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Chapter 7
CIRCULATION OF THE ATMOSPHERE
Answers to the Chapter Review
1.
Macroscale winds, the largest scale wind pattern, involve timescales of days (example:
hurricanes) to years (example: mean global airflow). Mesoscale winds involve a timescale of
minutes to days, and include local winds such as the sea breeze as well as phenomena such as
tornadoes. Microscale winds are very short-lived (from seconds to minutes) and involve such
things as turbulence.
2.
This would be unlikely because the global wind pattern is a statistical average of wind
observations over many years. On any given day, the pattern may be quite unlike the overall
average.
3.
The “norther” is produced by the circulation around an anticyclone, which is a synoptic scale
(macroscale) wind system. Since the wind is not generated locally, it is not a true local
(mesoscale) wind.
4.
At these locations, the temperature differential between land and sea is large. Consequently, the
sea-to-land pressure gradient will also be large.
5.
Katabatic winds originate when cold air, situated over higher terrain, falls or drains to nearby
lower elevations. The greater density of this cold air is the cause of this flow. Examples include
the mistral, which blows from the Alps over France, and the bora, which originates in the
mountains of the former Yugoslavia and blows to the Adriatic Sea.
6.
Cities can create their own local winds called a country breeze because of the urban heat island
effect. This usually happens on clear, calm nights when the relatively warm, less dense air over
the city rises, which in turn initiates the country-to-city flow.
7.
Hadley proposed that on a nonrotating Earth, the more intensely heated air near the equator would
rise and move poleward. Upon reaching the poles, it would sink and flow back along the surface
toward the equator. When the Coriolis force is added to this model, the flow aloft becomes
westerly, while the flow at the surface is easterly. Subsequent pressure-distribution observations
did not support this model of global circulation.
8.
The two factors that contribute to the general subsidence in this zone are as follows: a) radiation
cooling of the air aloft, making it denser, and b) the Coriolis force deflects this poleward-moving
air into a nearly west-to-east flow, which results in the convergence of air aloft.
9.
A stronger Coriolis force would create convergence aloft at lower latitudes, so the location of the
Earth’s belts of subtropical high pressure would be nearer to the equator than they presently are.
10.
Most of the United States is situated in the zone of prevailing westerlies.
11.
a.
Since the southern ocean in this zone is continuous, there is no differential heating of land
and water to complicate the pattern.
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b.
During winter, high pressure exists over the cold continents. During summer, however,
the heat of the land creates low pressure over the continents. This difference in pressure is
balanced by an increase in pressure over the oceans. Thus, the subtropical highs in the
North Atlantic are stronger in July than in January.
c.
Latitudinal temperature contrast in the Northern Hemisphere is greatest during the winter
and is also greatest further to the south in winter than in summer. This influences the
pattern of the jet stream as it moves further south in winter than in summer. The jet
stream influences the path of cyclonic storms, so cyclonic storms are more common in
the winter.
d.
This anticyclone is chiefly the result of the very frigid temperatures experienced in
Siberia in the winter. The greater density of the frigid air produces the cell of high
pressure.
12.
The Asian monsoon is driven by pressure differences that are generated by unequal heating of
Earth’s surface. In the summer, intense solar heating in India and surrounding Southeast Asia
causes temperatures to soar, generating a low-pressure area over southern Asia. This in turn
generates outflow aloft and encourages inward flow at the surface, which brings in moistureladen air from the Indian Ocean landward. In winter, the Siberian high dominates circulation over
Asia and produces predominantly offshore winds. To a lesser extent, the seasonal migration of the
ITCZ also affects the Asian monsoon. Summer is the wet season of the Asian monsoon.
13.
Large areas of the southwestern United States and northwestern Mexico.
14.
When examining the pressure gradient aloft, it is directed from the tropics toward the poles. That
is, pressures aloft near the equator are higher than pressures at similar altitudes farther poleward.
When the effect of the Coriolis force is added to this, the flow aloft becomes westerly. When one
examines the pressure gradient aloft, it is directed from the tropics toward the poles. That is,
pressures aloft near the equator are higher than pressures at similar altitudes farther poleward.
When the effect of the Coriolis force is added to this, the flow aloft becomes westerly.
15.
In the winter. Because the large wintertime temperature gradients (especially in the midlatitudes)
create stronger pressure gradients and thus stronger winds.
16.
The discovery of the existence of jet streams was first made by bombers flying toward Japan
during World War II. They encountered extremely strong winds that did not allow them to make
much headway. Upon abandoning their missions, the planes experienced strong tailwinds during
their flight home.
17.
Pressure distribution aloft is shown by height contours that show the height of a given pressure
level, rather than giving the pressure at a fixed height as surface maps do. Areas of high pressure
appear on these maps as having higher heights and areas of low pressure are indicated by lower
heights for the pressure value that the map depicts.
18.
The dishpan experiments used rotating fluids to duplicate Earth’s circulation. A large circular pan
was heated around the outer edge to represent the equator and the center was cooled to duplicate
the poles. Colored particles were added to the fluid so that the flow patterns could be observed.
These experiments added greatly to our understanding of global circulation, for when the pan was
rotated, the simple convection cell pattern broke down and was replaced by a wavy pattern with
eddies embedded between meanders. The experiments indicated that changes in either the rate of
rotation or in the temperature gradient largely controlled the nature of the flow pattern.
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19.
Major El Niňo events generally cause the following: winters in the northern United States and
Canada to be warmer than normal; generally dry portions of Peru and Ecuador, as well as the
eastern United States, to experience wet conditions; drought conditions in Indonesia, Australia,
and the Philippines; and suppress the number of Atlantic hurricanes.
20.
La Niňa and El Niňo are climatic opposites. La Niňa events are characterized by colder-thanaverage surface temperatures in the eastern Pacific, while El Niňo events are characterized by
warmer-than-average surface temperatures in the eastern Pacific.
21.
Factors other than wind and pressure that influence the distribution of precipitation include
mountain barriers, degree of continentality, and ocean currents.
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