1. In winter a cP air mass is very cold and dry, whereas
in summer it is cool and dry. In both instances, such an air mass is usually
associated with high pressure and clear skies. Its cool temperatures are often
welcome relief in summer.
2. A maritime tropical (mT) air mass is humid because it
originates over water and warm because it forms in tropical latitudes. Source
areas for mT air masses are the Gulf of Mexico, Caribbean Sea and adjacent
Atlantic Ocean, and the Pacific, west of
3. Warm, moist air (which is usually unstable) is
abruptly lifted along the steeply sloping cold front. Cumulonimbus clouds are
created, which may bring thunderstorms and occasionally other severe weather
such as hail or tornadoes. After the front passes, a sharp temperature drop is
experienced as the winds shift to the northwest.
4. An occluded front forms in the late stage of
development of a middle-latitude cyclone when the faster-moving cold front
catches up to the warm front and the warm (mT) air is forced aloft. The warm,
moisture-laden air is wedged out of the picture, and eventually the cyclone
dissipates. Once there is no warm, moist air being lifted, there is little
condensation and latent heat release.
5. As the warm front approaches, winds will blow from the
east or southeast and pressure will drop steadily. Cirrus clouds will be sighted
first, followed by cirrostratus, altostratus, and finally nimbostratus. Cloud
cover will progressively increase, from a few tenths coverage with cirrus, to
completely overcast with the coming of the nimbostratus. Gentle precipitation
will begin as the nimbostratus clouds move overhead. As the warm front passes,
temperatures will rise, precipitation will cease, and winds will shift to the
south or southwest. Further, the sky clears and the pressure stabilizes.
Later, with the approach of the cold front, cumulonimbus clouds
fill much of the sky and bring the likelihood of heavy precipitation and the
possibility of hail and tornado activity. The passage of the front is
accompanied by a drop in temperature, clearing skies, a wind shift to the
northwest, and rising pressure. Fair weather can probably be expected for the
next day or two.
6. As the low approaches, cool temperatures are the rule,
for the warm sector of the cyclone is to the south. The pressure drops and the
sky becomes increasingly overcast. Further, precipitation is to be expected,
and if it is winter or early spring, possibly snow, sleet, or glaze. As the
occluded front slowly passes, winds shift from the north or northeast to the
northwest. The sky begins to clear and the barometric pressure rises.
Temperatures, however, remain cool or cold.
7. Divergence aloft initiates upward air movement,
reduced surface pressure, and cyclonic air movement. In contrast, convergence
along the jet stream results in general subsidence of the air column, increased
surface pressure, and anticyclonic surface winds.
8. Tornadoes, with diameters of about 0.25 kilometer, and
hurricanes, with diameters of about 600 kilometers, are both smaller and more
violent than middle-latitude cyclones, whose diameters may be 1600 kilometers
or more. Thunderstorms, which are characterized by up-and-down air movements
rather than the inward spiral of a cyclone, are related in some manner to all
three types of these cyclones.
9. Since thunderstorms are produced in towering
cumulonimbus clouds, a prime requirement is warm, moist, unstable air.
10. In areas where warm, moist,
and unstable air is very common, that is, the tropics. In the
11. Because of the very low
pressure within the tornado there is a very steep pressure gradient and, hence,
very high wind speeds.
12. Tornadoes are most often
spawned along the cold front of a middle-latitude cyclone in association with
severe thunderstorms. During spring, the air masses on either side of the cold
front are most likely to have greatly contrasting conditions.
13. Although tornadoes can occur
in every month of the year, spring (April–June) is the period of greatest
tornado activity.
14. A tornado watch alerts the
public to the fact that conditions are right for the formation of tornadoes. A
tornado warning is issued when a tornado has actually been sighted in an area
or is indicated by radar.
15. With
wind speeds between 61 and 115 kilometers per hour, a tropical storm has
stronger winds than a tropical depression.
16. (a) Wind
speeds were probably highest on Thursday, because Hurricane Fran had a lower
pressure and closer-spaced isobars on that day.
(b) The hurricane moved approximately 400
miles. The average rate of movement was 400 miles/24 hours = 16.6 miles per
hours (mph).
17. The three broad categories of
hurricane damage are (1) wind damage, (2) storm surge, and (3) inland
freshwater flooding. Storm surge is responsible for the greatest percentage of
hurricane-related deaths.
18. The most likely cause is the
heavy rains and inland flooding that can affect places far from the coast for
several days.
19. Since the hurricane is so much larger and lasts not for a fraction of
an hour but for days, the destruction it causes is considerably greater than
that caused by a tornado.
Answers
to Earth System Questions
1. High
snowfalls on the leeward shores of the lakes occur when the atmosphere,
hydrosphere (the
2. The
most devastating damage from a hurricane is caused by the storm surge. As the
water moves over low-lying land, loss of life, destruction of buildings, and
severe erosion are possible. Wind damage can affect a much larger area than the
storm surge, often uprooting trees and destroying buildings. Heavy rains may
also cause extensive flooding and severe erosion hundreds of kilometers from
the coast. Following a hurricane, it may take years for the eroded land,
disrupted drainage network, and destroyed natural vegetation to reestablish or
be repaired.