CH-17-20 Moisture, Clouds, and Precipitation – Earth Science : Book Guide

This Document Contains Chapters 17 to 20 Chapter 17 Moisture, Clouds, and Precipitation Moisture, Clouds, and Precipitation begins with an examination of the processes and energy requirements involved in changing the state of water, including the ability of water to store and release latent heat. After the various methods used to express humidity are presented, the relations between temperature, vapor pressure, mixing ratio, relative humidity, and dew-point temperature are explored. Also investigated is the adiabatic process and condensation aloft. Following an examination of the processes that lift air, the conditions that influence the stability of air are discussed. Included in the chapter is the classification of clouds as well as the formation and types of fog. The chapter concludes with a discussion of the processes involved in the formation of precipitation and the various forms of precipitation. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 17.1 List and describe the processes that cause water to change from one state of matter to another. Define latent heat and explain why it is important. 17.2 Distinguish between relative humidity and dew point. Write a generalization relating how temperature changes affect relative humidity. 17.3 Explain how adiabatic cooling results in cloud formation. 17.4 List and describe the four mechanisms that cause air to rise. 17.5 Describe how atmospheric stability is determined and compare conditional instability with absolute instability. 17.6 List the necessary conditions for condensation and briefly describe the two criteria used for cloud classification. 17.7 Define fog and explain how the various types of fog form. 17.8 Describe the two mechanisms that produce precipitation. 17.9 List the different types of precipitation and explain how each type forms. 17.10 Explain how precipitation is measured. TEACHING MOISTURE, CLOUDS, AND PRECIPITATION Relative humidity is the concept to which students can relate the most when exploring the topic of water vapor content of the air. Consider making a sling psychrometer (see Additional Resources) as a demonstration or have students make them in class. You can use the chart on the web page about constructing a sling psychrometer to determine the relative humidity of your air. Have students try to discern why the psychrometer is effective for measuring humidity. Most people are familiar with evaporation and condensation but may be less familiar with the phase of matter changes of deposition or sublimation. You can demonstrate deposition with the “Make Dew or Frost” experiment (see Additional Resources). Have students figure out why water vapor is appearing on the can as frost. If you have access to a small amount of dry ice, you can bring this to show sublimation. Often students have difficulty understanding adiabatic cooling. You can relate this to how the troposphere cools with altitude, but explain that adiabatic cooling simply involves no net heat exchange with the environment. Have students sketch out, either working alone or in groups, the ways air can be forced to rise. Having them recreate this for themselves will help cement the ways air can rise for them. Be sure to use the diagrams included in the book when comparing conditional instability to absolute instability. This is another topic students will often struggle to understand. Presenting the information visually makes these concepts easier to grasp for many. The same is true for teaching about absolute stability. A common misconception is that hail is a winter precipitation event, since hail is made from ice. Stress that hail can only form in thunderstorms and thunderstorms are a summer phenomenon. It may help to discuss how hail and sleet differ and have students deduce for themselves why sleet must be the winter type of precipitation, rather than hail. Sometimes students think that when water evaporates, it disappears or ceases to exist. Put evaporation into context with a diagram of the water cycle and emphasize that all Earth’s water is part of a selfcontained system. Have students try to sketch their own version of the hydrologic cycle and ask them if there is any place for water to “leave.” A common misconception is that fog is made of water vapor. Fog is actually condensed water in liquid form, in a cloud at the surface of the Earth. Make a cloud in a jar or a bottle (see Additional Resources). This activity also works if you use a plastic bottle and squeeze it to simulate pressure, rather than using a glove and a jar as described in the resource. Ask students why you needed to add smoke particles. Have your class deduce what pressure variations have to do with whether or not condensation occurs to make a cloud in your bottle. Encourage students to observe clouds for a week and report what they find. Have them check their results using a cloud chart. CONCEPT CHECK ANSWERS Concept Check 17.1 Summarize the processes by which water changes from one state of matter to another. Indicate whether energy is absorbed or released. Answer: Water can change from a solid to a liquid via melting, from a liquid to a gas via evaporation, or from a solid to a gas via sublimation. These processes all absorb energy. Water can change from a gas to a liquid via condensation, from a gas to a solid via deposition, or from a liquid to a solid via freezing. These processes all release energy. What is latent heat? Answer: It is energy that is stored in water and not released to its surroundings. What is a common example of sublimation? Answer: When dry ice (solid) turns directly to vapor. How does frost form? Answer: Deposition of water vapor to a solid that is at or below freezing. Concept Check 17.2 Describe how the water vapor content of air at saturation is related to air temperature. Answer: Higher temperatures require more water vapor to reach saturation. List three measures that are used to express humidity. Answer: Mixing ratio, relative humidity, and dew point temperature. How do relative humidity and mixing ratio differ? Answer: The mixing ratio is a ratio of the mass of water vapor to the mass of dry air while relative humidity is the ratio of water vapor content in the air to water vapor content potential of the air. If the amount of water vapor in the air remains unchanged, how does a decrease in temperature affect relative humidity? Answer: It causes an increase in relative humidity. On a warm summer day when the relative humidity is high, it may seem even warmer than the thermometer indicates. Why do we feel so uncomfortable on these muggy days? Answer: Less water vapor is able to evaporate from our skin. Concept Check 17.3 How is the formation of dew different from cloud formation? Answer: Dew forms on the surface when Earth experiences radiation cooling. Clouds form as air rises and cools adiabatically at warmer times of day. Why does air cool when it rises through the atmosphere? Answer: As air rises, it enters a region of fewer air molecules. The air expands and as it does so it cools. What do meteorologists mean when they use the word parcel? Answer: It is a volume of air that acts independently of the air around it. Why does the adiabatic rate of cooling change when condensation begins? Why is the wet adiabatic rate not a constant number? Answer: Latent heat of condensation stored in the water molecule is released. The wet adiabatic rate is not constant because the amount of latent heat released depends on how much moisture is present in the air. The contents of an aerosol spray can are under very high pressure. Explain why the spray feels cold when it is allowed to escape the container. Answer: As the contents are released, they expand; therefore the contents cool with expansion. Concept Check 17.4 List four mechanisms that cause air to rise. Answer: Convective lifting, orographic lifting, frontal wedging, and convergence. How do orographic lifting and frontal wedging force air to rise? Answer: Orographic lifting occurs when a laterally-moving mass of air encounters elevated terrain; it is forced up the mountainside. Frontal wedging occurs when warm and cold air collide, generating a front and forcing the warmer, less dense air to rise. Explain why the Great Basin areas of the western United States are dry. What term is applied to this situation? Answer: These areas are called rain shadow deserts. They are dry because they are on the leeward side of a mountain, where much of the moisture has been lost from the air as it moves over the mountain range, largely due to cooling and condensation due to orographic lifting on the other side of the mountain. What causes the Florida peninsula to experience the greatest frequency of midafternoon thunderstorms in the United States? Answer: On warm days, there is a convergence of air from two large water bodies and one landmass. Speed of the air moving off the water is reduced over land, causing air to pile up, generate uplift, and create thunderstorm clouds. Concept Check 17.5 Explain the difference between the environmental lapse rate and adiabatic cooling. Answer: The environmental lapse rate is a measure of the actual temperatures of the air as you move upwards or downwards in the troposphere. Adiabatic cooling is a change in temperature caused by expansion or compression as a parcel of air rises or descends. Describe absolute stability in your own words. Answer: Air tends to return to the surface rather than continuing to rise. This is true even if the parcel of air were forced above the condensation level. Compare absolute instability and conditional instability. Answer: Absolute instability is when air low in the atmosphere is warmer than air aloft, making the ascending air warmer than its environment and having a tendency to continue rising. Conditional instability is when the atmosphere is stable if the air parcel is unsaturated but unstable if the parcel is saturated. What types of clouds and precipitation, if any, form when stable air is forced aloft? Answer: Clouds tend to be thin layers with minimal to no precipitation. Describe the weather associated with unstable air. Answer: Unstable air tends to generate thunderstorms, towering clouds, and possibly tornadoes. Concept Check 17.6 As you drink an ice-cold beverage on a warm, humid day the outside of the glass or bottle becomes wet. Explain. Answer: The glass is cooler than the surrounding air and provides a surface on which the water vapor in the air can condense into a liquid. What is the function of condensation nuclei in cloud formation? Answer: They give the water vapor something to condense onto. What is the basis for the classification of clouds? Answer: Clouds are classified by their form and their height in the atmosphere. Why are high clouds always thin? Answer: They are made of ice crystals and there are small quantities of water vapor at those heights. Which cloud types are associated with the following characteristics: thunder, halos, precipitation, hail, lightning, mares’ tails? Answer: Thunder – cumulonimbus Halos – cirrostratus Precipitation – stratus, nimbostratus, cumulonimbus Hail – cumulonimbus Lightning – cumulonimbus Mares’ tails – cirrus Concept Check 17.7 Define fog. Answer: Fog is a cloud with its base at or near the ground. List five main types of fog and describe how each type forms. Answer: Radiation fog – air near the surface is close to saturation and a small amount of radiative cooling allows vapor in the air to condense. Upslope fog – humid air moves up a slope, adiabatically cools, and reaches the dew point along the surface. Evaporation fog – water vapor is added to the air at the surface and it condenses. Steam fog – cool air moves over warm water, allowing water evaporated from the water surface to cool and condense. Frontal fog – with frontal wedging, warm air is lifted over cold air that is at or near the dew point, causing enough rain to evaporate and generate fog. Concept Check 17.8 What is the difference between precipitation and condensation? Answer: Condensation is when water vapor forms liquid cloud droplets. Precipitation is when these cloud droplets fall to the ground. Describe the Bergeron process in your own words. Answer: Supercooled water exists below freezing in cloud tops with few condensation nuclei. As ice crystals form in this environment, they create a condensation nuclei, allowing the supercooled water to help the ice crystals grow in size. These ice crystals begin their descent as snowflakes but generally warm enough to melt into raindrops before hitting the ground. What conditions favor the collision-coalescence process? Answer: When the clouds are warm. Concept Check 17.9 List the forms of precipitation and the circumstances of their formation. Answer: Rain – forms in nimbostratus clouds or towering cumulonimbus clouds. Snow – forms when temperatures are below freezing. Sleet – precipitation starts to fall as a liquid but freezes into ice pellets before hitting the ground. Glaze – precipitation falls as a liquid but freezes upon contact with the ground or other surface at or below freezing. Hail – produced in cumulonimbus clouds where ice pellets are repeatedly blown back into cloud tops by updrafts. It is a summer phenomenon. Rime – ice crystals form when supercooled fog or cloud droplets freeze on a surface that is below freezing. Explain why snow can sometimes reach the ground as rain, but the reverse does not occur. Answer: Snow is an aggregation of ice crystal formed in clouds; it cannot form from falling droplets of rain. Snow can, however, melt into liquid raindrops. How is sleet different from glaze? Which is usually more hazardous? Answer: Sleet is frozen rain that freezes before hitting the ground as ice pellets. Glaze does not freeze until it hits a surface that is below freezing. Glaze is more hazardous. Concept Check 17.10 Sometimes, when rainfall is light, it is reported as a trace. When this occurs, how much (or how little) rain has fallen? Answer: Less than 0.025 centimeters. Why is rainfall easier to measure than snowfall? Answer: The amount of water in a volume of snow is not constant. GIVE IT SOME THOUGHT ANSWERS Refer to Figure 17.2 to complete the following: In which state of matter is water densest? In which state of matter are water molecules most energetic? In which state of matter is water compressible? Answer: liquid water vapor water vapor The accompanying photo shows a cup of hot coffee. What state of matter is the “steam” rising from the liquid? Explain your answer. Answer: The steam is actually in the liquid state. Water is evaporating out of the coffee cup and as it rises it cools and condensation into tiny liquid droplets occurs—hence the steam is actually tiny liquid droplets. The primary mechanism by which the human body cools itself is perspiration. Explain how perspiring cools the skin. Refer to the data for Phoenix, Arizona, and Tampa, Florida, in Table A. In which city would it be easier to stay cool by perspiring? Explain your choice. Answer: Perspiration cools our skin by evaporation. As the liquid evaporates, it absorbs heat energy from our body surface, which in turn cools our bodies down. Check. Phoenix. The much lower dew point temperature allows for a much greater rate of evaporation, so it would be easier to stay cooler by perspiring. During hot summer weather, many people put “koozies” around their beverages to keep the drinks cold. In addition to preventing a warm hand from heating the container through conduction, what other mechanisms slow the process of warming beverages? Answer: Evaporation of the liquid in the cup will slow the warming process as it requires heat energy. Refer to Table 17.1 to answer this question. How much more water is contained in saturated air at a tropical location with a temperature of 40°C compared to a polar location with a temperature of −10°C? Answer: 45 grams of water vapor per kilogram of air. Refer to the data for Phoenix, Arizona, and Bismarck, North Dakota, in Table B, to complete the following: Which city has a higher relative humidity? Which city has the greatest quantity of water vapor in the air? In which city is the air closest to its saturation point with respect to water vapor? In which city does the air require the most water vapor in order to reach saturation? Answer: Bismarck Phoenix Bismarck Phoenix The accompanying graph shows how air temperature and relative humidity change on a typical summer day in the Midwest. Assuming that the dewpoint temperature remained constant, what would be the best time of day to water a lawn to minimize evaporation of the water spread on the grass? Answer: Around 5:00 to 6:00 a.m. The accompanying diagram shows air flowing from the ocean over a coastal mountain range. Assume that the dew-point temperature remains constant in dry air (that is, relative humidity less than 100 percent). If the air parcel becomes saturated, the dew-point temperature will cool at the wet adiabatic rate as it ascends, but it will not change as the air parcel descends. Use this information to complete the following: Determine the air temperature and dew-point temperature for the air parcel at each location (B–G) shown on the diagram. At what elevation will clouds begin to form (with relative humidity = 100 percent)? Compare the air temperatures at points A and G. Why are they different? How did the water vapor content of the air change as the parcel of air traversed the mountain? (Hint: Compare dew-point temperatures.) On which side of the mountain might you expect lush vegetation, and on which side would you expect desert-like conditions? Where in the United States might you find a situation like what is pictured here? Answer: a. B: temp = 17°, dew point = 17°; C: temp = 12°, dew point = 12°; D: temp = 7°, dew point = 7°; E: temp = 17°, dew point = 7°; F: temp = 27°, dew point = 7°; G: temp = 37°, dew point = 7°. b. 1 km. Temperatures are warmer on the leeward side due to the air warming at the dry adiabatic rate as it descends. The water vapor content decreased as the air ascended over the mountain as moisture was lost due to condensation. Lush vegetation on the windward side and dry, desert conditions on the leeward side. Cascade Range of the Pacific Northwest or the Sierra Nevada mountains in California. The cumulonimbus cloud pictured in Figure 17.21H is roughly 12 kilometers tall, 8 kilometers wide, and 8 kilometers long. Assume that the droplets in each cubic meter of the cloud total 0.5 cubic centimeter. How much liquid does the cloud contain? How many gallons is this? (Note: 3785 cm3 = 1 gallon.) Answer: 12,000 m × 8000 m × 8000 m = (7.68 × 1011 m3) × 0.5 = 3.84 × 1011/3785 = 101,453,104 gallons. Cloud droplets form and grow as water vapor condenses onto hygroscopic condensation nuclei. Research has shown that the maximum radius for cloud droplets is about 0.05 millimeter. However, typical raindrops have volumes thousands of times greater. Explain how cloud droplets become raindrops. Answer: Cloud droplets become the size of raindrops by the Bergeron and the collision-coalescence processes. In the Bergeron process, supercooled water nucleates onto ice crystals, growing the size of the crystals until they fall from the cloud, melt on the way down, and fall as raindrops. The collision-coalescence process involves water vapor using aerosols as cloud condensation nuclei, and growing to raindrop size by colliding and coalescing with other water droplets in the air. Why does radiation fog form mainly on clear nights rather than on cloudy nights? Answer: Radiation fog forms mainly on nights because the lack of clouds allows for more cooling of surface air (due to radiational cooling). Consequently air temperatures are more likely to reach the dew point, resulting in fog. Which winter storm is likely to produce deeper snowfall: a low-pressure system that passes through the midwestern states of Nebraska, Iowa, and Illinois (26°F average temperature at the time of the storm) or exactly the same system passing through North Dakota, Minnesota, and Wisconsin (16°F average temperature at the time of the storm). Answer: The storm traveling through Nebraska, Iowa, and Illinois will likely produce a deeper snowfall. The air temperature of 26° would contain more water vapor than the same storm at 16° and therefore more snowfall would occur. Weather radar provides information on the intensity of precipitation in addition to the total amount of precipitation that falls over a given time period. Table C shows the relationship between radar reflectivity values and rainfall rates. If radar measured a reflectivity value of 47 dBZ for 2½ hours over a location, how much rain will have fallen there? Answer: 1.3 inches/hour × 2.5 hours = 3.25 inches. What are the advantages and disadvantages of using rain gauges compared to weather radar in measuring rainfall? Answer: Rain gauges have the advantage in that they do not require any instrumentation or electrical components and they are much less expensive. The disadvantages are that errors can occur if the rain gauge is improperly placed and also they are not very accurate in windy conditions. EXAMINING THE EARTH SYSTEM ANSWERS The interactions among Earth’s spheres have produced the Great Basin area of the western United States, which includes some of the driest areas in the world. Examine the map of the region in Figure 6.30. Although the area is only a few hundred miles from the Pacific Ocean, it is a desert. Explain why. Did any geologic factor(s) contribute to the formation of this desert environment? Do any major rivers have their source in the Great Basin? Explain. (For information about deserts in the United States, visit the U.S. Geological Survey’s [USGS’s] “Deserts: Geology and Resources” Website, at http://pubs.usgs.gov/gip/deserts/.) Answer: Although only a few hundred kilometers from the Pacific, the Great Basin desert of the western United States is situated on the eastern side of the imposing Sierra Nevada range, which acts as a moisture barrier for the region. Without the geologic evolution of the mountains to the west, the Great Basin region would not be located in a rainshadow and hence would have a much different climate. Because precipitation is scanty, drainage is essentially interior, infiltration rates are often high, and the region has high evaporation, no major rivers have their source in the Great Basin. When Earth is viewed from space, the most striking feature of the planet is water. It is found as a liquid in the global oceans, as a solid in the polar ice caps, and as clouds and water vapor in the atmosphere. Although only one-thousandth of 1 percent of the water on Earth exists as water vapor, it has a huge influence on our planet’s weather and climate. What role does water vapor play in heating Earth’s surface? How does water vapor act to transfer heat from Earth’s land–sea surface to the atmosphere? Answer: Water vapor is a potent greenhouse gas. Its presence in the atmosphere is important in retaining heat so that Earth can be habitable. Water vapor transfers heat from the surface to the atmosphere by way of evaporation and condensation. The process of evaporation cools the environment around it but as the water vapor is transported to a higher altitude and cools, it condenses, a process that releases tremendous amounts of latent heat. The amount of precipitation that falls at any particular place and time is controlled by the quantity of moisture in the air and many other factors. How might each of the following alter the precipitation at a particular locale? An increase in the elevation of the land A decrease in the area covered by forests and other types of vegetation Lowering of average ocean-surface temperatures An increase in the percentage of time that the winds blow from an adjacent body of water A major episode of global volcanism lasting a decade Answer: An increase in elevation often brings more precipitation, especially on windward slopes. A decrease in the area covered by forests and other types of vegetation would reduce precipitation because less moisture would be added to the atmosphere from plants. The immediate response to lowering ocean-surface temperatures would be an increase in precipitation as global temperatures fell. However, eventually, the lower water temperatures would result in less evaporation of water to the air and a drop in precipitation. Winds blowing more frequently from an adjacent body of water would increase the amount of precipitation as more moisture was brought to the area. A major long-lasting episode of global volcanism would at first produce more precipitation as the atmosphere cooled. Eventually, less precipitation would fall owing to lower evaporation rates as a consequence of cooler temperatures. Phoenix and Flagstaff, Arizona, are both located in the southwestern United States, less than a 2hour drive apart. Using the accompanying climate diagram (which gives the elevations of the two cities), describe the impact that elevation has on the precipitation and temperature of each city. Use the Internet to compare and explain the natural vegetation of these locations. Next, check the current weather conditions for Phoenix and Flagstaff, Arizona, by using The Weather Channel Website, at www.weather.com. Do the current conditions seem to fit climate data? Explain. Answer: Although the pattern of monthly temperature changes for each place is similar, Flagstaff, at the higher elevation, has cooler temperatures and more precipitation owing to orographic lifting. As a consequence of these differences, vegetation surrounding Phoenix is typical of a dry desert, whereas that in Flagstaff is characteristic of the Colorado Plateau, with vegetation of broadleaf evergreen and dwarf shrub variety. Student answers will vary. ADDITIONAL RESOURCES DVDs and Movies The Weather (2003) BBC, 230 minutes. Includes subheadings Wind, Wet, Cold, and Heat. Available on DVD. Time-Lapse: Mesmerizing “Stormscapes” Dominate Skies. National Geographic, 3 minutes. Time lapse of storm clouds. Available for free streaming from http://video.nationalgeographic.com/video/ news/environment-news/140220-storms-timelapse-vin/ How Do Clouds Form? About.com, 1 minute. http://video.about.com/weather/How-Do-CloudsForm-.htm Websites Earth Cloud Cover Scientific Visualization. From NASA. http://svs.gsfc.nasa.gov/vis/a000000/ a002300/a002394/index.html Cloudman’s Mini Atlas of Cloud Types. Online cloud chart. http://www.cloudman.com/atlas.htm Mountain Weather Simulation. http://www.pbslearningmedia.org/resource/ess05.sci.ess.watcyc. mountainwea/mountain-weather/ The Weather Channel Online. http://www.weather.com Make Dew or Frost. http://www.weatherwizkids.com/experiments-frost.htm Make a Sling Psychrometer. http://science-edu.larc.nasa.gov/SCOOL/psychrometer.html Atmospheric Stability Infrared Imagery. http://severewx.atmos.uiuc.edu/index.5.html Make a Cloud in a Jar. From UCAR. http://eo.ucar.edu/webweather/cloudact2.html Chapter 18 Air Pressure and Wind Air Pressure and Wind opens with a description of the units and instruments used for measuring atmospheric pressure. A definition of wind is followed by an analysis of the factors that affect it—the pressure gradient force, the Coriolis effect, and friction. A discussion of anticyclones and cyclones includes associated movements of air and weather patterns. Also presented are the general global patterns of pressure and wind. A more detailed discussion of atmospheric circulation in the midlatitudes is followed by descriptions of several local winds. Wind measurement and instruments are also briefly mentioned. The chapter closes with an examination of El Niño/La Niña and the relations between global precipitation and Earth’s pressure and wind belts. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 18.1 Define air pressure and describe the instruments used to measure this weather element. 18.2 Discuss the three forces that act on the atmosphere to either create or alter winds. 18.3 Contrast the weather associated with low-pressure centers (cyclones) and high-pressure centers (anticyclones). 18.4 Summarize Earth’s idealized global circulation. Describe how continents and seasonal temperature changes complicate the idealized pattern. 18.5 List three types of local winds and describe their formation. 18.6 Describe the instruments used to measure wind. Explain how wind direction is expressed using compass directions. 18.7 Describe the Southern Oscillation and its relationship to El Niño and La Niña. List the climate impacts to North America of El Niño and La Niña. 18.8 Discuss the major factors that influence the global distribution of precipitation. TEACHING AIR PRESSURE AND WIND When describing air pressure, it is useful to explain that air pressure is a result of the overlying weight of air molecules. Show students a periodic table of the elements and have them recall that the atmosphere is 78% nitrogen and 21% oxygen. Show that these elements have mass, and that combined with the effects of gravity, that gives air weight. It is this weight that we know of as air pressure. An analogy that sometimes helps students to understand the difference between a steep pressure gradient and a more gradual one is the analogy of a hill. A steep hill has a large change in elevation over a short horizontal distance. Similarly, a steep pressure gradient has a large change in pressure over a relatively short horizontal distance. You can help students to further remember this by having them realize that if they were on a bicycle, they would coast faster down a steep hill; likewise wind will move faster across a steep pressure gradient. The Coriolis effect can be demonstrated with some type of rotating disk or table, paper, and a writing utensil. Sometimes the turntables from inside some types of microwaves work well. Instruct a student volunteer to draw a straight line on the paper placed on the turntable. Then set the turntable spinning and tell the volunteer to again draw a straight line. This is a good way to illustrate how the Coriolis effect operates on a rotating Earth. A common misconception is that the Coriolis effect influences water flow in our drains. Visit the Bad Coriolis website (see Additional Resources) for information on how this simply is not true. In addition, there is a wealth of video footage of people near the equator in Africa showing tourists how water will spin in a bowl in opposite directions, depending upon which side of the equator they are standing. You might consider finding one of these videos on YouTube and asking students in what way the perpetrators are hoaxing the tourists. In actuality, you must be about 6 degrees of latitude from the equator and have a sizable mass of water, such as a sea basin, for this to work. Wind direction can be confusing for those who have not dealt with it from a meteorological point of view. The best thing to tell students is that it is somewhat counterintuitive; a south wind is blowing from the south, not towards it. The three-cell model of atmospheric circulation is actually three-dimensional on the actual Earth, but can be hard to visualize, since it can only be represented in two dimensions in figures. The beginning of The Weather DVD (see Additional Resources) has a good 3-D animation of what this circulation looks like on a spherical Earth. Have students draw the three-cell model in their notebooks or on a piece of paper, either alone or with a group, without referring to their notes or a picture. Have them note the locations where air is rising and where air is descending. A common error is that students draw loops approximately where the cells begin rising, without extending the entire circulation all the way to where it descends, especially with the Polar cell. Emphasize that these circulation cells encompass the entire globe. Have students relate the major wind belts to the three-cell model and the Coriolis effect before explaining the connection. It is important to understand how these things all work in tandem on a real Earth. NOAA has a good website that monitors sea-surface temperatures in the Pacific Ocean (see Additional Resources). You can easily access these and show the real-time data to students. Have them determine if the anomalies are consistent with an El Niño, a La Niña, or neither. CONCEPT CHECK ANSWERS Concept Check 18.1 Describe air pressure in your own words. Answer: It is the pressure exerted on Earth’s surface due to the weight of the overlying air molecules. What is standard sea-level pressure in millibars, in inches, and in pounds per square inch? Answer: 1013.25 millibars, 29.9 inches, and 14.7 pounds per square inch. Describe the operating principles of the mercury barometer and the aneroid barometer. Answer: The mercury barometer consists of a tube filled with mercury inverted into a dish of mercury. Mercury flows out of the tube to balance the weight of the mercury column by the pressure exerted on the mercury in the dish. The aneroid barometer has a partly evacuated vacuum chamber that compresses as the pressure increases. Levers are connected to the chamber and transmit readings to a pointer on a dial that is calibrated to read the correct atmospheric pressure. List two advantages of the aneroid barometer. Answer: It is small and portable, and it can be readily connected to a recording mechanism. Concept Check 18.2 List the factors that combine to direct horizontal airflow (wind). Answer: Pressure gradient force, Coriolis effect, and friction with Earth’s surface. What force is responsible for generating wind? Answer: Pressure gradient force. Write a generalization relating the spacing of isobars to wind speed. Answer: The closer together the isobars are, the faster the wind speed. Briefly describe how the Coriolis effect influences air movement. Answer: In the Northern Hemisphere, the Coriolis effect causes the deflection of the path of a moving object, including moving air, to the right. In the Southern Hemisphere, this deflection is to the left. The effect is greater with increasing latitude. Unlike winds aloft, which blow nearly parallel to the isobars, surface winds generally cross the isobars. Explain what causes this difference. Answer: At the surface, friction affects wind and as a result alters its direction. The pressure gradient force and the Coriolis effect at the surface causes air to move across the isobars. Aloft, geostrophic winds lack friction with Earth’s surface and can travel more quickly as the Coriolis effect balances the PGF. Concept Check 18.3 Prepare a diagram with isobars and wind arrows that shows the winds associated with surface cyclones and anticyclones in both the Northern and Southern Hemisphere. Answer: See Figure 18.12 for Northern Hemisphere reference; the opposite will hold true for the Southern Hemisphere. In this diagram: • Anticyclones (high-pressure systems) have outward-flowing winds (clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere). • Cyclones (low-pressure systems) have inward-flowing winds (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). For a surface low-pressure center to exist for an extended period, what condition must exist aloft? Answer: Divergence of air. What general weather conditions are to be expected when the pressure tendency is rising? When the pressure tendency is falling? Answer: When the pressure tendency is rising, weather is expected to be fair or good. When the pressure tendency is falling, stormy or bad weather is expected. Concept Check 18.4 Referring to the idealized model of atmospheric circulation, in which belt of prevailing winds is most of the United States? Answer: Westerlies. The trade winds diverge from which pressure belt? Answer: Subtropical high. Which prevailing wind belts converge in the stormy region known as the polar front? Answer: Westerlies and polar easterlies. Which pressure belt is associated with the equator? Answer: Equatorial low. Explain the seasonal change in winds associated with India. What term is applied to this seasonal wind shift? Answer: As the land surface heats up in summer, it generates a thermal low pressure. Air from the relatively highpressure region over the ocean blows into this thermal low. This is called the monsoon. Concept Check 18.5 What is a local wind? Answer: It is a small-scale wind produced by a locally-generated pressure gradient. Describe the formation of a sea breeze. Answer: During the summer solar radiation heats the land surface near the sea more quickly than it heats water with its high thermal inertia. A thermal low pressure develops over the land, and air flows onto the land from the sea, which is at a relatively higher pressure. Does a land breeze blow toward or away from the shore? Answer: Away. A land breeze blows from the land toward the sea. It occurs at night when the land cools more quickly than the sea, causing the air over the land to become cooler and denser, flowing towards the warmer sea. During what time of day would you expect to experience a well-developed valley breeze—midnight, late morning, or late afternoon? Answer: Late afternoon. You would expect to experience a well-developed valley breeze in the late morning. Valley breezes typically occur when the sun heats the valley slopes, causing air to rise and flow upslope during the day. Concept Check 18.6 What are the two basic wind measurements? What instruments are used to make these measurements? Answer: Direction and speed. A wind vane is used to measure direction and an anemometer is used to measure speed. From what direction does a northeast wind blow? Toward what direction does a south wind blow? Answer: A northeast wind blows from the northeast. A south wind blows toward the north. Concept Check 18.7 Describe how a major El Niño event tends to affect the weather in Peru and Chile compared to Indonesia and Australia. Answer: It will make Peru and Chile wetter than normal and Indonesia and Australia dryer than normal. Describe the sea-surface temperatures on both sides of the tropical Pacific during a La Niña event. Answer: The western Pacific has relatively warm water and the eastern Pacific has relatively cool water. How does a major La Niña event influence the hurricane season in the Atlantic Ocean? Answer: It increases hurricane activity. Briefly describe the Southern Oscillation and how it is related to El Niño and La Niña. Answer: The Southern Oscillation is a shift in high and low atmospheric pressures in the eastern and western tropical Pacific Ocean. An El Niño is associated with an increase in surface pressure near Australia and a drop in pressure off the coast of Peru. The opposite occurs with La Niña. Describe how an El Niño event might affect the climate in North America during the winter. Describe the same for a La Niña event. Answer: El Niño might cause the southern portion of North America to be wet, with the eastern part also being cool. The northern portion of North America might be warmer. A La Niña might cause the southern portion of North America to be warm and dry and the northern portion to be cool. Concept Check 18.8 With which global pressure belt are the rain forests of Africa’s Congo basin associated? Which pressure system is linked to the Sahara Desert? Answer: The equatorial low is associated with the Congo and the subtropical high is linked to the Sahara. What factors, in addition to the distribution of wind and pressure, influence the global distribution of precipitation? Answer: Temperature of the air, distribution of land and water, and mountain barriers. GIVE IT SOME THOUGHT ANSWERS Mercury is 13.5 times denser (heavier) than water. If you built a barometer using water rather than mercury, how tall, in inches, would it have to be to record standard sea-level pressure? Answer: 29.92 inches × 13.5 = 404 inches high. This satellite image shows a tropical cyclone (hurricane). Examine the cloud pattern and determine whether the flow is clockwise or counterclockwise. In which hemisphere is the storm located? What factor determines whether the flow is clockwise or counterclockwise? Answer: Clockwise. Southern Hemisphere. The Coriolis effect. If divergence in the jet stream above a surface low-pressure center exceeds convergence at the surface, will surface winds likely get stronger or weaker? Explain. Answer: Winds are likely to get stronger. As divergence aloft exceeds the air converging at the surface, the air is pulled into the low-pressure system faster, resulting in faster wind speeds. The accompanying map is a simplified surface weather map for April 2, 2011, on which three pressure cells are numbered. Identify which of the pressure cells are anticyclones (highs) and which are cyclones (lows). Which pressure cell has the steepest pressure gradient and therefore the strongest winds? Refer to Figure 18.2 to determine whether pressure cell 3 should be considered strong or weak. Answer: 1 and 3 are lows, 2 is high. 3. Strong. You and a friend are watching TV on a rainy day, when the weather reporter says, “The barometric pressure is 28.8 inches and rising.” Hearing this, you say, “It looks like fair weather is on its way.” Your friend responds with the following questions: “I thought air pressure had something to do with the weight of air. How does inches relate to weight? And why do you think the weather is going to improve?” How would you respond to your friend’s queries? Answer: The “inches” refer to the level of mercury in a barometer, an instrument for measuring air pressure. The level of the mercury rises or falls, depending on the weight of the air present in the atmosphere (i.e. higher levels = a greater weight of air present). The fact that the mercury level is increasing indicates higher pressures in the atmosphere. Higher pressure is caused by sinking or stable air, and this creates conditions of lower relative humidity and clear skies. If you live in the Northern Hemisphere and are directly west of the center of a cyclone, what is the probable wind direction at your location? What if you were west of an anticyclone? Answer: Directly west of a cyclone in the Northern Hemisphere would be characterized by north winds due to the counterclockwise rotation around the low. Directly west of an anticyclone would have just the opposite situation—south winds. If Earth did not rotate on its axis and if its surface were completely covered with water, what direction would a boat drift if it started its journey in the middle latitudes of the Northern Hemisphere? (Hint: What would the global circulation pattern be like for a nonrotating Earth?) Answer: The boat would move due south. Without a rotating Earth and the resulting Coriolis effect, the only factor affecting the wind would be the pressure gradient force. Higher pressure at the colder North Pole would move towards the lower pressures at the equator in a north to south direction. The accompanying sketch shows a cross section of the idealized circulation in the Northern Hemisphere. Match the appropriate number on the sketch to each of the following features: a. equatorial low polar front subtropical high polar high Answer: 4 2 3 1 The accompanying maps of Africa show the distribution of precipitation for July and January. Which map represents July, and which represents January? How were you able to figure this out? Answer: Map A is July and map B is January. Higher rainfall would occur associated with low pressure, which is more prevalent during the summer over land in the Northern Hemisphere (map A) and during summer over land in the Southern Hemisphere (map B). EXAMINING THE EARTH SYSTEM ANSWERS This satellite image shows a portion of a wildfire that occurred in May and June 2011. Known as the Wallow Fire, it burned more than 538,000 acres (840 square miles) in southeastern Arizona. It was the largest wildfire in Arizona history. Suggest two ways that wind contributed to this wildfire. How might this event influence the geosphere and the biosphere? Answer: Southeastern Arizona is located in the Westerly wind belt. Winds blowing from the southwest naturally occur in this area and could have fanned the fire. In addition, this region tends to become warm and generate thermal lows in the summer. Wind could have blown in from higher-pressure regions, including those over the relatively cooler Pacific Ocean, and contributed to the fire. This event might influence the biosphere by way of the fire destroying the vegetation. This could subsequently affect the geosphere because if the soil-stabilizing vegetation is gone, it could increase erosion. Examine this classic image of Africa from space and pick out the region dominated by the equatorial low and the areas influenced by the subtropical highs in each hemisphere. What clue(s) did you use? Speculate on the differences in the biosphere between the regions dominated by high pressure and the zone influenced by low pressure. Answer: The region dominated by the equatorial low is both cloud-covered and darker, which indicates vegetation. Both conditions are the result of the moisture and precipitation associated with low pressure. To the north and south of this region, clear skies and desert conditions with sparse vegetation prevail beneath the subtropical highs. The accompanying map shows wintertime sea-surface temperature anomalies (differences from average) over the equatorial Pacific Ocean. Based on this map, answer the following questions: In what phase was the Southern Oscillation (El Niño or La Niña) when this image was made? Would the trade winds be strong or weak at this time? If you lived in Australia during this event, what weather conditions would you expect? If you were attending college in the southeastern United States during winter months, what type of weather conditions would you expect? (Hint: See Figure 18.25.) Answer: La Niña. Strong. Warm and wet. Warm and dry. How are global winds related to surface ocean currents? What is the ultimate source of energy that drives both of these circulations? Answer: Because surface ocean currents are set in motion by friction from the global winds, both follow the same general circulation—clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The ultimate source of energy that drives both the atmospheric and oceanic circulation is the Sun. ADDITIONAL RESOURCES DVDs and Movies The Weather (2003) BBC, 230 minutes. Includes subheadings Wind, Wet, Cold, and Heat. Available on DVD. Chasing El Nino (1998) NOVA, PBS, 60 minutes. Available on DVD. El Nino. National Geographic, 3 minutes. Available for free streaming from http://video.nationalgeographic.com/video/environment-natural-disasters/landslides-and-more/el-nino/ The Coriolis Effect. NOVA, PBS, 3 minutes. Available for free streaming from http://www.pbs.org/ wgbh/nova/earth/coriolis-effect.html Websites Chasing El Nino: website to accompany the video. Includes an El Niño scorecard and information about mapping El Niño. http://www.pbs.org/wgbh/nova/elnino/now/ NOAA’s El Nino page. Includes real-time sea-surface temperature data. http://www.elnino.noaa.gov NOAA’s Climate Prediction Center’s ENSO Discussion. Updates on El Niño and La Niña conditions. http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html Bad Coriolis. From Penn State University. Addresses common misconceptions about the Coriolis effect. http://www.ems.psu.edu/~fraser/Bad/BadCoriolis.html Chapter 19 Weather Patterns and Severe Storms Weather Patterns and Severe Storms begins with a discussion of air masses and their source regions, and a description of the weather associated with each air mass type. Following a detailed examination of warm fronts and cold fronts is an in-depth discussion of the evolution of the midlatitude cyclone and its idealized weather patterns. The chapter concludes with investigations of thunderstorms, tornadoes, and hurricanes. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 19.1 Discuss air masses, their classification, and associated weather. 19.2 Compare and contrast typical weather associated with a warm front and a cold front. Describe an occluded front and a stationary front. 19.3 Summarize the weather associated with the passage of a mature midlatitude cyclone. Describe how airflow aloft is related to cyclones and anticyclones at the surface. 19.4 List the basic requirements for thunderstorm formation and locate places on a map that exhibit frequent thunderstorm activity. Describe the stages in the development of a thunderstorm. 19.5 Summarize the atmospheric conditions and locations that are favorable to the formation of tornadoes. Discuss tornado destruction and tornado forecasting. 19.6 Identify areas of hurricane formation on a world map and discuss the conditions that promote hurricane formation. List the three broad categories of hurricane destruction. TEACHING WEATHER PATTERNS AND SEVERE STORMS If you have covered the previous chapters about atmospheric phenomena, be sure students have a good understanding of those topics. You can use this prior information to build more complex ideas with this chapter. A good rule of thumb when teaching about air masses is to have your class remember that maritime air is moist because it is associated with large water bodies and continental air is dry because it forms over the relatively drier continents. It is essential that students understand the Coriolis effect before they try to comprehend midlatitude cyclones or any other type of cyclonic storm. It is not enough for them to have memorized that the Coriolis effect causes deflection of wind. Have students draw airflow into a low-pressure system, and then ask them how it will be deflected. Establish that it is the combination of inflow and deflection that causes the cyclonic rotation. Then have them make the connection between air flowing into the low and air rising from the low, leaving room for the horizontal inflow of air. An understanding of front movement has its basis in understanding the different densities of warm and cool air. Have students draw their own cross sections of incoming warm fronts and cold fronts with their associated vertical air motions. Be sure students understand that warmer air will tend to rise up regardless of which type of front is moving into an area. You can demonstrate how warm and cold air masses initially do not mix by using hot and cold water with a clear jar or container. Use food coloring to color ice water in a clear jar blue. Color hot water red and slowly pour the hot water into the container with the blue water. The red, hot water will initially sit on top of the cold, blue water. This is analogous to how warm and cold air behave. Figure 19.17 shows the occurrence of lightning and thunderstorms in the United States, while Figure 19.24 shows the occurrence of U.S. tornadoes, which are spawned by thunderstorms. These maps are very different. Have students discuss the differences and why these two maps do not match up, when they both represent thunderstorm phenomena. There are a number of good video resources about hurricanes and tornadoes (see Additional Resources). In addition, the BBC’s The Weather has an excellent segment on lightning. These videos can make severe storms such as these come more alive for students. Consider showing at least one and having students discuss it. A common misconception about hurricanes is that the wind is the deadliest aspect of them, when in reality it is the storm surge. Remind students about the power of moving water and have them discern why storm surge can be more deadly than wind speed. Another common misconception about hurricanes is that the low pressure will blow out windows as it passes over buildings. It is not the pressure, but the winds. Opening windows in a house will do nothing but let rain and debris in during a storm. CONCEPT CHECK ANSWERS Concept Check 19.1 Define air mass. What is air-mass weather? Answer: An air mass is a large body of air with similar temperature and moisture characteristics. Air-mass weather is when an area experiences fairly consistent weather over a period of several days due to the length of time it takes for a large air mass to move through the region. On what basis are air masses classified? Answer: They are classified based on their source regions. Compare the temperature and moisture characteristics of the following air masses: cP, mP, mT, and cT. Answer: Both mP and mT air masses will be humid, but mT will be warm and mP will be cool. In contrast, cP and cT air masses will both be dry, but cP will be cold and cT will be hot. Which air mass is associated with lake-effect snow? What causes lake-effect snow? Answer: Lake-effect snow is associated with the cP air mass. Lake-effect snow generally occurs in late fall or early winter when the dry cP air mass moves across relatively warm Great Lakes waters. The air gains a great deal of heat and moisture, generating humid, unstable air that brings heavy snow to the land over which the air mass moves next. Concept Check 19.2 Compare the weather of a typical warm front with that of a typical cold front. Answer: Warm fronts cause a gradual increase in temperature as they move into an area and typically produce light or moderate precipitation. Cold fronts tend to cause a rapid decrease in temperature and are often associated with heavy rains and thunderstorms. Why is cold-front weather usually more severe than warm-front weather? Answer: Cold fronts move more quickly than warm fronts and they approach at a steeper angle, causing more rapid uplift of air and storm generation. Describe a stationary front and an occluded front. Answer: A stationary front is when a front is not moving and airflow is almost parallel to the line of the front. An occluded front is when a cold front overtakes a warm front and acts as a boundary between two different types of air. Concept Check 19.3 Briefly describe the weather associated with the passage of a mature midlatitude cyclone when the center of low pressure is about 200 to 300 kilometers (125 to 200 miles) north of your location. Answer: There would first be cirrus clouds and then would come lower, thicker clouds and falling air pressure. Precipitation would increase as would the temperature as the warm front associated with the cyclone passes. A cold front follows, bringing gusty winds and heavy precipitation that could possibly bring severe storms as well. After the cold front moves through, skies will clear. If the midlatitude cyclone described in Question 1 took 3 days to pass your location, on which day would temperatures likely be warmest? On which day would they likely be coldest? Answer: Temperatures would likely be warmest on day 2. It would be coldest on day 3. What winter weather might be expected with the passage of a mature midlatitude cyclone when the center of low pressure is located about 100 to 200 kilometers (60 to 125 miles) south of your location? Answer: There would first be a steady air pressure drop, overcast conditions, and probably snow. As an occluded front forms in this area, there is a low-pressure counterclockwise rotation of air that can persist for a week, keeping poor weather, clouds, and snow in the region during this time. Briefly explain how flow aloft aids the formation of cyclones at the surface. Answer: If flow aloft is diverging above a low-pressure system at the surface, it causes rising air within the low. Air then flows into the low pressure at the surface, contributing to sustaining this cyclone. Concept Check 19.4 Briefly compare and contrast midlatitude cyclones, hurricanes, and tornadoes. How are thunderstorms related to each? Answer: All three of these storms have a low-pressure center and cyclonic airflow. Midlatitude cyclones are the largest of these storms, with diameters up to 1000 miles and tornadoes are the smallest, with diameters far smaller than a half mile. Thunderstorms can form in conjunction with cyclones, tornadoes can be spawned from them, and hurricanes can generate thunderstorm activity in a wide area. What are the basic requirements for the formation of a thunderstorm? Answer: You need warm, moist, unstable air and an air uplifting mechanism. The basic requirements for the formation of a thunderstorm include moist and unstable atmospheric conditions, a lifting mechanism (such as frontal boundaries or heating of the surface), and sufficient atmospheric instability to allow for the rapid upward movement of air. Where are thunderstorms most common on Earth? In the United States? Answer: On Earth, thunderstorms are most common in the tropics. In the United States, Florida has the most thunderstorm activity. Summarize the stages in development of a thunderstorm. Answer: The cumulus stage is marked by updrafts and building of the cloud. The mature stage has heavy precipitation and updrafts and downdrafts. The dissipating stage is where downdrafts predominate and precipitation gradually stops. Concept Check 19.5 Why do tornadoes have such high wind speeds? Answer: There is a very strong pressure gradient associated with a tornado. What general atmospheric conditions are most conducive to the formation of tornadoes? Answer: Severe thunderstorms associated with cold fronts. During what months is tornado activity most pronounced in the United States? Answer: April through June. Name the scale commonly used to rate tornado intensity. How is a rating on the scale determined? Answer: The Enhanced Fujita intensity scale. A rating is determined by assessing the worst damage caused by the tornado. Distinguish between a tornado watch and a tornado warning. Answer: A tornado watch is issued when conditions are right for the possibility of tornadoes occurring. A tornado warning is issued by the local National Weather Service office when a tornado has been spotted in person or on radar. Concept Check 19.6 Define hurricane. What other names are used for this storm? Answer: A hurricane is a strong storm that forms over tropical waters and has a deep low-pressure center and high, sustained winds. Hurricanes are also called typhoons and cyclones. In what latitude zone do hurricanes develop? Answer: Between 5° and 20° latitude over tropical oceans. Distinguish between the eye and the eye wall of a hurricane. How do conditions differ in these zones? Answer: The eye is the center of the hurricane and is marked by its lack of winds and precipitation. The eye wall is just around the eye and marks the region of the highest sustained winds and heaviest precipitation in the storm. What is the source of energy that drives a hurricane? Answer: Latent heat from condensation of water over tropical oceans. Why do hurricanes not form near the equator? Explain the lack of hurricanes in the South Atlantic and eastern South Pacific. Answer: A hurricane is large storm that rotates due to the Coriolis effect; there is no Coriolis effect near the equator. There are no hurricanes in the South Atlantic or the eastern South Pacific because the ocean waters are too cold and hurricanes require warm, deep waters to form. When do most hurricanes in the North Atlantic and Caribbean occur? Why are these months favored? Answer: Most hurricanes form in the late summer months, when ocean temperatures are warm enough for hurricane formation. Why does the intensity of a hurricane diminish rapidly when it moves over land? Answer: Hurricanes require warm, moist air over warm oceans to sustain themselves; when they move over land, they lack fuel to be sustained. What are the three broad categories of hurricane damage? Answer: Storm surge, wind damage, and heavy rains with inland flooding. GIVE IT SOME THOUGHT ANSWERS Refer to Figure 19.4 to answer these questions: Thunder Bay and Marquette are both on the shore of Lake Superior, yet Marquette gets much more snow than Thunder Bay. Why is this the case? Notice the narrow, north–south zone of relatively heavy snow east of Pittsburgh and Charleston. This region is too far from the Great Lakes to receive lake-effect snowfall. Speculate on a likely reason for the higher snowfalls here. Does your answer explain the shape of this snowy zone? Answer: In the late autumn and early winter, the cP air from Canada blows across Lake Superior and picks up a considerable amount of moisture from the warmer lake waters. The saturated air cools when it hits the leeward shore (where Marquette is located) and falls as snow in the areas south and east of Lake Superior. Thunder Bay, located on the windward shore, received much less snow for this reason. The band of heavy snows east of Pittsburgh and Charleston is caused by lifting of air onto the higher Appalachian Mountains. The moist air rises and cools to the dew point as it is forced upward, resulting in increased snowfall in the higher elevations. Refer to the accompanying weather map to answer the following questions: What is a likely wind direction at each city? Identify the likely air mass that is influencing each city. Identify the cold front, warm front, and occluded front. What is the barometric tendency at city A and city C? Which one of the three cities is probably coldest? Which one is probably warmest? Answer: City A: from NW; City B: from SW; City C: from SE. City A: cP; City B: mT; City C: mP. Cold front = lower left line, warm front = lower right line, occluded front = upper line. City A = rising barometer, City C = dropping or falling barometer. City A is coldest, City B is warmest. Apply your knowledge of fronts to explain the following weather proverb: Rain long foretold, long last; Short notice, soon past. Answer: “Rain long foretold, long last” refers to a warm front. Warm fronts move quite slowly compared to cold fronts and long before the warm air arrives it is preceded by a long period of increasing cloud cover that is followed by a long period of rain, hence the rain long foretold, long last comment. “Short notice, soon past” refers to a cold front. Cold fronts move much faster and the clouds arrive shortly before or with the intense, short-lived rainfall—the clouds give short notice and the rain will soon be past. If you hear that a cyclone is approaching, should you immediately seek shelter? Why or why not? Answer: Not necessarily. The term cyclone refers to a low-pressure region and it can refer to a relatively weak storm system, a much stronger storm system, a tropical storm or even hurricane, and even a tornado. So using the phrase “cyclone” requires much more information to decide whether or not seeking shelter is necessary. The accompanying diagrams show surface temperatures with isotherms labeled in degrees Fahrenheit for noon and 6 p.m. on January 29, 2008. On this day, a powerful front moved through Missouri and Illinois. What type of front passed through the Midwest? Describe how the temperature changed in St. Louis, Missouri, over the 6-hour period. Describe the likely shift in wind direction in St. Louis during this time span. Answer: A cold front. The temperature changed from 70° to about 18°F in this time. Winds changed from a southerly direction to a north westerly direction. If you were located 400 kilometers ahead of the surface position of a typical warm front that had a slope of 1:200, how high would the frontal surface be above you? Answer: 2 kilometers (1.2 miles). Assume that after seeing a lightning bolt you heard thunder 10 seconds later. About how far away did the lightning occur? Answer: 2 miles away. The accompanying table lists the number of tornadoes reported in the United States by decade. Propose a reason to explain why the totals for the 1990s and 2000s are so much higher than for the 1950s and 1960s. Answer: The higher number of tornadoes in the 1990s and 2000s is probably the result of more amateur storm spotters watching the skies and also perhaps to the improved technology of Doppler radar. The number of tornado deaths in the United States in the 2000s was less than 40 percent the number that occurred in the 1950s, even though there was a significant increase in population. Suggest a likely reason for the decline in the death toll. Answer: Better technology and more spotters allow meteorologists to identify tornado threats earlier. In addition, there are more and faster ways to disseminate tornado warnings to the public with the invention of cell phones, cable television, and the Internet, for example. A television meteorologist is able to inform viewers about the intensity of an approaching hurricane. However, the meteorologist can report the intensity of a tornado only after it has occurred. Why is this the case? Answer: Hurricanes are sustained storms that can be detected long before they make landfall. Tornadoes are more sudden occurrences. It is also not currently possible to directly measure tornado intensity and the Enhanced Fujita scale classifies tornado intensity based on the damage that has been done. Refer to the graph in Figure 19.30. Explain why wind speeds are greatest when the slope of the pressure curve is steepest. Answer: When the pressure curve is steep, this indicates a strong pressure gradient between the storm and its surroundings. This strong pressure gradient will generate fast winds. Assume that it is late September 2016, and that the eye of Hurricane Gaston, a category 5 storm, is projected to follow the path shown on the accompanying map of Texas. Answer the following questions: Name the stages of development that Gaston must have gone through to become a hurricane. At what stage did the storm receive its name? If the storm follows the projected path, will the city of Houston experience Gaston’s fastest winds and greatest storm surge? Explain why or why not. What is the greatest threat to life and property if this storm approaches the Dallas–Fort Worth area? Answer: Tropical disturbance, tropical depression, tropical storm, hurricane. Gaston received its name when it became a tropical storm. No, the greatest storm surge and highest wind speeds will occur on the eastern side of the hurricane, due to the counterclockwise rotation and the direction of movement. The greatest threat to life and property in Dallas would be flooding from heavy rainfall and wind damage, perhaps even from tornadoes. EXAMINING THE EARTH SYSTEM ANSWERS This image shows the effects of a major snowstorm that dropped nearly 2 meters (7 feet) of snow on Buffalo, New York, in December 2001. This weather event was unrelated to a midlatitude cyclone. Places not far from Buffalo received only modest amounts of snow or no snow at all. Which spheres of the Earth system interacted in the Great Lakes region to produce this snowstorm? What term is applied to heavy snows such as this? Answer: High snowfalls on the leeward shores of the lakes occur when the atmosphere, hydrosphere (the Great Lakes), and solid Earth interact. This lake-effect snow develops during autumn and winter as cold cP air travels over the warm lakes, acquires large quantities of moisture from the water, and becomes humid and unstable. The result is often heavy snow showers over the cooler land on the downwind shores of the Great Lakes. The situations described below involve interactions between the atmosphere and Earth’s surface. In each case indicate whether the air mass is being made more stable or more unstable. Briefly explain each choice. An mT air mass moving northward from the Gulf of Mexico over the southeastern United States in winter. An mT air mass from the Gulf of Mexico moving northward over the southeastern United States in summer. A wintertime cP air mass from Siberia moving eastward from Asia across the North Pacific. Answer: More unstable. The mT air mass will collide with a cP air mass, generating steep uplift and severe weather. More stable. The mT air mass will merge with another mT air mass. More unstable. The cP air mass becomes a cool, moist, unstable mP air mass as it moves across the ocean. This world map shows the tracks and intensities of thousands of hurricanes and other tropical cyclones. It was put together by the National Hurricane Center and the Joint Typhoon Warning Center. What area has experienced the greatest number of category 4 and 5 storms? Why do hurricanes not form in the very heart of the tropics, astride the equator? Explain the absence of storms in the South Atlantic and the eastern South Pacific. Answer: The eastern portion of the North Pacific. There is no Coriolis effect to give the storm its rotation. The waters are too cold to sustain a hurricane, which relies on the latent heat from warm tropical waters. This satellite image shows Tropical Cyclone Favia as it came ashore along the coast of Mozambique, Africa, on February 22, 2007. This powerful storm was moving from east to west. Portions of the storm had sustained winds of 203 kilometers (126 miles) per hour as it made landfall. Letters A–D relate to Question c. Identify the eye and the eye wall of the cyclone. Based on wind speed, classify the storm using the Saffir–Simpson hurricane scale. Which one of the lettered sites should experience the strongest storm surge? Explain. Describe the possible effects of the storm on coastal lands (geosphere), drainage networks (hydrosphere), and plant and animal life (biosphere). Answer: The eye is in the center. Category 3. Location B. Storm surge is strongest on the right side of the eye as viewed from the ocean. 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. ADDITIONAL RESOURCES DVDs and Movies The Weather (2003) BBC, 230 minutes. Includes subheadings Wind, Wet, Cold, and Heat. Available on DVD. Killer Typhoon (2013) NOVA, PBS, 53 minutes. What made Typhoon Haiyan so deadly? Available for free streaming from http://www.pbs.org/wgbh/nova/earth/killer-typhoon.html DVD also available for purchase. Oklahoma’s Deadliest Tornadoes (2013) NOVA, PBS, 53 minutes. Stories from survivors and storm chasers. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/oklahomatornadoes.html DVD also available for purchase. When Hurricane Sandy Went Rogue (2013) NOVA, PBS, 3 minutes. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/sandy-rogue.html Hunt for the Supertwister (2004) NOVA, PBS, 53 minutes. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/hunt-for-the-supertwister.html Lightning (2005) NOVA Science NOW, PBS, 9 minutes. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/lightning.html Hurricanes (2005) NOVA Science NOW, PBS, 12 minutes. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/hurricanes.html Mythbusters: Hurricane Windows. Discovery Channel, various length short segments. Available for free streaming from http://www.discovery.com/tv-shows/mythbusters/videos/hurricane-windows.htm Websites National Weather Service Lightning Safety. http://www.lightningsafety.noaa.gov/distance.htm National Hurricane Center. Includes marine forecasts and ocean monitoring. http://www.nhc.noaa.gov National Weather Service Watch, Warning, and Advisory Display. http://www.spc.noaa.gov/ products/wwa/ Severe and Hazardous Weather. From the University of Illinois. http://severewx.atmos.uiuc.edu/ index.html Real-Time Weather Data. From the National Center for Atmospheric Research. http://weather.rap.ucar.edu Tornado Safety Tips. From National Geographic. http://environment.nationalgeographic.com/ environment/natural-disasters/tornado-safety-tips/ Chapter 20 World Climates and Global Climate Change World Climates and Global Climate Change begins with a brief description of Earth’s climate system, followed by an overview of world climates. The Köppen system of climate classification, used throughout the chapter, and its five principal groups are presented and discussed. Beginning with the humid tropical (A) climates, the location, characteristics, and subtypes of each of the climate groups are examined in detail. The chapter then looks at the impact humans have had on global climate and shows evidence for these changes. Greenhouse gases are discussed in the context of how they have influenced climate change and where they have originated. Positive- and negative-feedback mechanisms are briefly examined and the role they play in climate change explored. This is followed up with a description of aerosols and they ways they influence climate. The chapter concludes with an overview of some of the possible consequences of global climate change and how scientists use models to simulate the future. FOCUS ON CONCEPTS After reading, studying, and discussing the chapter, students should be able to: 20.1 List the five parts of the climate system and provide examples of each. 20.2 Explain why classification is a necessary process when studying world climates. Discuss the criteria used in the Köppen system of climate classification. 20.3 Compare the two broad categories of tropical climates. 20.4 Contrast low-latitude dry climates and midlatitude dry climates. 20.5 Distinguish among five different humid midlatitude climates. 20.6 Contrast ice cap and tundra climates. 20.7 Summarize the characteristics associated with highland climates. 20.8 Summarize the nature and cause of the atmosphere’s changing composition since about 1750. Describe the climate’s response. 20.9 Contrast positive- and negative-feedback mechanisms and provide examples of each. 20.10 Discuss the possible impacts of aerosols on climate change. 20.11 Describe some possible consequences of global warming. TEACHING WORLD CLIMATES AND GLOBAL CLIMATE CHANGE When examining the parts of the climate system, it is easy to relate this topic to what has already been studied. Earlier chapters discuss Earth as a system. Have students find the similarities between the Earth system and the climate system. Have them recall how a system works. Climate classification is partially intuitive; you can draw upon this when teaching it. Students will already understand that in general, warmer climates are closer to the equator and cooler climates are more poleward. When introducing climate subclasses, have students look at a map such as Figure 20.5. Have them analyze which locations seem to have ocean influences and those which seem to be only continentbased. Then have them look for patterns in climate types and make correlations between wetter and drier overall climate types. Often students think that the topic of climate change is one that is highly debated in the scientific community. It is important to stress that the consensus among scientists is that the climate is changing and it is not a topic of debate. When discussing climate change, be sure to show students the data, such as those in the many figures in the chapter. Allow students to see for themselves how greenhouse gases have changed and how global temperatures have changed. It is also important to have students examine data showing what humans have contributed to the atmosphere so that students understand why the scientific community feels that humans are contributing to the problem of global climate change. A common misconception is that the greenhouse effect and global warming are the same thing. Be sure to have students understand that the greenhouse effect is what makes life on Earth possible; it is the enhancing of this effect that is causing climate change and that is where the problems arise. Often there is a misconception that global warming is causing the ozone hole, or vice versa. You can explain that while CFCs have contributed to both of these problems, they are actually separate issues. If you want students to explore the topic of global climate change more in-depth or more independently, have them engage in one of the activities from Teaching Climate Change: Lessons from the Past (see Additional Resources). Feedback mechanisms are challenging for many students to grasp. A good way to have them understand positive and negative feedback mechanisms in general is to have them individually or in small groups try to identify mechanisms in their everyday lives. Then you can have them take the next step and understand the mechanisms as they relate to climate change. Engage students by having them think of some possible consequences of climate change. They can elaborate on those outlined in the chapter or think of some other ways that global warming may directly or indirectly impact humans. Show your class the different types of proxy data, such as tree rings, ice cores, coral cores, and fossils, that scientists use to piece together the climate puzzle. When students see how the climate data from the past are reconstructed, they gain a better understanding of how scientists understand the nature of climate changes. CONCEPT CHECK ANSWERS Concept Check 20.1 What are the five major parts of the climate system? Answer: Atmosphere, hydrosphere, geosphere, biosphere, and cryosphere. List at least five connections between climate and Earth’s external and internal processes. Answer: Climate can affect weathering, rainfall that triggers flooding, and formation of glaciers. Volcanic activity can put gases in the atmosphere that affect climate, and mountain building processes can affect temperatures, precipitation, and wind. Concept Check 20.2 Why is classification often a necessary task in science? Answer: Science encompasses a large, diverse body of information; classification can group data with common characteristics to bring order to large amounts of information. This helps comprehension and analyses. What climate data are needed to classify a climate using the Köppen system? Answer: Mean monthly and annual precipitation and temperature values. Should climate boundaries, such as those shown on the world map in Figure 20.5, be regarded as fixed? Explain. Answer: Climate boundaries should not be regarded as fixed because they are based on average values collected over many years. Therefore boundaries should be seen as transition zones rather than fixed boundaries. Concept Check 20.3 What is the main factor that distinguishes Aw climates from Af and Am? How is this difference reflected in the vegetation of these climate regions? Answer: Precipitation; Aw has a dry season and the others do not. Af and Am have a more lush vegetation where Aw has a savanna with drought-tolerant trees. How do the equatorial low and the subtropical high influence the seasonal distribution of rainfall in the Aw climate? Answer: As the equatorial low migrates away from the equator in summer, it brings rains to the Aw climate. The subtropical high moves into the region when the equatorial low retreats and brings sustained dryness. Concept Check 20.4 Why is the amount of precipitation that defines the boundary between humid and dry climates variable? Answer: Dryness is more about a water deficiency. Some regions have a great deal of evaporation of the rainfall due to high temperatures and will be dry as will a region that gets little rainfall and little evaporation. What is the primary reason (control) for the existence of the dry subtropical realm (BWh and BSh)? Answer: Subtropical high-pressure belts. What factors contribute to the existence of midlatitude deserts and steppes? Answer: They are landlocked and far removed from an ocean and they are on the lee sides of mountains. Concept Check 20.5 Describe and explain the differences between summertime and wintertime precipitation in the humid subtropical climate (Cfa). Answer: Summer has abundant rainfall while winters have very little. The humid subtropics have high humidity and high temperatures in the summer, making them similar to a tropical rainforest with its heavy rainfall. Cooler winter temperatures end this similarity. Why is the marine west coast climate (Cfb) represented by only slender strips of land in North and South America, and why is it very extensive in Western Europe? Answer: The west coasts of North and South America have mountain ranges blocking the inward movement of cool maritime air while Western Europe does not have mountains. The dry-summer subtropics are described as transitional. Explain why this is true. Answer: These regions have a winter rainfall maximum and stable summer conditions. Therefore, they alternate between being part of the dry subtropics and the humid midlatitudes during the course of the year. Why is the humid continental climate confined to the Northern Hemisphere? Answer: There is no significant land mass to allow for a continental type of climate at the appropriate latitudes in the Southern Hemisphere. Describe and explain the annual temperature range you should expect in the realm of the taiga. Answer: This region has a very large temperature range between winter and summer because it is a continental climate. There is no moderating effect of maritime air. Concept Check 20.6 Although polar regions experience extended periods of sunlight in the summer, temperatures remain cool. Explain. Answer: These regions receive solar radiation at very oblique angles, not allowing for intense heating. Why are precipitation totals low in polar climate? Which season has the most precipitation? Why? Answer: There is a small amount of water vapor in the air because of the low temperatures. Summer has the most precipitation because the warmer air has a higher moisture content. Where are EF climates most extensively developed? Answer: Greenland and Antarctica. Concept Check 20.7 1. The Arizona cities of Flagstaff and Phoenix are relatively close to one another yet have contrasting climates. Briefly describe the difference and why they occur. Answer: Flagstaff is at a much higher elevation. Therefore its climate is much cooler. Concept Check 20.8 Why has the CO2 level of the atmosphere been increasing over the past 200 years? Answer: The industrial revolution has caused humans to increase the burning of fossil fuels. How has the atmosphere responded to the growing CO2 levels? Answer: It has become warmer. How are temperatures in the lower atmosphere likely to change as CO2 levels continue to increase? Answer: They are likely to continue to warm. Aside from CO2, what trace gases are contributing to global temperature change? Answer: Methane, nitrous oxide, and chlorofluorocarbons. Concept Check 20.9 Distinguish between positive and negative climate-feedback mechanisms. Answer: A positive-feedback mechanism is an effect that reinforces any initial disturbance, causing the disturbance to continue to propagate. A negative-feedback mechanism yields results that are opposite from the initial disturbance and tend to cause it to slow or stop. Provide at least one example of each type of feedback mechanism. Answer: Positive – melting sea ice due to warming causes lower surface albedo, which absorbs more solar radiation, leading to more warming. Negative – an increase in some types of cloud cover due to climate change will reflect more solar radiation, leading to less warming. List some factors that influence the accuracy of computer models of climate. Answer: The models are simplified versions of Earth, they require assumptions about future conditions such as population, fossil fuel consumption, energy efficiency, etc. Concept Check 20.10 What are the main sources of human-generated aerosols? Answer: Sulfur dioxide from fossil fuel combustion and vegetation burning. What effect does black carbon have on atmospheric temperatures? Answer: It warms them. What is the net effect of aerosols on temperatures in the troposphere? Answer: They cause cooling. How long do aerosols remain in the atmosphere before they are removed? Answer: A few days to a few weeks. How does the residence time of aerosols compare to that of CO2? Answer: Carbon dioxide remains for many decades while aerosols only remain in the atmosphere a very short time. Concept Check 20.11 List and describe the factors that are causing sea level to rise. Answer: Melting of land-based ice causes an increase in water in the sea. As the ocean warms, it also expands due to the thermal expansion properties of water. Is global warming greater near the equator or near the poles? Explain. Answer: It is greater near the poles. The poles experience a melting of sea ice, glaciers, and permafrost. The albedo of the poles also changes because darker land surfaces are exposed, leading to a positive feedback of more warming. Based on Table 20.1, what projected changes relate to something other than temperature? Answer: Changes in precipitation amounts, leading to flooding or droughts, and increases in tropical cyclone activity. GIVE IT SOME THOUGHT ANSWERS Refer to Figure 20.1, which illustrates various components of Earth’s climate system. Boxes represent interactions or changes that occur in the climate system. Select three boxes and provide an example of an interaction or change associated with each. Explain how these interactions may influence temperature. Answer: Answers will vary depending on which components are chosen. Also, more than one type of interaction is possible with various components. 1. Ocean Heat Transport: The transfer of heat from the ocean to the atmosphere influences temperature by moderating coastal climates. 2. Ice-Albedo Feedback: Melting ice reduces Earth's reflectivity, absorbing more solar radiation and increasing temperatures further. 3. Atmospheric Circulation: Changes in wind patterns affect temperature distribution globally by redistributing heat from the equator to the poles. Describe one way in which changes in the biosphere can cause changes in the climate system. Next, suggest one way in which the biosphere is affected by changes in some other part of the climate system. Finally, indicate one way in which the biosphere records changes in the climate system. Answer: Changes in the biosphere, such as deforestation on a global scale, are capable of producing changes in the climate system. Removal of significant amounts of vegetation will increase the amount of carbon dioxide in the atmosphere, thus contributing to the greenhouse effect. Changes in global temperatures will significantly impact weather patterns and the resulting droughts would affect vegetation. The biosphere records changes in the climate system with proxy data such as fossil pollen, corals, and tree-growth rings. Refer to the monthly rainfall data (in millimeters) for three cities in Africa. Their locations are shown on the accompanying map. Match the data for each city to the correct location (1, 2, or 3) on the map. How were you able to figure this out? Bonus: Which figure in Chapter 18 would be especially useful in explaining or illustrating why these places have rainfall maximums and minimums when they do? Answer: 1 = City B, 2 = City A, 3 = City C. Matching the cities to the rainfall data can be done by realizing that City 1 has summer in the Northern Hemisphere and City 3 has summer in the Southern Hemisphere. Figure 18.25 and the diagram from question # 11 in Chapter 18 will be helpful in answering this question. Refer to Figure 20.5, which shows climates of the world. Humid continental (Dfb and Dwb) and subarctic (Dfc) climates are usually described as being “land controlled”— that is, they lack marine influence. Nevertheless, these climates are found along the margins of the North Atlantic and the North Pacific oceans. Explain why this occurs. Answer: These land-controlled climates are found along the margins of the North Atlantic and North Pacific oceans because of the large continental landmasses in the Northern Hemisphere. Despite their proximity to the ocean basins, they are more influenced by the large, continental landmasses. It has been suggested that global warming over the past several decades likely would have been greater were it not for the effect of certain types of air pollution. Explain how this could be true. Answer: Aerosols can cause cooling in the troposphere. Because humans have put a lot of aerosols into the air in the last several decades, it is possible that the cooling effects offset some of the warming. Motor vehicles are a significant source of CO2. Using electric cars, such as the one pictured here, is one way to reduce emissions from this source. Although these vehicles emit little or no CO2 or other air pollutants directly into the air, can they still be connected to such emissions? If so, explain. Answer: Yes, these vehicles can be connected to these emissions. Electricity is generated by the burning of fossil fuels, so while the cars are not directly polluting, they require a source of electricity. If a fellow student who, unlike you, had not studied climate were to ask, “Isn’t the greenhouse effect a bad thing because it’s responsible for global warming?” how would you respond? Answer: The greenhouse effect refers to the heating of the lower atmosphere by the absorption of terrestrial radiation by carbon dioxide and water vapor. These gases act much like the glass in a greenhouse in that they allow shorter wavelengths to pass through them while absorbing longer wavelengths. This effect is not the same as global warming—global warming may have many contributing factors and certainly an increase in the greenhouse effect could contribute to an increase in global temperatures. However, the natural heating of the lower atmosphere by various gases does not necessarily cause global warming. During a conversation, an acquaintance indicates that he is skeptical about global warming. When you ask why he feels that way, he says, “The past couple of years in this area have been among the coolest I can remember.” While you assure this person that it is useful to question scientific findings, you suggest to him that his reasoning in this case may be flawed. Use your understanding of the definition of climate along with one or more graphs in the chapter to persuade this person to reevaluate his reasoning. Answer: The climatic patterns over a relatively short time period (a few years) are certainly not indicative of global warming or cooling. Natural climatic variability can bring about changes over several years that appear to be outside the “normal” patterns that people come to expect. In order to accurately determine if such changes are real, and even perhaps caused by other factors (including human activity), climatic data over a longer period of hundreds or thousands of years should be studied and evaluated. EXAMINING THE EARTH SYSTEM ANSWERS The Köppen climate classification is based on the fact that there is an excellent association between natural vegetation (biosphere) and climate (atmosphere). Briefly describe the climate conditions (temperature and precipitation) and natural vegetation associated with each of the following Köppen climates: Af, BWh, Dfc, and ET. Answer: Af: The wet tropics are characterized by constantly high temperatures and year-round precipitation. The most luxuriant vegetation found in any climatic region, the tropical rain forest, is located in this climate. BWh: In this arid or desert climate, yearly precipitation is not as great as the potential loss of water by evaporation. Vegetation is sparse and adjusted to the low and infrequent rainfall. Dfc: In the subarctic climate, precipitation totals are low, with a maximum occurring during the warmer summer months. Although scrawny, the spruce, fir, larch, and birch trees in the taiga represent the largest stretch of continuous forest on the surface of Earth. ET: The tundra climate is a treeless climate found almost exclusively in the Northern Hemisphere. The amount of water vapor in the air is low, and precipitation, most abundant during the summer months, is scanty. Examine the precipitation map for the state of Nevada. Notice that the areas receiving the most precipitation resemble long, slender “islands” scattered across the state. Provide an explanation for this pattern. Are average temperatures in these wetter areas likely different from those in nearby less rainy places? Why or why not? A look back at Section 6.9 and Figure 6.32 (page 195) might be helpful. Answer: This pattern is most likely due to the presence of elongated elevated ridges in this area. The wetter areas are probably warmer, as they are on the windward sides of the mountains, and air will expand and cool as it ascends the mountainside. How might the burning of fossil fuels, such as the gasoline to run your car, influence global temperature? If such a temperature change occurs, how might sea level be affected? How might the intensity of hurricanes change? How might these changes impact people who live on a beach or barrier island along the Atlantic or Gulf coasts? Answer: The burning of fossil fuels adds great quantities of carbon dioxide to the atmosphere. Carbon dioxide absorbs heat. Therefore, increasing levels of carbon dioxide in the atmosphere will result in warmer global temperatures. Global warming will result in a rise in sea level and a higher frequency and greater intensity of hurricanes. The effect on people who live on a beach or barrier island will include greater and more frequent flood and storm damage. This satellite image from August 2007 shows the effects of tropical deforestation in a portion of the Amazon basin in western Brazil. Intact forest is dark green, whereas cleared areas are tan (bare ground) or light green (crops and pasture). Notice the relatively dense smoke in the left center of the image. How does deforestation of tropical forests change the composition of the atmosphere? Describe the effect that tropical deforestation has on global warming. Answer: Deforestation changes atmospheric composition by removing a source of moisture, the trees. The atmosphere will be more dry. There is also less vegetation for the uptake of carbon dioxide. Tropical deforestation contributes to global warming. Burning of the forests puts more greenhouse gases into the atmosphere and the reduced carbon dioxide uptake also contributes to an increase in warming. ADDITIONAL RESOURCES DVDs and Movies The Weather (2003) BBC, 230 minutes. Includes subheadings Wind, Wet, Cold, and Heat. Available on DVD. What’s Up with the Weather? (2007) NOVA, PBS, 53 minutes. Discusses global warming. Available on DVD. Global Warming: It’s All About Carbon. National Geographic and National Public Radio. Series of five cartoon shorts aimed at adults and that address global warming issues. All five videos available for free streaming from http://www.npr.org/news/specials/climate/video/ Extreme Ice (2009) NOVA, PBS, 53 minutes. Documents the melting of Arctic ice sheets due to global warming. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/extremeice.html Secrets Beneath the Ice (2011) NOVA, PBS, 53 minutes. Examines Antarctica’s future as Earth warms. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/secrets-beneathice.html Fastest Glacier (2005) NOVA Science NOW, PBS, 7 minutes. Available for free streaming from http://www.pbs.org/wgbh/nova/earth/fastest-glacier.html Websites What’s Up with the Weather website to accompany video. Also has stand-alone information on global warming. http://www.pbs.org/wgbh/warming/ National Weather Service Climate Prediction Center. http://www.cpc.ncep.noaa.gov National Climatic Data Center. http://www.ncdc.noaa.gov Global Warming from the Natural Resources Defense Council. http://www.nrdc.org/globalwarming Teaching Climate Change: Lessons from the Past. Activities for college-level students. http://serc.carleton.edu/NAGTWorkshops/climatechange/activities.html Solution Manual for Earth Science Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa 9780321928092, 9780321934437