国家地理-2008-05-19 Tornadoes 龙卷风的形成

Call them twisters or tornadoes². They are nature's most violent storms with swirling³ winds that can top 300 miles per hour. About 800 twisters sweep through the US every year, more than anywhere else in the world. The hardest-hit area is a swath of the Great Plains from Texas to South Dakota, known as Tornado¹ Alley⁴.
 
Here, warm air flows up from the Gulf⁵ of Mexico in the spring and summer and crashes into cold air pushing down from Canada. The meeting produces violent thunderstorms called supercells. Scientists don't completely understand how or when tornados⁶ form, but they do know a supercell like this one can produce a twister if the conditions are right.
 
As more moist air flows into a storm, it gets pushed up and twisted by upper level winds. As this rotating column of air gathers force, conditions are right for a collision below. When rain cooled downdrafts hit warm air near the ground, a low hanging revolving⁷ cloud forms beneath the cell. A tornado is imminent⁸.
 
Tornadoes don't last long, anywhere from 20 seconds to an hour. But it can take years to recover from the devastation⁹. These storms kill nearly 90 people each year in the US and cause millions of dollars worth of damage. When a tornado is spotted¹⁰, experts advise going to a basement staying away from any windows or climbing into a first floor bathtub.
 
While most people run for safety when a twister appears, some scientists actually race to need it. These storm chasers hunt down tornadoes, trying to get right in the twister's path. They encounter incredible cloud movement, torrential rain, severe winds and hail, lightening, breathtaking storm structures. When they finally locate a twister, they measure it using special tools.
 
These scientists hope to someday predict exactly when and where tornadoes will strike. Little can prevent the damage caused by tornadoes, but better forecasting could save more lives, giving survivors¹¹ the chance to rebuild after living through one of the most violent storms on earth.
 
1. swath/swathe: n.
A long thin area of something, especially land
 
2. Great Plains: n. 美国大平原
The Great Plains are the broad expanse of prairie and steppe which lie east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S. states of Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas and Wyoming, and the Canadian provinces of Alberta, Manitoba and Saskatchewan. In Canada the term prairie is more common, and the region is known as the Prairie Provinces or simply "the Prairies".
 
3. Tornado Alley: n.
Tornado Alley is a colloquial¹² term most often used in reference to the area of the United States in which tornadoes are most frequent. Although an official location of the term is not defined, the areas in between the Rocky Mountains and Appalachian Mountains are the areas usually associated with it.
 
4. supercell: n. 超大胞
A thunderstorm with a persistent¹³ rotating updraft. While rare, it produces the most severe weather such as tornadoes, strong winds, and hail.
 
5. downdraft: n.
A strong downward current of air

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 swirling   

v.旋转，打旋( swirl的现在分词 )

参考例句：

• Snowflakes were swirling in the air. 天空飘洒着雪花。 来自《现代汉英综合大词典》
• She smiled, swirling the wine in her glass. 她微笑着，旋动着杯子里的葡萄酒。 来自辞典例句

4 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。

5 gulf   

n.海湾；深渊，鸿沟；分歧，隔阂

参考例句：

• The gulf between the two leaders cannot be bridged.两位领导人之间的鸿沟难以跨越。
• There is a gulf between the two cities.这两座城市间有个海湾。

6 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

7 revolving   

adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想

参考例句：

• The theatre has a revolving stage. 剧院有一个旋转舞台。
• The company became a revolving-door workplace. 这家公司成了工作的中转站。

8 imminent   

adj.即将发生的，临近的，逼近的

参考例句：

• The black clounds show that a storm is imminent.乌云预示暴风雨即将来临。
• The country is in imminent danger.国难当头。

9 devastation   

n.毁坏；荒废；极度震惊或悲伤

参考例句：

• The bomb caused widespread devastation. 炸弹造成大面积破坏。
• There was devastation on every side. 到处都是破坏的创伤。 来自《简明英汉词典》

10 spotted   

adj.有斑点的，斑纹的，弄污了的

参考例句：

• The milkman selected the spotted cows,from among a herd of two hundred.牛奶商从一群200头牛中选出有斑点的牛。
• Sam's shop stocks short spotted socks.山姆的商店屯积了有斑点的短袜。

11 survivors   

幸存者，残存者，生还者( survivor的名词复数 )

参考例句：

• The survivors were adrift in a lifeboat for six days. 幸存者在救生艇上漂流了六天。
• survivors clinging to a raft 紧紧抓住救生筏的幸存者

12 colloquial   

adj.口语的，会话的

参考例句：

• It's hard to understand the colloquial idioms of a foreign language.外语里的口头习语很难懂。
• They have little acquaintance with colloquial English. 他们对英语会话几乎一窍不通。

13 persistent   

adj.坚持不懈的，执意的；持续的

参考例句：

• Albert had a persistent headache that lasted for three days.艾伯特连续头痛了三天。
• She felt embarrassed by his persistent attentions.他不时地向她大献殷勤，使她很难为情。