Weather and Climate Flash Flood! sections When cool, dry air meets warm, moist air 1 Earth’s Atmosphere Lab Visualizing a dramatic things can happen. Many desert Temperature Inversion environments are familiar with flash floods that can result from such an event. Dry river 2 Weather beds can suddenly become raging torrents of 3 Climate water, rocks, and mud. 4 Earth’s Changing Climates Science Journal In your Science Journal, describe Lab Investigating some of your observations of severe weather. Hypothesize Microclimate what might cause these weather events. 516 Byron Aughenbaugh/Getty Images Start-Up Activities Weather and Climate Make the following Foldable to com- pare and contrast the character- Atmospheric Pressure istics of weather and climate. Changes in atmospheric pressure are involved in producing winds and weather. You may STEP 1 Fold one sheet of paper lengthwise. not be aware of how much pressure the atmosphere exerts, but you can see it in this Lab. STEP 2 Fold into thirds. 1. Fill a glass to the brim with water. 2. Place a piece of thick paper or cardboard on top. 3. Hold the paper or cardboard securely to the brim of the glass. Turn the glass STEP 3 Unfold and draw overlapping ovals. upside down. Cut the top sheet along the folds. 4. Release your hand from the paper 5. Think Critically What keeps the paper or cardboard against the brim of the glass and the water from flowing out? STEP 4 Label the ovals as shown. Weather Both Climate Constructing a Venn Diagram As you read Preview this chapter’s content the chapter, list the characteristics unique to and activities at weather under the left tab, those unique to cli- gpescience.com mate under the right tab, and those elements common to both under the middle tab. 517 Byron Aughenbaugh/Getty Images Earth’s Atmosphere Reading Guide New Vocabulary ■ Describe the composition of the Heat and water are essential for life troposphere atmosphere. on Earth. • temperature inversion ■ Explain how the atmosphere is • greenhouse effect heated and include the role of Review Vocabulary • latent heat land surface and water. nucleus: a central point about • ■ Describe Earth’s system of water which concentration or accretion cycling. takes place Atmospheric Composition You probably never think about the air you breathe. Your body uses only oxygen, but air is a mixture of gases. Nitrogen is the largest component with 78 percent and oxygen is next with 21 percent by volume. Most of the remaining one percent is the inactive gas argon and water vapor in varying amounts. The small remaining portion is a mixture of trace gases, so called because they are present in such small, barely detectable amounts. For example, carbon dioxide makes up only about 0.03 percent, and the other trace gases—methane, nitrous oxide, and ozone—together make up less than 0.001 percent of the atmosphere. Still, these trace gases are critical for life on Earth. What are the trace gases? Figure 1 In northern latitudes, Biological Processes Living organisms produce trace carbon dioxide concentration gases, except ozone. Cellular respiration by organisms produces increases during summer and water vapor and carbon dioxide (CO ). Photosynthetic organ- decreases during winter. 2 isms use carbon dioxide and produce almost all the oxygen in the atmosphere. Organisms alter atmos- Comparison of CO2 Concentration to Time of Year and Latitude pheric CO2 concentration at various lati- tudes throughout the year, as shown in 360 Figure 1. Microorganisms in swamps, 350 rice paddies, and soil produce nitrogen 340 90N (ppm) and methane. The microorganisms in the 330 0 Concentration 1982 digestive tracts of animals such as ter- 2 1983 1984 -90S CO Latitude mites, cows, and sheep produce methane. 518 CHAPTER 17 Weather and Climate Formation of the Atmosphere Earth’s early atmosphere contained mostly hydrogen and helium. These gases were lost and were replaced by gases from volcanic eruptions, including water vapor and CO2.Oxygen from photosynthetic marine organisms accumulated in the atmosphere and intense solar Visualizing radiation converted some of it into ozone. The ozone layer Convection shielded Earth from harmful ultraviolet rays. This allowed pho- Procedure tosynthetic organisms to emerge on land, where they produced 1. Place an ice cube in the more oxygen. center of a beaker. Some scientists think it took millions of years for our 2. Add room-temperature atmosphere to reach its current state—a delicate equilibrium water until the beaker is between processes producing and destroying atmospheric three-fourths full. 3. Place one drop of food gases. Unfortunately, human activities might be threatening coloring on the surface of this equilibrium. the water. 4. Observe what happens. Atmospheric Structure Analysis Earth’s atmosphere extends more than 1,000 km above Earth’s 1. Describe what happened surface. Most of our weather takes place within the troposphere, to the color. 2. Explain why this occurred. a layer extending 30 km above Earth’s surface. In this layer, as shown in Figure 2, temperature normally decreases with height. Sometimes, however, temperature increases with height. This is called a temperature inversion. When this happens, the air is very stable—it resists the rising motion needed to form clouds or to disperse air pollution. The Stratosphere Above the troposphere is the stratosphere, which is extremely dry and rich in ozone. Here, temperature always increases with height, creating a permanent temperature inversion. The place where this tem- perature inversion begins is called the tropopause. It acts like a lid that Temperature Change with Height keeps air in the troposphere from 200 rising into the stratosphere. The uppermost layers, the mesophere and thermosphere, are very low in density and do not affect weather. 100 75 Figure 2 Temperature decreases Height (km) Ozone layer with height in the troposphere up to 50 the tropopause. Above the tropopause, 25 Stratosphere Tropopause temperature increases with height in Troposphere 0 the stratosphere. –120 –60 0 60 120 180 300 400 600 800 Identify The ozone layer is found in Temperature (˚C) which atmospheric layer? SECTION 1 Earth’s Atmosphere 519 Heating the Atmosphere The energy that heats the atmosphere ultimately comes from the Sun. In the stratosphere, solar rays split oxygen molecules into single atoms. The oxygen atoms then react with other oxygen molecules, forming ozone. Ozone absorbs nearly all of the Sun’s ultraviolet radiation. This absorption by ozone is why temperature increases with height in the stratosphere. The remaining solar rays pass to Earth’s surface where they are either absorbed or reflected back to the atmosphere. As Earth’s surface is heated, it emits long-wave, infrared radiation. Trace gases, such as carbon dioxide and water vapor, absorb long wavelengths and re-emit some of them back to Earth’s surface. The term greenhouse effect refers to this re-emission of infrared radiation back to Earth’s surface, as shown in Figure 3. Oxygen and nitrogen absorb little radiation and contribute little to atmospheric heating. Although water vapor and trace gases make up less than 0.03 percent of the atmosphere, they Figure 3 Trace gases absorb are strong absorbers and heat the atmosphere the most. infrared radiation and are heated. Conduction, convection, and latent heat also contribute to These gases then re-emit infrared heating Earth’s atmosphere. Latent heat is heat energy released in all directions, sending part of it or absorbed during the phase changes of water, such as evapo- back to Earth’s surface. rating water or melting snow. It is released to the atmosphere Infer How does this compare to when water vapor condenses as clouds. being covered by a blanket at night? A Varied Surface Earth’s surface is not uni- Sun Ultraviolet form and therefore, heats the absorbed by atmosphere unevenly. Snow, ozone ice, water, vegetation, and Visible light bare soil reflect different reflected by Infrared emitted amounts of solar radiation clouds by atmospheric CO and H O back to space and heat at dif- 2 2 ferent rates when they absorb radiation. For example, dry land heats rapidly and emits much radiation to the atmos- phere. In contrast, water tem- perature changes slowly and Emitted infrared stores heat, releasing it at a by Earth later time. This uneven pat- tern of surface heating gives rise to pressure differences and wind. 520 CHAPTER 17 Weather and Climate Water in the Atmosphere Uneven heating has another effect. It produces currents of air that carry water vapor aloft and form clouds. Air generally rises over warm surfaces and sinks over cold surfaces. Many birds and hang gliders soar on these warm currents, called thermals. As air rises, it expands and cools. To form clouds, moist air must rise high enough to cool to its dew point. At this tempera- ture, air is saturated and water vapor condenses to form cloud droplets. Small particles in the air, called condensation nuclei, trigger this process. When present in high quantities, such as in dust or polluted city air, these nuclei can trigger condensation in unsaturated air. This is how smog forms. Explain how smog forms. Precipitation Cloud formation is the first step in the precip- itation process. Two basic cloud types are the puffy cumulus type and the flat, elongated, stratus type. Cumulus clouds form from rising air parcels. If they produce rain, it is usually only brief showers. Stratus-type clouds form mainly when layers of air rise gently. They usually produce drizzle or long-lasting rain. Many in-between forms of clouds exist, depending on how sta- ble the air is and how high in the atmosphere the clouds form. You can see some of these types in Figure 4.