant inrush of air tightens the rotational motion.
The tornado cyclone is an area of low pressure about 8 to 24 km (5 to 15 mi) in diameter, with wind speeds of approximately 240 km/h (150