Why and Where Do Tornadoes Form?

Transcription

1 LESSON PLAN 1 Tornado Science Form? The word tornado comes from the Spanish word tronada, which means thunderstorm. Although a tornado is not a thunderstorm, it would not exist without strong thunderstorms. A tornado is a violently rotating column of air extending from a thunderstorm to the ground. The most violent tornadoes have rotating winds of 250 miles (402 kilometers) per hour or more. Key Terms and Concepts anvil cloud condense convection cumulonimbus cloud cumulus cloud debris cloud downdraft front funnel cloud hail mesocyclone occluded front supercell thunderhead thunderstorm tornado updraft vertical wind shear vortex wind shear Purposes To impart to students an understanding of how tornadoes form and the weather cycle of tornadoes To have the students identify tornado-prone locales in the United States and describe the unique interactions of geography and climate that result in tornadic storms Objectives The students will Watch a demonstration of tornado formation, hypothesize about its formation and describe their observations. Research tornado formation using How Form. Write about the experiences of a water drop on a journey from the Gulf of Mexico to Tornado Alley. Research to collect information on tornadoes, downbursts and microbursts; use the information to present an illustrated report. (Linking Across the Curriculum) Create a glossary to support a study of the connections among tornadoes, geography and climate. 1

2 LESSON PLAN 1 Form? Research and use maps to illustrate answers to questions about the relationships among tornadoes, geography and climate on A Cartographer s Guide to. Use information from their glossary and research to write reports on tornadoes, geography and climate. Share and exchange information with their families about tornadoes; research the authenticity and science associated with new facts; compile a book of tornado facts and fiction. (Home Connection) Research to find and graph statistics on tornado activity and tornado deaths by state using the Internet and Tornado Mapping; determine whether improved forecasting technology has improved tornado death statistics. (Linking Across the Curriculum) Activities You re the Meteorologist Tornado Alley 2

3 You re the Meteorologist SET UP 40 minutes CONDUCT two 40-minute classes Science: Earth Science; Language Arts: Research and Writing LESSON PLAN 1 Form? Vacuum cleaner Electric fan Block of dry ice Materials How Form, 1 copy per student Chalkboard and chalk or poster paper and markers Help the students understand the weather science of tornadoes through the following demonstration, research and presentations. TEACHING NOTE Use protective gloves and tongs when handling dry ice. 1. Gather materials and then set up the tornado demonstration. Place the electric fan about 20 feet (6 meters) from the block of dry ice. Turn the fan on, blowing toward the ice. Hold the vacuum cleaner so that its suction end is about 6 inches (15 centimeters) above the block of ice. A tiny, short-lived tornado forms, violent enough to pick up pieces of the frost from the dry ice and blow it from the vortex. 2. Have the students describe their observations and hypothesize answers to the following questions: Why does the tornado form? (Wind generated by the fan creates a shear in the general airflow of the room.) Why was it able to pick up pieces of dry ice frost? (The airflow from the fan that passes over the block of ice is then caught in the suction, intensifying the vortex motion, stretching it up toward the vacuum.) 3. Challenge the class to use dictionaries or glossaries to define the words they may not know in How Form. cumulonimbus cloud debris cloud front funnel cloud mesocyclone supercell thunderhead tornado updraft wind shear Work with the class as a whole to write the definitions on the chalkboard or a large piece of poster paper. 4. Distribute How Form to students and give them time to read the information. When they have finished, discuss the steps nature takes to generate a tornado. Ask the students to imagine themselves as drops of water that eventually become part of a tornado. What events and what changes would the drops experience? 3

4 Wrap-Up LESSON PLAN 1 Form? Challenge students to write about the journey of a water drop that begins as water vapor in a warm front over the Gulf of Mexico and ends in a tornado in Kansas. The account can be written as a diary, a letter to friends who remained in the Gulf or a cartoon strip. Instruct the students to illustrate the journey of their water drop and include the following scientific information on the formation of tornadoes: The collision of warm and cold fronts: What happens to the water drop when the fronts collide? The formation of cumulus and eventually cumulonimbus clouds: How do the cumulus clouds become cumulonimbus clouds or thunderheads? Would the drops freeze? Would they be bounced around in the developing storm? The formation of a mesocyclone: What happens when the drops experience wind shear? What sounds might the drops hear? How might the perspective of the water drops change? The formation of a funnel cloud: How do the drops end up in the funnel cloud? What will they encounter in the cloud of water and dust? The formation of the tornado: What is the tornado s strength? What is it like to be part of a huge vacuum as it touches down to the earth? How big is the tornado that the drops have joined? What do the drops see happening on the earth as the tornado moves along its path? Students must use as much scientific detail as possible in their journeys. However, remind them that the best stories weave the science into the narrative creatively to make the fictional journey more interesting and more real. When students have completed their writing, share the stories in a class presentation or as a bulletin-board display. Linking Across the Curriculum Science: Earth Science and Physical Science Severe storms, including tornadoes, downbursts and microbursts (stronger downbursts), have all occurred in the Lansing, Michigan, area between 1997 and Divide the class into three groups. Assign one specific type of weather event from the Web site and Severe Weather ( to each group to read. 2. Then, have them use the resources below to search online for pictures and graphic representations of as many of these types of storm as possible. 3. Using their information, have them make a brief presentation for a meteorological conference, including a lecture and accompanying pictures and graphics. 4

5 LESSON PLAN 1 Form? Resources Microbursts and Downbursts Microburst Animation ( All About Derechos ( Deadly Winds from Thunderstorms ( National Weather Service: Microbursts (Three slides: Microbursts, Wet Microburst and Dry Microburst ) ( National Weather Service Glossary for Storm Spotters ( University of Illinois: Microbursts ( cro/home.rxml) National Weather Service Report: Brief Description of Microbursts and Downbursts ( The Weather Channel: Special Reports Tornado! ( index.html) Tornado Project Online ( The University of Illinois, WW2010: ( home.rxml) National Oceanic and Atmospheric Administration Photo Library: ( Horsburgh.com: Tornado Alley ( Think Quest: Thunderstorms and ( 5

6 Tornado Alley SET UP minutes CONDUCT two 40-minute classes Science: Earth Science; Social Studies: Geography and Mapping LESSON PLAN 1 Form? Computer access Materials Books on weather and geography of the United States Dictionaries and weather glossaries A Cartographer s Guide to, 1 copy per team Tornado Mapping, 1 copy per student (Linking Across the Curriculum) Chalkboard and chalk or poster board and markers 1. Divide the class into three teams, provide them with dictionaries and weather glossaries and have students define onethird of terms below. On a large poster board or chalkboard, work with the class to compile the teams definitions into a complete glossary. Briefly, work with a globe or world map to make sure students can locate the natural features and lines of latitude and longitude listed in their glossary. anticyclone Appalachian Mountains climate cold front continental cyclone downslope Great Plains of the United States jet stream latitude longitude maritime polar latitudes 2. Distribute A Cartographer s Guide to to each team. Give them time to answer the questions on the activity sheet, using the books on weather and geography and the Internet. Answers to A Cartographer s Guide to occluded front Rocky Mountains tropical latitudes upslope warm front 1. Weather in the United States is influenced by four air masses. What are they? Tropical: These air masses form over the tropic latitudes. They are warm, humid and have low air pressure. Polar: These air masses form north of the 50 o line of latitude. They are cold and have high pressure. Maritime: These air masses form over the oceans, so they are humid. Continental: These air masses form over land, so they tend to be drier than maritime air masses. 2. What forces move these air masses around? What direction will they take as they move toward and into the United States? The jet stream is a prevailing, upper-level, westerly wind. It moves from west to east in a sinuous line that changes with the strength of the cold fronts moving south. A cyclone is an area of low pressure around which the winds flow counterclockwise in the Northern Hemisphere. A developing cyclone is typically formed by a warm front pushing northward and a cold front pulling southward. 6

7 Air masses move south from the arctic land mass, southwest from the northern Pacific, southeast from the northern Atlantic, north and then northeast from the Tropics. LESSON PLAN 1 Form? 3. How might the landforms of the United States affect the air masses moving through the area? When air is confronted by a mountain, it is lifted up and over the mountain; as it rises, it cools. If it reaches its dew point, it will condense and form a cloud and probably precipitation. Usually, the wind releases its moisture on the west side of the mountains, and as it flows down onto the plains, the drier air begins to warm. There is no barrier to the movement of air masses between the Gulf of Mexico and the states of the Great Plains. 4. What is a cold front and what is a warm front? What happens when the two air masses collide? A cold front is an air mass characterized by cold, dense air. Cold fronts have winds that move in a clockwise direction. They are sometimes called anticyclones. A warm front is an air mass of light, warm air. Warm fronts have winds that move counterclockwise and are called cyclones. When a cold front collides with a warm front, it slides under the warm front and pushes the lighter, warmer air upward. The warm air cools down, condenses and forms cumulus clouds. If there is enough warm air, as in the summer, it may form cumulonimbus clouds and even tornadoes. 5. Based on information about the formation of cumulonimbus clouds, why does an occluded front create excellent conditions for the formation of severe thunderstorms and eventually tornadoes? TEACHING NOTE Information about the formation of cumulonimbus clouds and their relationship to the formation of tornadoes is found in the preceding activity You re the Meteorologist. An occluded front occurs when a warm air mass is trapped between two cold air masses. The warm air is pushed upward when the two cold air masses meet in a kind of squeeze action. The warm air mass is completely cut off from the ground by the colder air below. The warm air has nowhere to go but up, resulting in the creation of high, strong cumulus clouds. As it cools, it will fall and then be pushed up again, adding energy to the updraft. 6. Collisions between cold, dry air masses and warm, moist air masses take place in the Great Plains. This part of the United States is sometimes called Tornado Alley. Compare an alley in your town to Tornado Alley. How are they similar? 7

8 Possible answer: An alley is a narrow street with walls on both sides. Tornado Alley is a geographic corridor in the United States, which stretches north from Texas to Nebraska and Iowa. In the case of Tornado Alley, the walls on either side of the alley are the two mountain ranges, the Rocky Mountains and the Appalachian Mountains. LESSON PLAN 1 Form? 7. Tornado season tends to move north with the sun. That is, tornado season starts earlier in the southern part of Tornado Alley than in its northern regions. Why is spring the most active time for tornadoes? Use the same reasoning to explain why the southeastern states sometimes have a mini-tornado season in the fall. Spring and summer comprise the prime thunderstorm season; so it is also prime tornado season in the Great Plains. The reason is that during these seasons, the air temperature decreases dramatically as the air rises (called the temperature gradient). Moreover, as the earth rotates around the sun, the surface warms, releasing energy (heat) and water vapor. Severe thunderstorms need large infusions of energy to build into supercells and tornadoes. The warmer the surface, the more energy is available. Energy and water vapor are released from the warm surface and rise in buoyant plumes which, when combined and organized, form a thunderstorm cell. Therefore, spring and summer have the greatest possibility for the development of thunderstorms. TEACHING NOTE In the discussion that follows, make sure each team appoints a member to act as secretary. As the teams compare their findings, the secretaries must update any information or data missing from their teams notes. 3. Ask students to share their findings and then work with them to correct any misconceptions and complete any answers that need more detail. Remind them they will need correct and thorough information for the Wrap-Up that follows. Wrap-Up Divide the following writing assignments among the three teams of student writers: Print Journalism: Background on Geography and for a local newspaper Broadcast Journalism: Feature piece on Tornado Alley Illustrated glossary in which all the vocabulary words listed at the beginning of the activity are defined, illustrated and combined in two or three brief paragraphs on Tornado Alley. Students will work together to create the text and images for their writing assignment. They must incorporate the facts about geography, climate and tornadoes from the class research and discussion. Have writers share their work in a class presentation. 8

9 LESSON PLAN 1 Form? Home Connection Have students share their information with their families and then ask family members to share any facts or concepts they know, or think they know, regarding tornadoes. Ask students to bring the new facts back to school to research for authenticity and science. As a class, compile a booklet of fact and fiction on tornadoes based on what the students have learned in their research. Linking Across the Curriculum Mathematics: Charts and Graphs Have the students research the National Weather Service s Weather Storm Prediction Center ( monthlytornstats.html) and examine Tornado Mapping to find statistics on tornado activity and tornado deaths by state. What are the state averages? They will use this information to develop a graph showing tornado activity and tornado deaths by state. Challenge the students to calculate whether or not the percentage of deaths caused by tornadoes is decreasing now that forecasting technology has improved. Students may also research living conditions that contribute significantly to loss of life during tornadoes, specifically, growing numbers of people living in manufactured homes. 9

10 How Form Page 1 of 3 Name A tornado is a violently rotating column of air, extending from a thunderstorm to the ground. The most violent tornadoes have rotating winds of 250 miles (402 kilometers) per hour or more. form in the following sequence: Fronts In the atmosphere, cool air pushes against warm air. The place where the two masses of air meet is called a front. A front can stretch over 100 miles (161 kilometers). As the cool air presses forward, it slides underneath the warm air. The warm air is pushed upward and water droplets form. Fast-growing clouds take shape. These clouds are called thunderheads. A line of thunderheads 100 miles (161 kilometers) or more in length may grow along a front. Thunderheads Thunderheads, or cumulonimbus (kyu-mya-lo-nim-buhs) clouds, are the giant clouds that produce storms with lightning and thunder. When you see a thunderhead, you are looking at a place in the sky where warm, moist air is rising quickly through cool air. This can happen along and ahead of fronts as well as on hot, sunny days. When the sun heats the ground, the air near it grows warm, too. The warm air rises, but it sometimes becomes trapped by a layer of cooler air above it. As the day continues, the sun keeps shining and more heated air pushes its way skyward. Finally, it breaks through. The warm air blasts high into the sky, like water shooting up from a fountain, and a thunderhead grows. The thunderheads most likely to cause tornadoes are those that form along and ahead of fronts. This is because strong winds often blow high above fronts. The power of these winds, along with slower winds closer to the ground, can make the rising air in a thunderhead start rotating. This difference in wind direction and speed is called wind shear. At first the rotating winds spin around a horizontal axis parallel to the ground. However, as the warm air continues to rise, the updraft becomes strong enough to lift the rotating air into a vertical spin, roughly perpendicular to the ground. A supercell is a thunderstorm with a persistent rotating updraft. Supercells are rare, but they are responsible for a remarkably high percentage of severe weather events, especially tornadoes, extremely large hail and damaging straight-line winds. Supercells HOW TORNADOES FORM

11 How Form Page 2 of 3 frequently travel to the right of the main environmental winds; that is, they are right movers. Mesocyclones If the rising air in a thunderhead begins to rotate, the column of spinning winds is called a mesocyclone (mez-uh-sy-klon). As a mesocyclone rotates, it stretches toward warm air near the ground. The lower part of the mesocyclone narrows. The narrower it becomes, the faster it spins. The mesocyclone acts like a giant vacuum-cleaner hose. Warm air is drawn in through the lower end of the mesocyclone and pulled upward through the thunderhead. The air swirls higher and higher. The spinning air may soar all the way to the top of a thunderhead, 10 miles (16 kilometers) above the ground. Some mesocyclones spin like this for a few minutes and then just disappear. In others, however, a smaller column of faster-spinning air forms inside the bottom of the mesocyclone. This column is usually less than a half-mile (800 meters) wide. As it spins, it reaches toward the ground. Funnel Clouds When the column of tightly spinning winds dips down from the mesocyclone, it draws in warm, moist air. The air cools as it is pulled up into the column. Tiny droplets of water form and a whirling cloud appears. This cloud is called a funnel cloud. Funnel clouds are named for their shape. They are often shaped like funnels tubes that are wide at the top and narrow at the bottom. Some funnel clouds hang straight down from the storm cloud. Others stretch sideways through the sky. A funnel cloud may dip down and then retract into the mesocyclone. Or, it may touch the ground. If it does, the funnel cloud is called a tornado. Sometimes when a tornado is forming, no funnel cloud can be seen. The air near the ground is so dry that, when it is sucked into the whirling column, no water droplets form. Then the fast-spinning air stays invisible until it becomes a tornado, stirring up dust and soil into a spinning debris cloud. If you see a funnel cloud dip down from a thunderhead, it is usually a sign that a tornado is on its way. But not all tornadoes look like funnels. They can be shaped more like jars HOW TORNADOES FORM

12 How Form Page 3 of 3 with the same width from top to bottom. Or, they may have more than one funnel. Large tornadoes may have several narrow, twisting funnels circling around. Some of the largest, most dangerous tornadoes do not look like funnels at all. These tornadoes appear to be big clouds moving along the ground. also change shape with time. Many funnels become thin, like pieces of rope, as they lose power. They look like giant elephant trunks snaking through the sky. The winds of a tornado can be so strong that they can blow large objects, such as parts of buildings, trees and cars, for miles. Tornado Types There are three types of tornadoes: weak, strong and violent. On the Enhanced Fukita Scale (EF Scale), these range in intensity from EF0 to EF5. Weak (EF0, EF1) If the winds of a tornado spin at 110 miles (177 kilometers) per hour or less, scientists consider the tornado weak. Weak tornadoes usually leave behind a path of damage less than 3 miles (5 kilometers) long and 50 yards (46 meters) wide. Weak tornadoes are the most common of the three tornado types. Strong (EF2, EF3) Strong tornadoes have winds ranging from 111 to 165 miles (178 to 266 kilometers) per hour. These tornadoes average a path about 9 miles (14 kilometers) long and 200 yards (183 meters) wide. Violent (EF4, EF5) Violent tornadoes are the least common type of tornado. Only 1 in 50 tornadoes in the United States is classified as violent. These tornadoes have winds ranging from 166 to more than 200 miles (267 to 322 kilometers) per hour and may last several hours. A typical violent tornado leaves a path of destruction about 26 miles (42 kilometers) long and 425 yards (389 meters) wide. A few violent tornadoes have left paths that were more than 100 miles (161 kilometers) long and 1 mile (1.6 kilometers) wide. HOW TORNADOES FORM

13 A Cartographer s Guide to Page 1 of 3 Name Directions: Research to find the answers to the following questions. You will need to investigate both books and Internet resources to find the answers. 1. Weather in the United States is influenced by four air masses. What are they? On the map on the third page, show where these air masses can be found. 2. What forces move these air masses around? Hint: Find out about the jet stream and prevailing westerlies. Hint: Learn the definitions of a cyclone, warm front and cold front. How does the cyclone affect the movement of the warm and cold air masses? On the map on the third page, show the directions these air masses are likely to take as they move toward and into the United States. 3. How might landforms of the United States affect the air masses moving through the area? Hint: The Rocky Mountains and Appalachian Mountains are major players in this weather drama. Find out about upslope and downslope winds and how they affect the movement of air. Hint: Where are there no barriers to the movement of air? 4. What is a cold front and what is a warm front? What happens when the two air masses collide? 5. Think back to what you know about how tornadoes form. Based on information about the formation of cumulonimbus clouds, why does an occluded front create excellent conditions for the formation of severe thunderstorms and, eventually, tornadoes? 6. Collisions between cold, dry air masses and warm, moist air masses take place in the Great Plains. This part of the United States is sometimes called Tornado Alley. Compare an alley in your town to Tornado Alley. How are they similar? 7. Tornado season tends to move north with the sun. That is, tornado season starts earlier in the southern part of Tornado Alley than in its northern regions. Why is spring the most active time for tornadoes? Use the same reasoning to explain why the southeastern states sometimes have a mini-tornado season in the fall. A CARTOGRAPHER S GUIDE TO TORNADOES

14 A Cartographer s Guide to Page 2 of 3 Resources: Think Quest: Thunderstorms and ( USA Today: Weather and Climate Science: Thunderstorms ( The National Weather Servie: Tornado Climatology ( The National Weather Service: F5 of the United States ( Physical Geography ( The National Weather Service: Jetstream: An Online School for Weather ( Weather Patterns: Chapter 17 (a slide presentation by Cobb County Schools in Georgia) ( %2017.ppt) The Weather Channel: Special Reports Tornado! ( center/specialreports/tornado/index.html) National Severe Storms Laboratory, : Nature s Most Violent Storms ( The Why Files (pages 1 5) ( A CARTOGRAPHER S GUIDE TO TORNADOES

15 A Cartographer s Guide to Page 3 of 3 A CARTOGRAPHER S GUIDE TO TORNADOES Masters of Disaster Tornaodes, Tornado Science, Lesson Plan 1/ Form?

16 Tornado Mapping Page 1 of 1 Name Poplar Bluff, Missouri May 8, killed Flint, Michigan June 8, killed Xenia, Ohio April 4, killed Wichita Falls, Texas April 10, killed Waco, Texas May 11, killed Purvis, Mississippi April 23, tornadoes; 55 killed Texas to Kansas April 9, killed in Glazier, Texas Super Outbreak April 3 4, states; 148 tornadoes 315 killed Widespread Outbreak November 21 23, killed Adapted from The Weather Channel s The Weather Classroom The Dixie Outbreak April 23 24, tornadoes 320 deaths Worcester, Massachusetts June 9, killed Palm Sunday Outbreak March 27 28, killed (20 in Piedmont, Alabama) The Tri-State Tornado March 18, killed Arkansas Outbreak March 1, killed 8 Oklahoma to Kansas May 3, killed TORNADO MAPPING