【英语时差8,16】陷入干旱的洛基山脉

The deserts of the southwestern United States stretch, in an irregular pattern, from Oregon southward to beyond the Mexican border and from California to West Texas.

  

Although they vary widely in terrain¹ and temperature, these lands share one trait: extreme dryness. 

 

Dryness in the southwest U.S. can be traced to two sources: a high-pressure system called the North Pacific High, and a phenomenon called the rain-shadowing effect of mountains. 

 

The North Pacific High is part of a relatively² stable high pressure system in the Pacific Ocean that influences the weather from northern Mexico, to the far-west and Southwest United States. In a high pressure system, air from up above tends to move downward to ground level. As the air descends³, it grows warmer and its relative humidity drops. Clear skies and dry weather result. 

 

Rain shadow is the result of the prevailing⁴ westerly winds losing most of their moisture to the mountain ranges on the western edge of the desert lands. The western Sierra Nevada, for example, receives ten times as much precipitation as areas immediately to the east. 

 

Combined, the North Pacific High and rain-shadowing create an extremely dry climate. Parts of the Sonoran and Mojave Deserts receive only one and a half inches of rainfall a year. When rain does come, it is often in short cloudbursts that dump water on the dry land more quickly than it can be absorbed, resulting in flash floods. During "false" thunderstorms, common during the hot summer months, rain evaporates before reaching the ground.  

 

1 terrain   

n.地面，地形，地图

参考例句：

• He had made a detailed study of the terrain.他对地形作了缜密的研究。
• He knows the terrain of this locality like the back of his hand.他对这一带的地形了如指掌。

2 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。

3 descends   

v.下来( descend的第三人称单数 )；下去；下降；下斜

参考例句：

• This festival descends from a religious rite. 这个节日起源于宗教仪式。 来自《简明英汉词典》
• The path descends steeply to the village. 小路陡直而下直到村子。 来自《简明英汉词典》

4 prevailing   

adj.盛行的；占优势的；主要的

参考例句：

• She wears a fashionable hair style prevailing in the city.她的发型是这个城市流行的款式。
• This reflects attitudes and values prevailing in society.这反映了社会上盛行的态度和价值观。