Unit 2 Water and Weather - Spokane Public Schools

Chapter 4Water and the Water CycleThe amount of water on Earth is about the same now as itwas during the age of the dinosaurs, 65 to 220 million yearsago. With about 70 percent of its surface covered with water,Earth is truly a water planet. However, only a small amountof this water is available for household, agricultural, andindustrial use. Since Earth has been around for such a longtime, why haven’t we run out of water? In this chapter, youwill learn how water moves naturally around Earth so that itis available to use year after year.1. Where is most of Earth’s water found?2. How is a mud puddle part of the water cycle?3. What is the difference between an aquifer and awatershed?

4.1 Water on Earth’s SurfaceAbout 70 percent of Earth’s surface is covered with water. This water is found inoceans, rivers, lakes, under the ground, and as ice.The hydrosphereWhat is thehydrosphere?Water phases onEarthWater in theatmosphereAll the water on Earth is part of a large system called thehydrosphere (Figure 4.1). A set of processes called the water cyclekeeps water moving from place to place on Earth. You will learnabout the water cycle in the next section.In Chapter 2, you learned that matter is anything that has massand takes up space. Phases of matter include liquid, solid, and gas.On Earth, water occurs in all three phases. Most of the water onEarth is liquid. The estimated volume of liquid water on Earth is1.386 billion cubic kilometers. The next most common phase ofwater is ice. If all the ice on Earth melted, the level of the oceanswould rise about 70 meters!Gaseous water is located in the atmosphere, the layer of gasesthat surrounds Earth. Moisture in the atmosphere replenishes ourwater supplies when it becomes rain or snow and returns to Earth.hydrosphere - an Earth systemthat includes all the water on theplanet.atmosphere - the layer of gasesthat surrounds Earth.Figure 4.1: Earth’s hydrosphereincludes all the water on the planet.The clouds in the picture are alsopart of the hydrosphere. Can youfind the hurricane? It’s part of thehydrosphere too.80UNIT 2 WATER AND WEATHER

CHAPTER 4: WATER AND THE WATER CYCLEThe distribution of water on EarthSalt water and alittle fresh waterWater is animportantresourceWhere do we findwater?About 97% of Earth’s water is salt water found in oceans. Almost2% of Earth’s water is frozen at the North and South Poles and onmountain tops. Finally, less than 2% of the water on Earth is freshwater that humans, plants and animals can consume. If all thewater on Earth could fit into a one-liter container, the amount offresh water would equal only about 17 milliliters (Figure 4.2).Most living things rely on fresh water. The hydrosphere and thewater cycle allow our limited supply of fresh water to be recycled.This table lists how water is distributed on Earth.Figure 4.2: If all the water on theEarth could fit into a one-litercontainer, the amount of fresh wateravailable for human consumptionwould be equal to about 17 milliliters.How big is a cubic kilometer?One cubic kilometer is1,000 m 1,000 m 1,000 mor 1,000,000,000 m 3 (one billioncubic meters)!If the volume of a swimming poolis 1,000 m 3 , how many swimmingpools fit inside one cubickilometer?To find out how many swimmingpools equal all the world’s rivers,you would have to multiply thenumber you just got by 2,120!4.1 WATER ON EARTH’S SURFACE81

Places where water is foundWhere watercollectsSurface waterFrozen waterGroundwater andthe water tableAfter a rainstorm, water collects in low areas on the ground. On asmall scale, these low areas form mud puddles. On a large scale,low areas that collect water include oceans and rivers. Earth’swater can also be found frozen in glaciers and underground.Surface water on Earth refers to water that collects on the ground.This water includes oceans, lakes, rivers, streams, and reservoirs.A reservoir is a protected artificial or natural lake that is used tostore water.Frozen water is found at the poles and on mountain tops asglaciers and ice sheets. A glacier is a huge mass of ice thatforms on land when snow and ice accumulate faster than theymelt (Figure 4.3). Most of Earth’s fresh water is in the form ofglacier ice.Groundwater is water that collects under ground. Some of thewater on Earth’s surface moves down through the soil to the watertable. The water table is the upper level of underground water.Below this level, the spaces between particles of soil and rock aresaturated (filled) with groundwater. The water table changesdepending on the season. A well’s water level indicates the watertable for an area.surface water - water found onEarth’s surface in places likeoceans, lakes, rivers, andreservoirs.reservoir - a protected artificial ornatural lake that is used to storewater.glacier - a huge mass of ice thatforms on land when snow and iceaccumulate faster than they melt.groundwater - water thatcollects under ground.water table - the upper level ofwater under ground; below thewater table, all spaces are filledwith groundwater.Figure 4.3: A glacier.82UNIT 2 WATER AND WEATHER

CHAPTER 4: WATER AND THE WATER CYCLEWater as a resourceWater for lifeWater dissolvesmany thingsThe temperature range on Earth’s surface is just right for water toexist in all three phases—liquid, solid, and gas (Figure 4.4). Mostwater on Earth is in the liquid phase. Liquid water is extremelyimportant for living things. For example, a human body is 60% to75% water (Figure 4.5). You need water to keep your blood, brain,and lungs working properly.One of the reasons why water is so useful is that it can dissolvemany things. When you eat food, water in your body dissolvesnutrients so they can be carried through your bloodstream. Oxygenis another important substance that is dissolved in your blood.Oxygen dissolved in rivers and lakes keeps fish alive and healthy.Water also dissolves the minerals that make up rocks. Over longperiods of time, water changes Earth’s surface by dissolving andwearing down rocks and mountains. For example, the GrandCanyon was formed when the water of the Colorado River woredown the rocks in its path.Figure 4.4: The surface temperaturesfor some planets in our solar system.Additional waterusesWater is necessary for all forms of agriculture and farming. Forexample, water is needed to grow grain for bread and to grow fruitsand vegetables. Water is also used in industry and in many ways inyour home.Figure 4.5: The human body is 60%to 75% water.4.1 WATER ON EARTH’S SURFACE83

CHAPTER 4: WATER AND THE WATER CYCLE4.2 The Water CycleThe Sun keeps water moving through the hydrosphere by providing energy. In thissection, you will learn about the water cycle and where water goes so that it isavailable for people, animals, and plants.Recycling waterSharing waterwith thedinosaursThe Sun drivesthe water cycleWind andweatherGravityFor millions of years, only a small percentage of fresh water hasbeen available to meet the basic needs of life on Earth. Rememberthat our total water supply today is the same as when thedinosaurs were around. Therefore, the water you drink wasprobably used by other organisms during the past millions of years.A set of processes called the water cycle keeps our watercontinuously recycled and naturally filtered. The water cycle issometimes called the hydrologic cycle.The Sun is the source of energy that drives the water cycle. Wind,weather, and gravity are additional natural forces that keep watermoving from place to place (Figure 4.7). Of course, people also playa role in transporting water on Earth.Wind and storms provide forces that cause water to be blown ormoved from once place to another. For example, wind blowingclouds moves water vapor from one place to another. Precipitation(rain or snow) is a way water moves from the sky to the ground.In Chapter 2, you learned that the more mass an object has, thegreater the force of gravity is on that object. Water has mass and isaffected by gravity. For example, when raindrops get big enough ina rain cloud, gravity causes them to fall to the ground. Gravity alsocauses water to run down mountains to the coast (Figure 4.7). Andgravity is the primary force that moves water from Earth’s surface,through the ground, to become groundwater.water cycle - a set of processesenergized by the Sun that keepwater moving from place to placeon Earth; also called thehydrologic cycle.Figure 4.7: The Sun, wind, weather,and gravity drive the water cycle.4.2 THE WATER CYCLE85

Water cycle processesFour mainprocessesEvaporationTranspirationThe four main processes of the water cycle are evaporation,transpiration, condensation, and precipitation.Evaporation occurs when liquid water has enough energy to leavethe liquid phase and become a gas called water vapor. The sourceof this energy is heat from the Sun. The Sun warms the surfaces ofmud puddles, lakes, rivers, and oceans. As a result, water obtainsenough energy to evaporate and become water vapor in theatmosphere.Transpiration is the process in which plants lose water throughtiny pores on their leaves. The pores open to gain carbon dioxide.Once the pores are open, the plants lose water, and release oxygen.The water vapor contributes to the water cycle. All livingorganisms benefit from the released oxygen. It’s what we breathe!evaporation - the process bywhich a substance in its liquidphase gains energy and enters itsgaseous phase; a phase of thewater cycle.water vapor - water in gas form.transpiration - the process bywhich plants lose water throughtiny pores on their leaves; a phaseof the water cycle.The water moleculeYou have probably heard watercalled “H-two-O” and written asH 2 O. This way of talking aboutwater refers to a water moleculethat is made of two hydrogenatoms and one oxygen atom. Inthis text, we represent the watermolecule like this:86UNIT 2 WATER AND WEATHER

CHAPTER 4: WATER AND THE WATER CYCLECondensationPrecipitationFollowing thewater cycleCondensation occurs when water in its gaseous phase loses energy.This tends to happen high in the atmosphere as the molecules cooldown. Water molecules cool and slow down so much that theygroup and form droplets of liquid. When these droplets are heavyenough, they fall to Earth as rain.Precipitation is any form of condensed water vapor in theatmosphere falling back to Earth. This includes rain, snow, sleet,and hail.The diagram below illustrates the water cycle. Trace the pathof water from the ocean to groundwater and back to the ocean.condensation - the process bywhich a substance in its gaseousphase loses energy and enters itsliquid phase; a phase of the watercycle.precipitation - condensed watervapor in the atmosphere fallingback to Earth in the form of rain,hail, sleet, or snow; a phase of thewater cycle.Imagine you are a snowflake in anicecap on the top of a mountain.Describe what happens to you asthe seasons change starting withwinter. Describe your path throughthe water cycle. Also, describe anypoints along your journey whereyou might interact with humanbeings!4.2 THE WATER CYCLE87

How water moves in the water cycleSurface runoffPercolationAquifersThe importanceof aquifersPrecipitation that reaches Earth’s surface often flows over theland. This water, called surface runoff, eventually reaches lakes,rivers, and oceans. Surface runoff dissolves and collects mineralsand nutrient-rich soil as it flows. Many of the minerals andnutrients in fresh water and salt water come from surface runoff.Water that flows over the land can percolate through the soil tobecome groundwater. Percolation is the process of liquid movingthrough a substance that is porous (has many tiny holes or“pores”). Groundwater can move through soil because the soilis porous.The destination for percolating groundwater can be anunderground area of sediment and rocks called an aquifer. Whengroundwater is removed from an aquifer for human consumption,it can take 300 to 1,000 years or more to replenish the supply.Groundwater that is not collected from an aquifer will continue toflow through sediments and may eventually enter the ocean, thuscontinuing the water cycle.Aquifers are important water sources. For example, the waterobtained from the Ogallala Aquifer in the mid-western UnitedStates has made agriculture profitable in this dry region.The Ogallala is one of the largest aquifers in the world. Itsunderground area (450,000 km 2 ) is in parts of South Dakota,Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico,and Texas. With such a demand on its water supply, the OgallalaAquifer is in danger of becoming depleted because the water isbeing used faster than it can be replenished.surface runoff - water that flowsover land until it reaches lakes,rivers, and oceans.percolation - the process ofliquid moving through a poroussubstance.aquifer - a underground area ofsediment and rocks that is filledwith groundwater.Figure 4.8: Surface runoff reachessurface water locations or percolatesinto an aquifer. Groundwater that is notcollected from the aquifer flows tooceans.88UNIT 2 WATER AND WEATHER

CHAPTER 4: WATER AND THE WATER CYCLEWatershedsWhat is awatershed?WatershedsNaturalresourcesA watershed is an area of land that catches all precipitation andsurface runoff. This water is collected in a body of water such as ariver. Eventually, all this water flows to an ocean (Figure 4.9). Theboundaries of a watershed are often steep mountain ridges.The water in a watershed is directly connected to the groundwater.Water collects in a place like a river, but some of the surface runoffbecomes groundwater. The water that comes to many homes in theUnited States originates in a watershed that can be local or fromanother region.In addition to supplying our drinking water, watersheds alsoprovide habitat for plants and animals, areas of natural beauty,and bodies of water for recreation. As communities grow andchange, it is important to protect these natural resources.watershed - an area of land thatcatches all precipitation andsurface runoff and collects it in abody of water such as a river.OceanAtlanticSome sources of waterSt. Lawrence River, theGreat Lakes, eastern NorthAmerica, South Americaeast of the Andes, northernEurope, western-Sub-Saharan Africa, CaribbeanSea basin, MediterraneanSea basinPacificIndianArcticSouthernChina, southeasternRussia, Japan, Korea,South America west of theAndes, Pacific Islands, andwestern North Americaeastern coast of Africa,India, Burma, Australia,Indonesia, southeast AsiaMost of Russia andNorthern CaliforniaAntarcticaFigure 4.9: Some sources of water forthe world’s oceans. See if you can findthese places on a globe!4.2 THE WATER CYCLE89

The water cycle and volcanoesWater in hot rockWater vapor fromeruptionsYou may be surprised to learn that volcanoes are part of Earth’swater cycle. This is because water is an ingredient in the hot,molten rock that is inside a volcano. Inside the volcano, this hot,molten rock is called magma. Outside the volcano, it is called lava.You will learn more about volcanoes in Chapter 12.When a volcano erupts, water is released as water vapor intothe atmosphere. The water vapor eventually condenses and fallsas rain or another form of precipitation.Hot springs andgeysersHot springs are the result of groundwater coming in contact withhot rock or magma below Earth’s surface. The hot rock heatsthe water. A hot spring can become a geyser. A geyser is a hotspring with constricted passageways to the ground’s surface. Theconstriction causes water pressure to build up so that the watereventually explodes from the ground. The water passagewayis not constricted for other types of hot springs (Figure 4.10). OldFaithful in Yellowstone National Park is a geyser (Figure 4.11).Water that evaporates from geysers or hot springs—both volcanicfeatures—becomes part of the water cycle.Figure 4.10: A diagram of a geyserand a hot spring.Figure 4.11: Old Faithful inYellowstone National Park is a geyser.90UNIT 2 WATER AND WEATHER

CHAPTER 4: WATER AND THE WATER CYCLE4.2 Section Review1. List the sources of energy and forces that drive the water cycle.2. Give an example of how people participate in the water cycle.3. All the water on Earth is recycled. What does that mean aboutthe water you drank today? Give an example of where yourdrinking water could have been in the past.4. What has to happen for liquid water to become water vapor?5. Plants need water but they lose water by opening pores on theirleaves. Why do they open their pores?6. Which process of the water cycle is similar to water dropletsforming on a bathroom mirror when you take a shower? Pickthe correct answer and explain your choice.a. condensation b. precipitationc. evaporation d. transpiration7. Which of these items is porous under normal conditions?a. a cotton shirt b. a piece of steelc. a raincoat d. a plastic cup8. In which of these situations is percolation occurring?a. A mud puddle driesc. Water goes through coffeegrounds to make coffee9. What is the difference between an aquifer and a watershed?10. You learned that it might take 300 to 1,000 years or more toreplenish any groundwater that is removed from an aquifer.Why do you think it would take so long?11. How are volcanoes part of the water cycle?b. You pour a glass of orangejuiced. Snow melts outside on a hot,sunny dayResearch the answers to thesequestions for your town.1. What is the name of thewatershed or aquifer that yourtown uses for drinking water?2. Is there a local organizationthat monitors the water qualityof your watershed?Learning new wordsYou can learn and remember thedefinitions of new words by usingthem in a sentence.For each of the vocabulary wordsin this chapter, write a sentencethat uses the word correctly. Youmay want to make a drawing thathelps you remember the newword. For example, make adrawing of the water cycle and fillin the terms you know!4.2 THE WATER CYCLE91

The Wild World of CavesChapter 4 ConnectionCaves are one of the natural wonders of our world. You'llfind that they exist in many areas around the globe. In theUnited States alone, there are over two hundred caves thatare open to the general public. People of all ages arefascinated by caves and the many legends and stories thathave been told over the years. Why are we drawn to caves?Maybe it's because caves are known to be secret hidingplaces. They are dark and dangerous and often mysterious.Yet many are places of spectacular beauty. All are home tomany bat species and other creepy crawling cave animalsthat dwell in the darkness.There are more than 40,000 known caves in the UnitedStates. Mammoth Cave in Kentucky is the world's longestcave with more than 350 miles of passageways.Types of cavesThe formation of a cave is dependent on the material fromwhich it is made. The process evolves slowly over millions ofyears and changes constantly. Basically, there are four maintypes of caves: ice caves, sea caves, lava caves, and limestonecaves.Ice caves form when the Sun melts the ice on a glacier. Thewater seeps down into cracks of the glacier. The warm watermelts away the ice inside. The cracks also known as fracturesincrease in size. These caves often appear blue in color fromthe light passing through the ice.Sea caves are formed by the actionof water. A cave forms when anarea of rocky shore has a weak spotlike a fracture. Constant waveswear away the rock at the weakspot causing a cave to form. Overtime it can become a largeunderwater cave system.Lava caves, often called lava tubes, form quickly compared toother cave types. They form from molten lava that spills overduring a volcanic eruption. Tubes form when the outer layerof lava hardens into rock and the hot molten lava continuesto flow like a river inside. The tubes drain of all the lavawhen the molten flow stops and the result is a tube-like cave.Limestone caves—like Mammoth Cave— are by far thelargest and most common caves in the world. Most limestonecaves are created when surface water seeps into cracks anddissolves the limestone underground. Surface water includesrives, lakes, and oceans. Carbonic acid is largely responsiblefor the chemical weathering of rocks and the formation ofcaverns in limestone.92

Show caves versus wild cavesA cave in its natural untouched state is called a wild cave.Wild caves can be explored freely, but are extremelydangerous. You must be well equipped and knowledgeable toexplore wild caves on your own. In order to avoid the hazardsand dangers of wild caves, show caves were developed andmany are maintained by the National Park Service. Showcaves allow the public to safely view the beauty of a cave.These caves have guides, established paths, lighting, a placeto eat lunch, and bathrooms—all far beneath Earth’ssurface. The most famous show caves in the United Statesare located at Carlsbad Caverns National Park in Carlsbad,New Mexico.Carlsbad Caverns contains one of the world's largestunderground chambers called the Big Room. The Big Roomis the largest room in the cavern. It is also the largest cavechamber in the United States. It is located 754 feet below thesurface, is 25 stories high, and about a third of a mile wide.Just how large is the Big Room? According to the NationalPark Service, this room is about the size of 6 football fields.Visitors travel to the chamber by elevator. Once there, theycan walk a one-mile path that circles the room.Formation of the Big RoomHow did the large chambers of Carlsbad Caverns form?Groundwater, mixed with carbon dioxide (and other gases)from the air and soil forms an acid which dissolved thelimestone to create underground chambers. Acidic rain alonedid not do all of the work. Oil and gas deposits locatedunderground contain hydrogen sulfide. Hydrogen sulfidemixed with groundwater created sulfuric acid whichdissolved the limestone and created large pathways. Then,the mountainous land surrounding the cave rose upwardscausing the whole area to be above the water table. Thewater drained away leaving behind the spectacular cavesand chambers.Cave dwellersOrganisms that spend their entirelives living only underground incaves are called troglobites. Thisterm is from the Greek word trogloswhich means cave. These organismscan not live outside the caveenvironment. Troglobites includeblind crayfish, blind salamanders,blind fish, and blind shrimp. These organisms are whitebecause they lack pigmentations.Trogloxenes are organisms that move freely in and out ofcaves. The suffix xenos means guest. These cave dwellingguests include bats, raccoons, bears, and bobcats. The thirdgroup of cave-dwelling organisms are called troglophiles. Theword origin is Greek and means “cave lover.” Theseorganisms like to live in caves, but can also survive outsidethe cave environment. They include different species ofbeetles, crickets, spiders, and salamanders.Questions:1. Why have many caves in the U.S. become National Parks?2. What role does water play in the formation of caves?3. Explain how lava tubes are formed.4. Why might a cave animal be blind or have poor eyesight?UNIT 2 WATER AND WEATHER93Chapter 4 Connection

Conserving Water While You BrushCurrently, underground water is being used at a faster ratethan it can be replenished. In the U.S., about 50% of thepopulation depends on underground aquifers for their water.In addition, energy is necessary to treat water before andafter it is used and returned to the environment. Wastingclean water often leads to emptying valuable undergroundaquifers we depend on and wastes the energy necessary totreat the water.In this activity, you will determine just how much water iswasted if the faucet is left running each time you brush yourteeth. You will learn that you can conserve a lot of water byturning off the faucet while you brush!Materials• Toothbrush and toothpaste• One or more containers that fits in your sink under thefaucet• Metric measuring cup (with milliliter markings)• CalculatorWhat you will do1. Prepare your toothbrush to clean your teeth.2. Place the container beneath the faucet to catch the water.3. Begin brushing your teeth but do not turn off the faucet.Take the regular amount of time it takes for you to brush.When the container in the sink is nearly full, remove itand place another, empty container under the faucet.4. Do not spit out the toothpaste foam from your mouth intothe containers!5. Be sure to turn off the faucet once you are done brushingand have rinsed your mouth.6. Now, use the measuring cup to determine how muchwater was used. Copy Table 4.1 into your notes andrecord your results. Convert your measurements tomilliliters. (Conversion: 1 cup = 237 milliliters)7. Once you have finished, attempt to reuse the water bypouring it in a plant, drinking it, or using it to cleandishes.8. In school, share your data with others. Record the classaverage in the Table 4.1.Table 4.1: Amount of Water UsedYouClass AverageApplying your knowledgeAmount of water collected when thefaucet is left running while brushing(milliliters)a. Calculate the difference between your results and theclass average. Was there a big difference or not? Why doyou think so?b. If the average person uses only 125 milliliters of water tobrush their teeth (when they don’t leave the faucetrunning), how much water is lost if the faucet is leftrunning? Use the class average to calculate your results.c. If a person brushes their teeth twice a day, how muchwater could they save, per day, by turning the faucet offwhile brushing?d. How much water could be saved in a week, if a personturned off the faucet while brushing?e. How many people live in your town? How much water canbe saved weekly in your town. (Only answer this questionif you are provided with your town population.)f. Now, come up with a catchy slogan to help peopleremember to turn off the faucet while they brush andconserve water!94

Chapter 4 AssessmentVocabularySelect the correct term to complete the sentences.hydrospheresurface waterreservoircondensationaquiferatmosphereSection 4.11. All the water on Earth is included in the _____.2. _____ is water that collects underground.3. A(n) _____ forms when more ice accumulates than melts.4. A(n) _____ is a protected lake that is used to store water.5. An ocean, lake, or river is an example of _____.6. Gaseous water is found in Earth’s _____.7. The upper surface of the saturated zone underground is the_____.Section 4.2glacierwater cycleevaporationprecipitationwatershedwater vapor8. Evaporation is one of four processes in the _____.9. Rain and snow are forms of _____.10. Water in gaseous form is called _____.11. _____ occurs when water goes from being a gas to a liquid.12. _____ occurs when water goes from being a liquid to a gas.13. _____ is the release of water from plants.14. A(n) _____ is an underground area filled with groundwater.15. A(n) _____ is an area of land that catches and collects water.16. _____ is water that flows over land.groundwaterwater tabletranspirationsurface runoffpercolation17. _____ occurs when liquid water moves through a poroussubstance.ConceptsSection 4.11. How is Earth’s atmosphere a part of the hydrosphere?2. The amount of water on Earth has remained about the samefor millions of years. How is this possible?3. If all the water on Earth could fit in a one gallon container,the amount of frozen water would be equal to about onethirdof a cup. How does this amount of water compare tothe amount of freshwater and ocean water on Earth.4. True or False? The water table level stays the same yearround? Explain your answer.5. Why is Earth a good place to find ice, liquid water, andwater vapor?Section 4.26. List a way that you could participate in the water cycle.7. Compare and contrast condensation and evaporation.8. When plants open the pores on their leaves:a. water enters the plant b. sugar enters the plantc. water and oxygen leave and car-d. sunlight enters the plantbon dioxide enters9. If you were to do an analysis of what is in groundwater,what might it contain? Why?10. What land area is the watershed for the Southern Ocean?11. Use a map of the United States to fine the St. LawrenceRiver. It is located by the Great Lakes.a. In what direction does it flow?CHAPTER 4 WATER AND THE WATER CYCLE95

. Into what body of water does it flow?12. Name one process of the water cycle that is involved in avolcanic eruption. Explain your answer.13. What is the difference between a geyser and a hot spring?Math and Writing SkillsSection 4.11. Match these water resources with their percentage ofEarth’s total water resources:Freshwater a. 0.001%Soil moisture b. 1.7%Ocean (salt water) c. 96.5%2. Pick a freshwater lake that you know about and research it.Make a colorful brochure that highlights the benefits of thislake to people. Include photographs if you have or find them.3. Select one of your favorite foods or products and find outhow water is involved in making it. Make a poster to displayyour findings.Section 4.24. In a short paragraph, explain how the Sun, wind, andgravity are involved in the water cycle.5. Explain how water could go from precipitation, to surfacerunoff, to groundwater, to an aquifer, to the ocean.6. Imagine you are a raindrop.a. Write a paragraph that explains what could happen to youafter you fall to the ground in a desert environment.b. Now, write a paragraph that explains what could happen toyou after you fall to the ground in an environment that isbelow 0°C. Note: Icy ground is not porous.7. Evapotranspiration is evaporation from surface water plustranspiration from plants. This graph showsevapotranspiration over one year. Come up with ahypothesis to explain the data shown in the graph.1501209060300Section 4.3Chapter Projects—Snow-making and theWater CycleDuring the winter, some people like to go skiing. However, theweather doesn’t always cooperate and ski resorts have to maketheir own snow. In other words, the ski resorts participate in thewater cycle by forcing liquid water to become snow (frozensnow).• Making snow takes a lot of water. For example, it takes about285,000 liters of water to create a 6-inch blanket of snow covering 61 61 meters. The system in a good-sized ski slope can convert 18,927to 37,854 liters of water to snow every minute!• Making snow also takes a lot of energy. Snow-making machines usefossil fuels and cause pollution.Research and write a report on how snow-making affects theenvironment in snow resort towns. Find out how ski resortswork to minimize their impact on the environment.If you go skiing in the winter, find out how the ski resort youvisit makes snow. Find out if the ski resort takes steps to protectthe environment!96CHAPTER 4 WATER AND THE WATER CYCLE

Chapter 5Earth’s AtmosphereIn Chapter 4, you learned about Earth’s hydrosphere. In thischapter, you will learn about another important system—theatmosphere. Earth’s atmosphere is a blanket of gases thatsurround the planet, protecting and sustaining life. Theatmosphere contains the carbon dioxide needed by plantsfor photosynthesis, and the oxygen that most organismsneed to breathe. Earth stays warmer at night because of theatmosphere. The ozone layer, in the stratosphere (a layer inthe atmosphere), protects us from the Sun’s ultraviolet rays.These rays can cause eye and skin damage. Every time youbreathe, you are benefiting from the atmosphere. Read on tofind out more about it!1. What gases are in the atmosphere?2. What are the layers of the atmosphere?3. Why is Earth neither too cold nor too hot?

5.1 The AtmosphereEarth’s atmosphere is made of a mixture of gases called air. Because we can’t seeair molecules, sometimes we forget they’re there. However, air molecules createatmospheric pressure. This pressure affects the weather. Understanding theatmosphere helps us to understand the weather. This section is an introductionto Earth’s atmosphere.What’s in Earth’s atmosphere?NitrogenThe nitrogencycle and livingthingsOxygenTrace gasesYou may be surprised to learn that the most abundant gas inEarth’s atmosphere is nitrogen. Nitrogen gas makes up about78 percent of the atmosphere (Figure 5.1). Nitrogen is releasedinto the air by volcanoes and decaying organisms.Nitrogen is an important component of protein. Protein is anessential substance in the body tissues of all living things. Thenitrogen used to make protein in living things can’t be absorbeddirectly from the air. Instead, nitrogen is changed into nitrogencontainingmolecules by bacteria in the soil. Plants absorb thesemolecules from the soil and use them to make proteins. Animalsand people eat plants to obtain these proteins. The bacteria in thesoil eventually return nitrogen to the atmosphere (Figure 5.2).The second most abundant gas is oxygen, which makes up21 percent of Earth’s atmosphere. When we take a breath of air,the most important gas that we breathe in is oxygen. Humans andother living things need oxygen to survive.The remaining 1 percent of Earth’s atmosphere is made up of0.93 percent argon and 0.04 percent carbon dioxide. There arealso tiny amounts of neon, helium, methane, krypton, andhydrogen, which we call trace gases.air - the mixture of gases thatmake up Earth’s atmosphere.Figure 5.1: Gases in Earth’satmosphereFigure 5.2: The nitrogen cycle.98UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHEREThe story of Earth’s atmosphereEarth is just rightWhy Earth has anatmosphereNo atmosphereon MercuryVenus, Earth, andMarsIn the last chapter, you learned that Earth’s surface temperature isjust right for all phases of water to exist. This is because Earth isnot too close or too far from the Sun. Earth’s special atmosphereexists because our planet has the right balance of mass anddistance from the Sun (Figure 5.3).Earth’s atmosphere formed early in its geologic history. Heat fromthe Sun drove off most of the lightweight elements like hydrogenand helium. Earth would have remained a rocky, airless worldexcept that as it cooled, earthquakes and volcanoes spewedout heavier gases like nitrogen and carbon dioxide. Earth’sgravitational pull held on to these gases, creating the atmosphere.The planet Mercury is too small and too close to the Sun to haveretained an atmosphere during its formation. Venus, Earth, andMars, however, are far enough away and have enough gravitationalpull to hold on to their atmospheres.The atmospheres of Venus, Earth, and Mars contain similarelements. Table 5.1 compares the atmospheres of these planets.Table 5.1: The atmospheres of Venus, Earth, and Mars.PlanetMercuryMajor gases in atmosphereCarbon dioxide Nitrogen Other gasesNo atmosphereVenus 96% 3% 0.1% waterEarth 0.04% 78% 21% oxygen 0.93% argonMars 95% 3% 1.6% argonFigure 5.3: Atmospheres of some ofthe planets.Use the data in Table 5.1 to makea pie graph that shows thecomposition of the atmosphere onVenus. Assume the percentage for“other gases” equals 1%.How does this pie graph compareto the pie graph in Figure 5.1?5.1 THE ATMOSPHERE99

Earth’s unique atmosphereVenus and MarsOxygen entersEarth’satmosphereStoring carbonHow Earth storescarbonThe atmospheres of Venus and Mars are mostly carbon dioxidewith a small amount of nitrogen. Earth’s atmosphere is different.Ours is the only planet with a large amount of oxygen and just atiny amount of carbon dioxide. Why is Earth’s atmosphere unique?During Earth’s ancient history, some of the earliest forms of lifebegan to use the Sun’s energy to survive. The process used bythese early life forms and still used today by all plants is calledphotosynthesis. Plants use carbon dioxide and release oxygen inthis process. As a result, Earth’s atmosphere changed and filledwith oxygen.The bodies of living things are made mostly of carbon atoms.Carbon enters the atmosphere when organisms exhale carbondioxide and when organisms decompose. If all of this carbon usedby life processes returned to Earth’s atmosphere, most of theorganisms here wouldn’t be able to survive. Fortunately, longlivingorganisms, like trees, store carbon for long periods of time.Also, when organisms die and decompose, some of the carbonfrom their bodies becomes stored in the ground. Fossil fuels (oil,coal, and natural gas) are created when carbon from decayingplants and animals is stored in the ground.The White Cliffs of Dover (see sidebar) provide a visual example ofhow carbon is stored on Earth. These cliffs are made of the shellsof tiny, water-dwelling organisms. The organisms use carbon andcalcium to form shells of calcium carbonate, or chalk. When theorganisms die, the shells sink to the ocean floor. Piles of calciumcarbonate build up over many centuries. Due to certain geologicalevents, the calcium carbonate ocean floor off the coast of Englandbecame a land structure, the White Cliffs of Dover.One way that Earth storescarbonSingle-celled organisms like thiscoccolithophore use carbondioxide dissolved in seawaterfor photosynthesis. They also usethe carbon to form intricate calciumcarbonate shells like the oneshown above. Although eachorganism is only 0.002 to0.02 millimeters across, these andother calcium carbonate shells pileup over the centuries, creatingbeautiful chalk structures like theWhite Cliffs of Dover in Britain.100UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHEREPressure in the atmosphereA giant pile ofcotton ballsPressure at sealevelAltitude andpressureEarth’s gravity prevents the nitrogen and oxygen molecules in ouratmosphere from flying off into space. Imagine these molecules arelike a giant pile of cotton balls. The cotton balls at the top of the pileare loosely spread out, but they press down on the ones below. Thecotton balls at the bottom of the pile are packed together muchmore tightly than the ones at the top because of the pressure.In the atmosphere, the molecules closest to Earth’s surface arepacked together very densely. This is because the weight of themolecules above presses down, creating atmospheric pressure. Thispressure is greatest at sea level (the bottom of the atmosphere).Altitude is a measure ofthe distance an object isabove sea level. As thealtitude of an objectincreases, the density ofthe air moleculesaround it is less,because there are fewermolecules above theobject pushing down.This means thatpressure decreases asaltitude increases(Figure 5.4).\altitude - a measure of thedistance an object is above sealevel; usually the object isairborne.Figure 5.4: As altitude (height abovesea level) increases, atmosphericpressure decreases rapidly.(mbar = millibars of pressure)5.1 THE ATMOSPHERE101

What is atmospheric pressure?Air moleculesexert pressureHolding up underpressureYou have learned that our atmosphere is composed of airmolecules. These molecules press down and create greaterpressure close to Earth’s surface (lower altitude). At highaltitudes, there is less pressure. Atmospheric pressure is ameasure of the force per unit area of air molecules in theatmosphere at a given altitude.At sea level, the weight of the columnof air above a person is about9,800 newtons (2,200 pounds)! This isequal to the weight of a small car. Whyaren’t we crushed by this pressure?Why don’t we feel pressure pushingdown on us? The answer is that theforces inside and outside the body arebalanced. The air and tissue inside ourbody pushes out with the same amountof pressure as the forces pushing in!atmospheric pressure - ameasure of the force per unit areaof air molecules in the atmosphereat a given altitude.How underseaanimalswithstandpressureDeep-sea creatures that live at a depth of 3,000 meters below sealevel have 300 times more pressure than we have at Earth’ssurface. These creatures survive because they generally lack airpockets and have body tissues that are jelly-like. At underwaterpressure, the jelly-like body tissue holds its shape and functionsproperly (Figure 5.5).Figure 5.5: Deep-sea fish areadapted to living at the high pressuresfound under water.102UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHEREHow is atmospheric pressure measured?What is abarometer?AneroidbarometersA barometer is an instrument that measures atmosphericpressure. Long ago, mercury barometers were used (Figure 5.6).They consisted of a tube sealed at one end and partially filled withmercury. The open end of the tube was placed in a dish containingmore mercury. As air pressed down on the mercury in the dish, itforced the liquid in the tube to rise. The mercury in this kind ofbarometer rises 29.92 inches at sea level. This is equivalent to1 atmosphere or 1,013 millibars of pressure (see chart below).Since mercury is a poisonous liquid, aneroid barometers are usedtoday (Figure 5.7). They have an airtight cylinder made of thinmetal. When pressure increases, the walls of the cylinder squeezeinward. At lower pressures, the walls bulge out. A pointer attachedto the cylinder moves as the cylinder changes shape, indicating thechange in atmospheric pressure (Figure 5.7).Unit of pressure Description Relationshipbarometer - an instrument thatmeasures atmospheric pressure.Figure 5.6: A mercury barometer.inches of mercury(in Hg)Unit describing the height of a columnof mercury in a barometer.29.92 in Hg = 1 atmatmospheres(atm)pounds persquare inch(psi)One atmosphere is the standardatmospheric pressure at sea level.Used by divers to compare pressureunder water with surface pressure.English unit commonly used tomeasure pressure of air in a container,like a tire or an inflatable ball.1 atm = 1.013 bars =1,013 millibars1 psi = 6,895 Papascals(Pa)Metric unit commonly used to measurepressure of air in a container. 1 Pa = 1 newton/m 2barsMetric unit used to measureatmospheric pressure, most often inthe form of millibars.1 bar = 100,000 PaFigure 5.7: An aneroid barometer.The units on this barometer are inchesof mercury and millibars.5.1 THE ATMOSPHERE103

5.1 Section Review1. What are the two main gases in Earth’s atmosphere?2. Why is nitrogen an important element for sustaining life?3. Give one reason why life exists on Earth and not on otherplanets.4. How are these two things related: the White Cliffs of Doverand the gasoline you put in your car?5. As a person moves higher above sea level, how does:a. the density of air molecules change?b. the atmospheric pressure change?6. Mountain climbers who try to reach the summit of MountEverest carry oxygen tanks. Why do you think they do this?7. What does the term altitude mean?8. Indicate where you would find higher water pressure andlower water pressure in Figure 5.8. Explain your answer.9. In Earth’s atmosphere and even under water, molecules presson objects. What prevents the human body and a deep-sea fishfrom being crushed by all this pressure?10. How does an aneroid barometer work?11. Convert an atmospheric pressure of 2 atmospheres to:a. inches of mercury (in Hg)b. barsImagine that you are a sciencewriter at a local newspaper. Eachweek, readers ask questions andyou try to answer them. Here’s thisweek’s question:Why do my ears sometimes hurtand “pop” during airplanetakeoffs and landings?Research and then answer thequestion. Remember, you areresponding to a reader of yournewspaper, so begin with “Dearreader,” and make your responseinteresting!Figure 5.8: Question 8.104UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHERE5.2 Layers of the AtmosphereYou probably know that temperature at the top of a high mountain is usually colderthan at the base. But did you know that the temperature doesn’t just keep decreasingas you go farther and farther up in the atmosphere? Actually, the temperature firstdecreases, then increases, then decreases, and then increases again. Scientists divideEarth’s atmosphere into layers based on these zigzags in temperature (Figure 5.9).The troposphereThe troposphereTemperaturedecreases as yougo upWeather in thetroposphereWe live in the troposphere, the layer that extends from 0 toapproximately 11 kilometers (36,000 feet) above Earth’s surface.About 75 percent of the atmosphere’s mass is found in thetroposphere. Almost all of Earth’s water vapor, carbon dioxide,dust, airborne pollutants, and terrestrial life forms exist here.The Sun warms Earth’s surface. Heat radiates from the surfaceand warms the troposphere. As a result, the troposphere iswarmest closest Earth’s surface. For every 1 kilometer you go up inthe atmosphere, the temperature drops about 6.5 Celsius degrees.At the top of the troposphere, the temperature is about –60 °C.The name troposphere contains the Greek root tropo, meaning “toturn or change.” The troposphere is the region where clouds formand where all weather happens. When you hear about airplanes“flying above the weather,” this means that they are flying abovethe troposphere.troposphere - a layer ofatmosphere that occurs from 0 toabout 11 kilometers above Earth’ssurface; where all weather occurs.Figure 5.9: Earth’s atmosphere isdivided into layers based ontemperature.5.2 LAYERS OF THE ATMOSPHERE105

The stratosphere, mesophere, and thermosphereStratosphereMesosphereThermosphereHeat transfer inthe thermosphereAbove the troposphere lies the stratosphere, extending from about11 to 50 kilometers above Earth’s surface. The temperatureincreases as you go up in the stratosphere because of a thin layerof ozone. The ozone layer absorbs the Sun’s high-energy ultraviolet(UV) radiation. As a result, the stratosphere is warm and we areprotected from the skin and eye damage caused by UV radiation.Above the stratosphere, the temperature begins to drop again.This marks the beginning of the mesosphere, which extends from50 to 80 kilometers above Earth. The mesosphere is the coldestlayer of the atmosphere. At its outer reaches the temperature canbe as low as –90 °C. Most meteors or “shooting stars” burn up inthe mesosphere.The layer that begins at about 80 kilometers above Earth’s surfaceis called the thermosphere. This layer has a low density of airmolecules—there are 100,000 times more air molecules in a cubicmeter of air at Earth’s surface than in the thermosphere. Thesemolecules have a lot of kinetic energy, because the energy from theSun hits them first. Temperatures in this layer can reach 1,800 °C.If you could hop out of a space shuttle into the thermosphere, youwouldn’t feel hot. Temperature, as you remember, measures theaverage kinetic energy of the particles (atoms and molecules) of asubstance. Heat, on the other hand, involves the transfer of energyfrom one object to another. Because the air molecules in thethermosphere are so far apart, very few of them would collide withyou, so there would be very little heat transferred.stratosphere - a layer ofatmosphere that occurs fromabout 11 kilometers to50 kilometers above Earth’ssurface; the location of the ozonelayer.mesosphere - a layer ofatmosphere that occurs fromabout 50 kilometers to80 kilometers above Earth’ssurface; the coldest layer.thermosphere - a layer ofatmosphere that occurs fromabout 80 kilometers to about500 kilometers; this layer has alow density of air molecules and avery high temperature.exosphere - the region of theatmosphere that begins at about500 kilometers above Earth andextends into space; the location ofthe orbits of satellites (see nextpage).ionosphere - portions of theatmosphere in the region of thethermosphere where electricitycan be transmitted (see nextpage).106UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHEREThe exosphere and the ionosphereThe exosphereSatellites in theexosphereThe exosphere begins at about 500 kilometers above Earth anddoes not have a specific outer limit (Figure 5.10). Lightweightatoms and molecules escape into space from this region.Satellites orbit Earth in the exosphere. Most satellites that we relyon orbit 36,000 kilometers above the equator and travel at thesame speed that Earth rotates. This orbit path is called the ClarkeBelt. Communication on Earth depends on satellites. Satellitestransmit information used for television shows, radio broadcasts,data and photos used in weather reports, and long distancetelephone calls.The ionosphereThe ionosphere is part of the thermosphere and is where the Sun’sultraviolet light creates charged atoms and molecules called ions(Figure 5.10). The energy released in this process causes the hightemperatures in the thermosphere. Ions easily transmit electricityand electromagnetic waves. The ionosphere makes it possible foryou to tune into short wave radio stations that originate a thousandor more miles away. The radio signals are rebroadcast by the ionsin the ionosphere back to Earth.Figure 5.10: The layers of theatmosphere.5.2 LAYERS OF THE ATMOSPHERE107

Chlorofluorocarbons and the ozone layerThe thinningozone layerCFCsRepairing thedamageIn the 1970s, scientists noticed that the ozone layer in thestratosphere above Antarctica was thinning. The detection ofchlorine in the stratosphere led to the discovery that humanactivity was responsible for the loss of ozone. The culprit, it turnsout, was a group of chemicals called chlorofluorocarbons (or CFCs).CFCs were once commonly used in air conditioners, in aerosolspray cans, and for cleaning machine parts. While most airbornechemicals break down in the troposphere, chlorofluorocarbons stayintact until they travel up to the stratosphere. This journey cantake anywhere from 6 to 26 years! In the stratosphere, the CFCsbreak down and release chlorine. The chlorine reacts with ozonemolecules, leaving behind ordinary oxygen, which does not blockincoming ultraviolet radiation (Figure 5.11).In the London Agreement of 1991,more than 90 countries banned theproduction and use of CFCs exceptfor limited medical uses. Throughinternational cooperation, we canmake progress in repairing damageto our atmosphere. Currently,there is general agreementamong scientists that loss ofozone seems to be slowing downthanks to the ban on CFCs.However, it will take manydecades for the existing CFCs tobreak down.Figure 5.11: CFCs and the ozonelayer.108UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHERE5.2 Section Review1. Almost all of Earth’s weather occurs in which layer of theatmosphere?2. In which layer of the atmosphere is the ozone layer located?How does this affect the temperature of this layer?3. Why is the ozone layer important for life on Earth?4. Which layer of the atmosphere is the coldest?5. In which layer do most meteors or “shooting stars” occur?6. In which atmospheric layer would you encounter 1,800 °Ctemperatures? Would you feel hot? Why or why not?7. What is the Clarke Belt?8. Explain how you and a friend could demonstrate the termgeo-stationary.9. Which layer of the atmosphere is responsible for transmittedAM radio waves? How is this possible?10. Oxygen is a molecule made up of two oxygen atoms. Ozone is amolecule made up of three oxygen atoms. In what other ways isoxygen different from ozone?11. What are CFCs?12. Why does the ozone layer seem to be recovering?13. Research weather satellites. You may want to talk to ameteorologist to find out the answer to these questions.a. What kind of things can you see in a satellite photograph?b. How are satellite photographs helpful to people?c. What kind of technology is used to record this information?d. Bonus Question: What is the name of the first successfulweather satellite?Now that you have learned allabout the layers of Earth’satmosphere, you need a way toorganize the information.Design an information table thatlists and describes all the layers ofEarth’s atmosphere.Things to include in yourinformation table:• Name of the layer• Distance from Earth’s surface• Thickness of the layer• Special facts about the layerMake up a game or activity thatyou can play with friends to helpyou remember the different layersof the atmosphere.5.2 LAYERS OF THE ATMOSPHERE109

5.3 Earth Is Just RightEarth is “just right” because its temperature is not too hot or too cold (Figure 5.12).Metals like lead melt on the hot surface of Venus, but not on Earth. Some gasesfreeze solid on Neptune, but not on Earth. Earth’s temperature is especiallynurturing for living things. This section is about how Earth’s temperature stays “justright.”The importance of Earth’s atmosphereTemperaturerangeEarth’s surface temperature stays within a narrow range—it isnot too hot or too cold. The average temperature of Earth’s surfaceis about 15 °C. This temperature is maintained because Earth hasan atmosphere that traps some of the Sun’s energy. Without anatmosphere, Earth’s surface temperature would be about –18 °C.Surface temperature(°C)Mercury –170 to 390Venus 450 to 480Earth –88 to 56Mars –89 to 20Jupiter –108Saturn –139Uranus –197Neptune –201Figure 5.12: The surfacetemperatures for planets in our solarsystem.How to “read” diagramsHow do you read a diagram?1. Read the caption and title.2. Study the diagram to determinewhat information it is showingyou.Question: Refer to the diagram atthe left. In your estimation, whatwas the most common land surfacetemperature for July 2003?110UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHEREHeat transfer and waterThe Sun’s energyHeat transferHeating Earth’ssurfaceWater andspecific heatMost of the heat energy on Earth’s surface comes from the Sun. Atthe same time that the Sun adds heat to Earth’s surface, heat isbeing lost to space. The balance between the Sun’s heat and heatlost into space is what determines Earth’s surface temperature.The Sun’s heat reaches Earth by a heat transfer process calledradiation. Radiation is heat transfer through empty space. Onceheat has arrived on Earth, there are three ways that it movesthrough the atmosphere: radiation, convection, and conduction(Figure 5.13). You learned about these processes of heat transfer inChapter 3. Heat transfer by radiation occurs without direct contactor movement of atoms. Convection is the transfer of heat throughthe motion of gases and liquids such as air and water. Conductionis the transfer of heat by the direct contact of atoms and molecules.When solar radiation reaches Earth, it is either absorbed orreradiated by the surfaces it encounters. When solar radiation isabsorbed by a surface, the surface gets warmer. Land gets warmquickly during the day, and quickly loses this heat at night. Water,on the other hand, warms up and loses heat more slowly.Compared to land surfaces, water has a high specific heat. Specificheat is the amount of energy needed to raise the temperatureof 1 gram of a substance by 1 degree Celsius. Having a higherspecific heat means that it takes more energy to raise a substance’stemperature, but once the substance is warm, it takes longer to cooloff (Figure 5.14). The large amount of water on Earth prevents theplanet from getting too hot or cold.specific heat - the amount ofenergy needed to raise thetemperature of 1 gram of asubstance by 1 degree Celsius.Figure 5.13: Heat transfer on Earth.Figure 5.14: The specific heat ofwater is higher than the specific heat ofland.5.3 EARTH IS JUST RIGHT111

Earth’s motionMotion andtemperatureRotationRevolutionThe motion of Earth also helps to balance its surface temperature.Read on to find out how two of these motions, rotation andrevolution, affect the temperature of every place on Earth.Rotation is the turning motion of a planet as it spins on its axis(Figure 5.15). It takes one day for Earth to make one completespin. For half of a day, your side of Earth faces the Sun andexperiences daytime. For the other half of the day, your side ofEarth faces away from the Sun and experiences nighttime.Revolution is the motion of a planet around its star. Earthrevolves around the Sun. It takes about 365.25 days for Earth tomake one revolution, or one trip, around the Sun. The path thatEarth takes is called its orbit (Figure 5.15). Later in this chapterwe’ll learn how the revolution of Earth is related to the seasons.rotation - the motion of Earthspinning on its axis; one rotation iscalled a day.revolution - the motion of Earthmoving around the Sun; onerevolution is called a year.Figure 5.15: Earth rotates on its axisand revolves around the Sun.112UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHERETemperature and Earth’s rotationMercury is toohot and too cold!What happens if you put a burger on a hot grill and forget to turnit? The bottom will be burned to a crisp, and the top will be undercooked.The planet Mercury is like that. One day on Mercury lastsfor about 58 Earth days! The long day causes the temperature onthe Sun-facing side of Mercury to reach about 390 °C. Somethingmade out of the metal lead would melt at this temperature! At thesame time, the dark nighttime side plunges to –170 °C. That’sextremely cold!Greenhouse GasesThe Earth is justright—not too hotor too cold!Even though Earth is farther away from the Sun than Mercury, ournight side never gets as cold as Mercury’s night side. Why not?Think about burgers again. A good chef turns the burger so itbrowns nicely on both sides. Similarly, the Earth turns rapidlyenough so that there isn’t enough time for our night temperature tosink too low. There also isn’t enough time for Earth’s daytemperature to rise too high.A greenhouse is a glass buildingwhere plants can be grown in awarm, moist environment.Scientists use the term“greenhouse gases” to describecertain gases in Earth’satmosphere. Like the glass in agreenhouse, greenhouse gasescan slow down Earth’s naturalheat-loss processes. These gasesare useful because they keepEarth warm. However, the amountof these gases is increasing in ouratmosphere. Because of thisincrease, less heat energy will beable to leave Earth. Scientists areconcerned that the resulting rise inEarth’s average surfacetemperature might alter climatesand other natural systems in ourenvironment.5.3 EARTH IS JUST RIGHT113

Revolution and Earth’s seasonsWhy does Earthhave seasons?Earth is tiltedThe diagram below shows Earth at four different places in itsrevolution around the Sun. Why is it warmer in summer andcooler in winter in the northern hemisphere? In other words,why do seasons occur?One guess might be that Earth is closer to the Sun duringsummer. But this isn’t the correct answer. Earth has seasonsbecause it is tilted on its axis. During our summer, the northernhemisphere receives sunlight that is more direct than it is in thewinter, and in summer there are more hours of daylight. Thismeans we have warmer temperatures in summer than we do inwinter.Earth’s axisEarth rotates about an imaginaryaxis that goes through its center.This axis is drawn on the imagesof Earth in the diagram on thispage. The diagram shows thatEarth is tilted at 23.5° as itrevolves around the Sun.The axis connects the North Poleand the South Pole. The north endof the axis points toward the NorthStar throughout the year.Make your own sketch of thediagram at the left. Based ontoday’s date, indicate on yourdiagram where Earth is on its patharound the Sun.114UNIT 2 WATER AND WEATHER

CHAPTER 5: EARTH’S ATMOSPHERE5.3 Section Review1. Describe two reasons why Earth’s climate is “just right” for life.2. What is the source of most of Earth’s heat energy?3. Some of Earth’s heat energy is lost to space. Why is thisimportant?4. What are the three ways that heat energy moves through theatmosphere?5. How does water help keep Earth from getting too cold or hot?6. Define the term rotation. How long is one rotation of Earth?7. Define the term revolution. How long is one revolution of Eartharound the Sun?8. Earth’s surface does not get too hot or too cold compared toMercury’s surface. What differences between the two planetsmakes this possible?9. What role do greenhouse gases play in keeping Earth warm?10. Why does Earth have seasons?11. During winter in the northern hemisphere, is the southernhemisphere tilted toward or away from the Sun?12. How many degrees is Earth’s axis tilted?13. There are more hours of sunlight and more direct sunlightduring summer. How does winter compare to summer in termsof hours of sunlight?14. Research: You will need to do research on the Internet or at thelibrary to answer these questions.a. What are the main greenhouse gases?b. Which planet—Venus or Earth—exhibits a strongergreenhouse effect? Why?What are the seasons like whereyou live?Write about how the seasonschange over the year where youlive. Describe your favorite part ofeach season.Why is January a winter month inthe northern hemisphere but asummer month in the southernhemisphere?5.3 EARTH IS JUST RIGHT115

Hurricane HuntersChapter 5 Connection116If there's a hurricane to be hunted, it's usually done by one ofthe specially equipped NOAA (National Oceanic andAtmospheric Administration) planes. Two of the world'smost popular research planes are based in Tampa, Florida.They are both Lockheed WP-3D Orion planes and arecommonly known as Kermit and Miss Piggy. In fact, thenoses of both planes are painted withthe pictures of these famous Muppetcharacters. These hurricane huntingplanes log between 300 and 400hours of flight time each year. Theprimary purpose of their missions isto help forecast hurricanes.Information like the intensity andstrength of a storm and when it willmake landfall is gathered. A typicalflight aboard Kermit or Miss Piggycan last up to eight hours and cover over 2000 nauticalmiles. One nautical mile is equal to 1,852 meters. It's notyour typical vacation fight.Flying a hurricane missionYou could think of Kermit and Miss Piggy as flyingmeteorological laboratories. The planes are equipped withstate of the art instrumentation. On a typical hurricanemission, the plane will be occupied by eighteen highlyqualified individuals. Hurricane hunting crew membersinclude pilots, flight engineers, navigators, scientists, andmeteorologists. The pilots have a difficult job trying to keepthe plane level. They fly through high winds and poundingrains filled with turbulence. Turbulence is any irregularatmospheric motion. In simpler terms, it's more of an upand-downmotion or the feeling of bumpiness. The crew fliesthrough a lot of turbulence before they reach the storm’s eyewall and finally the eye. The center of the hurricane is calledthe eye. It is often a calm and clear area. The eye wallsurrounds the eye of the hurricane and has the highest windspeeds of the storm. As you can imagine, everything must bebolted down securely towithstand all the turbulence.Just about everything on theplane is tied down or velcroed,even the pencils and pens!Plane instrumentationDetailed pictures and data ofthe weather systems in theupper atmosphere are collectedduring a mission. The NOAAplanes are equipped withmany cameras and sensinginstruments to accomplish thistask. The mass of the plane isapproximately 61,235 kilograms(135,000 pounds) whenit is fully loaded with people,fuel, cameras, and all theinstruments. That's one bigload flying into thosehurricanes!

The dropsonde is one of the most important instruments onboard. It's a tube-like canister the size of a paper towel tube.These canisters contain several sensors used to measure airtemperature, humidity, and atmospheric pressure atdifferent places in the storm. They are dropped from thebottom of the plane through a chute. A parachute attached tothe canister allows it to drop downward slowly. As it falls,data are collected and transmitted back to the plane. A GPS(Global Positioning System) receiver is used to monitor thelocation and wind speed of the storms. Scientists can drop asmany as 50 dropsondes during a hurricane mission.Hurricane factsHurricanes are tropical cyclones, which are warm, lowpressure storms that form in the tropics. They rotatecounter-clockwise (to the left) in the Northern Hemisphere,and clockwise (to the right) in the Southern Hemisphere.You can see the direction in the NOAA satellite image thattracked hurricane Katrina in 2005. When these storms reacha wind speed between 63 and 118 km/h (39 and 73 mph),they are known as a tropical storm and are given a name bythe National Hurricane Center (NHC) in Miami, Florida. Atropical storm becomes a hurricane when the winds becomegreater than 119 km/h (74 mph). The NHC uses the Saffir-Simpson Hurricane Scale to categorize the hurricanes. Thescale goes from 1 through 5 and is based on wind speed.ForecastinghurricanesIsaac Ginis is aprofessor ofoceanography atthe GraduateSchool ofOceanography atthe University ofRhode Island. He is considered to be one of the most accuratehurricane forecasters in the world.According to Ginis, ocean water temperature is the keyfactor in forecasting hurricanes. Warm ocean water causehurricane winds to intensify. However, the winds stir up thewater so that deeper, cooler water rises to the ocean surface.The cooler water can reduce the intensity of the hurricane.This information helped Ginis develop an ocean model thatshows ocean currents and temperature. It is used today bythe NOAA to help predict hurricane intensity. Ginis' oceanmodel and an atmospheric model created by NOAA areconsidered some of the most accurate models in hurricaneforecasting since 2001.Questions:1. If a hurricane-hunting plane flew an 8 hour mission thatcovered 2,000 nautical miles, how many meters would thecrew have traveled?2. What conditions are needed to form a hurricane?3. Explain the major difference between a hurricane in theNorthern Hemisphere and the Southern Hemisphere.4. Why is it important to accurately forecast hurricanes?Chapter 5 ConnectionUNIT 2 WATER AND WEATHER117

Chapter 5 ActivityOur atmosphere and golf ballsBernoulli's PrincipleIn addition to providing us with air to breathe, the air in ouratmosphere is useful for playing sports, travelling, and allsorts of things. Because of air and how it flows aroundobjects, a baseball pitcher can throw a “sinker,” an airplanecan fly, and a golf ball can soar for long distances.A short history of golf ballsIn the 1840's, a golf ball was madefrom the heated and molded partsof a Malaysian tree—the guttaperchagum tree. They were calledgutties. Golf players at the timerealized that old gutties with nicks(little dents or scratches) wentfurther than new ones. So, golfersstarted to nick the gutties onpurpose. In the early 1900's, balls were made of rubber andcoated with a latex. Circular depressions called dimples weremade in the balls. By 1930, a standard weight and size wasestablished for golf balls and approximately 400 dimpleswere put on each ball.What is Bernoulli’s Principle?The Bernoulli’s principle states that as air moves faster itspressure decreases. If a golf ball were smooth, air would flowover it at the same speed at the top and bottom. Because ofthe dimples and the backspin caused by hitting the ball withthe golf club, the air flowing over the top is moving fasterthan the air flowing under the ball. The faster air creates alow pressure so the ball experiences a “lift.” Bernoulli’sPrinciple was developed by Daniel Bernoulli, a Swissmathematician and scientist. Now, try to create Bernoulli’sPrinciple using three methods.Materials(A) Cheeseball snack food and bendable straw, (B) ping-pongball and blow dryer, and (C) paper strip (3 inches 9 inches)What you will doA: Put the bendable straw in yourmouth with the short section bent ata ninety degree angle up into the air.Place the cheeseball on the end of thestraw. Blow through the straw. Canyou get the cheeseball to besuspended in the air above thestraw? Keep trying. It can be done.B: Use a blow dryer and ping pongball for the same effect. Hold theblow dryer up vertically so that theball can be supported by the air flow.C: Hold the paper strip with your hand so that the 3 inchside is just below your lips and the length of the paper stripis hanging below your lips. Blow over the paper strip.Applying your knowledgea. Explain how the three activities worked using Bernoulli'sPrinciple. You may diagram your answer if you want.b. One of the diagrams (below) represents a baseball calleda “sinker” thrown by a pitcher. The other represents agolf ball. High pressure (H) and low pressure (L) regions,and the direction of air currents around the balls areindicated. Identify which ball is the “sinker” and whichball is the golf ball. Explain your reasoning. Hint:Identify where the air is flowing faster over each ball.118

Chapter 5 AssessmentVocabularySelect the correct term to complete the sentences.airaltitudeatmospheric pressurebarometerstratosphere tropospheremesosphere thermosphere exosphereionospherespecific heat rotationrevolutionSection 5.11. Our atmosphere is composed of _____, a mixture of gases.2. The _____ of an airplane rapidly increases as it takes off.3. At sea level, _____ is equal to about 9,800 newtons.4. A _____ measures atmospheric pressure.Section 5.25. Shooting stars occur in the _____.6. The _____ extends into space.7. The _____ has a very low density of air molecules.8. The ozone layer occurs in the _____.9. All weather on Earth occurs in the _____.10. AM radio waves are transmitted in the _____.Section 5.311. Water has a higher _____ than land.12. It takes one day for Earth to make one _____.13. The time for one _____ on Earth is one year.ConceptsSection 5.11. Why doesn’t Mercury have an atmosphere?2. Nitrogen is 78% of the atmosphere. How is nitrogenimportant to living things?3. Why is there more carbon dioxide in the atmosphere onMars and Venus than on Earth?4. Explain what happens to the following factors as you gofrom sea level up to the top of a mountain:a. Atmospheric pressureb. The density of air moleculesc. The elevation5. Compare and contrast how humans and deep-sea creaturessurvive under pressure.6. How is a mercury barometer different from an aneroidbarometer?Section 5.27. Explain what happens to temperature as you go from sealevel to the top of the thermosphere.8. You are an airplane pilot and the weather is really badcausing a bumpy plane ride. What could you do to make theflight more comfortable for your passengers?9. What is the ozone layer?10. What does the term “geo-stationary” mean? Why are manysatellites geo-stationary?Section 5.311. What are the three ways that heat is transferred in Earth’satmosphere?12. Temperatures on Mercury can be much colder than on Earth,but Mercury is closer to the Sun. How is this possible?13. What are greenhouse gases?CHAPTER 5 EARTH’S ATMOSPHERE119

14. Explain how these factors help keep Earth’s temperaturewithin a narrow range that is good for life on the planet:a. The distance from the Sun.b. The atmosphere.c. The water on the planet’s surface.15. Earth is tilted at an angle of 23.5° as it revolves around the Sun.How does this tilt affect the amount of daylight that NorthAmerica receives in the summer versus the winter?Math and Writing SkillsSection 5.11. Imagine you are a space tourist guide. Some space touristswant to take a vacation on Earth. Make a one-page flyerthat advertises why Earth is a good place to visit. Your flyershould include information about the atmosphere, thetemperature range, other details, and drawings.2. Find out the atmospheric pressure for today. You can findthis value by listening to a local TV weather report or bygoing to a weather website on the Internet. Convert thispressure reading so that you have the value in inches ofmercury, atmospheres, and in millibars.3. In the chapter, you learned about the atmospheres of someplanets. Now find out about the atmosphere of one of theseplanets: Jupiter, Saturn, Uranus, and Neptune.Section 5.24. You are an expert speaker on Earth’s atmosphere and havejust given a talk. Now, someone from the audience asks youthis question: Why does Earth’s atmosphere have layers?What do you say to the audience member?5. Here is a research question: How does the density of airmolecules in the mesosphere compare to the density of airmolecules in the thermosphere?a. Come up with a hypothesis.b. List a way you could test your hypothesis.Section 5.36. How long does each event take? Give your answer in days.a. Five Earth rotationsb. Two Earth revolutionsChapter Project—Mile High City BaseballDenver, Colorado is the Mile High City, because it is one mileabove sea level. At this location, rumor has it that hittingbaseballs a long way is easier than in other cities and it is hardto throw curve balls or sinkers.1. Come up with a hypothesis for why this rumor might be true in theMile High City.2. If the rumor is true, how might a game played in the Mile High Citybe different from a game played at sea level in terms of:a. number of runs earned by a team during a game?b. number of hits and home runs earned by a team during a game?3. See if the rumor is true by researching this effect called “The CoorsField Effect” after the field, Coors Field, where the Colorado Rockiesprofessional baseball team plays. Then, write up your finding in areport!120CHAPTER 5 EARTH’S ATMOSPHERE

Chapter 6Weather and ClimateHow is the weather predicted? What factors influencewhether you will see sunshine, clouds, or precipitation on anygiven day? In this chapter, you will learn how temperature,pressure, and water content in the atmosphere work togetherto produce different kinds of weather. You’ll explore cloudformation, precipitation, air masses, and fronts. You’ll alsolearn what the symbols on a weather map mean, and howdifferent kinds of storms develop.1. What causes wind?2. What do clouds tell you about the weather?3. Why do different parts of Earth have differentclimates?

6.1 Introduction to WeatherWeather is a term that describes the condition of the atmosphere in terms oftemperature, atmospheric pressure, wind, and water. The major energy source forweather events is the Sun. Weather events tend to happen when air masses interactor changes locations. An air mass is a large body of air (sometimes coveringthousands of square kilometers) with consistent temperature and moisture contentthroughout. In this section, you will learn how weather happens. You will also learnimportant terms used for talking about weather.Weather factorsTemperaturePressureWhat is wind?The temperature of air determines whether it rises or sinks. TheSun warms Earth’s surface. As air near the surface is warmed, itexpands and becomes less dense. The less-dense air rises.Eventually the warm, less-dense air that rose from the surfacecools. The same chain of events that made the air rise now worksin reverse and the air sinks back to the ground (Figure 6.1).When warm air rises from Earth’s surface, an area of lowatmospheric pressure is created. This lower-pressure area drawsin air from surrounding higher-pressure areas. Eventually thewarm air that rose from the surface cools and becomes denser.This dense, cool air sinks back to the surface causing an area ofhigh atmospheric pressure.Wind is the horizontal movement of air that occurs as a result of apressure difference between two air masses. The greater thedifference in pressure, the greater the speed of the air flow. Mostof these pressure differences are due to unequal heating of theatmosphere.weather - the condition of theatmosphere as it is affected bytemperature, atmosphericpressure, wind, and water.air mass - a large body of air withconsistent temperature andmoisture content throughout.wind - the horizontal movement ofair that occurs as a result ofpressure differences between twoair masses.Figure 6.1: Convection in theatmosphere.122UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEConvection in the atmosphereThermalsBreezes andspecific heatSea breezesLand breezesA thermal is a small, upward flow of warm air. Gliding birds likehawks often ride a thermal as they hunt for food. Pilots ofsailplanes (which lack an engine) also ride thermals (Figure 6.2).Thermals usually come and go over a short period of time.Convection near coastlines causes sea breezes during the day andland breezes at night. These breezes occur because water has ahigher specific heat than land. This means that water warms andcools more slowly than the land.During the daytime, the land heats up faster than the ocean. Risingwarm air over the land creates a low-pressure area. Eventually therising air moves out over the sea, cools, and sinks toward the seasurface. The cooling, sinking air mass creates a high-pressure area.Air flows from high- to low-pressure areas. So, during daytimehours, there is a cool sea breeze from sea to land.During the evening hours, a land breeze occurs because the groundcools rapidly during this time but the ocean remains warm. Atnight, warm air rises over the sea, creating a low-pressure area.The air sinks over the land creating a high-pressure area. Thebreeze then flows from land to sea.thermal - a small, upward flow ofwarm air.Figure 6.2: A thermal is a risingcolumn of warm air. Gliding birds andsailplanes “ride” thermals. In fact, thepilots look for gliding birds to find theseinvisible air currents.6.1 INTRODUCTION TO WEATHER123

The Coriolis effectGlobalconvectionConvection cellsThe effects ofEarth’s rotationThe CorioliseffectConvection also occurs on a global scale. Warm, less-dense air atthe equator tends to rise and flow toward the poles. Then, cooler,denser air from the poles sinks and flows back toward the equator.Due to Earth’s rotation, rising warm air from the equator doesn’tmake it all the way to the poles. The combination of globalconvection and Earth’s rotation sets up a series of wind patternscalled convection cells in each hemisphere. Look at Figure 6.3and follow the arrows. Do you see where air is rising and sinking?Earth’s rotation also changes the direction of airflow. This causesthe path of the wind to be curved as it moves between the polesand the equator. In the northern hemisphere, winds bend to theright and move clockwise around a high pressure center (H). In thesouthern hemisphere, winds bend to the left and movecounterclockwise around a high pressure center (H).This bending of currents of air due to the Earth’s rotation is calledthe Coriolis effect. It is named after the French engineermathematicianGaspard Gustave de Coriolis (1792–1843), whofirst described the phenomenon in 1835.convection cells - large windpatterns in Earth’s atmospherecaused by convection.Coriolis effect - the bending ofcurrents of air or water due toEarth’s rotation.Figure 6.3: This diagram showsEarth’s convection cells and how windscurve due to the Coriolis effect.Graphic note: To understand “right”and “left,” imagine you are standing atthe base of each arrow on the globes.124UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEGlobal surface wind patternsWind and humanhistoryTrade windsPrevailingwesterliesPolar easterliesThe polar frontThree important global wind patterns exist in each hemisphere(Figure 6.4). Sailors have used these winds to travel to and explorenew lands throughout human history.The trade winds are surface wind currents that move between30° north or south latitude and the equator. Remember, the airaround the equator warms, rises, and flows toward the poles. Atabout 30° N and 30° S, it cools, sinks, and flows toward the equatoragain. The Coriolis effect bends the trade winds so that they flowfrom northeast to southwest in the northern hemisphere and fromsoutheast to northwest in the southern hemisphere.The trade winds set up a high-pressure area at about 30° Nlatitude. Air along the surface between 30° N and 60° N movesnorthward, from high to low pressure. The air bends to the rightdue to the Coriolis effect, creating the prevailing westerlies. Most ofthe United States is between 30° N and 60° N, so most of ourweather patterns move from southwest to northeast. In thesouthern hemisphere, the weather patterns between 30° S and60° S tend to move from the northwest to the southeast.Polar easterlies form when the air over the poles cools and sinkscreating a high-pressure area. Like the other global winds, thispolar wind is bent by the Coriolis effect. The air flows fromnortheast to southwest in the northern hemisphere, and fromsoutheast to northwest in the southern hemisphere.At about 60 degrees latitude, the polar easterlies meet theprevailing westerlies, at a boundary called the polar front. Here,the dense polar air forces the warmer westerly air upward. Somewarmer air flows toward the poles, and some flows back toward the30 degree latitude line.Which way does the wind blow?Here are some facts about winds tohelp you study.-Winds are described by the directionfrom which they originate. That meansthat a west wind blows from the west,for example.-Trade winds are named after traderoutes used by sailing merchants.-Prevailing westerlies are so namedbecause they blow from the west.-Polar easterlies are so namedbecause they come from polar regionsand blow from the east.Figure 6.4: Global surface windpatterns.6.1 INTRODUCTION TO WEATHER125

Air and water vaporWater vaporHow much watervapor can airhold?Relative humidityYou have just learned how air temperature and atmosphericpressure influence weather. Now let’s look at a third factor:water vapor in the air. Water vapor is the result of liquid waterevaporating. Liquid water from oceans, rivers, and even puddleschanges to water vapor and mixes with the air (Figure 6.5).An air mass can be compared to a sponge. Warm air is like a bigsponge that can contain a lot of water vapor. Cold air is like asmall sponge that can contain less water vapor. Air that containsthe maximum amount of water is saturated. Like a soggy sponge,saturated air can’t hold more water vapor. When more watervapor is added, it condenses and forms droplets.Relative humidity is a measure of how much water vapor an airmass contains relative to the total amount of water vapor it couldcontain at a certain temperature. Let’s say we have two air masseswith the same number of air molecules. The warm air mass has agreater volume because the molecules are more spaced out. Bothair masses contain 50% of the total amount of water vapor theycould contain. The graphic below shows that the warm air masshas a greater capacity to hold more water vapor than the cool airmass. It feels more humid on a warm day than on a cool daybecause warm air can hold so much more water.Figure 6.5: When a puddle dries, thewater can becomes water vapor in theatmosphere. However, water in a puddlecan also seep into the ground.126UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATE6.1 Section Review1. Define wind. Draw a diagram that illustrates how wind iscreated.2. How does convection help birds and sailplanes to fly?3. Why is the path of the wind curved as it moves from poles tothe equator?4. Why are there three different wind patterns in eachhemisphere? What are the names of these wind patterns?5. Which wind pattern most affects the United States?6. Which holds more water vapor, a warm or a cold air mass?7. When the air is filled to capacity with water vapor, it is said tobe ___________.8. What does it mean for an air mass to have 70% relativehumidity?9. An air mass cools to the point where it becomes saturated.What might happen next?10. A cool (10 °C) air mass warms to 30 °C.a. Does the volume of the air mass decrease or increase whenthe temperature goes up?b. If the amount of water vapor in the air mass stays thesame, does the relative humidity increase or decrease whenthe temperature goes up?In this section, you learned thatsailors have used global windpatterns to travel to and explorenew lands throughout humanhistory.Research one of the more famousship captains—Captain JamesCook (1728–1779). Who was he?What is he known for?Write a short report about oneor more of Captain Cook’sadventures or achievements.6.1 INTRODUCTION TO WEATHER127

6.2 Weather PatternsAs you have learned, our weather is part of Earth’s atmosphere. We can learn abouttoday’s or tomorrow’s weather by listening to a meteorologist. You can also find outabout weather on your own by looking at clouds in the sky and by taking your ownweather data. This section is all about observing weather patterns.MeteorologyWhat is ameteorologist?Tools used bymeteorologists tohelp peopleA meteorologist is a person who uses scientific principles toexplain, understand, observe, or forecast Earth’s weather. Manymeteorologists have college degrees in physics, chemistry, ormathematics. Radio and television weathercasters are oftenprofessional meteorologists.Meteorologists use satellite and computer technology to informpeople about the weather. For example, meteorologists can usedata to predict hurricanes. Before 1960, a hurricane could hitwithout warning. Since 1960, weather satellites have helpedpredict and track hurricanes. Figure 6.6 shows a satellite image ofHurricane Hugo about to make landfall on the coast of SouthCarolina in 1989. Government organizations like the NationalHurricane Center (NHC) monitorstorms that might becomehurricanes. The NHC issueshurricane watches and warnings sothat people can evacuate athreatened area.meteorologist - an individualwho uses scientific principles toforecast the weather.Figure 6.6: A weather satellite imageof Hurricane Hugo making landfall onthe coast of South Carolina in 1989.What is it like to be ameteorologist? Find out byinterviewing a meteorologist orby researching the job of ameteorologist on the Internet.Write about your findings in areport. Include photographs orpictures in your report.128UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEWater in the atmosphereWater inthe atmosphereThree phases ofwater in theatmosphereTemperature andpressureDew pointRain, snow, sleet, and hail occur because water exists in theatmosphere. Even when the skies are blue, there is water present.The amount varies from just 0.1 percent in the atmosphere aboveAntarctica to as much as 3 percent above a tropical rainforest.Water in the atmosphere exists in all three phases (solid, liquid,and gas). Ice crystals occur high in the troposphere. Tiny waterdroplets, much too small to see, are suspended throughout thetroposphere virtually all the time. They are considered liquid waterand not gas because they are made of microscopic “clumps” of watermolecules. Water in the atmosphere also occurs as water vapor—water in the gas phase.As temperature increases, the rate of evaporation increases(Figure 6.7). Higher temperatures cause the liquid water moleculesto move fast so they have enough energy to break free of theirbonds with each other. These water molecules become water vaporin the atmosphere. In contrast, as atmospheric pressure increases,the rate of evaporation decreases (Figure 6.7). This is because thepressure makes it harder for water molecules to escape from theliquid to the gas phase.Both condensation and evaporation occur in the atmosphere all thetime. However, each process may happen at different rates. Whenthe rate of evaporation is greater than the rate of condensation, wesee clearing skies. When the rate of condensation exceeds the rateof evaporation, we say that the air’s dew point has been reached.This is the temperature at which more water vapor is condensingthan evaporating in an air mass. The water in the air mass isgetting colder, slowing down, and forming “dew” or droplets.dew point - the temperature atwhich more water condenses thanevaporates in an air mass at aconstant atmospheric pressure.Figure 6.7: The relationship betweentemperature and pressure whenevaporation occurs.6.2 WEATHER PATTERNS129

Cloud formationWhat is a cloud?CumuliformcloudsWhen more water in the atmosphere is condensing thanevaporating, we begin to see clouds. A cloud is a group of waterdroplets or ice crystals that you can see in the atmosphere. Theflat bottom of the cloud marks the level of the atmosphere wherecondensation first exceeds evaporation. Clouds are divided intotwo broad categories: cumuliform clouds (cumulus means “piledup”) and stratiform clouds (stratus means “layer”).Cumuliform clouds, which look like heaps of popcorn, form as anair mass rises because of convection (Figure 6.8). Air is commonlywarmed over a dark surface (like a road) that absorbs a lot of heat.It is rare to see a line of these clouds right above a dark surfacethough, because wind currents blow the rising air masses aroundbefore they condense and form clouds.cloud - a group of water dropletsor ice crystals that you can see inthe atmosphere.Cirrocumulus: Small, puffy, “cotton ball” type clouds high in theatmosphere (above 6,000 meters) are called cirrocumulus. Theyusually indicate fair weather.Altocumulus: Altocumulus clouds form between 2,000 and 6,000meters high. They usually form larger, darker puffs thancirrocumulus clouds. Sometimes they appear in rows. If thealtocumulus clouds look like towers, they are called altocumuluscastellatus. These clouds often appear before a storm.Cumulus: The base of a cumulus cloud can occur anywhere from1,000 meters to 5,800 meters high. Cumulus clouds are the tall,puffy clouds that form when the air over land is heated. As aresult, these clouds often break down as the Sun sets.Cumulonimbus: When a cumulus cloud is dark and stormylooking, it is called cumulonimbus. Thunderstorms develop fromcumulonimbus clouds.Figure 6.8: Cumuliform clouds.130UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEStratiform cloudsStratiform clouds form when a large mass of stable air graduallyrises. As this air rises, it expands and cools, allowing condensationto spread evenly throughout the layer. Stratiform clouds look likesmooth, flattened blankets (Figure 6.9). They can cover as much as300,000 square miles! A sky with stratiform clouds appearsuniformly gray.Cirrostratus: Cirrostratus clouds look like a translucent whitecoating across the sky. They are high clouds, located at least6,000 meters above the ground. These clouds are made of icecrystals. As a result, sunlight shining through the crystals isrefracted (bent) causing a halo-like effect around the Sun.Altostratus: Altostratus clouds are the most easily recognizablestratiform clouds. If the sky looks like a smooth gray sheet and noshadows form on the ground, you are seeing altostratus cloudslocated between 2,000 and 6,000 meters high.Stratus: Stratus clouds form below 2,000 meters. Stratus cloudslook like fog that doesn’t quite reach the ground.Figure 6.9: Stratiform clouds.StratocumuluscloudsCirrus cloudsNimbostratus: When a stratus cloud turns dark gray, it signals theapproach of rain. These rain clouds are called nimbostratus.Stratocumulus clouds have aspects of both cumuliform andstratiform clouds (Figure 6.10). They form when convection occursinside a stratiform cloud. As rising air cools, the water in the cloudcondenses, creating a cumuliform cloud within the stratiform cloud.This causes the smooth cloud to look lumpy.Cirrus clouds are thin lines of ice crystals high in the sky, above6,000 meters (Figure 6.11). A curved cirrus cloud is commonlycalled a “mare’s tail.” The curving is due to a change in winddirection, and as a result may indicate that the weather is going tochange.Figure 6.10: Stratocumulus clouds.Figure 6.11: Cirrus clouds.6.2 WEATHER PATTERNS131

PrecipitationRainSnow and sleetDew and frostFogIf air cools to a temperature lower than the dew point, and thepressure remains constant, water vapor condenses into liquid. Atfirst, the water molecules condense on particles such as dust,pollen, or volcanic ash. Once a few water molecules condense, theycreate a site for other molecules to condense too. What starts asjust a few water molecules quickly grows to millions of moleculesthat form water droplets. If the droplets become big enough, theyform visible clouds. Clouds will produce rain when the drops geteven bigger and have a volume of about 1 milliliter. At this size,they become heavy enough to fall as raindrops.Snow usually forms when both ice crystals and water droplets arepresent in the sky. The water droplets attach to ice crystals andfreeze there. When the ice crystals are large enough, they will fallto the ground as snow. However, if the air temperature near theground is warm, the crystals will melt and the precipitation willfall as rain. Sometimes very cold air lies below warmer air,causing the water to refreeze and hit the ground as sleet.Because the ground cools quickly, the temperature of the ground isoften below the dew point late at night or early in the morning. Airnear the ground gets cooled and some water vapor condenses inthe form of dew. If the temperature is low enough, the dew freezesand turns to frost.If air within a few hundred meters of the ground is cooled belowthe dew point, fog will form. Fog can form under two conditions.Warm moist air could move over a cooler surface, or the groundbelow could cool below the dew point at night. Either way, fogconsists of suspended water droplets. Fog is a ground-level cloud.Condensation warms the airCondensation is actually awarming process. Why? Energywas needed when the waterchanged from a liquid to a gas.This energy is released when thewater changes back into the liquidform. As a result, if it is not toowindy, you can sometimes feel theair warm up a few degrees whenprecipitation begins to fall.132UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEFrontsLarge bodiesof airMoving air andfrontsCold frontsAs you learned in Section 6.1, air masses are large bodies of airsometimes covering thousands of square kilometers. Air massesform when air is stationary over an area long enough to take on thecharacteristics of the surface below. Two common air massesaffecting the United States are the continental polar air mass,which forms over the Canadian plains, and the maritime tropicalair mass, which forms over the Gulf of Mexico (Figure 6.12). Thecontinental polar air mass contains cold, dry air. In contrast, themaritime tropical air mass contains warm, moist air.Changing atmospheric conditions and global wind currents causeair masses to move. The continental polar air mass tends to slidesouth or southeast, while the maritime tropical air mass tends toslide north or northwest. When two different moving air massescollide, the border between them is called a front.A cold front occurs when cold air moves in and replaces warm air.The warm air is forced sharply upward by the cold, denser air. Therising warm air cools. This causes condensation. Often rain or snowshowers accompany a cold front. As a cold front moves throughan area, the temperature and water content of the air decreaserapidly. The temperature can sometimes cools as much as 15 °F inone hour.front - the border between twodifferent air masses.cold front - a front that occurswhen a cold air mass moves inand replaces a warm air mass.Figure 6.12: Two air masses thataffect the weather in the United States.6.2 WEATHER PATTERNS133

Warm frontsA warm front occurs when warm air moves in and replaces coldair. The warm air slides up over the colder air. The warm air risesand cools, but in this case the lifting is very gradual and steady. Asa result, long bands of light precipitation often move ahead of awarm front. As a warm front moves through an area, there will bea noticeable increase in temperature and moisture in the air.warm front - a front that occurswhen a warm air mass moves inand replaces a cold air mass.jet streams - high-altitude, fastmovingwinds.Jet streamsSpeed and pathof a jet streamHigh-altitude, fast-moving winds are called jet streams. There aretwo big jet streams in each hemisphere, formed where there aresharp boundaries between cold and warm temperatures. A jetstream acts as a border between cold and warm air masses. Whenthe jet stream changes its path, air masses to either side of it tendto move too.The jet stream winds are found near the top of the troposphere,and have speeds of at least 87 kilometers (54 miles) per hour, andsometimes as great as 320 kilometers (200 miles) per hour. The jetstreams flow around the globe from west to east. A jet streamattains its fastest speeds during winter of its hemisphere when thetemperature difference between that pole and the equator isgreatest. The path and speed of a jet stream can be altered by landfeatures such as mountain ranges, or by giant cumulus clouds thatact like boulders in a rushing river.On a weather map, a cold front isshown using a line marked withtriangles. The triangles point in thedirection the front is moving. Awarm front is shown using a linemarked with semicircles.134UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATELow- and high-pressure areasLow-pressurecentersHigh-pressurecentersIsobarsWhen a cold front moves into a region and warm air is forcedupward, a low-pressure center is created near Earth’s surface atthe boundary of two air masses (Figure 6.13). Cold air rushes in tofill that low-pressure region. This cold air forces more warm air tobe pushed upward. A cycle begins to develop. Due to the Corioliseffect, the air masses move in curved paths. As a result, the movingair begins to rotate around the low-pressure center (Figure 6.13).In the northern hemisphere, the moving air rotatescounterclockwise, while in the southern hemisphere, the air rotatesclockwise. Strong winds and precipitation often accompany theserotating systems.A high-pressure center tends to be found where a stable, colder airmass has settled in a region. Colder air is denser than warm air,and therefore creates higher atmospheric pressure. Sinking air in ahigh-pressure center inhibits the development of the upward airmovement needed to create clouds and precipitation. High-pressurecenters, therefore, are associated with fair weather and blue skies.Winds rotate clockwise in the northern hemisphere and counterclockwisein the southern hemisphere.This is the opposite of what happens ina low-pressure center.The wavy lines on a weather map areoften associated with high- (H) and low-(L) pressure centers. Each line, calledan isobar, connects the places that havethe same atmospheric pressure. Isobars help meteorologistspinpoint the location of high- and low-pressure centers, and provideinformation about the movement of weather systems.low-pressure center - a lowpressurearea created by risingwarm air.high-pressure center - a highpressurearea created by sinkingcold air.isobar - a line on a weather mapthat connects places that have thesame atmospheric pressure.Figure 6.13: (1) Warm air is forcedupward when a cold front moves into anarea. A low-pressure center is created.(2) The cold air moving toward the lowpressurecenter begins to rotate aroundit in a counterclockwise direction.6.2 WEATHER PATTERNS135

ThunderstormsStorm cellsLightning andthunderThunderstorms occur because ofconvection in the atmosphere. Warmair rises from the ground to the top ofthe troposphere. This is called anupdraft. As the updraft rises, it coolsand condenses, forming a toweringcumulonimbus cloud. Eventually, someof the cloud droplets become largeenough to fall as rain. Cold air from thetop of the troposphere is dragged downalong with the rain. This cold, denseair is called a downdraft. The downdraft and updraft form a typeof convection cell called a storm cell within the cloud. A stormends when cool air from the downdraft replaces all the warm airon the ground. The updraft stops flowing. Next, the rain stops andthe thunderstorm ends.Lightning is a bright spark of light that occurs within a stormcloud, between a cloud and Earth’s surface, or between two stormclouds. Lightning occurs when the bottom of a storm cloudbecomes negatively charged (–) and the top becomes positivelycharged (+) (Figure 6.14). When this happens, a spark travelsbetween negatively and positively charged surfaces. Thunder isthe sound we hear that is associated with lightning. Thunder iscaused by the rapid heating and expanding of air that is nearlightning.storm cell - a convection cellwithin a cloud that is associatedwith a storm.lightning - a bright spark of lightthat occurs inside a storm cloud,between a cloud and Earth’ssurface, or between two clouds.thunder - a sound that occurswhen a lightning spark heats airand the air expands.Figure 6.14: Lightning occurs whena spark travels between negative andpositive charges.136UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEHurricanesCyclones andhurricanesHow hurricanesformHurricaneconditionsA cyclone is a low-pressure center that is surrounded byrotating winds. The Coriolis effect causes these winds to rotatecounterclockwise in the northern hemisphere and clockwise in thesouthern hemisphere. A hurricane is a tropical cyclone with windspeeds of at least 74 miles (119 kilometers) per hour. The Saffir-Simpson Hurricane Scale is one scale used for rating hurricanes(Figure 6.15).Warm, moist air over the tropical ocean provides the initial energysource for a hurricane. As the warm air rises, the water vapor in itcondenses. Clouds and thundershowers form. The condensationreleases heat, warming the surrounding air even more. As all ofthis air expands and rises, it creates an area of low pressure atthe surface of the water. This pressure difference causes thesurrounding air to rush toward the center. The path of this rushingair curves due to the Coriolis effect, and a rotating system forms.Several conditions must be present for a rotating system to becomea hurricane. First, the ocean water must be warm (about 27 °C).Second, the layer of warm ocean water must be deep enough sothat cooler water does not get stirred up to the surface by thestorm. Cooler water decreases the strength of the storm. Next,the air must be warm and moist to a point high above sea level.Water vapor from high-level air is pulled into the storm. When itcondenses, heat is released, and the storm strengthens. Finally,the wind conditions must also be just right. Winds blowing fromdifferent directions or at different speeds can break the stormapart.cyclone - a low-pressure centersurrounded by rotating winds.hurricane - a tropical cyclonewith wind speeds of at least74 miles per hour (119 kilometersper hour).Figure 6.15: The Saffir-SimpsonHurricane Scale.6.2 WEATHER PATTERNS137

TornadoesComparinghurricanes andtornadoesHow tornadoesformHigh wind speedscause damageA tornado, like a hurricane, is a system of rotating winds around alow-pressure center. An average tornado is less than 200 meters indiameter—tiny, compared with the 640 kilometer (640,000 meter)average diameter of a hurricane! However, the wind speeds of atornado are much greater than those of a hurricane. A tornado’swind speed can reach 400 kilometers per hour.A tornado begins to form when the updrafts in a storm cell reachmore than 160 kilometers per hour. Winds near the top of thecumulonimbus cloud begin rotating at a high speed. As more airflows in to the low pressure center of the storm, the rotationextends downward. The diameter of the rotating wind patternnarrows, causing the wind to speed up. As the rotating windpattern narrows and lengthens, it forms a funnel cloud(Figure 6.16). If the funnel cloud reaches the ground, it becomesa tornado.The rushing wind of a tornado can flatten houses and even lift carscompletely off the ground. A tornado in Broken Bow, Oklahomaonce carried a motel sign 48 kilometers and dropped it inArkansas! Most tornadoes lastaround 10 to 20 minutes, althoughthe strongest tornadoes can last anhour or more. They travel along theground at speeds of about 40 to60 kilometers per hour.tornado - a system of rotatingwinds around a low-pressurecenter; a tornado is smaller than ahurricane, but has faster winds.Figure 6.16: A funnel cloud formswhen updrafts in a storm cell reachhigh speed and begin to rotate. As thediameter of the rotation narrows andextends downward, a funnel cloud takesshape.138UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEEl Niño Southern OscillationA storm patternin the PacificEl Niño SouthernOscillationEl NiñoStorm patterns across the globe can happen in cycles. One suchpattern is in the tropical Pacific. Usually, the trade winds blowwarm water from east to west across the Pacific Ocean, from Peruon the ocean’s eastern coast toward Indonesia on the western coast(Figure 6.17). As a result, the average water temperature off thecoast of Indonesia is 6 °C warmer than the average watertemperature off the coast of Peru. The warm water of the westernPacific typically generates thunderstorms of greater frequency andintensity than what is normally seen near Peru.For reasons not fully understood, every so often the trade windsweaken and the warm water reverses direction, flowing from thewestern Pacific toward South America (Figure 6.17). Along withthat warm water comes greater thunderstorm activity across thePacific. Indonesia and other western Pacific nations experiencedrier than normal conditions, while the eastern Pacific countriesget more precipitation. This change in wind flow, air pressure, andthunderstorm activity is known as the El Niño SouthernOscillation.Peruvian fishermen were among the first to notice the change inwater temperature along their shores. When the warm water fromthe west flows toward South America, it cuts off a normal patternin which cold water from the ocean depths flows up to the surfacealong the coast of Peru. The upwelling cold water brings nutrientsnecessary for fish and other aquatic life to flourish. During an ElNiño event, the warm water flowing over the cold water acts like alid (Figure 6.18). It prevents the cold water from reaching thesurface. As a result, nutrients are not available for aquatic life andthe fish population declines.Figure 6.17: The usual pattern of aircurrent flow compared to what happensduring El Niño.Figure 6.18: The usual pattern ofwater current flow compared to whathappens during El Niño.6.2 WEATHER PATTERNS139

6.2 Section Review1. What does a meteorologist do?2. If you wanted to increase the rate of evaporation of water, howwould you change the temperature and pressure?3. Name one type of cloud you would expect to see on a day whenthe weather is cool, dry, and clear. Name one type of cloud youwould see if a thunderstorm were about to happen.4. Which kind of cloud has the characteristics of both cumuliformand stratiform clouds? Describe this cloud.5. What causes frost to form?6. How is the weather associated with a cold front different fromthe weather associated with a warm front?7. Indicate which characteristics below apply to a high-pressurecenter and which apply to a low-pressure center.a. rising warm airb. sinking cold airc. wind rotates counterclockwise around this pressure centerin the northern hemisphered. precipitatione. dry and clear8. How is convection of air involved in the development of athunderstorm?9. What conditions are needed for a hurricane to develop?10. List three differences between a hurricane and a tornado.11. On the Saffir-Simpson Hurricane Scale, what is the differencebetween a Category 1 hurricane and a Category 5 hurricane?12. Fish populations decline as a result of the El Niño SouthernOscillation. Why?This photo of the jet stream wastaken by the GOES-8 satellite inorbit 36,000 kilometers aboveEarth. Arrows were added toindicate wind direction.Research one important aspectof the jet stream and write ashort report on it.When Hurricane Andrew hit Florida in1992, its winds were 265 km/h and itproduced a storm surge of 5.2 meters.What category was Hurricane Andrewon the Saffir-Simpson Scale?Research the answer to the followingquestion. How does HurricaneKatrina, which hit New Orleans in2005, compare to Hurricane Andrew?140UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATE6.3 Climates and BiomesImagine that someone gave you an airplane ticket to travel to Africa to see SerengetiNational Park in Tanzania. If you like adventures, you might say “Great! When do Ileave?” Then you would want to pack your suitcase. But what would you take? Whatis the climate like in Africa?ClimateFactors thataffect climateClimate is the type of weather patterns that a place has, onaverage, over a long period of time. If you wanted to know about theclimate in a place you were about to visit, you might ask questionslike “How hot and how cold does it usually get? Does it rain a lot?How often is the temperature below freezing?” Climate dependson many factors, including latitude, precipitation, elevation,topography, and distance from large bodies of water.climate - the long-term record ofweather patterns and includes thetemperature, precipitation, andwind for a region.Packing for an adventure in theSerengeti1. On a world atlas, find theSerengeti. Describe where it islocated.2. Make a prediction about thekind of weather the Serengeti willhave next week.3. Then, research the seasonalweather on the Internet or in thelibrary. Were you correct in yourprediction?4. Using what you learned, make alist of things you would need topack in your suitcase to visit theSerengeti.6.3 CLIMATES AND BIOMES141

Characteristics of biomesWhat is a biome?Latitude,humidity, andbiodiversitySunlight at theequator vs. highlatitudesLatitude andsolar radiationScientists divide the planet into climate regions. Each region iscalled a biome. Earth has six major biomes: deserts, grasslands,temperate deciduous forests, rainforests, taigas, and tundras.These biomes generally differ in their latitude, weather andrelative humidity, amount of sunlight, and topography. Eachbiome has a unique set of plants and animals that thrive in itsclimate.Recall that relative humidity is a measure of how much watervapor an air mass contains relative to how much it can contain.From the poles to the equator, humidity, and the biodiversity ofplants and animals increase. Biodiversity refers to the measure ofthe variety and number of organisms that live in an area.Earth is hottest near the equator where the Sun is closest to beingdirectly overhead year round. At the north and south poles,temperatures are much colder. This effect is related to the factthat light travels in straight parallel lines. To demonstrate what ishappening, imagine shining a flashlight on a sheet of paper(Figure 6.19). The light makes a bright, small spot. By tilting thepaper, you can make the light spot bigger and less intense.At the equator, sunlight is direct and intense. Earth’s north andsouth poles are tilted away from or toward the Sun depending onthe time of year. The locations of the poles relative to the Sun andEarth’s spherical surface mean that sunlight reaching these areasis spread out and less intense (Figure 6.19). As a result, theaverage yearly temperature at the equator is 27 °C (80 °F), whileat the North Pole it is –18 °C (0 °F). Generally, as latitude (ordistance from the equator) increases, the amount of incoming solarradiation decreases.biome - a major climate regionwith particular plants and animals.Earth has six major biomes.Figure 6.19: A flashlight shiningon a piece of paper represents solarradiation reaching Earth. If you tiltthe paper, the spot of light spreads outand becomes less intense, like at thepoles.142UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATEOther factors besides latitude can affect climatesTemperatures ininland regionsHave you ever wondered why cities near the ocean don’t get as hotin the summer or as cold in the winter as inland cities at the samelatitude? Portland, Oregon and Minneapolis, Minnesota are twocities near the same latitude (Figure 6.20). Look at Table 6.1 belowto see the average daily temperature ranges for these cities.Water helpsregulatetemperatureElevationTable 6.1: Average daily temperature ranges for Portland and Minneapolis.Average daily temperature rangeMonth Portland MinneapolisJanuary 1–7 °C, (34–45 °F) -16– -6 °C (3–21 °F)July 14–27 °C (57–80 °F) 17–29 °C (63–84 °F)The differences in temperature between the two cities have to dowith water. Because of its higher specific heat, water warms up andcools down slowly. In contrast, land warms up and cools downquickly because of its lower specific heat. Therefore, regions nearwater—like Portland—do not have extremely hot or cold weather.Latitude is an important factor in defining a biome. However,elevation is also a factor. Elevation is the height or distance of anobject or area from sea level. The range of biomes that exist onEarth from the equator to the poles also exists if one goes from thebottom of a mountain to the top of a mountain (Figure 6.21).Figure 6.20: Portland andMinneapolis are near the same latitudebut they have different climates.Questions about Table 6.1:1. It is January 3rd and –10 °Coutside. Where am I?2. It is July 4th and 20 °C. Can youfigure out from the table where Iam? Why or why not?Figure 6.21: Latitude versuselevation for the Northern Hemisphere.6.3 CLIMATES AND BIOMES143

Earth’s biomes144UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATETypes of biomesDesertsGrasslandsTemperatedeciduousforestsRainforestsTaigaTundrasA desert averages less than 35 centimeters of rainfall per year.Most deserts are found around the latitudes of 30° N and 30° S.Deserts have large variations in daily high and low temperatures.Grasslands are on every continent except Antarctica. There aretwo types: tropical grasslands, known as savannas; and temperategrasslands. Savannas occur where there is not enough rainfall tocreate a rainforest. Temperate grasslands are in the mid-latitudesand receive most of their precipitation in the spring and summer.Temperate deciduous forests are found in middle-latitude regions,where there are four distinct seasons. Average yearly rainfall is75 to 150 centimeters, enough to support the growth of broadleafed,deciduous trees like oak and maple. Deciduous means thesetrees lose their leaves the end of the growing season.Tropical rainforests are near the equator—between the latitudes of23.5° N and 23.5° S. They have an average rainfall of at least200 centimeters per year. The temperature of these rainforests isnearly constant and in a narrow range—20 to 25 °C. Temperaterainforests, another kind of rainforest, are in the middle-latituderegions, and experience about 250 centimeters of rain per year.The taiga is the largest biome. The taiga can be found betweenthe latitudes of 50° N and 70° N in North America, Europe, andAsia. The average temperature in the taiga is below freezing forat least six months of the year.The tundra is the coldest biome on Earth. The word tundra comesfrom a Finnish word for “treeless land.” There are two types oftundra—Arctic tundra, found in a band around the Arctic Ocean,and alpine tundra, found high in mid-latitude mountains.desert - a climate region thataverages less than 35 centimetersof rainfall per year.grasslands - climate regions withtoo little rainfall to support a forest.Grasslands have grasses as themain vegetation.temperate deciduous forests- climate regions in the midlatitudesthat have four seasons.tropical rainforests - climateregions found near the equatorthat have a lot of rainfall and highbiodiversity.taiga - the largest climate region,found in the higher latitudes; alsoknown as a boreal or coniferousforest.tundra - a climate region locatedin high latitudes; the coldest landbiome.6.3 CLIMATES AND BIOMES145

Plants and animals in biomesCommunitiesAdaptationsEcosystemsHow many roles?A biome is characterized by its plant and animal communities.The plants and animals in a community interact with each otherand survive in a shared environment. The plants and animals inthe environment have adaptations that allow them to obtainenough resources (such as food, water, or sunlight) to survive.Jackrabbits have an adaptation to keep cool in the hot desert—enormous ears with many blood vessels near the surface(Figure 6.22). Blood running through the vessels speeds up heattransfer from the jackrabbit’s body to the air so the jackrabbitstays cooler.Biomes are large geographic areas. Within a biome, there aremany interrelated ecosystems. An ecosystem is made up of theplants and animals that live there, plus nonliving things like soil,air, water, sunlight, and nutrients. The living and nonliving partsof an ecosystem work together, and each organism plays animportant ecological role.The number and types of organisms that an ecosystem cansupport depends on the resources available (food sources) andon environmental factors. Environmental factors include theamount of available sunlight, water, and the temperature. Theroles within a biome ecosystem depend on the quantity and typeof resources. Each ecosystem of a particular biome type hasorganisms that play similar roles. For example, both a rainforestin South America and a rainforest in Australia have predators,herbivores (plant eaters), and decomposers suited to surviving inthe rainforest environment.Figure 6.22: The large ears of ajackrabbit help this desert animal tocool down.BiodiversityDoes this statement surprise you?Why or why not?The biodiversity of the desert isgreater than for all other biomeswith the exception of the tropicalrainforest.Why is biodiversity in anecosystem important?Write your response as a shortessay.146UNIT 2 WATER AND WEATHER

CHAPTER 6: WEATHER AND CLIMATE6.3 Section Review1. What are three factors that affect climate?2. Are climate and weather the same thing? If not, explain howthese terms are different.3. What happens to the intensity of solar radiation and Earth’saverage yearly temperature as you move from the equator tothe South Pole or North Pole?4. Find San Francisco, California and Topeka, Kansas on a map ofthe United States. How would the weather in the these twoplaces compare? Explain your answer.5. Refer to the Earth’s biome map on page 136. What kind ofbiome occurs at 30° S and 150° E? Describe what this biome islike.6. Alpine and Arctic tundra occur at a mid-latitude location nearIndia (25° N 80° E). Why do you think this biome occurs here?(Hint: Find out what land form occurs at this location.)7. A photograph of an Arctic hare is shown in Figure 6.23. Thisanimal lives in cold environments.a. What adaptations do you see that this animal has?b. How does the appearance of this animal compare to thejackrabbit in Figure 6.22?8. The main grass in a grassland in North America is prairiegrass. The main grass in a South American grassland ispampas grass. Would you expect the ecological role of thesegrasses in these two locations to be the same or different?Explain your answer.What’s your climate?1. From the reading, list the factorsthat affect the climate of an area.2. Use these factors to describethe climate where you live.Figure 6.23: An Arctic hare.6.3 CLIMATES AND BIOMES147

Meteorologists Weather it AllChapter 6 Connection148Neither rain nor sleet nor cold shall keep a mail carrier fromdoing his or her job (or you from walking the dog). The samecan be said of your local meteorologist. Every daymeteorologists broadcast weather reports. Millions of peopleplan what they will wear, what they will do after work or onthe weekend, and if they will carry their umbrellas based onthose reports.But only a very fewmeteorologists in the UnitedStates wear a microphone orappear on camera at work.Most meteorologists work forthe National Weather Service(NWS), a government agencythat is part of the NationalOceanic and AtmosphericAdministration (NOAA).NOAA was formed in 1970, and its mission is to predictchanges in the atmosphere and ocean environments. Thistask includes predicting the weather.Meteorologists observe and study Earth's atmosphere and itsphenomena. Many work to forecast the weather andchanging climate conditions, while others do scientificresearch. They try to understand how the atmosphere affectsthe environment. They study the constant changes in ouratmosphere. They create computer models to predict howstorms will form, when rivers will flood, and what areas willsuffer droughts. Their work can go far beyond telling anaudience whether it will be sunny or cloudy tomorrow.Meteorologists at workJulie Dian is a meteorologist who works at the NationalWeather Service Ohio River Forecast Center in Wilmington,Ohio. One of her responsibilities is to compare readings oftemperature, winds, atmospheric pressure, precipitationpatterns, and other variables. She draws conclusions andmakes predictions about local weather with these data.Dian and other meteorologists use many tools of their trade.They gather information in many different ways.• More than 11,000 volunteers from all over the UnitedStates and beyond provide daily reports. They phone theirreports to warning and forecast centers.• Satellites collect data and record images. The TV imagesyou see of hurricanes in the Gulf of Mexico or CaribbeanSea, for instance, are provided by cameras on satelliteshigh above Earth.• Ground-based radar scans for precipitation and clouds.• Weather balloons are launched to gather data.Up, up, and awayWind direction, air pressure, temperature, and humidity ofair masses high in the sky all affect our weather down on theground. Weather balloons can monitor these conditions.Weather balloons are released atleast twice a day from a structure(like the one at right) at theNational Weather Service office inWilmington. Additional balloonsare released more often duringsevere weather.The balloons are filled with helium.When they are inflated on theground, they are about 2 metersacross. As they rise, they grow to adiameter of about 6 meters. This is because the air pressureis lower at higher altitudes, so the gas inside the balloonexpands.

One type of balloon carries a radiosonde, which is aminiature radio transmitter with instruments on it. Theballoon rises 27,400 meters (90,000 feet) or higher. All alongthe way, the radiosonde measures data such as temperature,air pressure, and humidity, and transmits themeasurements to a ground receiver or a satellite.Dian uses atheodolite totrack balloonsthat have beenlaunched fromher center. Atheodolite is asurveyor'sinstrument formeasuringangles and, inthis case, forfollowing the altitude and movement of the balloon. In thisphoto, Dian shows a student the radio theodolite at the NWSoffice. In her left hand, she holds an unopened weatherballoon. The theodolite in the photo shows the wind speed atdifferent altitudes. Some theodolites contain telescopes, andothers have radio receivers.Methods for predictingThere are several different ways to predict the weather. Allof the information collected—from volunteers, radar,satellites, and weather balloons—is used in different models.Some of the older methods use historical information topredict future weather events. The most complex of theseinvolves finding very similar conditions at some point in thepast. Then the weather is predicted based on what happenedin the “same” situation back then.Today, computers have made forecasting much moresuccessful. Numerical weather prediction, or NWP, is used tocreate computer models of the atmosphere. With NWP,many variables are considered. Air temperatures at differentaltitudes, wind speeds, humidity, high and low pressureareas—all of this is fed into a computer. The computercreates a complex model of the atmosphere and provides themost accurate forecasts available.Questions:1. What is the mission of the National Oceanic and AtmosphericAdministration?2. What causes weather balloons to expand in diameter from 2to 6 meters?3. Why are today's weather forecasts more accurate than in thepast?Chapter 6 ConnectionUNIT 2 WATER AND WEATHER149

Chapter 6 ActivityRainy Day MysteryIt’s summertime and raining in Savannah, Georgia. You callyour friend in Los Angeles, California and find out it’ssunny. During the summer it hardly ever rains in LosAngeles. You decide to do some investigative meteorologicalwork to find out why the climates of these two cities are sodifferent.What you will do1. Find out the latitude for each city using a globe, atlas, oran Internet mapping web site. Also, be sure to find both ofthese cities on a map.2. Imagine that you have collected data and made thegraphs on this page. Write a paragraph that describeseach graph and answers these questions: (a) What doesthe graph show for Savannah, Georgia? (b) What does thegraph show for Los Angeles, California?3. Based on the graphs, you can identify relationships. On aseparate piece of paper, copy and fill in this table.What relationship do you see between...... ocean water temperatureand air temperature?... ocean water temperatureand precipitation?... air temperature andprecipitation?4. Based on your work so far, write one hypothesis toexplain why it rains more in Savannah than in LosAngeles.Applying your knowledgea. Do you think latitude explains the difference in climate ofthese two cities? Why or why not?b. Which city has ocean water whose temperature varies asmaller amount during the year?c. In what two months were the ocean water temperaturesnearly the same?d. Which city has air temperatures which vary the smallestamount during the year?e. In what two months were the air temperaturesapproximately the same?f. What do you notice about the answers to questions c ande?g. Do you think that there is a relationship between oceanwater and the climates of coastal cities?150

ConceptsSection 6.11. What causes wind?2. A weather map shows a high pressure area located overTown A and a low pressure area located over Town B. Whichdirection will the wind blow? From Town A to Town B orfrom Town B to Town A?3. Explain the difference between a land and a sea breeze.4. Why is atmospheric pressure low at the equator?5. What causes the Coriolis effect?6. In what direction would you expect a global wind pattern tobe blowing at 15° S latitude? What is the name of this globalwind pattern?7. A weather report states that the relative humidity is fortypercent. What does this value mean?Section 6.28. Explain how temperature and pressure affect the amount ofwater in Earth’s atmosphere.9. Copy this table on to your own paper and fill it in:Cloud category How it forms TypesCumuliformStratiform10. When precipitation occurs, does air temperature get warmeror cooler? Why?11. You hear a weather report that a warm front is movingthrough your town. What kind of weather do you expect?12. Would a hurricane form under these conditions? Why orwhy not? The conditions: The ocean water temperature is30° C, the wind is blowing from one direction, the layer ofwarm ocean water is 50 meters deep, and the air is warmand moist up to 5,750 meters.13. The Coriolis effect is minimal along the equator. As a result,what might you expect at the equator:a. Sinking cold air. b. Few or no cyclones forming.c. A high pressure center. d. A tornado.14. What is the weather like in Indonesia during an El Niñoevent? Why?Section 6.315. Identify whether these comments are talking about theweather or about the climate for an area.a. A cold front is moving into the area.b. A region has two main seasons—a wet and a dry season.c. My region averages only 20 centimeters of rain a year.d. Tomorrow will be windy and sunny.16. What is a biome and how many main biomes are on Earth?17. Explain why the average yearly temperature at the equatoris hot (27° C) and the average yearly temperature at thenorth pole is cold (-18° C).18. To travel to a different climate from the one you are in now,what would you need to do?19. You can expect to find tundra in the high northern latitudesof the northern hemisphere. Where would you expect to finda tundra ecosystem on a mountain?20. How many seasons are there in temperate deciduousforests?152CHAPTER 6 WEATHER AND CLIMATE

CHAPTER 6 ASSESSMENTMath and Writing SkillsSection 6.11. You are a pilot who wants to fly anairplane from St. Paul, Minnesota,700 miles south to Little Rock, Arkansas.If you set your compass and try to flystraight south, you will probably end up inNew Mexico! Why?2. The trade winds were named by sailors who crossed theNorth Atlantic in the 17th and 18th centuries in search ofgoods to bring back to Europe. The trade winds provided ahelpful push on their journey west. Find out more aboutfamous global winds. Research one of the following topics:a. Horse Latitudesb. Alizec. Roaring Forties3. A warm (25° C) air mass contains 80% of the water it couldcontain. The air mass warms to 30° C.a. Does the volume of the air mass decrease or increase when thetemperature goes up?b. Does the relative humidity of the air mass increase ordecrease when the temperature goes up? (Assume thatthe amount of water in the air mass stays the same.)Section 6.24. Locate an image of a weather map in a newspaper or findone on the Internet. Copy a portion of the map and identify:a high pressure center, a low pressure center, one or moreisobars, a warm front, and a cold front.5. Read this paragraph and then answer the question:Warm, moist air crosses over the Pacific Ocean and reachesthe Washington coast. At first, the air mass flows up thewestern side of a mountain which has a lot of trees andplants. Cool temperatures at the top of the mountain on thewest side cause the mass to decrease in size so that watervapor becomes first a cloud and then rain droplets. Theresulting cool, dry air mass sinks down the eastern side ofthe mountain into warm temperatures. The land that thisdry air passes over will have a dry climate.Now, look at the illustration below. Which city would receivemore rain per year—Olympia or Yakima? Explain youranswer. Go to the Internet and find out what the averagerainfall actually is for each of these cities. This data willhelp you determine if your answer is correct!Section 6.36. The desert is home to more different types of animals thanany other place except the rainforest. How can animalssurvive in such a hot climate? Use the library or Internet tolearn how animals are able to survive in a desert climate orone of the other climates.UNIT 2 WATER AND WEATHER153

7. Study the following map showing population density andthe Earth’s biomes map from the chapter.a. Which biomes have the most densely populated areas?b. Which biomes have the least densely populated areas?c. Propose an explanation as to why different biomes havesuch different population densities.9. Use this table to answer the questions below.Temperature rangeBiome Low temp (°C) High temp (°C)Tropical rainforest 20 25Tundra -34 12a. Which biome has the largest range of temperature?b. Which biome gets the warmest?c. Which biome gets the coldest?d. Using the data above, construct a bar graph that showsthe average high temperatures and the average lowtemperatures for the rainforest compared to the tundra.8. Answer these questions using the Earth’s biome map:a. What biome is located at 60° N and 100° E?b. What biome is located at 0° and 60° W?c. What biome is located at 40° N and 80° W?d. Give the latitude and longitude for one grassland biome.e. Give the latitude and longitude for one desert biome.Chapter Projects—Demonstrating theCoriolis EffectPlace a large foam ball on a woodenskewer. Use a marker to draw the northand south poles and the equator on theball. Ask a partner to rotate the skewerso that the ball turns in acounterclockwise direction as seen fromthe north pole. Using a permanentmarker, try to draw a line from thenorth pole toward the equator. Next,start at the equator and try to draw aline straight up. What happened?Now turn the ball over and switch roles.Your partner should demonstrate theway air currents would flow in thesouthern hemisphere from the south pole to the equator. Theball needs to be turned clockwise in this position.154CHAPTER 6 WEATHER AND CLIMATE

Chapter 7OceansImagine you are an astronaut in a space shuttle looking backat Earth. What does it look like? You probably know that it ismostly blue. That blue color comes from the five oceans thatcover most of Earth’s surface.The United States has two oceans at its east and westborders: the Atlantic Ocean and the Pacific Ocean. Have youseen either of these oceans? When you see an ocean, it is easyto appreciate what a massive body of water it is.Aside from being big, what characteristics does an oceanhave? You might know that ocean water is salty and thatwaves form in oceans. In this chapter, you’ll learn much moreabout oceans, waves, beaches, and the features of the deepocean floor!1. How many oceans does Earth have?2. What factors affect the size of ocean waves?3. Where does sand come from?

7.1 Introduction to OceansAbout 97% of Earth’s water is contained in five oceans. The oceans cover most ofEarth’s surface and are important to life on the planet. However, we can’t drinkocean water. It’s too salty! In this section you will learn why the oceans are salty.You’ll also learn about ocean currents.Salt waterSalt in oceanwaterSources of saltOcean water is about 3.5 percent salt. The word salinity is used todescribe the saltiness of water. Most of the salt in ocean water issodium chloride. You use sodium chloride, or table salt, on yourfood. Sodium chloride is found in nature as the mineral halite(Figure 7.1). In some places, special ponds called salt evaporationponds are set up to harvest salt from the ocean (Figure 7.2).The salt in the oceans comes from minerals in the ocean floor, fromgases released by volcanoes, and from rivers that carry dissolvedminerals from land to sea. These dissolved minerals come fromchemical weathering of rocks on the continents.salinity - a term that describesthe saltiness of water.Figure 7.1: Sodium chloride, or tablesalt, comes from the mineral halite.Figure 7.2: Salt evaporations pondsin the Dead Sea are used to harvest saltfor human consumption.156UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSEarth’s oceansEarth from spaceFive oceansAstronauts are amazed when they see our blue planet from space.Earth is mostly bright blue because of its vast oceans.Four of Earth’s oceans are easy to identify because of the shape ofthe surrounding continents. These four oceans are the Atlantic,Pacific, Indian, and Arctic oceans. The fifth ocean, the SouthernOcean, is composed of the waters surrounding Antarctica. TheSouthern Ocean includes the water south of 60° S latitude.The importanceof Earth’s oceansOceans are an important source of water for the water cycle. Theyalso help maintain Earth’s heat balance. Because water has a highspecific heat, the oceans do not heat up or cool down quickly. As aresult, our climate does not become too hot or too cold. Also, oceansspread energy and heat from the hot equator to the colder polesthrough ocean currents and waves. In addition to moving heat,ocean currents help propel ships as they navigate the globe. Theoceans are also important because tiny, single-celled oceanorganisms called phytoplankton that live in the oceans producemost of the oxygen in the atmosphere (Figure 7.3).Figure 7.3: Tiny, single-celled oceanorganisms called phytoplanktonproduce most of the oxygen in theatmosphere.7.1 INTRODUCTION TO OCEANS157

Oceans and Earth’s climateStoring heat inthe oceansWhere do youfind milderclimates?Earth’s oceans are warmed by the Sun during daylight hours andthat heat energy is stored. The oceans are able to store heatenergy for two reasons. First, water has a high specific heat, so ittakes a long time for it to cool down once it is warm. Second, solarradiation penetrates the water surface and allows the Sun’s heatenergy to be stored many meters deep (Figure 7.4). Because of thisheat storage, the water on Earth prevents the planet from gettingtoo hot or too cold.The climates on the coastline are milder than they are inland. Thisis because ocean-warmed wind and air masses move over theoceans toward the land. In Europe, the prevailing westerlies blowover the ocean toward the coastline (Figure 7.5). As a result,Europe tends to have mild winters. The northeastern UnitedStates has more severe winters because the prevailing westerliesblow away from its coast. But even so, the nearness of watermakes the winters milder there than in places like the GreatPlains of the United States. This area can be extremely coldbecause it is far from the ocean.Figure 7.4: Two reasons why theoceans store heat energy.Figure 7.5: The prevailing windsbetween 30° and 60° N latitude.158UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSSurface currents and gyresWind drivessurface oceancurrentsSurface currentstransport heatenergyGyresThe Sun’s unequal heating of Earth and the Coriolis effect causepermanent global wind patterns (see Chapter 6). As they blowacross the ocean, these winds push water in the direction they aremoving. This creates surface ocean currents that can travel forlong distances. Small “pushes” to the surface ocean currents alsocome from the tides as they move in and out along coastlines.Surface currents move enormous quantities of water. The GulfStream is a surface ocean current that transports 80 million cubicmeters of water per second past Cape Hatteras (Figure 7.6).Because the Sun heats this water, the currents also transport heatenergy. The heat transported by the Gulf Stream is equivalent tothe output of 1 million power stations! Surface ocean currentsusually carry heat from regions near the equator toward the poles.The Coriolis effect and the shape of the coastlines cause surfaceocean currents to form large rotating systems called gyres. Gyresnorth of the equator—like the North Atlantic gyre—turn in aclockwise direction. The North Atlantic gyre is composed of foursurface ocean currents. Gyres south of the equator turn in acounterclockwise direction.surface ocean currents - winddrivencurrents that move at theocean surface, often for longdistances.gyres - large rotating oceancurrent systems.Figure 7.6: The Gulf Stream is asurface ocean current. The Gulf Streamis part of the North Atlantic gyre.7.1 INTRODUCTION TO OCEANS159

Deep ocean currentsWhat is a deepocean current?Evaporation nearthe equatorTemperature anddensityDeep ocean currents move below the surface of the ocean. Theyare slower than surface ocean currents. Deep ocean currents aredriven by density differences. Denser water sinks and less-densewater floats. Since temperature and salinity affect the density ofwater, the currents are also called thermohaline currents. Thermomeans temperature and haline means salt.Global wind patterns and heat speed up evaporation of water nearthe equator. When ocean water evaporates, the water leaves andthe salt stays behind. When this happens, surface ocean currentsnear the equator become saltier.A surface ocean current cools as it moves from the equator towardthe poles. Because this water is saltier than surrounding waterand because it is now cooler, it sinks to the ocean floor as a hugeunderwater waterfall. What was once a warm surface oceancurrent now flows along the ocean floor as a cold deep oceancurrent. After hundreds to thousands of years, the slow-movingdeep ocean current water returns to the surface in a upwardmovingupwelling. Upwellings return the original surface waterand nutrients from the ocean bottom back to the ocean surface.deep ocean currents - densityandtemperature-driven currentsthat move slowly within the ocean;also called thermohaline currents.Will an object float or sink?On average, salt water has asalinity of 3.5% (also written as35 parts per thousand or 35 ppt).Determine if the following fluidswould sink or float in average saltwater that is 25 °C.a. Salt water that is 35 ppt and50 °C.b. Salt water that is 35 ppt and4 °C.c. Salt water that is 40 ppt and25 °C.d. Water that is 10 ppt and 25 °C.160UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANS7.1 Section Review1. What does the term salinity mean?2. Where does the salt in the oceans come from?3. Name Earth’s five oceans.4. List two reasons why Earth’s oceans help make the planetsuitable for life to exist.5. In which of these places would winter be the most extreme:central Asia or western Canada? Explain your answer. Ifnecessary, look at a globe to answer this question.6. What keeps surface ocean currents moving?7. Name the four currents of the North Atlantic Gyre.8. What characteristics of deep ocean currents affect theirmotion?9. At a coastline, freshwater flows into salty water. Which of twothese events might be occurring at a coastline? Explain youranswer.a. The freshwater floats ontop of the salt water.10. Challenge: How does the Coriolis effect influence the movementof surface ocean currents in both hemisphere?11. Challenge: Pick one of these terms and find out its meaning.Write a short paragraph about each term based on yourresearch. Include a diagram with your paragraph to helpexplain each term.a. thermoclineb. estuaryb. The freshwater sinks inthe salt water.In this section, you learned theaverage temperatures in Januaryfor certain cities.• Describe what winter is like inyour city. Do you live near anocean or a large body of water?• What is the average Januarytemperature for your city?• How does this averagetemperature compare to thoselisted in the text?Predict which mass of water willsink and which will float in a massof water that is 10 °C with a densityof 1.0260 g/cm 3 .a) 15 °C, density = 1.0255 g/cm 3b) 10 °C, density = 1.0270 g/cm 37.1 INTRODUCTION TO OCEANS161

7.2 WavesThis section is about waves. It is easy to see waves in water. After throwing a stoneinto a pond, you will see water periodically bobbing up and down on the surface. Thisbobbing motion represents a wave. Read on to learn more about waves.Making wavesA disturbancemoving forwardWaves are caused by a disturbance moving forward (Figure 7.7).To understand this, think about making a wave with a piece ofrope. If you snap the rope sharply up and down, waves will traveltoward the other end of the rope while your end of the rope staysin your hand. In the case of water waves, the water moves up anddown as the disturbance moves forward.Waves occur as a repeating pattern of crests and troughs. A crestis the high point of a wave. A trough is the low point. Theamplitude of a wave is the distance between a wave crest or troughand the average level of motion (see diagram below). Wavelengthis the length of one complete wave. It is measured from any pointon a wave to the same point on the next wave. The time that ittakes for one wavelength to pass a single point is called the periodof a wave.crest - the high point of a wave.trough - the low point of a wave.amplitude - the vertical distancebetween a wave crest or troughand the average level of motion.wavelength - the distancebetween two wave crests, or thedistance between two wavetroughs.period - the time it takes for onewavelength to pass by a singlepoint.Figure 7.7: A disturbance is amovement that begins in one locationand sets things in motion farther away.162UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSMore about wavesCircular motionObservationsabout wavesA wave causes a circular motion in the water as it passes by. In thegraphic below, you see the water before the wave arrives (A). Then,the wave approaches (B). Next, the trough of the wave arrives (C).The water rises as the crest approaches (D). Finally, the water ispushed forward at the top of the crest (E).The seagull and the dolphin in the graphic below both trace acircular path, but the dolphin’s path is smaller than the seagull’s.Also, the wave has no effect on the water below the wave base. Thewave base is located at a depth that is half the wavelength of thewave. Submarines avoid being affected by waves by traveling belowthis level. Figure 7.8 summarizes these observations.Wave ObservationsSize ofwavemotionDepth ofwavemotionDecreasesbelow theocean surface.There is nowater motionbelow the wavebase. The wavebase occurs ata depth that isis about halfthe wavelengthof the wave.Figure 7.8: A summary of waveobservations.7.2 WAVES163

Wind causes wavesHow does windcause waves?The BeaufortWind Force ScaleWaves and swellsWave trainsMost ocean waves are caused by friction between the wind and theocean surface. At first, small ripples form as the wind begins toblow. The ripples allow the wind to “grip” the water. As the windgets stronger, the ripples become bigger waves with more height,longer wavelengths, and longer periods. The size of ocean wavesformed by wind depends on wind speed, the amount of time thewind blows, and fetch (Figure 7.9). Fetch is the amount of openwater over which wind blows. The greater the fetch, the larger thewaves that are created.The Beaufort Wind Force Scale is used to describe the intensity ofwind. The scale goes from 0 to 12. Each level of the scale refers to aparticular wind speed and its effects. The Beaufort Scale is usedon land to record wind speed as a measure for weather conditions.It can also be used to predict the size and strength of ocean waves.Storms in the open ocean cause waves with short, medium, andlong wavelengths. A variety of water wavelengths makes the searough. The waves travel together, away from the storm, but thelong-wavelength waves travel faster and leave the shorterwavelengthwaves behind. Only long-wavelength waves occur farfrom a storm. These long, fast-moving waves are called swells.Waves traveling together are called a wave train. When wavetrains that were formed in different places come together, thewaves add to and subtract from each other. Two medium crestswill form a single large crest. Two medium troughs will createa really deep trough. What do you think would happen if ahigh crest came together with an equally deep trough? Theywould cancel each other out, leaving a flat spot in the water(Figure 7.10).fetch - the amount of open waterover which wind blows.swells - long, fast-moving waves.wave train - many wavestraveling together.The size ofocean wavesdependson...Wind speedThe length of time that thewind blowsFetchFigure 7.9: Factors that affect thesize of waves.Figure 7.10: What happens whenwaves meet?164UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSTsunamis compared to wind wavesWhat is atsunami?Tsunamis in theopen oceanWaves in shallowwaterA tsunami is a huge wave made by a large disturbance like anunderwater earthquake, landslide, or volcanic eruption. The energyfrom these movements on the sea floor spreads as a wave on theocean surface. Figure 7.11 compares wind waves and tsunamis.In the open ocean, wind-driven waves and tsunamis are about thesame height. But the wavelength of a tsunami is much longer thanthe wavelength of a wind-driven wave. The wavelength of a winddrivenwave may measure 10 to 200 meters from crest to crest. Itmay take 5 to 20 seconds or so for a wind-driven wave to pass by.Wind-driven waves are small splashes compared to tsunamis. Thewavelength of a tsunami can be thousands of meters long! Becausethe surface of Earth is curved, you can’t see enough of it to detectthe crest of a tsunami as it approaches. If a tsunami approached aship you were in, you would see only a flat sea. As it passed underthe ship, the tsunami would cause the ship to rise gently, about tenmeters, and then gently settle back after several minutes.When a wind wave or a tsunami approaches land, the wave basebegins to drag on the shallow bottom. As the front of the waveslows, the back of the wave catches up. This shortens thewavelength making the wave crest higher. Eventually, the result isa breaking wave and surf. In the case of a tsunami, the crest ofwater can be up to 35 meters high or more. A tsunami crashing onshore may destroy buildings and wash ships inland. A hugetsunami occurred in the Indian Ocean in 2004.tsunami - a huge wave made bya large disturbance like anunderwater earthquake, landslide,or volcanic eruption.Period(seconds)Wavelength(meters)Speed(km/h)Height(m)WindwaveTsunami5–20 300–3,60010–200100,000–700,000< 50 500-1,0000–14+ ~35Figure 7.11: How a wind wavecompares to a tsunami.1. Convert the wavelengths of awind wave and a tsunami tokilometers.2. The period of a tsunami is600 seconds. What is the period inminutes?3. The height of a single storybuilding is about 3 meters. Howmany stories high is a tsunami?7.2 WAVES165

7.2 Section Review1. Name each labeled part of the wave diagram below.Surf while you studyYou can improve how fast youlearn by applying your knowledgeto new situations.2. How long is the wave in the diagram? Give your answer inwavelengths.3. What is fetch?4. Which situation described below would produce the biggestwave? Explain your answer.a. The fetch is 0.5 mile, the wind blows for 5 minutes, and thewind speed is 10 km/h.b. The fetch is 1 mile, the wind blows for 10 minutes, and thewind speed is 10 km/h.5. A boat is floating in the open ocean. A wave passes beneaththe boat. Describe how the boat moves when this happens.6. Describe how wave motion changes as you go from the oceansurface to below the wave base.7. Two waves with the same amplitude meet.a. What happens when the crest of the first wave meets thetrough of the second wave?b. What happens when two crests meet?8. What causes a tsunami?For example, big waves are foundat the shore lines of the HawaiianIslands. These big waves are whythe sport of surfing is very popularthere.Do some Internet surfing andapply what you’ve already learnedfrom reading this chapter, to findout why Hawaii is such a goodspot for big breaking waves.166UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANS7.3 Shallow Marine EnvironmentsIf you ask someone about their favorite place to visit, they might say, “The beach!”They probably wouldn’t say, “A shallow marine environment!” But shallow marineenvironments, which you will learn about in this section, include beaches and otherlocations that are marine, or related to the ocean.The parts of a beachBeach zonesOnshore andoffshore regionsA beach is an area of coastal sand between the low tide line and theline of permanent vegetation. The backshore is the part of thebeach above the high tide line which is only submerged duringstorms. The foreshore of a beach lies between the high and low tidelines (Figure 7.12). Marine biologists have a different name for theforeshore. They call it the intertidal zone.Below the foreshore is the shoreface. The shoreface is alwaysunderwater because it is below the low tide level. Passing wavesaffect the sediments of the shoreface, especially the upper partnearest the beach. Waves smooth land surfaces. Because waveshave little effect on the lower part of the shoreface, the surface ofthis region is bumpy. Anything that is on the beach, foreshore, orshoreface is considered to be “onshore.” Anything beyond theshoreface is “offshore.”marine - a term that describesthings that are part of or from theocean.beach - an area of coastal sandbetween the low tide line and theline of permanent vegetation.backshore - the part of a beachabove the high tide line.foreshore - the part of a beachbetween the high and low tidelines; also called the intertidalzone.Figure 7.12: The range of landbetween the high and low tide lines iscalled the foreshore. Sea level is theaverage ocean height between the highand low tide levels.7.3 SHALLOW MARINE ENVIRONMENTS167

Sandy beaches and tidal flatsBeaches havesandTidal flats havemudWhy are tidalflats and beachesdifferent?Sand is the most obvious feature of a beach. The light-colored,rounded grains slip easily through your hands. (Figure 7.13). Sandis not sticky. Blankets and towels only need a quick shake toremove dry sand.Tidal flats, which are often part of salt marshes, are also located inthe intertidal zone (Figure 7.14). However, tidal flats are differentfrom beaches. Tidal flats commonly have sandy areas, but most ofa tidal flat is dark, sticky mud. And the sticky mud can smell verybad! Why are tidal flats different from beaches?Tidal flats and beaches are both covered by sediment. Streams andrivers carry the sediment down from the mountains and otherhigh places. The sediment includes particles of various sizes whenit arrives at both areas. What happens to the sediment after itarrives is what makes tidal flats and beaches different.tidal flat - a flat, muddy area inthe foreshore.Figure 7.13: People enjoy the clean,light-colored, rounded sand grains thatslip easily through their hands.Figure 7.14: A tidal flat is in thesame area as a beach, yet the sedimentfound on tidal flats and beaches is verydifferent.168UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSWaves and sandWaves affectparticlesSand grainsWhat is sand?Waves are the key difference between tidal flats and beaches.Beaches are affected by strong wave action. Tidal flats are not.Waves change the size of sediment particles. A sample of tidal flatmud contains different kinds and different sizes of sedimentparticles.If you have ever stood on a beach, you knowthat waves seem to come in and go out fromthe edge of the beach. Swimming at thebeach is a thrilling experience. As each wavepasses over you, you feel the strong rush ofwater. This same rush and crash of thewaves churns the sandy ocean floor. Sandgrains are rounded by wave action.The largest particles of sediment are heavyenough to settle to the ocean floor. Thesmallest particles and broken grains arecarried out to sea with the waves and oceancurrents. The remaining particles, calledcoarse sand, build the beach (Figure 7.15).The coarse sand grains tumble over eachother with every passing wave. Thetumbling action wears away any sharpedges. It also polishes the grains. Some grains that are hardenough to withstand this harsh treatment are minerals calledquartz and feldspar. Both quartz and feldspar contain silica. Beachsand in many locations is made mainly of rounded grains of quartzand feldspar.Figure 7.15: (A) Scientists usespecial digital cameras to photographand then measure the size of sandgrains on a beach. (B) This image ofsand grains in a one centimeter section.By studying sand grains on a beach overtime, scientists can determine how muchwave energy affects the beach.7.3 SHALLOW MARINE ENVIRONMENTS169

Beaches in winter and summerWinter versussummer beachesBeaches changeover timeHow does abeach get toomuch sand?Fast-moving water will move both small sand grains and large,heavy particles. Slow-moving water will drop these particles.During the winter, waves are stronger on the coasts of the UnitedStates than during the summer. Gentle summer waves tend tocarry sand from deeper water onto the beaches. The strongerwinter waves carry the sand back to deeper water (Figure 7.16).This back-and-forth action creates two distinctly differentenvironments on the same beach: a summer beach and a winterbeach (Figure 7.17). See page 168 for a photo of a summer beach.Waves that create summer and winter beaches are not the sameyear after year. Just like one summer may have a little more orless rain than another, waves may be more or less energetic fromyear to year. During the winter, the sand that is removed from thebeach winds up in sandbars, not far out from shore. During aharsh winter, the beach may be eroded by a series of very strongstorms. High-energy waves carry away more sand than usual,carrying the sand further out from the shore. After a harsh winter,it may take years for the beach to recover from the erosion.On the other hand, the gentle waves of a mild winter may notremove all of the summer sand. In this case, when the nextsummer arrives, the beach may start out with an extra amount ofsand, and the summer waves will build up even more sand. Afterseveral mild winters, the sand may reach unusually high levels.Figure 7.16: Gentle summer wavescarry sand from deep ocean water tobeaches. Strong winter waves carry thesand from the beaches to deep oceanwater.Figure 7.17: This is a winter beach.170UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSMoving sandBeaches andheadlandsRivers andstreams bringnew sandLongshore driftBy moving sand and wearing away rock, waves change beaches.For example, more sand tends to be lost in winter from a beachthan is returned in summer. This is because sand is carried too farfrom shore for gentle waves to return it. Over time, beaches losemore and more sand. Some places along a beach resist beingchanged by the waves. Headlands are places where the shore sticksout from the coast. Waves will cut away the softer rock at aheadland and leave behind more durable rock. Eventually, aheadland may become a sea stack (Figure 7.18).Beaches never completely wear away because rivers and streamsbring new sand from the mountains to the beaches. But this sanddoesn’t stay in one location. Instead, it flows along the coast.A coast is the boundary between land and a body of water like theocean. This movement of sand along a coast is called longshoredrift. The beach sand that is lost to deep water is replaced by newsediments transported by a rivers and streams.coast - the boundary betweenland and a body of water like theocean.longshore drift - the flow ofsand along a coast.Figure 7.18: Some sediment is takenfrom beaches by the action of wavesagainst the shore. In some places theshore resists wearing away. Waves cutaway the softer rock on both sides ofthese more durable places. Eventually,the durable places, called sea stacks,will stand in the water separated fromthe shore.7.3 SHALLOW MARINE ENVIRONMENTS171

How does longshore drift work?Waves carry sandin the directionthey moveLongshore drift shapes beaches. Waves carry sand grains in samedirection that the waves move. For example, as a wave movestoward and away from the beach, it drags sand grains forward andbackward. If a wave came in a straight line to the beach, sandwould go up and back the same path. The sand grains would endup just about where they began before the wave broke. Longshoredrift occurs because waves approach the beach at an angle. Thismeans the waves come in at one direction (the upwash) and thenleave the beach at a different angle (the backwash). This processcauses sand grains to move along the coastline of a beach.Figure 7.19: A jetty is a barrier tolongshore drift. Sand gets trapped onone side of the jetty, but the beach erodeson the other side.Barriers tolongshore driftBecause the sand of a beach is constantly coming and going, abeach is like a river of sand. Evidence of the flow of sand at abeach can be seen wherever there are barriers to longshore drift.A jetty is a barrier that is built to control or slow down oceancurrents along a coast (Figure 7.19). Another barrier is abreakwater, which protects a harbor from waves.172UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANSWhat happens tosand at a barrierProtecting aharbor leads to anew problemContinentalshelves andcanyonsWhen a jetty or breakwater is located along the coast of the ocean,longshore drift will be disrupted. Sand will quickly build up on theside of the barrier where the waves first hit. At the same time, thebeach will erode away on the other side of the barrier.Many breakwaters have been built in front of marinas or harborentrances to protect them from high waves. But soon after solvingthe problem of high waves, a new problem appears. The waterbehind the breakwater is calmer than it used to be. The calm waterdrops its sediment and the marina or harbor entrance fills withsand (Figure 7.20). The only solution is to remove the breakwateror use pumps, called dredges, to remove the sand.Eventually, beach sand may find its way to the edge of thecontinental shelf and drop off into very deep water. Sand driftingdown the steep face of a continental shelf cuts into the shelf justlike streams cut into valleys. These cuts are called submarinecanyons. As a canyon is cut, the cut grows in the direction of theshore. Some canyons are so close to the shore that sand movingalong the coast by longshore drift lands in the canyon and getsdeposited directly into the deep ocean basins. Beaches can lose alot of sand quickly at submarine canyon locations.continental shelf - the oceanbottom that extends from a coastor shoreline to the continentalslope.Figure 7.20: A breakwater is abarrier to longshore drift that protectsharbors. Excess sand can build up neara breakwater.7.3 SHALLOW MARINE ENVIRONMENTS173

7.3 Section Review1. Describe the parts of a beach.2. What are the two names given to the area that lies betweenthe high and low tide lines?3. What is different about the sediment you find at a beachversus what you find at a tidal flat?4. How do waves affect the smoothness of sand grains?5. Name two minerals that are common in beach sand.6. How do seasonal waves affect the shape of a beach?7. Is the amount of sand moved between the beach and deepocean water the same over time? Explain.8. What is the main source of beach sand?9. If a dam was built to block a river from flowing toward abeach, what might happen to this beach over time?10. Answer correct or incorrect. If a statement is incorrect, rewriteit so that it is correct.a. Longshore drift occurs because waves move toward andaway from a beach along the same path.b. A jetty is a barrier that disrupts longshore drift.c. The water behind a breakwater is very calm.d. Submarine canyons prevent beaches from losing sand.11. How does longshore drift move sand along the beach?12. What happens when a breakwater is built in front of a harbor?Tidal flats and beaches are specialenvironments. Use the Internet orreference books to find out whatkinds of plants and animals live ontidal flats. Then, find out whatkinds of plants and animals live onbeaches. Make a poster to displaywhat you learn.174UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANS7.4 The Ocean FloorIt is possible that scientists know more about space than about the oceans on Earth.This is because scientists can use telescopes to see far-away space objects. But manyof the important features of the oceans, especially the ocean floor, are hidden in deepwater. In this section, you will learn about these hidden features.Features of the ocean floorThe continentalmarginThe ocean floor can be divided into the continental margin and thedeep ocean floor. The continental margin is the region aroundcontinents that includes the continental shelf, continental slope,and continental rise. The continental slope begins where the seafloor slopes toward the deep ocean floor. The continental rise ismade of sediments that have washed down from the continentalshelf and slope. Continental shelves surround many continents.They are shallow extensions of the continent, covered by a hundredor so meters of ocean water (Figure 7.21).continental margin - the regionaround continents that includesthe continental shelf andcontinental slope.Features of thecontinental shelfA barrier island is a low, sandy island that lies parallel to theshoreline. It blocks waves that come into shore and providessheltered water between the island and the shore. A bank is a low,flat region on the continental shelf. Its surface is relatively close tothe ocean surface. These features are shown on the diagram onpage 176.Figure 7.21: The light blue coloraround the continents shows thecontinental shelf.7.4 THE OCEAN FLOOR175

The deep ocean floorThe abyssal plainMountains,trenches, andislandsThe true ocean floor is called the abyssal plain. It is flat andsmooth because a thick layer of sediment covers its features. Itlies between 2,200 and 5,500 meters deep.A seamount is a steep-sided mountain that rises from the oceanfloor. Seamounts begin life as volcanoes over hot spots, but mostbecome inactive as plate tectonics moves them off of the hot spot.Some are tall enough to reach the surface and form a volcanicisland. A guyot is a seamount that has eroded so that it has a flattop and is underwater. Mid-ocean ridges mark places where twotectonic plates are separating and new ocean crust is being made.Mid-ocean ridges are a system of tall mountain ranges that passthrough the world’s oceans. Deep-ocean trenches are the deepestparts of the ocean. The deepest trench is the Mariana Trench nearGuam in the North Pacific Ocean. A volcanic island arc is a stringof volcanic islands that lies in a curving line along a trench.Each feature of the deep oceanfloor was a cool discovery. Forexample, guyots were discoveredby Harry Hess, an importantscientist in the development ofplate tectonics.Pick one feature of the deep oceanfloor and go on a “knowledge hunt”to find out more about it.Note: Guyot is pronounced “geeoh.”176UNIT 2 WATER AND WEATHER

CHAPTER 7: OCEANS7.4 Section Review1. It is possible that scientists know more about space than theydo about Earth’s ocean floor. Why?2. What three parts of the ocean floor are included in thecontinental margin?3. What is the difference between a barrier island and a bank?4. Why is the abyssal plain so smooth?5. The abyssal plain is 2,200 and 5,500 meters deep. Convert thisrange to kilometers and miles. Conversion factors: 1,000 meters= 1 kilometer = 0.62 mile, or 1.61 miles = 1 kilometer.6. What is a guyot?7. What is the difference between a seamount and a mid-oceanridge?8. Many features of the deep ocean floor are volcanic. Why do youthink this is so?9. What is a volcanic island arc?10. Research questions:a. Look at a globe and see if you can find an example of avolcanic island arc. Here’s one example: the Lesser Antillesin the Caribbean Sea is a volcanic island arc (Figure 7.22).b. You learned that the Mariana Trench is the deepest one onEarth. Find out how deep it is!c. If you could go down and explore a mid-ocean ridge, whatwould you find?d. Find out about Marie Tharp. Who was she and whatimportant contribution did she make to our understandingof the ocean floor?Figure 7.22: Question 10a.7.4 THE OCEAN FLOOR177

Chapter 7 ConnectionRip CurrentsHave you ever been at the beach and noticed currentsmoving away from the shore? These currents are usually adarker color due to the sand and sediments mixed into thewater from the bottom. These currents are called ripcurrents and they are good to know about. Their powerfulflow can pull a swimmer away from the shore. They areespecially dangerous when they are hard to see. Read on tofind out how to identify a rip current and to know how toescape from them. This knowledge may one day save yourlife!How rip currents formTo begin, it is good to knowother names for rip currents.Sometimes they are calledriptides, but rip currents arenot a result of tides, so“riptides” is not an appropriateterm to use. Another term thatis mistakenly used is“undertow.” Rip currents aresurface currents. They mayknock you over, but they willnot pull you under. Ripcurrents cause a swimmer tobe pulled out to sea.Sandbars are long, narrow hills of sand that usually runparallel to the shore. Some sandbars are higher than thewater surface and can easily be seen. Other sandbars are nottall enough to break through the water's surface and can't beseen from the shore.As the waves come in from the ocean, the pass over thesandbar and lose energy in the process. Because the waterhas lost energy, it piles up between the sand bar and theshore. Then piled up water returns to the ocean by thefastest route available. Many times, the water rushesthrough the break in a sandbar. That's when the rip currentis formed. The flow of a rip current can go on for severalminutes or continue for hours since the waves from the oceankeep bringing more water in to this area.Where rip currents occurRip currents can occur at any beach with breaking waves.They can also happen along jetties or under piers. In theseplaces, the rip currents can actually be permanent.178A rip current forms whenwater piles up near the shoreand moves away from theshore all at one time. There aredifferent ways that this canhappen, but one of the mostcommon is the result of a breakin a sandbar.Rip currents are strongest when the surf is rough or the tideis low. They can be seen as a break in the wave patterncoming towards shore and by the color of the water.Remember, the rip currents are darker in color because of

the sediment they are carrying. Polarizing sunglasses are agood way of cutting down on the glare from the surface of thewater in order to see the currents better.What to do if you get stuck in a rip currentIf you find yourself quickly being moved out to sea in a ripcurrent, don't ever fight it and try to swim back through thecurrent to shore. By doing that, you will waste a lot of neededenergy and not get very far. You should always swim parallelto the shore until you are out of the rip current and thenswim back to shore. Sometimes, it is hard to swim out of therip current when it is very strong. In this case, you shouldfloat or tread water and wave for help.You may notice that you are getting pulled sideways andthen straight out. That can happen as water is being pulledfrom all directions through the opening in the sandbar.You usually just find yourself in a rip current withoutnoticing right away. But, once the current meets up withwater at its level, past the opening in the sandbar, it willreturn to normal.Rip currents do have some benefits. Surfers can hitch a rideon a rip current to catch an incoming wave. Lifeguards canuse them to rescue someone out from the shore much fasterthan paddling through the waves.Safe swimmingGoing to the beach is a lot of fun. However, it is important tobe safe while you are enjoying sunshine, sand, and waves.Rip currents are the number one reason for deaths atbeaches. People caught in a rip current try to swim againstit, get tired, and then drown!You can keep yourself and others safe AND have fun at thebeach by knowing and following these safety tips!Questions:1. Why is “rip current” a better term than “riptide” and“undertow”?2. What does a swimmer experience when he or she is caughtin a rip current?3. Describe how a rip current forms in your own words.4. Make a safety poster to help people know how to avoid ripcurrents and how to escape from them.Chapter 7 ConnectionUNIT 2 WATER AND WEATHER179

Circumnavigating the GlobeChapter 7 Activity180The map on this page shows the world surface oceancurrents. Currents that are relatively cold are marked inblue. Warm currents are marked in red. Currents the aremarked in black have an intermediate temperature. You willuse this map to plot a sailboat route for circumnavigatingthe globe from the coast of Massachusetts to the coast ofCalifornia. This means you can’t just go around NorthAmerica. You need to go around the world!MaterialsBathymetric map and colored markers (red, blue, andpurple)What you will do1. With a partner, study the mapon this page. Find the coast ofMassachusetts (marked MA).Then, find the coast ofCalifornia (marked CA).2. Large surface currents aremostly driven by winds. Withyour partner, decide whatcurrents to use so that your sailtakes you from Massachusetts toCalifornia. Before you getstarted on “sailing around theworld” come up with a name foryour sailboat.3. As you choose currents, drawthem on your bathymetric map.Use a red to indicate a warmcurrent, blue to indicate a coldcurrent, and purple to indicateother currents. Also use yourblack pencil or marker to labeleach current you draw.Applying your knowledgea. Do the warm currents flow towards or away from theequator? Do the cold currents flow towards or away fromthe equator?b. On which side of the ocean basins are warm currentsfound? On which side of the ocean basins are coldcurrents found?c. List any uninterrupted currents. They flow around theglobe without being blocked by land.d. How many currents did you need to use to sail fromMassachusetts to California? How does your routecompare with the routes used by other teams?e. How would you sail back to Massachusetts?

Chapter 7 AssessmentVocabularySelect the correct term to complete the sentences.salinityamplitudetsunamimarinecoastforeshorebackshorewave trainSection 7.11. A circular ocean current system is called a(n) _____.2. A density-driven current that moves slowly within the oceanis called a _____.3. The Gulf Stream is an example of a(n) _____.4. _____ describes the saltiness of water.Section 7.2surface ocean currentsdeep ocean currentswavelengthcontinental margincontinental shelflongshore driftswells5. _____ is the amount of open water over which the windblows.6. _____ is the distance between two wave crests.7. Many waves traveling together form a _____.8. The low point of a wave is the _____, while the high point ofa wave is the _____.9. A sudden movement of the sea floor created by anunderwater earthquake could cause a(n) _____.10. Long, fast-moving waves are called _____.gyrescresttroughperiodtidal flatbeachfetch11. The _____ of a wave is the distance between a wave crest ortrough and the average level of motion.12. The time it takes for one wavelength to pass a single point isthe _____ of a wave.Section 7.3 and 7.413. Between the low and high tide lines the _____ can be found.14. The movement of sand along the coast is _____.15. The term _____ refers to objects that are related to theocean.16. The part of the ocean floor that extends from the coast to thecontinental slope _____.17. The boundary between a body of water and land is the _____.18. The area that is between the low tide line and the line ofpermanent vegetation is called a(n) _____.19. The continental shelf, slope, and rise make up the _____.20. The part of a beach that is above high tide is called the_____.21. A(n) _____ us a muddy area in the foreshore region.ConceptsSection 7.11. What makes the oceans salty?2. Why are the oceans are able to store heat energy?3. The interior of a continent is more likely to be extreme coldin the winter than a coastal areas. Why?4. How do surface ocean currents affect the movement of heatat Earth's surface?5. List the factors that affect how:a. surface currents move.b. deep ocean currents move.CHAPTER 7 OCEANS181

6. What two factors cause gyres?7. Why are deep ocean currents also called thermohalinecurrents?Section 7.28. Draw a diagram of a wave. Include crest, trough,wavelength, and amplitude.9. What is the difference between the amplitude and thewavelength of a wave?10. A huge storm can affect boats and ships at the oceansurface. However, a submarine can avoid the effects of astorm by travelling deep underwater. Why doesn’t the stormaffect the submarine?11. What three factors affect the size of ocean waves?12. What is the Beaufort Wind Force Scale?Section 7.313. List two names for the region between low tide and hightide.14. What is the difference between a tidal flat and a beach?15. From where does most of the sediment for tidal flats andbeaches come?16. Why do particles of sand tend to be round and polishedlooking?17. How does a beach get too much sand?18. Can longshore drift be stopped? Why or why not?Section 7.419. What are the three parts of the continental margin?20. What function do barrier islands naturally perform?21. What is the difference between a seamount and a guyot?Math and Writing SkillsSection 7.11. You have a sample of ocean water that is 20° C and has asalinity of 35 ppt. If you poured a sample of 20° C that was37 ppt, would that sample of water sink or float in the firstsample?2. A sample of ocean water in a beaker is allowed to sit outsidein the Sun so that water in the sample can evaporate.a. What would happen to the salinity of the sample overtime?b. Would the amount of salt change in the sample overtime? Why or why not?c. What would happen to the salinity of the sample if itstarted to rain into the beaker?3. Answer these questions about Earth’s oceans. ReviewChapter 4 to help you answer these questions.a. Name Earth’s five oceans.b. How much of Earth’s surface is covered by oceans.c. How much of Earth’s water is in the oceans?4. One of the deep ocean currents is called the AntarcticCircumpolar Current. It is so called because it circlesAntarctica. It aids in the circulation of deep and middlerangewaters between the Atlantic, Indian, and PacificOceans. The average speed is about 10 cm/s. How manykilometers would this represent for a day’s time?5. If upwellings bring nutrient-rich water to the ocean surface,then why might areas where upwellings occur be importantto humans?Section 7.26. Is a tsunami the same as a water wave caused by wind?Write a short paragraph in response to this question.182CHAPTER 7 OCEANS

CHAPTER 7 ASSESSMENT7. If the period of a wave is 15 seconds, how many wavelengthspass a certain point in 2 minutes?8. If the wavelength of a wave is 20 meters, at what depth is itswave base?9. If two wave troughs approach each other, what happenswhen they meet?10. What happens when the crests of two large waves meet?11. If the maximum speed of a commercial jet at cruisingaltitude is about 600 mph, how does this compare to thespeed of a tsunami? Conversion factor: 1 km = 0.62 miles.12. Why does the wavelength of a water wave or a tsunamishorten as it reaches a shoreline?Section 7.3 and Section 7.413. What kinds of plants and animals might you find living on abeach? How do they survive in this environment? Researchthe answer to these questions or visit a beach a make a listof the organisms you see.14. Structures called sea arches arefeatured in the photo at theright. How do you think thesestructures were formed? Writeyour answer as a shortparagraph.15. Imagine you could walk from asand dune on the east coast ofthe U.S. all the way to the Mid-Atlantic Ridge in theAtlantic Ocean. Describe what you would see on yourjourney.Chapter Projects—A Water TrickSee if you can setup two jars inverted on one another such thatthe liquid in one jar does not mix with the liquid in the other.Important hints: Ask an adult to help you. Work in a tray tocatch any spills. Use two same-sized baby food jars that havebeen cleaned. Fill them to the rims with water. Make choicesabout the temperature and saltiness of the water in each jar.Add red food coloring to jar A and blue food coloring to jar B.Place an index card over the mouth of the jar B. Using bothhands to hold the card to the rim of jar B, invert it on top of jarA. Gently pull out the card.a. Do the two volumes of water initially mix or stayseparated?b. What will happen to the two volumes of water over timein a room that is at constant temperature?c. Write up a short report that describes what you did andthe results.UNIT 2 WATER AND WEATHER183