VOA慢速英语2011--Understanding How Tornadoes Work

SCIENCE IN THE NEWS - Understanding How Tornadoes² Work

KATHERINE COLE: This is SCIENCE IN THE NEWS in VOA Special English. I'm Katherine Cole.
BOB DOUGHTY³: And I'm Bob Doughty. This week, we will tell about the science of tornadoes. Tornadoes have been observed inwmany parts of the world. But the storms are most often found in the United States.
(MUSIC)
BOB DOUGHTY: Tornado¹ season has begun in the United States. Violent storms struck several parts of the country last week. The National Weather Service said there were ten reports of tornadoes across the central and southern Plains states last Thursday.
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 funnel⁵: 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.
Nathaniel Ramey comforts Megan Hurst at her grandmother's house in Askewville, North Carolina, after a tornado on Saturday
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.
KATHERINE COLE: 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 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.
A huge funnel cloud touches down in Orchard⁶, Iowa, on June 10, 2008
The National Oceanic and Atmospheric⁷ 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 Alley⁸.” 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.
KATHERINE COLE: 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.
A car sits in a drainage⁹ ditch in Colerain, North Carolina, after a tornado ripped¹⁰ through the area Saturday
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.
BOB DOUGHTY: 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 seven hundred people were killed.
A "tornado outbreak" is often defined¹¹ 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 destructive¹² hit Xenia, Ohio. The sound you are about to hear comes from the website www.xeniatornado.com. It is one man's recording¹³ of the tornado moving closer.
(SOUND)
KATHERINE COLE: 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 humidity¹⁴. 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 radar¹⁵ 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.
KATHERINE COLE: 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 Enhanced¹⁶ Fujita scale or the EF scale.
Ted⁴ Fujita was a weather expert who developed a system to rate tornados¹⁷ in the nineteen seventies. The EF scale is a set, or collection, of wind estimates. They are based on levels of damage to twenty-eight different kinds of structures and other objects. Tornadoes that cause only light damage are called an EF-zero. Those with the highest winds that destroy well-built homes and throw vehicles great distances are called an EF-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.
Recently, an international team of scientists completed a tornado research project called VORTEX2. More than one hundred researchers traveled throughout America’s Great Plains in two thousand nine and two thousand ten. They used weather measurement instruments to collect scientific information about the life of a tornado. The goal of the project was to examine in detail how tornadoes are formed and the kinds of damage they cause.
A film about the VORTEX2 project opened at some theaters in the United States last month. The film includes never before seen images of tornadoes. To safely capture up-close film footage of tornadoes, some project participants traveled in a seven-ton, armored tornado intercept¹⁸ vehicle directly into tornadoes as they formed.
KATHERINE COLE: 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 relatively¹⁹ 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. June Simms was our producer. I'm Bob Doughty.
KATHERINE COLE: And I'm Katherine Cole. Read and listen to our programs at voaspecialenglish.com. And if you have a science question, send it to [email protected]. 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.

1 tornado   

n.飓风，龙卷风

参考例句：

• A tornado whirled into the town last week.龙卷风上周袭击了这座城市。
• The approaching tornado struck awe in our hearts.正在逼近的龙卷风使我们惊恐万分。

2 tornadoes   

n.龙卷风，旋风( tornado的名词复数 )

参考例句：

• Tornadoes, severe earthquakes, and plagues create wide spread havoc. 龙卷风、大地震和瘟疫成普遍的毁坏。 来自互联网
• Meteorologists are at odds over the working of tornadoes. 气象学者对龙卷风的运动方式看法不一。 来自互联网

3 doughty   

adj.勇猛的，坚强的

参考例句：

• Most of successful men have the characteristics of contumacy and doughty.绝大多数成功人士都有共同的特质：脾气倔强，性格刚强。
• The doughty old man battled his illness with fierce determination.坚强的老人用巨大毅力与疾病作斗争。

4 ted   

vt.翻晒，撒，撒开

参考例句：

• The invaders gut ted the village.侵略者把村中财物洗劫一空。
• She often teds the corn when it's sunny.天好的时候她就翻晒玉米。

5 funnel   

n.漏斗；烟囱；v.汇集

参考例句：

• He poured the petrol into the car through a funnel.他用一个漏斗把汽油灌入汽车。
• I like the ship with a yellow funnel.我喜欢那条有黄烟囱的船。

6 orchard   

n.果园，果园里的全部果树，(美俚)棒球场

参考例句：

• My orchard is bearing well this year.今年我的果园果实累累。
• Each bamboo house was surrounded by a thriving orchard.每座竹楼周围都是茂密的果园。

7 atmospheric   

adj.大气的，空气的；大气层的；大气所引起的

参考例句：

• Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
• Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。

8 alley   

n.小巷，胡同；小径，小路

参考例句：

• We live in the same alley.我们住在同一条小巷里。
• The blind alley ended in a brick wall.这条死胡同的尽头是砖墙。

9 drainage   

n.排水系统，下水道，排水，放水

参考例句：

• This is a drainage area.这里是排水区。
• Bad drainage caused the land to be flooded.排水不利容易使土地淹水。

10 ripped   

adj. <美俚>喝醉的，受毒品麻醉的 动词rip的过去式和过去分词

参考例句：

• He had ripped up the carpet, leaving only the bare boards. 他用力扯去了地毯，只剩下裸露的地板。
• I ripped my jeans on the fence. 我的牛仔裤在栅栏上划破了。

11 defined   

adj 定义的; 清晰的

参考例句：

• These categories are not well defined. 这些类别划分得不太明确。
• The powers of a judge are defined by law. 法官的权限是由法律规定的。

12 destructive   

adj.破坏（性）的，毁灭（性）的

参考例句：

• In the end,it will be destructive of our whole society.它最终会毁灭我们整个社会。
• It is the most destructive storm in 20 years.这是20年来破坏性最大的一次风暴。

13 recording   

n.录音，记录

参考例句：

• How long will the recording of the song take?录下这首歌得花多少时间？
• I want to play you a recording of the rehearsal.我想给你放一下彩排的录像。

14 humidity   

n.湿度，潮湿，湿气

参考例句：

• The house is not comfortable tonight ,because of the high humidity.由于湿度高，今晚屋子里不舒服。
• It's difficult to work because of the humidity.由于空气潮湿，工作很困难。

15 radar   

n.雷达，无线电探测器

参考例句：

• They are following the flight of an aircraft by radar.他们正在用雷达追踪一架飞机的飞行。
• Enemy ships were detected on the radar.敌舰的影像已显现在雷达上。

16 enhanced   

a.加强的

参考例句：

• Peak updraft strength is slightly enhanced with hodograph curvature. 山顶上升气流强度随速矢端迹曲率加大而稍有加强。
• The black wimple enhanced the whiteness of her skin. 黑色的包头巾使她的皮肤显得更加白皙。

17 tornados   

n.龙卷风，旋风( tornado的名词复数 )

参考例句：

• And the national weather service reports several tornados touch down. 国家气象中心报告预测龙卷风将来袭。 来自互联网
• They had stock footage of lightning, tornados, and hurricanes. 他们存有关于闪电、龙卷风和飓风的电影胶片。 来自互联网

18 intercept   

vt.拦截，截住，截击

参考例句：

• His letter was intercepted by the Secret Service.他的信被特工处截获了。
• Gunmen intercepted him on his way to the airport.持枪歹徒在他去机场的路上截击了他。

19 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。