The Atmosphere and the Oceans ff the Na Pali coast in Hawaii, clouds stretch toward O the horizon. In this unit, you’ll learn how the atmo- sphere and the oceans interact to produce clouds and crashing waves. You’ll come away from your studies with a deeper understanding of the common characteristics shared by Earth’s oceans and its atmosphere. Unit Contents 11 Atmosphere14 Climate 12 Meteorology15 Physical Oceanography 13 The Nature 16 The Marine Environment of Storms Go to the National Geographic Expedition on page 880 to learn more about topics that are con- nected to this unit. 268 Kauai, Hawaii 269 1111 AAtmospheretmosphere What You’ll Learn • The composition, struc- ture, and properties that make up Earth’s atmos- phere. • How solar energy, which fuels weather and climate, is distrib- uted throughout the atmosphere. • How water continually moves between Earth’s surface and the atmo- sphere in the water cycle. Why It’s Important Understanding Earth’s atmosphere and its interactions with solar energy is the key to understanding weather and climate, which con- trol so many different aspects of our lives. To find out more about the atmosphere, visit the Earth Science Web Site at earthgeu.com 270 DDiscoveryiscovery LLabab Dew Formation Dew forms when moist air near 4. Repeat the experiment outside. the ground cools and the water vapor Record the temperature of the in the air changes into water droplets. water and the air outside. In this activity, you will model the Observe In your science journal, formation of dew. describe what happened to the out- 1. Fill a glass about two-thirds full of side of the glass in step 3 and step 4. water. Record the temperature of Relate your observations to the the room and the water. formation of dew. Graph the temperature of the water 2. Add ice cubes until the glass is full. during both experi- Record the temperature of the ments. Did the results water at 10-second intervals. vary with location? 3. Observe the outside of the glass. Explain. Note the time and the temperature at which changes occurred on the outside of the glass. 11.111.1 Atmospheric Basics OBJECTIVES Imagine living in the blazing heat of the Sahara desert, near the equa- • Describe the composi- tor. Then imagine living in the frozen vastness above the arctic circle. tion of the atmosphere. Why are these places so different? The answer lies in how solar energy interacts with the atmosphere, and how the interactions com- • Compare and contrast bine to produce weather and climate. the various layers of the atmosphere. ATMOSPHERIC COMPOSITION • Identify three methods The ancient Greeks thought that air was one of the fundamental ele- of transferring energy ments that could not be broken down into anything else. Today, we throughout the atmo- know that air is a combination of many gases, each with its own sphere. unique characteristics. Together, these gases form Earth’s atmo- sphere, which extends from Earth’s surface to outer space. VOCABULARY About 99 percent of the atmosphere is composed of nitrogen and oxygen, with the remaining one percent consisting of small amounts ozone exosphere of argon, hydrogen, carbon dioxide, water vapor, and other gases. The troposphere radiation percentages of the main components, nitrogen and oxygen, are criti- stratosphere conduction cal to life on Earth. If either were to change significantly, life as we mesosphere convection know it could not exist. Among the lesser-percentage gases, however, thermosphere 11.1 Atmospheric Basics 271 Figure 11-1 Nitrogen makes up 78 percent of the Percentages of Gases That Make Up Earth's Atmosphere gases in Earth’s atmosphere. Oxygen makes up 21 per- cent. The remaining one Argon percent consists of small 0.93% Nitrogen amounts of various other 78% gases. Carbon dioxide 0.03% Water vapor 0.0 to 4.0% Oxygen 21% Trace gases 0.01% Neon Helium Methane Krypton Hydrogen Ozone Xenon there is some variability, particularly in water vapor and carbon diox- ide. Figure 11-1 shows the composition of the atmosphere. Key Atmospheric Gases The amount of water vapor in the atmosphere at any given time or place changes constantly. It can be as much as four percent of the atmosphere or as little as almost zero. The percentage varies with the seasons, with the altitude of a par- ticular mass of air, and with the surface features beneath the air. Air over deserts, for instance, is drier than air over oceans. Carbon diox- ide, another variable gas, makes up under one percent of the atmo- sphere. Why is it necessary to even mention these seemingly insignificant gases? The level of both carbon dioxide and water vapor are critical because they play an important role in regulating the amount of energy the atmosphere absorbs. Water vapor, the gaseous form of water, is the source of clouds, rain, and snow. In addition, water is the only substance in the atmosphere that exists in three states: solid, liq- uid, and gas. This is important because when water changes from one state to another, heat is either absorbed or released, and this heat greatly affects the atmospheric motions that create weather and cli- mate. The atmosphere also contains solids in the form of tiny particles of dust and salt. Dust is carried into the atmosphere by wind. Salt is picked up from ocean spray. Dust and salt play a role in cloud for- mation, as you’ll learn later. Ice is the third solid found in the atmo- 272 CHAPTER 11 Atmosphere sphere, usually in the form of hail and snow. Ozone Another component of the atmosphere, ozone (O3), is a gas formed by the addition of a third oxygen atom to an oxygen Environmental Connection molecule (O2). Ozone exists in small quantities mainly in a layer well above Earth’s surface. It is important because it absorbs ultraviolet radiation from the Sun. If ozone did not control the amount of ultra- violet radiation reaching Earth’s surface, our fragile skin could not tolerate exposure to the Sun for long. Evidence indicates that the ozone layer is thinning. You’ll learn more about this issue in the Science in the News feature at the end of this chapter and in later chapters. Figure 11-2 The five main STRUCTURE OF THE ATMOSPHERE layers of the atmosphere The atmosphere is made up of several different layers, as shown in vary in temperature and Figure 11-2. Each layer differs in composition and temperature. chemical composition. (km) 700 Exosphere 600 Satellite 500 400 Aurora caused by particles from the Thermosphere 300 Sun interacting with Earth’s atmosphere 200 100 Meteor Mesosphere 50 Ozone layer Stratosphere Weather balloon 10 Troposphere 0 11.1 Atmospheric Basics 273 Temperature Variations with Altitude Lower Atmospheric Layers The 120 layer closest to Earth’s surface, the troposphere, contains most of the 110 mass of the atmosphere, including Thermosphere water vapor. This is the layer in which 100 most weather takes place and most air 90 pollution collects. The troposphere is characterized by a general decrease in 80 Mesopause temperature from bottom to top. The upper limit of the troposphere, called 70 Mesosphere the tropopause, varies in height. It’s 60 about 16 km above Earth’s surface in the tropics and about 9 km or less at the Altitude (km) 50 Stratopause poles. The tropopause is where the Highest 40 concentration gradual decrease in temperature stops. of ozone Above the tropopause is the 30 Stratosphere stratosphere, a layer made up primarily of concentrated ozone. Ozone absorbs 20 more ultraviolet radiation than does air 10 Tropopause in the troposphere. As a result, the Troposphere stratosphere is heated, and air gradually 0 –80 –60 –40 –20 0 20 40 60 80 increases in temperature to the top of the layer, called the stratopause, located ° Temperature ( C) about 50 km above Earth’s surface. Figure 11-3 Differences in chemical composition cause Upper Atmospheric Layers Above the stratopause is the air temperatures to vary mesosphere. There is no concentrated ozone in the mesosphere, so throughout the atmosphere. the temperature decreases once again, as shown in Figure 11-3. The top of this layer, the mesopause, is the boundary between the meso- sphere and the next layer, the thermosphere. The thermosphere contains only a minute portion of the atmosphere’s mass. What air does exist in this layer increases in temperature once again, this time to more than 1000°C. In the thermosphere, however, the molecules that make up air are so sparse and widely spaced that, despite the high temperature, this layer would not seem warm to a human pass- ing through it. The ionosphere is part of the thermosphere. It is made up of elec- trically charged particles and layers of progressively lighter gases. The exosphere is the outermost layer of Earth’s atmosphere. Light gases such as helium and hydrogen are found in this layer. Above the exosphere lies outer space. There is no clear boundary between the atmosphere and space. There are simply fewer and fewer molecules with increasing altitude until, for all practical purposes, you have entered outer space. 274 CHAPTER 11 Atmosphere SOLAR FUNDAMENTALS The Sun is the source of all energy in the atmosphere. This energy is transferred to Earth and throughout the atmosphere in three ways. Radiation The Sun is shining on, and therefore warming, some portion of Earth’s surface at all times. This method of energy trans- fer is called radiation. Radiation is the transfer of energy through space by visible light, ultraviolet radiation, and other forms of elec- tromagnetic waves.