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Chapter 10: Thunderstorms and Tornadoes
Answers to the Chapter Review
1.
Not necessarily.
2.
Tornadoes are the smallest (1/4 km in diameter) and most short-lived of the three
phenomena, and produce the strongest winds on Earth. Midlatitude cyclones are the
largest of the three (1600 km or more in diameter) and have the least violent winds.
Averaging 600 km across, hurricanes are much larger and longer-lived than tornadoes,
but are smaller than midlatitude cyclones. To be classified as a hurricane, wind speeds
must be at least 115 km per hour.
3.
Flash floods.
4.
The primary requirement for thunderstorm development is warm, moist, and unstable air.
5.
In the tropics, where the general convergence associated with the ITCZ and warm, moist,
unstable air combine to make conditions right for thunderstorm development.
In the
United States, the Gulf Coast and Florida experience the greatest amount of thunderstorm
activity because this area is closest to the source region of mT masses.
6.
Thunderstorms are most frequent in midafternoon during the summer because that is
when surface heating (a factor that adds to the air's instability) is most intense.
7.
Entrainment intensifies thunderstorm downdrafts because the air added during
entrainment is cool and therefore heavy. The added air is also dry, which may cause
falling precipitation to evaporate (a cooling process), thereby cooling the air within the
downdraft.
8.
In a severe thunderstorm, downdrafts spread out along the ground forcing warm, moist
surface air into the thunderstorm, thus maintaining updrafts. A gust front is an outflow
boundary between the cool air of a downdraft and warmer surrounding air.
9.
Squall lines sometimes form along a dry line when cT air from the southwestern states is
pulled into the warm sector of a midlatitude cyclone just ahead of the cold front. Squall
lines form when the denser cT air acts to forcefully displace the less dense mT air
upward.
10.
The electrical discharge of lightning heats the air and causes it to expand explosively.
The expansion produces the sound waves that we hear as thunder.
11.
80% of all lightning strikes between parts of a cloud or from cloud to cloud. It is really no
different than cloud-ground lightning, but since our view of it is obscured by the cloud,
when we see the whole cloud light up from the flash, we often call it sheet lightning.
12.
Heat lightning (lightning seen without any accompanying thunder) is simply ordinary
lightning that occurs more than 20 km away from the observer. At this distance, the
sound energy dissipates before reaching the observer.
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13.
Tornadoes have exceedingly strong winds because the pressure gradient is very great (as
much as 100 mb from the outer edge of the storm to its center).
14.
Tornadoes are produced along the cold front of a midlatitude cyclone in association with
severe thunderstorms.
15.
Although tornadoes have been known to occur in every month of the year, spring and
early summer (April–June) is the period of greatest tornado activity. It is in spring when
the air masses associated with midlatitude cyclones have the greatest temperature
contrasts. The greater the contrast, the more intense the storm. The shifting of the region
of greatest tornado frequency is the result of the increasing penetration of warm, moist
(mT) air farther inland while cool dry (cP) air still surges in from the north.
16.
A tornado watch alerts the public to the fact that the conditions are right for the formation
of tornadoes, while a tornado warning is issued when a tornado has actually been sighted
in an area or is indicated by radar.
17.
Higher at point B; Doppler effect.
18.
In addition to performing the same tasks as conventional radar, Doppler radar can detect
motion within the storm directly. Because of this, Doppler radar can detect severe
weather earlier and more effectively, and can, therefore, provide greater warning time for
the public.
Answers to the Chapter Problems
1.
Three miles
2.
About 88 %
3.
Texas, Oklahoma, Kansas, Florida .The central United States generates more tornadoes
than any other part of the world.
Figure 10-29 is most useful for depicting the tornado hazard in the United States.
Figure 10-21 has the advantage of not being confined by state borders. This gives it an
advantage over both maps because it shows a more realistic distribution of average
annual tornado incidence.
4.
The total number of tornadoes reported in the 1990s was much more than those reported
in the 1950s simply because since that time, more tornadoes are being reported.
5.
Only half the tornado deaths occurred in the 1990s than during the 1950s due to better
watch and warning systems and improved forecasts.
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