Tricky twisters: springtime is tornado season--or is it? Recent studies shed new light on these spinning storms.Last November 6, a tornado tore through Indiana, killing 23 people. It was the deadliest tornado to hit the state in more than 30 years. But that was just the beginning. Six days later, nine twisters whirled  This article or section contains information about an unreleased video game.The content may change substantially as more information becomes available. through Iowa, followed on November 15 by a line of thunderstorms thunderstorms a storm characterized by thunder and lightning caused by strong rising air currents; identified as agents of animal disease because of their involvement causing (1) spasmodic colic; (2) lightning strike; (3) injuries of cattle acquired in stampedes initiated by storms. that spawned 35 tornadoes across five states. The twist: Spring is considered peak tornado season in the U.S., so people weren't expecting a funnel-filled fall. Plus, some of these twisters sprang up out of unusual storm systems. New research suggests that tornadoes may arise from unsuspected storms more often than once thought. RECIPE FOR DISASTER Whether it's springtime or fall, a tornado doesn't just strike out of the clear blue sky. These whirlwinds form inside of a thunderstorm thunderstorm, violent, local atmospheric disturbance accompanied by lightning, thunder, and heavy rain, often by strong gusts of wind, and sometimes by hail. . Three main ingredients are needed to cook up a thunderstorm: moist air near the ground, cold air above, and a trigger to make the moist air rise. "Where the air is forced to rise, that's where thunderstorms are triggered," says Paul Markowski, an atmospheric scientist at the Pennsylvania State University Pennsylvania State University, main campus at University Park, State College; land-grant and state supported; coeducational; chartered 1855, opened 1859 as Farmers' High School. . The rising air forms a cloud. The condensation, or water that changed from vapor to a liquid, within the cloud produces warming that is critical to sustain the thunderstorm. If a fourth ingredient--wind shear--gets added to the mix, trouble really brews. That's because these wild winds, which blow at different speeds or directions at different altitudes, can tm-n an ordinary thunderstorm into a supercell--a swirling thunderstorm most likely to produce a twister. Wind shear wind shear, a sudden, drastic change in wind direction or speed over a comparatively short distance. Most winds travel horizontally, as does most wind shear, but under certain conditions, including thunderstorms and strong frontal systems, wind shear will travel in a causes the air to spin like a rolling pin. Then, the storm's updraft up·draft n. An upward current of air. updraft An upward current of warm, moist air. With enough moisture, the current may visibly condense into a cumulus or cumulonimbus cloud. Compare downdraft. , or rising warm air, tugs the rolling column of air upward. Scientists think a tug-of-war between downdrafts, or cool, sinking air, and warm updrafts stretch the rotating air column into a tornado (see Nuts & Bolts, p. 20). TORNADO TARGET The Great Plains area, which extends from Texas to Nebraska, often experiences the perfect mix of ingredients for tornadoes, earning the region the nickname "Tornado Alley" (see map, p. 20). In this region, warm, moist air blowing north from the Gulf of Mexico Noun 1. Gulf of Mexico - an arm of the Atlantic to the south of the United States and to the east of Mexico Golfo de Mexico Atlantic, Atlantic Ocean - the 2nd largest ocean; separates North and South America on the west from Europe and Africa on the east collides with drier air from the high plateaus of Mexico. This collision, called a dryline, causes the moist air to rise and form thunderstorms. The gradually sloping terrain of the Great Plains region helps produce strong wind shear that's ideal for tornado formation. "Tornado Alley has more tornadoes than any other part of the world," says Markowski. Most of Tornado Alley's twisters form from supercells that develop on spring afternoons--when the sun's heat has had plenty of time to warm the surface air. This warmer, less dense air rises, helping to trigger the thunderstorm. EXTRA ORDINARY Most of what scientists know about tornado formation comes from studying supercells in Tornado Alley. But last fall's tornadoes show that terrible twisters can form anywhere--sometimes even developing from a completely different type of thunderstorm. Some of last November's disasters began in a squall line squall line n. A line of thunderstorms preceding a cold front. squall line A line of sudden, sometimes violent thunderstorms that develop on the leading edge of a cold front. . Unlike a supercell, this line made up of individual thunderstorms can stretch for hundreds of miles. But how much of a threat do squall lines actually pose? To find out, Robert J. Trapp, an atmospheric scientist at Purdue University Purdue University (pərdy  `, -d`), main campus at West Lafayette, Ind. in Indiana, and his colleagues studied storm records and radar images of 3,828 tornadoes that formed in the U.S. from 1998 to 2000. Their findings: Squall lines spin out tornadoes more often than previously thought, especially in regions outside of Tornado Alley. Overall, only 18 percent of the tornadoes they studied were spawned by squall lines. But when the team zeroed in on specific areas, some of the percentages were much higher. For example, they found that half of the tornadoes in Indiana--one of the states hit hardest last fall--spun out of squall lines. SNEAKY STORMS These tricky twisters also catch people off guard by striking at unexpected times. Because squall line thunderstorms are often triggered by weather fronts (boundary along which cold and warm air masses collide col·lide intr.v. col·lid·ed, col·lid·ing, col·lides 1. To come together with violent, direct impact. 2. ) rather than by the sun heating air at the earth's surface Noun 1. Earth's surface - the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water" surface , the storms can happen any season, day or night. Many squall line tornadoes in the study had hit late at night--when unsuspecting victims were sleeping and didn't hear the tornado sirens or TV and radio warnings. Also, the many winds in and around squall lines can come together to produce a tornado very quickly. Trapp says, "Strike one is the time of day. Strike two is the time of year. And strike three is that line tornadoes tend to form a lot faster than do cell tornadoes, so they don't give the weather forecasters as much warning." Although most squall line tornadoes are relatively weak, they can still kill someone caught unaware. Last fall's disasters underscore The underscore character (_) is often used to make file, field and variable names more readable when blank spaces are not allowed. For example, NOVEL_1A.DOC, FIRST_NAME and Start_Routine. (character) underscore - _, ASCII 95. the idea that tornadoes form under a wide variety of conditions. The November 15 scourge of twisters formed in a squall line, while the November 6 monster descended from a broken line that formed an out-of-season supercell. By identifying the kinds of storms that spawn To launch another program from the current program. The child program is spawned from the parent program. (operating system) spawn - To create a child process in a multitasking operating system. E.g. tornadoes, Trapp hopes to help forecasters give the public early warnings when danger swirls their way. WEB EXTRA For more on tornadoes, go to: www.spc.noaa.gov /faq/tornado Nuts & Bolts ONE WAY TWISTER FORM Meeting place: The layer between cold air above and warm air below, called the cap, sometimes starts rotating with incoming weather fronts. Crash course: Colliding cold and warm air causes the warm air to rise in an updraft. Water vapor within condenses to form rain clouds. The updraft tilts the rotating air column. Supercell Thunderstorm: A mesocyclone, or large mass of rotating air up to six miles wide, develops in the midst Adv. 1. in the midst - the middle or central part or point; "in the midst of the forest"; "could he walk out in the midst of his piece?" midmost of large storm clouds. This is a supercell thunderstorm. High-altitude winds tilt thunderclouds to create a characteristic anvil anvil Iron block on which metal is placed for shaping, originally by hand with a hammer. The blacksmith's anvil is usually of wrought iron (sometimes of cast iron), with a smooth working surface of hardened steel. shape. Tornado Touchdown: Scientists think downdrafts of cooled air yank Yank steamship stoker vainly tries to climb the social ladder, then fails in attempt to avenge himself on society. [Am. Drama: O’Neill The Hairy Ape in Sobel, 339] See : Failure (jargon) yank the swirling mesocyclone toward the ground, At the same time, updrafts stretch the whirlwind whirlwind, revolving mass of air resulting from local atmospheric instability, such as that caused by intense heating of the ground by the sun on a hot summer day. vertically, speeding it up and tightening it into a narrow and violent tornado. EARTH: Tornadoes Tricky Twisters DID YOU KNOW? * Some states in the U.S. experience fewer tornadoes than others. Here's a list of states with the lowest incidences of twisters, along with the total number of tornadoes for each of the states between the years 1950 and 2004: Alaska (2), Rhode Island Rhode Island, island, United States Rhode Island, island, 15 mi (24 km) long and 5 mi (8 km) wide, S R.I., at the entrance to Narragansett Bay. It is the largest island in the state, with steep cliffs and excellent beaches. (9), Hawaii (31), Vermont (37), Oregon (87). * A "tornado watch
A tornado watch (SAME code: TOA; sometimes referred to as a "red box" by meteorologists and storm chasers) is issued when weather conditions are favorable for the " means that twisters may be possible, and you should remain alert for storm updates. A "tornado warning A tornado warning is issued when:
CRITICAL THINKING: * How is a squall-line tornado more dangerous than one spawned by a supercell? CROSS-CURRICULAR CONNECTIONS: MATH: The Storm Prediction Center The Storm Prediction Center (SPC), located in Norman, Oklahoma, is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service (NWS), which in turn is part of the National Oceanic and Atmospheric Administration keeps monthly tornado statistics. Turn the data into a graphing activity. Access the data at: www.spc.noaa.gov/climo/torn/monthlytornstats.html RESOURCES * To learn more about the study on squall-line tornadoes, read this press release from Purdue University: www.purdue.edu/UNS/html4ever/2005/ 050401.Trapp.tornado.html * For general information about tornadoes, visit this Web site from the National Oceanic & Atmospheric Administration: www.outlook.noaa.gov/tornadoes/</p> <pre> DIRECTIONS: Match the word(s) in the left column with the correct phrase in the right column. -- 1. front a. cool, sinking air -- 2. squall line b. the layer between cold air above and warm air below -- 3. updraft c. boundary along which cold and warm air masses collide -- 4. downdraft down·draft n. 1. A strong downward current of air. 2. A downward trend; downturn: The business hit a downdraft. d. rising warm air -- 5. wind shear e. water that has changed from vapor to a liquid -- 6. supercell f. winds that blow at different speeds and directions at different altitudes -- 7. cap g. line made up of individual thunderstorms that can stretch for hundreds of miles -- 8. condensation h. type of swirling thunderstorm most likely to produce a tornado ANSWERS 1. c 2. g 3. d 4. a 5. f 6. h 7. b 8. e </pre> <p>RESEARCH/CRITICAL-THINKING SKILLS Name: -- TORNADO WATCH In "Tricky Twisters" (p. 18), you learned that tornadoes can cause a lot of damage. How do you protect yourself in the event of an oncoming on·com·ing adj. Coming nearer; approaching: an oncoming storm. n. An approach; an advance. twister? Follow this activity to devise a safety plan. DIRECTIONS: Study the tornado safety information on these Web sites: 1. www.fema.gov/hazards/tornadoes/tornadof.shtm 2. www.nssl.noaa.gov/NWSTornado/ Then, use the information to help you complete the parts below. PART A: FIND SHELTER Here are three locations where you might be when a tornado strikes: your home, school, or athletic field. Survey each location, and then find a place inside or closest to each location that could serve as a tornado shelter. Describe each shelter in the spaces provided below. [ILLUSTRATION OMITTED] PART B: BE PREPARED Experts recommend that you keep a disaster supply kit handy. In the spaces below, list 10 items that you should pack into your family's disaster supply kit. 1. -- 2. -- 3. -- 4. -- 5. -- 6. -- 7. -- 8. -- 9. -- 10. -- PART C: SPREAD THE KNOWLEDGE You've done your research and know what to do in the event of an oncoming twister. Now, share the information with your family. Create a tornado safety poster for your home. Be sure to include the following information on the poster: * What are some warning signs of a tornado? * Where can you obtain tornado information updates? * How should your family stay in contact? * Where should your family go for shelter? * What should your family AVOID doing during a tornado? * What should your family do immediately after a tornado? |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion