ce sg 2 · thunderstorms a thunderstorm is a distur - bance in the atmosphere that has some or all...

12 STC/MS™ CATASTROPHIC EVENTS

LESSON

INTRODUCTIONHurricanes and other rotating storms are strongforces of nature. Hurricane Andrew, whichcaused wide destruction in southern Florida inAugust 1992, had winds powerful enough to liftobjects and turn them into dangerous, high-speed missiles.

During this inquiry, you will use two bottles—one empty and one filled with water—to modelhow air moves in hurricanes, tornadoes, andother rotating storms. How is the water in yourbottle like the air in a tornado or hurricane?You’ll discuss this question and others as youmodel a rotating storm and then watch a videoof some actual storms.

2Introducing Storms

OBJECTIVES FOR THIS LESSON

View images of clouds taken from space

and identify patterns in the clouds.

Model the movement of air in a tornado

or hurricane.

Create a working definition for the word

“vortex.”

Read to learn more about thunderstorms,

tornadoes, and hurricanes.

The powerful winds of Hurricane Andrew drove this piece

of plywood through the trunk of a royal palm tree.

NATIONALOCEANIC

ANDATMOSPHERIC

ADMINISTR

ATION(NOAA)/DEPARTM

ENTOFCOMMERCE

STC/MS™ CATASTROPHIC EVENTS 13

Getting Started

1. Think back to Lesson 1. Where did yourgroup think most tornadoes and hurricanesoccurred? Share with the class the loca-tions your group chose and explain why.

2. Examine Figures 2.1 and 2.2. Then try toanswer the questions on page 14 with yourgroup and class.

MATERIALS FORLESSON 2

For you1 copy of Student

Sheet 2.1:Thunderstorms,Tornadoes, andHurricanes

For your group1 tote tray1 vortex model4 paper towels1 group concept map

(from Lesson 1)Assorted coloredmarkers

Figure 2.1 Hurricane Linda as it approached Baja California, Mexico, in September

1997. Scientists used images from three satellites to create this picture.

NASA/G

ODDARDSPACEFLIGHTCENTER/N

OAA


LESSON 2 INTRODUCING STORMS

Inquiry 2.1Modeling a Vortex

PROCEDURE

1. Watch as your teacher holds up the classvortex model. What happens to thewater? Discuss your observations with theclass. How can you explain what you see?

2. Watch as student volunteers practice get-ting the water in the top bottle to movequickly into the bottom bottle.

3. Now your group will try this. ReviewProcedure Steps 4 through 7 with yourteacher. Then pick up your group’smaterials.

4. Just as your teacher did, turn the modelso that the water is in the top bottle. Holdthe bottle very still. What happens? (Workabove your tote tray in case of spills.)

5. Try to get the water in the top bottle toflow into the bottom bottle. What mustyou do to make this happen? Investigatewith your group. Do this several times.

6. Observe what happens to the glitter andbeads when the water moves in a spiral.Discuss the following questions with yourgroup as you work:

A. Where are most of the glitter andbeads?

B. Where is the movement of the glitterand beads the fastest? Where is it theslowest?

C. How is the vortex model like a realtornado? How is it like a hurricane?

A. Think about the reading selection“Views From Space” in Lesson 1. Howwere the images in Figures 2.1 and 2.2taken?

B. How are the two images alike?

C. How are they different?

D. What patterns do you notice in theshapes of the clouds? Why do you thinkthese patterns form?

Figure 2.2 A computer-enhanced view of Hurricane Linda

as it approached Baja California, Mexico, in September

1997. This image was taken from the GOES-9 satellite.

NASA/G

ODDARDSPACEFLIGHTCENTER/N

OAA



C. How did the motion of the glitter andbeads change as they moved closer to thecenter of the spiral?

D. Think about your model as a tornado.What might the glitter and beads repre-sent? What does their movement tell youabout the movement of air within arotating storm?

E. Think about your model as a hurri-cane. What do you think causes theclouds of a hurricane to spiral?

2. Look carefully at Figures 2.3, 2.4, and 2.5.Knowing that the water formed a vortex,develop a working definition for the word“vortex.” Write your definition in yournotebook. Then discuss it with the class.

7. Clean up. Your teacher will tell you whatto do with the bottles.

REFLECTING ON WHAT YOU’VE DONE

1. Think about what happened duringyour inquiry. Relate it to what happensduring storms on the earth. Record inyour science notebook answers to thesequestions:

A. What happened when you first heldthe model so that the water was in thetop bottle? Why do you think this hap-pened? Draw a picture of your results.

B. How did you get the water to flowquickly into the bottom bottle?

Figure 2.4 A vortex forms in a tornado.

Figure 2.3 The water forms

a vortex in the model.

Water

Air



3. With your class, watch a video aboutstorms.

4. Listen as your teacher turns on the weatheralert radio in your classroom. Read“Tornado Watch or Warning?” Discuss thefollowing questions with your class:

A. Why are weather alert radios helpful?

B. Where might a weather alert radio bemost helpful?

Figure 2.5 The eye of a hurricane is the center of a large vortex.

OceanLand

Eye of hurricane

C. Why do you think it is important thatweather alert radios are available at lowcost to the public?

5. Look again at your group’s concept mapfrom Inquiry 1.1. Focus on what youalready know about storms. What newthings do you want to add? What do youwant to change? Use markers to revise orupdate the Storms portion of your con-cept map.



TORNADO WATCH OR WARNING?What is a “tornado watch”? What is a “tornadowarning”? Weather reporters use these termsto alert the public that a threatening weathersystem is approaching.

A tornado watch means that tornadoes arepossible. Thunderstorms with high winds andheavy rain that may produce a tornado are inthe area. A tornado warning means that a tor-nado has actually been spotted or detected byradar. That’s serious! People living in the areashould stay away from windows and outsidedoors. They must take shelter immediately bygoing to their basement or the lowest part oftheir home. If they have no basement, theycan go to a bathroom or a closet. Believe it ornot, a bathtub can be a safe place to wait outa tornado.

How do you know when a watch or warninghas been issued? Listen to the weather radio inyour classroom or your radio at home. The NOAAWeather Radio (also called NWR) is a specialradio. (NOAA stands for National Oceanic andAtmospheric Administration.) NWR providesweather information, watches, warnings, andother weather-related information directly fromthe National Weather Service (NWS) to the pub-lic. (NWS is a branch of NOAA.) An alert signalwill sound from the radio if a watch or warninghas been issued. If you hear this signal, followyour teacher’s instructions.

How does weather information get to the NOAA Weather Radio? This is a simplified version of how scientists collect,

process, and deliver severe weather data to the public.

Weathersatellite

AM/FMradio

NOAAWeatherRadio

Commercialbroadcasters

Federalweatheroffice

Radar

Weather

Reconnaissanceplane



What happened whenyou used the vortexmodel in this lesson?You moved the waterby swirling it. As thewater swirled aroundthe bottle, gravitypulled the liquidthrough the opening.At the same time, theair in the bottom bot-tle moved up throughthe center of theswirling water. Thiscirculation of liquidsor gases is called avortex.

Vortices (the pluralof “vortex”) form innature, too. Swirlingleaves, dust devilssuch as the one shownat the right, and torna-does are all examplesof vortices. A vortexcan also form in a hur-ricane that covers avery large geographicarea. The eye of a hur-ricane is an exampleof the center of a largevortex.

What causes a vor-tex to form in theatmosphere? Theuneven heating of theearth’s surfaces, theforce of gravity, andthe earth’s rotationcan all set air inmotion.

What Is a Vortex?

©ANNPURCELL;CARLPURCELL/W

ORDS&PICTU

RES/PNI

In the dry landscape of Kenya, Africa, a dust devil swirls brown dust upward. A dust

devil is a kind of vortex.



You know that the earth rotates. The rotationof the earth has a big effect on some storms,such as hurricanes. Try a demonstrationwith a partner and see for yourself.As the illustrations above show,first lay a piece of paper on atable. Hold a marking penin the center of the paperso the tip will write onthe paper. Slowly movethe pen’s tip towardthe edge of the paperand draw a straightline. Now have yourpartner rotate thepaper counterclock-wise as you try todraw a line from thecenter of the page toits edge. This time, theline curves to the right.

Something similar hap-pens to air (and water) onthe earth. Because of theearth’s rotation, air in the atmo-sphere does not flow in a straightline. In later lessons, you will learn moreabout how air moves and what causes the vor-tex of a storm to form. �

A straight line will curve when the paper rotates.

The earth’s rotation causes some

storms and winds to rotate.

Equator

of the characteristics of eachkind of storm. Keep in mindthat these storms have a fewthings in common. All three



NOAA/D

EPARTM

ENTOFCOMMERCE

THAT’SA FACTAn Introduction to Thunderstorms, Tornadoes, and Hurricanes

which is a tornado, and whichis a hurricane? Are there anyclues that help you decide?

Read on to learn about some

What do these three picturesshow? They are all differentkinds of storms, but can youtell which is a thunderstorm,

NOAA/D

EPARTM

ENTOFCOMMERCE

NOAA/D

EPARTM

ENTOFCOMMERCE



involve rain and high winds.Each usually occurs at certaintimes of the year in certainlocations. They can be fore-cast, detected, and tracked bythe National Weather Service.

ThunderstormsA thunderstorm is a distur-bance in the atmosphere thathas some or all of these: light-ning, thunder, gusty winds,heavy rain, and hail. A severethunderstorm can producehail the size of golf balls, flashfloods, and even tornadoes.Here are some key traits ofthunderstorms:

• In the southeastern UnitedStates, thunderstorms occurmost often along the GulfCoast, especially in Florida.

• Most thunderstorms occur inthe spring and summermonths during the warmestpart of the day. Although itis rare, some thunderstormsoccur during winter. Somethunderstorms, for example,in the Central Plains, occurat night.

• A well-developed thunder-storm can cover an area as

©HOWARDBLU

ESTEIN/PHOTO

RESEARCHERS,INC.

You probably recognize these clouds

as thunderclouds, or cumulonimbus

clouds, which are often seen during

a thunderstorm.



In May 1999, this tornado struck

Oklahoma City, Oklahoma. ©HOWARDB.BLU

ESTEIN

large as 8 to 16 square kilo-meters.

• If the temperature in part ofa thundercloud falls belowfreezing and winds are strong,the raindrops in the stormcan develop into hail.

• In a fraction of a second, atypical lightning bolt can dis-charge as much energy as amedium-sized nuclear reac-tor can in the same amountof time.

• At any given moment, anestimated 1500 to 2000thunderstorms are occurringon the earth. These stormscan trigger 6000 or morelightning flashes per minute.

TornadoesHow do tornadoes form? A tor-nado is a rotating column of airthat forms from thunderstormsover dry land under specialconditions: when moist warmair meets cool dry air head on.What’s more, hurricanes oftenbring on tornadoes. Here aresome things you might like toknow about tornadoes:

• The United States has moretornadoes than any othercountry in the world. Mosttornadoes in North Americahappen in “Tornado Alley.”This area is in the Central



F-Scale Intensity Phrase Wind Speed Type of DamageNumber

F0

F1

F2

F3

F4

F5

Gale tornado

Moderate tornado

Significant tornado

Severe tornado

Devastating tornado

Incredible tornado

65–116 kilometersper hour (kph)(40–72 milesper hour [mph])

117–181 kph(73–112 mph)

182–253 kph(113–157 mph)

254–332 kph(158–206 mph)

333–419 kph(207–260 mph)

420–513 kph(261–318 mph)

Some chimney damage.Tree branches broken and shallow-rooted trees pushed over.Sign damage.

Roof surfaces peeled off.Mobile homes overturned or pushed off foundations.Moving automobiles pushed off roads.Trees snapped.Windows broken.

Considerable damage.Roofs torn off frame houses, and mobile homes demolished.Railroad boxcars pushed over.Large trees uprooted.Light objects become missiles.

Walls torn from buildings.Cars overturned.Most trees in forests uprooted.

Well-constructed houses leveled.Buildings with weak foundations blown some distance.Cars thrown.Large objects become missiles.

Automobile-sized structures carried more than 100 meters.Bark stripped from trees.Steel-reinforced concrete buildings badly damaged.

Fujita Scale of Tornadoes

that form over water.• Much of a tornado’s destruc-

tive power comes from itsstrong winds, which can lifthuge objects and turn theminto dangerous, high-speedmissiles.

• Japanese-born meteorologistTetsuya “Ted” Fujita, whowas known as “Mr. Tornado,”developed the Fujita scalefor measuring tornadoes onthe basis of the damage theycause (see the table entitled“Fujita Scale of Tornadoes”).

• The diameter of most torna-does is between 100 and 600meters, although some arejust a few meters wide, andothers are wider than 1600meters (1 mile).

• Some tornadoes stand nearlystill, while others move atspeeds faster than 100 kilo-meters (62 miles) per hour.

• A tornado’s vortex containsswirling winds that canmove up to 350 kilometers(217 miles) per hour.

• Waterspouts are tornadoes

Plains between the RockyMountains and theMississippi River.

• About three-fourths of alltornadoes in the UnitedStates develop from Marchto July, during late after-noon. The month of Maynormally has the greatestnumber of tornadoes inthe United States (averag-ing about five per day),while the most violent tor-nadoes seem to occur inApril.



forms north of the equatorin the western Pacific Ocean.It is called a cyclone whenit forms in the Indian Oceanand off the coast of Australia.

• A hurricane is normally 550kilometers (342 miles) indiameter. It rarely gets biggerwhen it hits land, because itgets most of its energy fromthe warm ocean waterbeneath it.

• Hurricanes can move atspeeds of 8 to 24 kilometers(5 to 15 miles) per hour.Sometimes they can becomenearly stationary.

• Hurricanes begin as tropicalstorms, which have windspeeds of 64 to 118 kilo-meters (40 to 73 miles) per

HurricanesWhat distinguishes hurricanesfrom thunderstorms and tor-nadoes? One big difference isthat hurricanes are massiverotating storms. And, theyalways form when warm,moist air rises over tropicalwaters. Here are some otherthings you may want to knowabout hurricanes:

• People have different namesfor these rotating storms indifferent parts of the world.For example, a rotatingstorm is called a hurricanewhen it forms north of theequator in the Atlantic andeastern Pacific Oceans. It iscalled a typhoon when it

hour. Hurricanes have windspeeds of 119 to 250 kilo-meters (74 to 155 miles) perhour or more. (See the tableentitled “Saffir/SimpsonHurricane Scale.”)

• Because hurricanes can lasta week or longer and severalcan occur at the sametime, naming them reducesconfusion. (See the tableentitled “Selected Namesfor Northern HemisphereHurricanes.”) �

In late summer 1985, Hurricane

Elena affected more than 1 million

people when it moved from the Gulf

of Mexico to Louisiana, Mississippi,

Alabama, and central and northern

Florida.

NASA



Saffir/Simpson Hurricane Scale

1

2

3

4

5

119–153 kph(74–95 mph)

154–178 kph(96–110 mph)

179–210 kph(111–130 mph)

211–250 kph(131–155 mph)

250+ kph(155+ mph)

Minimal

Moderate

Extensive

Extreme

Catastrophic

No significant damage to buildings.Damage primarily to unanchored mobile homes, shrubbery, and trees.Some coastal flooding and minor pier damage.

Some damage to roofing, doors, and windows.Considerable damage to vegetation and mobile homes.Flooding damage to piers and small craft.

Some structural damage to small residences and utility buildings.Mobile homes destroyed.Flooding near coast destroys small structures; floating debrisdamages larger structures.Inland flooding possible.

Complete roof structure failure on small homes.Major erosion of beaches.Inland flooding possible.

Complete roof failure on many homes and industrial buildings.Some buildings completely destroyed.Small utility buildings blown over or away.Flooding causes major damage to lower floors of all structuresnear shoreline.Massive evacuation of people possible.

1–2 meters (m)(4–5 feet [ft])

2–2.5 m(6–8 ft)

2.7–3.7 m(9–12 ft)

4–5.5 m(13–18 ft)

5.5+ m(18+ ft)

Category Wind Speed Damage Type of Damage Storm Surge*

*An unusually high water level, primarily due to winds during a storm, especially a hurricane.

Selected Names for Northern Hemisphere Hurricanes(Atlantic Ocean, Gulf of Mexico, Caribbean Sea), Year 2002–2005

Arthur

Bertha

Cesar

Dolly

Edouard

Fran

Gustav

Hortense

Isidore

Josephine

Kyle

Lili

Marco

Nana

Omar

Paloma

Rene

Sally

Teddy

Vicky

Wilfred

Ana

Bill

Claudette

Danny

Erika

Fabian

Grace

Henri

Isabel

Juan

Kate

Larry

Mindy

Nicholas

Odette

Peter

Rose

Sam

Teresa

Victor

Wanda

Alex

Bonnie

Charley

Danielle

Earl

Frances

Gaston

Hermine

Ivan

Jeanne

Karl

Lisa

Matthew

Nicole

Otto

Paula

Richard

Shary

Tomas

Virginie

Walter

Arlene

Bret

Cindy

Dennis

Emily

Franklin

Gert

Harvey

Irene

Jose

Katrina

Lee

Maria

Nate

Ophelia

Philippe

Rita

Stan

Tammy

Vince

Wilma

NOTE Names were selected from library sources and agreed on at meetings of the World Meteorological Organization.

2002 2003 2004 2005

ce sg 2 · thunderstorms a thunderstorm is a distur - bance in the atmosphere that has some or all...

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