November 23, 2014 04:30 UTC

Science in the News

'Tornado Season' Begins in the United States

Click Arrow to Hear This Program:

Play Audio File

Or download MP3 (Right-click or option-click and save link)

BARBARA KLEIN: This is SCIENCE IN THE NEWS in VOA Special English. I'm Barbara Klein.

BOB DOUGHTY: And I'm Bob Doughty. This week, we will tell about the science of tornadoes. Tornadoes have been observed in many parts of the world. But the storms are most often found in the United States.

(MUSIC)

BARBARA KLEIN: Tornado season has begun in the United States. More than sixty tornadoes were reported in the country's southeast during the last weekend in April. One tornado measuring more than a kilometer wide struck the state of Mississippi. It destroyed homes, blocked roads and cut off electricity.

The storms were blamed for ten deaths in Mississippi, and two others in nearby Alabama. Weather experts believe it was the most intense tornado event since two thousand eight.

BOB DOUGHTY: A tornado is a violently turning tube of air suspended from a thick cloud. It extends from a thunderstorm in the sky down to the ground. The shape is like a funnel: wide at the top, narrower at the bottom.

Tornadoes form when winds blowing in different directions meet in the clouds and begin to turn in circles. Warm air rising from below causes the wind tube to reach toward the ground. Because of their circular movement, these windstorms are also known as twisters.

The most severe tornadoes can reach wind speeds of three hundred twenty kilometers an hour or more. In some cases, the resulting paths of damage can stretch more than a kilometer wide and eighty kilometers long.

BARBARA KLEIN: With a tornado, bigger does not necessarily mean stronger. Large tornadoes can be weak. And some of the smallest tornadoes can be the most damaging. But no matter what the size, tornado winds are the strongest on Earth. Tornadoes have been known to carry homes, cars and trees from one place to another. They can also destroy anything in their path.

Tornadoes have been observed on every continent except Antarctica. But experts say they are most commonly seen in the United States. On average, eight hundred tornadoes are reported nationwide each year.

The National Oceanic and Atmospheric Administration keeps records of tornado sightings. It says tornadoes kill eighty people and injure one thousand five hundred others nationwide in an average year.

(MUSIC)

BOB DOUGHTY: Tornadoes are observed most often in the central part of the United States, where the land is mostly flat. The area where the most violent tornadoes usually happen is known as “Tornado Alley.” This area is considered to extend from north-central Texas to North Dakota.

Tornadoes can happen any time of the year. But most happen from late winter to the middle of summer. In some areas, there is a second high season in autumn.

BARBARA KLEIN: Tornado seasons are the result of wind and weather patterns. During spring, warm air moves north and mixes with cold air remaining from winter. In autumn, the opposite happens. Cold weather moves south and combines with the last of the warm air from summer.

Tornadoes can strike with little or no warning. Most injuries happen when flying objects hit people. Experts say the best place to be is in an underground shelter, or a small, windowless room in the lowest part of a building.

People driving during a tornado are told to find low ground and lay flat, facedown, with their hands covering their head. People in the path of a tornado often have just minutes to make life-or-death decisions.

BOB DOUGHTY: The deadliest American tornado on record is the Tri-State Tornado of March eighteenth, nineteen twenty-five. It tore across Missouri, Illinois and Indiana. About seven hundred people were killed.

A "tornado outbreak" is often defined as six or more tornadoes produced by the same weather system within a day. But the outbreak of April third and fourth, nineteen seventy-four, set a national record. It is remembered as the "Super Outbreak." One hundred forty-eight tornadoes struck during a twenty-four-hour period. More than three hundred people were killed and nearly six thousand others injured.

One tornado that was especially destructive hit Xenia, Ohio. The sound you are about to hear comes from the Web site www.xeniatornado.com. It is one man's recording of the tornado moving closer.

(SOUND)

BARBARA KLEIN: No two tornadoes look exactly the same. And no two tornadoes act the same way.

It takes the right combination of wind, temperature, pressure and humidity to create even a weak tornado. Weather experts can identify these conditions. And, when they observe them, they can advise people that tornadoes might develop. But they are not able to tell exactly where or when a tornado will hit. Tornado warnings still depend in large part on human observations.

Usually a community will receive a warning at least a few minutes before a tornado strikes. But each year there are some surprises where tornadoes develop when they are least expected.

BOB DOUGHTY: The tornado reporting system involves watches and warnings. A tornado watch means tornadoes are possible in the area. A tornado warning means that a tornado has been seen. People are told to take shelter immediately.

Yet tornadoes can be difficult to see. Sometimes only the objects they are carrying through the air can be seen. Some night-time tornadoes have been observed because of lightning strikes nearby. But tornadoes at night are usually impossible to see.

Tornadoes that form over water are called waterspouts. But tornadoes cover a much smaller area than hurricanes, which form over oceans.

Tornadoes can be measured using wind speed information from Doppler radar systems. Tornadoes usually travel in a northeasterly direction with a speed of thirty-two to sixty-four kilometers an hour. But they have been reported to move in other directions and as fast as one hundred seventeen kilometers an hour.

BARBARA KLEIN: In the United States, the force of a tornado is judged by the damage to structures. Scientists inspect the damage before they estimate the severity of a tornado. They measure tornadoes on the Fujita scale. Ted Fujita was a weather expert who developed this system in the nineteen seventies.

There are six levels on the Fujita scale. Tornadoes that cause only light damage are called an F-zero. Those with the highest winds that destroy well-built homes and throw vehicles more than one hundred meters are called an F-five.

(MUSIC)

BOB DOUGHTY: Some people make a sport out of watching and following tornadoes. They are called tornado chasers or storm chasers. Their work can be seen in the extreme weather videos that are increasingly popular on television and on the Internet.

Some chasers do it just because it is their idea of fun. Others do it to help document storms and warn the public. Still others are part of weather research teams.

This month, more than one hundred researchers began deploying radar and other scientific instruments across America’s Great Plains. They are hoping to surround tornadoes in the second and final year of an international project known as VORTEX2. The goal of the project is to examine in detail how tornadoes are formed and the kinds of damage they cause.

Last year, the project collected information about a tornado in southeastern Wyoming. Researchers also observed several other powerful storms that were not tornadoes.

BARBARA KLEIN: The National Weather Service says the United States gets more severe weather than any other country. For one thing, it is also bigger than most other countries. And it has many different conditions that create many different kinds of weather.

There are seacoasts and deserts, flatlands and mountains. The West Coast is along the Pacific Ocean, which is relatively calm. The East Coast is along the Atlantic Ocean, which is known for its hurricanes. These strike mainly the southeastern states.

(MUSIC)

BOB DOUGHTY: This SCIENCE IN THE NEWS was written by Brianna Blake, who was also our producer. I'm Bob Doughty.

BARBARA KLEIN: And I'm Barbara Klein. Read and listen to our programs at voaspecialenglish.com. And if you have a science question, send it to special@voanews.com. We might answer it on our program. Join us again next week for more news about science, in Special English, on the Voice of America.

This forum has been closed.
Comments
     
There are no comments in this forum. Be first and add one

Learn with The News

  • Brazil Religion in Latin America

    Audio Latin America Catholics Converting to Protestants

    Almost 40 percent of the world’s Catholic population, or about 425 million people, lives in Latin America. But a recent study from the Pew Research Center says people in Latin America have increasingly lost faith in the Catholic Church. Membership has decreased as much as 20 percent. More

  • This undated handout image provided by Science and the University of Tokyo shows infectious particles of the avian H7N9 virus emerging from a cell.

    Audio What's the Matter?

    From the very big to the very small, everything in our universe is made up of matter. Matter is one of those very hardworking words that you need to master ... no matter what. We will get you to the hear of the matter with this Words and Their Stories. More

  • Cambodia's Prime Minister Hun Sen (L) stretches to shake hands with China's President Xi Jinping before a meeting at the Great Hall of the People in Beijing, November 7, 2014. REUTERS/Jason Lee/POOL

    Audio Cambodian Opposition Criticize Dependence on Chinese Aid

    China’s government recently promised more than $500 million in aid to Cambodia. Cambodian officials say they need about $1 billion in foreign aid each year to operate the government. Opposition members are worried about the country becoming too dependent on aid money from China. More

  • Obama Immigration

    Video Republicans Promise to Fight Obama on Immigration

    Republican Party lawmakers are promising to fight President Barack Obama’s executive order on immigration. The order protects millions of people who have been living in the United States illegally. The president’s announcement immediately angered Republicans in the U.S. Congress. More

  • A worker at state-owned Pertamina, the country's main retailer of subsidised fuel, fills a vehicle at a petrol station in Jakarta November 17, 2014. Indonesia's president raised the price of subsidised gasoline and diesel by more than 30 percent on Monday

    Audio Indonesians Protest Rising Fuel Prices

    Indonesian President Joko Widodo announced the government would cut the financial support on fuel. The move led to a 30 percent increase in fuel overnight. These rising prices have led some public transportation groups to go on strike. The government has had to prepare other forms of transportation. More

Featured Stories

  • Jonathan Evans Performs with Bonerama

    Video With Bonerama, Three Trombones Lead the Big Parade

    The New Orleans-based group brings together funk, rock, blues and jazz, creating a gumbo for the ears. Bonerama has horns like many bands. But, unlike most groups, the trombone players lead this band. Reporter Jonathan Evans performed with the band and wrote about it for American Mosaic. More

  • A line from Abraham Lincoln's Gettysburg Address is displayed at the Lincoln Memorial in Washington, DC.

    Audio Lincoln's Words at Gettysburg Still Have Meaning

    On November 19, 1863, President Abraham Lincoln said no one would remember his speech at a battlefield cemetery in Gettysburg, Pennsylvania. But Lincoln’s Gettysburg Address remains one of the most important speeches in U.S. history. More

  • PLASTIC DREAMS

    Audio Surgery Safaris: Looking for the Perfect Body

    Many people these days are going as far as South Africa to get their version of perfection. People from across Africa and the world come for so-called “surgery safaris.” There are no animals to see on these safaris. The visitors instead look for smaller stomachs, firmer bottoms or perhaps new eye. More

  • Video South Korea Attempting to Reuse More E-Waste

    South Korea is dealing with increasing amounts of waste from electronic devices. These useless or unwanted parts are often called “e-waste.” . The city of Seoul throws out about 10 tons of e-waste each year. Some local governments in South Korea are creating special "e-waste" recycling programs. More

  • FILE - Brittany Maynard, shown with her Great Dane puppy, Charlie, took a lethal dose of medication prescribed by a doctor in Oregon on Saturday. Maynard was battling brain cancer.

    Video Should You Have the Right to Die?

    The recent case of a 29 year old woman with brain cancer has again raised questions about the right to die. Americans are divided on whether doctors should be able to give deathly sick patients drugs to end their lives. Only four U.S states permit doctor, or physician, assisted suicide. More

Practice Your Writing

Confessions of an English Learner BlogConfessions of an English Learner Blog

Tell us About Our Programs