Temperature, Pressure, and Cloud Formation - Shorewood Sixth Grade … · · 2012-03-21tle. What...

68 STC/MS™ CATA S T R O P H I C EV E N T S

INTRODUCTIONImagine a cloud taller than Mt. Everest—thetallest mountain in the world! Or think of acloud so symmetrical that it looks like a perfectpinwheel in the sky. Hurricane Fran, pictured atleft, was like that—tall and evenly shaped. Howdo clouds form? Why do they sometimesbecome hurricanes? Evaporation, warm risingair, dust particles, condensation of water, andthe weight of air—called air pressure—are theingredients for making clouds.

In Lessons 4 and 5, you modeled the move-ment of air caused by the uneven heating of theearth’s surface. In this lesson, you will extendyour observations to investigate how waterevaporates and condenses into clouds. You willalso investigate how air pressure affects cloudformation. Finally, you will relate this informa-tion to weather on the earth.

6Temperature, Pressure, andCloud Formation

LESSON

OBJECTIVES FOR THIS LESSON

Model and describe how waterevaporates and condenses and howthese processes play a part in cloudformation.

Model and describe the air pressureconditions under which clouds form.

Analyze weather maps.

Interpret data from tables in order toplot the path of a hurricane.

Hurricane Fran lashed communities in the

southeastern United States, uprooting trees

and bringing the threat of flash floods.

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Getting Started

1. Look at the U.S. weather maps shown inFigure 6.1. Work with your group to makegeneral observations of the maps. Discussthese questions:

A. Where on each map do you think it iscloudy? How do you think clouds form?

B. What do you think “H” and “L” on themaps represent?

C. What type of weather would youexpect in an area marked with an “H”?What type of weather would you expectin an area marked with an “L”?

2. In this lesson, you will investigate some ofthe conditions under which clouds form.At the end of the lesson, you will look atweather maps again to relate what youobserved in the lab to weather on theearth.

MATERIALS FORLESSON 6

For you1 copy of Student

Sheet 6.2:Tracking HurricaneAndrew

1 copy of StudentSheet 6.3: ReadingWeather Maps

1 ruler1 green pencil or pen1 red pencil or pen

For your group1 tote tray2 clear bottles with

caps1 flashlight2 digital

thermometers1 beaker of hot

water1 beaker of cold

water1 ice cube3 consecutive daily

weather maps


LESSON 6 TE M P E R AT U R E, PR E S S U R E, A N D CL O U D FO R M AT I O N

Figure 6.1 Three consecutive daily

weather maps

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6. Collect your materials. Set them up asyour group has planned. Then conductyour investigation.

7. How does the temperature of the air affectevaporation and condensation? Try this:Rub the ice cube on the outside of eachbottle. (See Figure 6.2.) What happens?Rub your hands on the outside of the bot-tle. What happens? Discuss your observa-tions with your group.

8. Clean up according to your teacher’sinstructions.

REFLECTING ON WHAT YOU’VE DONE

1. Answer the following questions and thendiscuss them with your class.

A. What happened to the water in eachbottle?

B. In which bottle did you observe themost evaporation and condensation?Why do you think this happened?

C. Were you able to change the amount ofcondensation that occurred inside yourbottles? If so, how?

2. Read “Hurricane Formation and theWater Cycle” on page 72.

3. Relate what you observed in the lab tocloud formation on the earth. Recordyour ideas about the following:

A. Describe the water cycle and cloudformation.

B. If hurricanes get their energy fromwarm, evaporating water, where on theearth do you think hurricanes form mostoften?

Inquiry 6.1Observing Evaporation andCondensation

PROCEDURE

1. What do you already know about thewater cycle and how clouds form?Discuss your ideas with the class.

2. Look at the equipment you will use forthis lesson. Then try to answer the fol-lowing question: How does the tempera-ture of water affect evaporation andcondensation?

3. Record the question from Step 2 inyour notebook. Leave enough room towrite your observations.

4. How would you use the materials to testthis question? Share your ideas with theclass.

5. Discuss with your teacher how you willrecord your predictions and observationsin a table.

Figure 6.2 Rub an ice cube or the palms of your

hands on the outside of the bottle.

illustration of the water cycle shows, duringthe water cycle, clouds form when warm airrises or when warm air and cold air meet.Clouds are made up of billions of tinydroplets of water or ice and dust parti-cles. When water on the earth absorbsheat energy, it evaporates into a gascalled water vapor. When air rises, itcarries the water vapor with it. Air athigher altitudes within the tropo-sphere is cool. Cool air cannot holdas much water vapor as warm aircan. So some of the vapor turnsinto drops of liquid water. Theprocess by which water changesfrom a gas to a liquid is calledcondensation. The process ofcondensation, shown in the illus-tration, releases heat, whichfeeds more energy into the sys-

tem and evaporates the con-densed water, causing the vapor

to rise even higher. The liquidwater collects on dust particles and

forms clouds.



Why do hurricanes developover warm, tropical water nearthe equator? The warm waterprovides an almost endlesssupply of energy for thesestorms. Massive clouds formfrom the warm, evaporatingwater. Winds move the stormclouds along the hurricane’spath. When the hurricanemoves over land or cool north-ern water, it loses its energyand dies.

What process is at theheart of hurricane formation?It is the water cycle. As the

HURRICANE FORMATION AND THE WATER CYCLE

The water cycle on the earth

Condensation is the process by which water changes from a

gas to a liquid. The heat given off during condensation

“feeds” energy into a storm system.

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Sub

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Subl

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CondensationEvaporation

GAS (water vapor)

SOLID (ice)

LIQUID(water)

Heat gained

Heat lost

Condensation

Evaporation

Transpiration

Groundwater

Water table

Surfacerunoff

Precipitation



Inquiry 6.2Modeling the Effects of Air Pressure on Cloud FormationPROCEDURE

1. In this inquiry you will try to answer thefollowing question: How does air pressureaffect cloud formation?

2. Record the question in your notebook.

3. Discuss with the class how you will usethe bottle of hot water to investigate thisquestion.

A. What are the “ingredients”for cloud formation? (Thinkback to Inquiry 6.1 and thereader “Hurricane Formationand the Water Cycle.”)

B. How could you create theseconditions in your bottle?

C. If you want to test how airpressure affects cloud forma-tion, how could you create highpressure in the capped bottle?

D. How could you create low pressure inthe bottle?

E. How could you keep track of your pre-dictions and observations?

4. Review Procedure Steps 5 and 6 with yourteacher. Then collect your materials.Create a table to record your data andobservations.

5. Your teacher will use a burning punk stickto add smoke to your bottle, as shown inFigure 6.3. Keep the lit punk inside thebottle for approximately 3 to 5 seconds.When your teacher removes the punkstick, quickly cap the bottle.

Figure 6.3 Your teacher will

use the punk stick to add

smoke to each group’s bottle.



3. You will be asked to complete StudentSheet 6.2: Tracking Hurricane Andrew forhomework. As you do, consider thesequestions, which are listed on the studentsheet:

A. Where did Tropical Storm Andrewstart? Why do you think it started there?

B. At what point (longitude and lati-tude) did the tropical storm become ahurricane?

C. In what direction did the storm move?

D. Look back to the reading selection“Why Does the Wind Blow?” in Lesson 5.What do you think caused HurricaneAndrew to move along this path?

E. Where did Hurricane Andrew lose itsenergy and turn back into a tropicalstorm? Why do you think it happened inthat location?

F. If you had been working at theNational Hurricane Center whenHurricane Andrew struck, which citiesor areas would you have evacuated?What day would you have requested theevacuation? Why?

6. Before starting the investigation, swirl thewater inside the bottle to reduce fog.Then shine the flashlight on the bottle, asshown in Figure 6.4, while squeezing andholding the bottle.

7. When your group is finished, clean up.


1. Answer these questions and then discussyour answers with the class:

A. Why did you add smoke to the bottle?

B. What happened to the air when yousqueezed the bottle?

C. When you released the bottle, you cre-ated a low-pressure system. Describe theair inside the bottle when this happened.

D. Use your own words to describe howair pressure and cloud formation arerelated.

2. Read “The Truth About Air,” on pages76–77.

Figure 6.4 Squeeze and

hold the capped bottle while

someone else shines the

light on it. Do clouds form

under high or low pressure?




1. With the class, share your responses tothese questions, which are also listed onStudent Sheet 6.3:

A. What kind of weather is associatedwith a high-pressure system?

B. What kind of weather is associatedwith a low-pressure system?

C. What symbol represents a cold front?What symbol represents a warm front?

D. Pick one weather front on a map.What weather is associated with it?

E. Why are the triangles and semicircleson the symbol for a cold and warm frontfacing in one direction? What do youthink the direction of the symbol means?

F. How does weather move across theUnited States? Why is it important toknow this information?

2. Watch the video Hurricane. Relate theconcept of pressure to how hurricanesform and move.

Inquiry 6.3Reading Weather Maps

PROCEDURE

1. Working with your group, make generalobservations of the weather maps thatyou brought to school. You can also useFigure 6.1 for this purpose.

2. Share your observations with your class.

3. Line up your maps in order by date.Identify one weather system (front, low-pressure system, or high-pressure system)on each map. In what direction is the sys-tem moving across the country? What doyou think causes weather to move in thisway? (The reading selection “Why Doesthe Wind Blow?” in Lesson 5 can helpyou answer this.)

4. Look over Student Sheet 6.3: ReadingWeather Maps. Discuss it with yourteacher. Work on it with your group. Youmay have to complete it for homework.



Air PressureWater pressure is caused by the weight of water,and air pressure is caused by the weight of air.The heavier the air, the more pressure it exertson the earth.

Just as the leaves at the bottom of a pile aremore squished than those at the top, air ismore compressed (denser) at sea level than athigher altitudes. At the top of the atmosphere,air is less compressed and lighter. Close to theearth, air is more compressed and denser.

Air Pressure and WeatherAir pressure is one factor that creates the con-stant changes in weather on the earth.The formation of clouds, forexample, is a directresult of air pressure.Look up into the sky.Low clouds, such asstratus clouds, aredenser and thickerthan clouds high inthe sky. Clouds thatare high in the sky,such as cirrus clouds,are wispy and thinnerthan clouds at lowaltitudes.

Air pressure differ-ences also cause theair to move and createwinds. Like all fluids,air flows from high-pressure regions tolow-pressure regions.If you have everwalked into an air-conditioned buildingin the summer andfelt a rush of windagainst your body,

The Truth About Airyou know that air pressure affects the way airmoves. The difference between the high airpressure in the building and the low air pres-sure outside causes the air inside to moverapidly toward the open door. (This same differ-ence in air pressure created the movement ofair in your connected Convection Tubes.)

Because air masses are in constant motion,air pressure in any location on the earth canvary from day to day, or even from hour tohour. Since pressure differences can help scien-tists predict how air might move, monitoringand predicting changes in air pressure is funda-mental to weather forecasting. �

Why does a mountain climber sometimes need an oxygen mask? It is because the

higher a person goes, the lighter (less dense) the air becomes. That means there is

less oxygen for the climber to inhale. In this picture, the particles of air are repre-

sented by dots. Where do you think the density of air (air pressure) is greater?



In 1643, Evangelista Torricelli, a studentof Galileo, invented the mercury barome-ter. A barometer is an instrument thatdetects and measures air pressurechanges. Torricelli’s barometer was simi-lar to those in use today. It had a longglass tube that was open at one end andclosed at the other. Torricelli removed airfrom the tube; he covered the open endand submerged it in a dish of mercury.When he removed the cover from theopen end of the tube, the mercury rosein the tube to nearly 76 centimetersabove the dish. Torricelli correctly con-cluded that air outside of the tube waspressing on the mercury in the dish andthat this pressure forced the liquid up inthe tube. (The height of the liquid in the

Air pressure affects the types of clouds that form at different altitudes.

tube was a measure of atmospheric pres-sure. The greater the atmospheric pres-sure, the higher the mercury moves upthe tube.)

Why did Torricelli use mercury insteadof water? First, water would evaporate inthe tube. Second, water is less densethan mercury. This means that an atmos-pheric pressure of 76 centimeters of mer-cury would be equal to 1034 centimetersof water! Can you imagine a barometerthat tall?

What do you think Torricelli’s mercurybarometer looked like? Draw a picture ofit using information from this reader.Then look up Torricelli on the Internetand compare your drawing with the mer-cury barometer that Torricelli invented.

Torricelli: Inventor of the Mercury Barometer

Cumulonimbus

Cirrus

Cirrocumulus

Altostratus

Stratocumulus

Cumulus

Stratus

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In the aftermath of Hurricane Mitch, scientistswondered what had brought on such a mon-strous storm and what could be done to preventthe resulting damage from happening again.

In late October 1998, Hurricane Mitch roaredacross Central America for several days. Itaffected areas from Nicaragua and Hondurasthrough El Salvador, Guatemala, Belize, andsouthern Mexico. One ofthe strongest hurricanesin recorded history, itkilled about 11,000 peo-ple. (Prior to HurricaneMitch, only one otherAtlantic hurricane hadcaused more deaths. TheGreat Hurricane of 1780killed 22,000 people inthe eastern Caribbean.)Mitch destroyed roadsand bridges. It left morethan 2 million peoplewithout homes, food, ordrinking water. Morethan $10 billion in dam-age occurred across the region.

HURRICANE MITCH

Massive hurricane damage along a river in Honduras from Hurricane Mitch

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Off the coast of La Ceiba, Honduras, children walk through sea foam caused by the

churning water made rough by Hurricane Mitch.

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harvested and stored were destroyed by thehurricane. That year’s second planting was com-pletely washed away by the storm.

The people of Central America had beenpoorly prepared for a disaster of this magnitude.For one thing, the path of Mitch had not beenpredicted accurately. Meteorologists predicted amore northerly course, but Mitch turned southtoward Honduras and then slowed to a tropicalstorm. As it crawled across Honduras, itdumped several meters of rain in just a fewdays. Runoff eroded mountainsides. Thousandsof acres of land were swept away or were buriedtoo deeply to be farmed. Flooding destroyedcash crops, such as coffee, melons, andbananas. Thousands of kilometers of roads andmore than 100 bridges were left impassable.

Even if the people in Central America hadbeen warned of the approaching hurricane,few communities had programs to help peopleprepare for an event like Hurricane Mitch. Toprevent such devastation from occurringagain, leaders decided that better warning sys-tems were needed. In the meantime, people inCentral America realized it would take yearsto recover from Hurricane Mitch. �

Perfect Hurricane ConditionsOne of the key factors that created Mitch wasvery warm ocean water. During that hotOctober, the temperature of the Caribbean Seareached almost 30 °C. The warm water quicklyevaporated, creating huge amounts of watervapor in the atmosphere.

A second factor was a low-pressure area ofthunderstorms over Honduras and Nicaraguathat triggered the storm. These thunderstormseventually dumped 127 to 190 centimeters ofrainfall on Honduras and Nicaragua. Accordingto the National Climatic Data Center, 64 centi-meters of rain fell in just 6 hours.

A Region Unprepared Torrential rains would have devastated anycountry. But countries in Central America wereparticularly vulnerable. Many of the hillsideshad been cleared for farming. Saturated withrain, they became unstable. Rocks and mudrumbled down the south side of Nicaragua’sCasita Volcano. In all, nearly 2000 people losttheir lives in mudslides. Towns and villages thatwere built next to rivers flooded. Water coveredthe ground that was already saturated from therainy season. Most of the crops that had been

People living near La

Ceiba, Honduras, cross

the Rio Bonito on a

footbridge. Heavy rains

from Hurricane Mitch

damaged important

roads and bridges,

such as this one.

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Temperature, Pressure, and Cloud Formation - Shorewood Sixth Grade … · · 2012-03-21tle. What...

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