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Key Concept Review (Answers to in-text “Concept Checks”)
Chapter 8
1. About 1 meter (3.3 feet) of water evaporates each year from the surface of the
ocean. The great quantities of solar energy that cause this evaporation are carried
from the ocean by the escaping water vapor. When a gram of water vapor
condenses back into liquid water – usually at a distance from where it evaporated
-- the same 540 calories is again available to do work. If the water condenses as
precipitation in a cold climate, heat is given off and temperature is moderated.
2. Weather is the state of the atmosphere at a specific time and place, while climate
is the long-term average of weather in an area.
3. The lower atmosphere is a mixture of gases, mostly nitrogen (78.1%) and oxygen
(20.9%).
4. Pressure being equal, warm air can hold more water vapor than cold air.
5. Curiously, humid air is less dense than dry air at the same temperature—because
molecules of water vapor weigh less than the nitrogen and oxygen molecules that
the water vapor it displaces.
6. Air becomes cooler when it expands, and warms as it is compressed. Air
descending from high altitude warms as it is compressed by the higher
atmospheric pressure near Earth’s surface.
7. Water vapor in rising, expanding, cooling air will often condense into clouds
because the cooler air can no longer hold as much water vapor. If rising and
cooling continue, the droplets may coalesce into raindrops or snowflakes.
8. Over long periods of time the total incoming heat (plus that from earthly sources)
equals the total heat radiating into the cold of space; so Earth is in thermal
equilibrium. Some variation is observable over shorter time spans -- the current
episode of global warning is an example.
9. Near the poles light approaches the surface at a low angle, favoring reflection. At
tropical latitudes, sunlight strikes at a more nearly vertical angle, which
distributes the same amount of sunlight over a much smaller area. Tropical
latitudes thus receive significantly more solar energy than the polar regions. As
Earth revolves around the sun, the constant tilt of its rotational axis causes the
Northern Hemisphere to lean toward the sun in June but away from it in
December. The sun therefore appears higher in the sky in the summer but lower in
winter.
10. A convection current is a single closed-flow circuit of rising warm material and
falling cool material.
11. Understanding Coriolis effect depends on communicating the idea that objects
“inherit” their eastward momentum from their originating latitude. Objects bring
that eastward movement with them as they move north or south. In a sense, the
apparent motion of Coriolis effect is the difference in expected east-west position.
12. The angular velocity of Earth is 15° an hour (think of the pie slice of Figure
8.11). But the linear velocity depends on latitude. See how much farther Quito
must travel to make it around Earth in one day in that Figure?
13. Three air circulation cells exist in each hemisphere.
14. Instead of continuing all the way from equator to pole in a continuous loop in
each hemisphere, air rising from the equatorial region moves poleward and is
gradually deflected eastward; that is, it turns to the right in the Northern
Hemisphere and to the left in the Southern Hemisphere. This eastward deflection
is caused by the Coriolis effect
15. The great deserts of both hemispheres, dry bands centered around 30° latitude,
mark the intersection of the Hadley and Ferrel cells. Air falls toward Earth’s
surface in these areas, causing compressional heating.
16. Do your drawing without looking at Figure 8.13, and then check your accuracy.
17. The Northern Hemisphere contains much less ocean surface than the Southern
Hemisphere. Land masses have a lower specific heat than the ocean. An
irregular imaginary line of thermal equilibrium between the hemispheres, situated
about 5° north of the geographic equator, is called the meteorological equator.
18. Heating of the great landmass of Asia draws vast quantities of warm, moist air
from the Indian Ocean. Winds from the south drive this moisture toward Asia,
where it rises and condenses to produce a months-long deluge (a monsoon).
Monsoons occur in North America as warming and rising air over the South and
West draws humid air and thunderstorms from the Gulf of Mexico.
19. Warm land transfer heat to the air, which expands and rises, creating a zone of
low atmospheric pressure. Cooler air from over the sea then moves toward land to
form a sea breeze. The situation reverses after sunset, with land losing heat to
space and falling rapidly in temperature.
20. Large storms are either tropical cyclones or extratropical cyclones. Tropical
cyclones (sometimes called hurricanes or typhoons) form in a single tropical air
mass. Extratropical cyclones (named because they form outside the tropics) are
the frontal storms familiar to winter residents of mid-latitude continents.
Extratropical cyclones form at a front between two air masses.
21. An air mass is a large body of air with nearly uniform temperature, humidity, and
therefore density throughout. Air pausing over water or land will tend to take on
the characteristics of the surface below.
22. Tropical storms and extratropical storms are cyclones, huge rotating masses of
low-pressure air in which winds converge and ascend. A tornado is a much
smaller funnel of fast-spinning wind associated with severe thunderstorms.
23. Energy is required to mix air masses. Since that energy is not always available, a
dense air mass may slide beneath a lighter air mass, lifting the lighter one and
causing its air to expand and cool. Water vapor in the rising air may condense. All
of these effects contribute to turbulence at the boundaries of the air masses and
can lead to the formation of an extratropical cyclone.
24. The boundary between air masses of different density is called a front. Fronts are
typical of extratropical cyclones.
25. This apparent anomaly is caused by the Coriolis deflection of winds approaching
the center of a low-pressure area from great distances. In the Northern
Hemisphere there is rightward deflection of the approaching air. The edge spin
given by this approaching air causes the storm to spin counterclockwise in the
Northern Hemisphere.
26. The storm surge of a large tropical cyclone destroys more lives and property than
its violent wind and torrential rain.
27. Three aspects of a tropical cyclone can cause property damage and loss of life:
wind, rain, and storm surge. Of these, storm surge is the most devastating.
28. A record 27 tropical cyclones formed, and 15 of these became hurricanes. Three
hurricanes reached Category 5 strength. One of these was hurricane Katrina,
cause of the costliest natural disaster to befall the United States.
29. As is typical in large storms, storm surge caused the greatest loss of life and
property when Katrina struck the Gulf coast. The storm surge in Bay St. Louis
was 10.4 meters, or 34 feet, high.
30. The effects of a large tropical cyclone on a built-up area were clearly seen in the
city of New Orleans. Much of the city was built on land below sea level, and
when the levees failed because of storm surge stress, much of the city flooded.
The natural coast was also affected. Salt water driven inland by storm surge
killed marsh grasses along the Louisiana and Mississippi coasts. In Louisiana
alone, more than 260 square kilometers (100 square miles) of wetlands were torn
apart, their ability to support a rich variety of species essentially destroyed.
31. Although there is a strong suggestion of a relationship between the growing
greenhouse and intensification of tropical cyclones, researchers are unable to link
the two with certainty.