英语VOA慢速听力:龙卷风季节来临

2024年3月17日发(作者：四年级学生日记)

Several tornadoes hit the Dallas-Fort Worth area of Texas last week, causing vere damage but no deaths

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 explore the science of tornadoes. The violent storms strike in many

parts of the world but happen most commonly in the United States.

(MUSIC)

BARBARA KLEIN: Tornado ason has begun in the United States.

Last Tuesday a ries of storms tore across the Dallas-Fort Worth area in Texas. The tornadoes damaged or destroyed

hundreds of homes. Yet no deaths were reported.

On March cond, more than forty tornadoes moved through the Ohio and Tenne Valleys, and the South. Reports say

the storms killed at least thirty-nine people in five states.

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.

A funnel cloud of a tornado that hit the midwestern state of Iowa

Tornadoes form when winds blowing in different directions meet in the clouds and begin to turn in circles. Warm air rising

from below caus the wind tube to reach toward the ground. Becau of their circular movement, the windstorms are also

known as twisters.

The most vere tornadoes can reach wind speeds of three hundred twenty kilometers an hour or more. In some cas, the

resulting paths of damage can stretch more than a kilometer wide and eighty kilometers long.

BOB DOUGHTY: 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 trees, cars or homes from one place to another. They can also destroy anything in their

path.

Tornadoes have been obrved on every continent except Antarctica. But experts say they are most commonly en in the

United States. On average, more than one thousand are reported nationwide each year.

The National Oceanic and Atmospheric Administration keeps records of tornado sightings. It says tornadoes kill venty

people and injure one thousand five hundred others nationwide in an average year.

(MUSIC)

BARBARA KLEIN: Tornadoes are obrved most often in the middle 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 cond high ason in autumn.

BOB DOUGHTY: Tornado asons 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.

AP

A ries of tornadoes over two days in March killed forty people in Kentucky, Alabama, Indiana and Ohio

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 just have minutes to make life-or-death decisions.

BARBARA KLEIN: The deadliest American tornado on record was the Tri-State Tornado of March eighteenth, nineteen

twenty-five. It tore across Missouri, Illinois and Indiana. About ven hundred people were killed.

Between March and May of last year, there were one thousand one hundred fifty-nine confirmed tornadoes across the United

States.

Scientists say that is the most on record for any three-month period. The most active month was last April, when ven

hundred fifty-eight tornadoes were confirmed. That is the most ever for any month.

Last April, the country also broke a thirty-ven year old record for the largest tornado outbreak. A "tornado outbreak" is often

defined as six or more tornadoes produced by the same weather system within a day.

Scientists say the one hundred ninety-nine tornadoes on April twenty-venth were the most for any single day. They say the

storms killed three hundred sixteen people – the most ever in modern records for a twenty-four hour period.

(MUSIC)

BOB DOUGHTY: No two tornadoes look exactly the same. And no two tornadoes act the same way.

Even a weak tornado requires the right combination of wind, temperature, pressure and humidity. Weather experts can

identify the conditions. And, when they obrve them, they can advi 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 obrvations.

Usually a community will receive a warning at least a few minutes before a tornado strikes. But each year there are some

surpris where tornadoes develop when they are least expected.

BARBARA KLEIN: 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 en. People are told to take shelter immediately.

Yet tornadoes can be difficult to e. Sometimes only the objects they are carrying through the air can be en. Some night-

time tornadoes have been obrved becau of lightning strikes nearby. But tornadoes at night are usually impossible to

e.

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 venteen kilometers an hour.

BOB DOUGHTY: In the United States, the force of a tornado is judged by the damage to structures. Scientists inspect the

damage before they estimate the verity of a tornado. They measure tornadoes on the Enhanced Fujita scale or the EF

scale.

Ted Fujita was a weather expert who developed a system to rate tornados in the nineteen venties. The EF scale is a t,

or collection, of wind estimates. They are bad on levels of damage to twenty-eight different kinds of structures and other

objects. Tornadoes that cau only light damage are called an EF-zero. Tho with the highest winds that destroy well-built

homes and throw vehicles great distances are called an EF-five.

(MUSIC)

BARBARA KLEIN: Some people make a sport out of watching and following tornadoes. They are called tornado chars or

storm chars.

Their work can be en in the extreme weather videos that are increasingly popular on television and on the Internet.

Some chars do it just becau it is their idea of fun. Others do it to help document storms and warn the public. Still others

are part of weather rearch teams.

Two years ago, an international team of scientists completed a tornado rearch project called VORTEX2. More than one

hundred rearchers traveled throughout America's Great Plains in two thousand nine and two thousand ten. They ud

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