T he r eader ’

 
 
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TEST B
 
 
Read the following selection about tornadoes and then answer the questions. 
The basic atmospheric physics that gives rise to tornadoes is well understood by now. 
Thunderstorms usually contain updrafts, large rising swells of warm, moist air. As the updrafts 
move, they rotate; if the rotation grows sufficiently intense, the storm can evolve into a tornado 
or funnel cloud (a tornado whose bottom does not touch the ground). Supercomputer simulations 
depict this process quite dramatically.
Most tornadoes form within an especially intense weather system known as a supercell. 
Supercell thunderstorms occur when the warm updraft punches through an overlying, stable layer 
and continues upward into a zone of cool, dry air. The resulting instabilities produce powerful 
vortex motions, the lifeblood of tornadoes (a pair of computer-generated images depicts the 
difference between supercell and non-supercell storms). Within the fiercest tornadoes, wind 
speeds can approach 300 miles per hour. Air rushing in to fill the low-pressure void left by the 
tornado creates additional fierce, potentially damaging winds. Staying out of danger is no easy 
task when a tornado is anywhere near.
One of the most dangerous aspects of tornadoes is their capriciousness. Sometimes an 
updraft gives rise to a tornado; sometimes it does not. Scientists are still hard pressed to predict 
exactly when and where a tornado will appear; that uncertainty makes it difficult to raise the 
alarm in time to save lives. 
[“Turn! Turn! Turn!” Internet address: http://www.sciam.com/explorations/0520963 explorations.html ] 
1. One main reason tornadoes are extremely dangerous is because they are 
A. stable. 
B. fickle. 
C. dramatic. 
2. Large rising swells of warm, moist air in a thunderstorm are identified as 
A. funnel clouds. 
B. supercells. 
C. updrafts. 

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62 Chapter 13, Reading in the Life and Natural Sciences 
3. As underlined in the passage, capriciousness means 
A. extravagance. 
B. unpredictability. 
C. wastefulness. 
4. It is stated that in present day “atmospheric physics” theory, how tornadoes are formed is 
A. well understood. 
B. not understood. 
C. not studied. 
5. To manifest into a tornado, winds must 
A. be damaging. 
B. rotate. 
C. become cool. 

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Chapter 13, Reading in the Life and Natural Sciences 63 
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