万物简史 第369期:进入对流层(10)

 At the equator the convection process is generally stable and the weather predictably fair, but in temperate¹ zones the patterns are far more seasonal², localized, and random³, which results in an endless battle between systems of high-pressure air and low. Low-pressure systems are created by rising air, which conveys water molecules⁴ into the sky, forming clouds and eventually rain. Warm air can hold more moisture than cool air, which is why tropical and summer storms tend to be the heaviest. Thus low areas tend to be associated with clouds and rain, and highs generally spell sunshine and fair weather. When two such systems meet, it often becomes manifest in the clouds.

在赤道地区，对流过程一般比较稳定，天气总是不错，而在温带地区，季节变化、地区差异要明显得多，缺乏规律性。结果，高气压体系与低气压体系之间展开了永无穷尽的搏斗。低气压体系是由上升的空气创建的，把水分子送到天空，形成了云团，最终形成了雨。热空气比冷空气更能携带水气，这是热带和反季下暴雨最多的原因。因此，低的地方往往与云雨关系密切，高的地方一般阳光灿烂，天气不错。当两个这样的体系相遇的时候，往往从云团的样子看得出来。

For instance, stratus clouds—those unlovable, featureless sprawls⁵ that give us our overcast⁶ skies—happen when moisture-bearing updrafts lack the oomph to break through a level of more stable air above, and instead spread out, like smoke hitting a ceiling. Indeed, if you watch a smoker⁷ sometime, you can get a very good idea of how things work by watching how smoke rises from a cigarette in a still room. At first, it goes straight up (this is called a laminar flow, if you need to impress anyone), and then it spreads out in a diffused⁸, wavy⁹ layer. The greatest supercomputer in the world, taking measurements in the most carefully controlled environment, cannot tell you what forms these ripplings will take, so you can imagine the difficulties that confront meteorologists when they try to predict such motions in a spinning, windy, large-scale world.

比如，要是携带水汽的上升气流无法突破上面比较稳定的一层空气，就会像烟碰到了天花板那样向外展开，于是就形成了层云一那种不大讨人喜欢，毫无特色，弄得天空阴沉沉的云层。事实上，要是你观察一个人抽烟，望着烟雾怎样从一变香烟在无凤的屋子里袅袅上升，你就会有个很好的概念，知道这到底是怎么回事。起先，烟雾笔直上升（这被称之为“层流”要是你想在别人面前卖弄一下学问的话），然后向外展开，扩散成波形的一层。连用在精密受控环境里进行测量的世界上最大的超级计算机，也无法准确预测这类波形烟雾会成什么形状，而气象学家却要在一个不停自转、大而多风的世界里预测这种运动，你可以想像他们面对的困难有多大。

1 temperate   

adj.温和的，温带的，自我克制的，不过分的

参考例句：

• Asia extends across the frigid,temperate and tropical zones.亚洲地跨寒、温、热三带。
• Great Britain has a temperate climate.英国气候温和。

2 seasonal   

adj.季节的，季节性的

参考例句：

• The town relies on the seasonal tourist industry for jobs.这个城镇依靠季节性旅游业提供就业机会。
• The hors d'oeuvre is seasonal vegetables.餐前小吃是应时蔬菜。

3 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

4 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

5 sprawls   

n.（城市）杂乱无序拓展的地区( sprawl的名词复数 )；随意扩展；蔓延物v.伸开四肢坐[躺]( sprawl的第三人称单数 )；蔓延；杂乱无序地拓展；四肢伸展坐着（或躺着）

参考例句：

• The city sprawls out to the west, north and south. 该市向西、北、南方不规则地扩张[延伸]。 来自互联网
• Explanation: Our magnificent Milky Way Galaxy sprawls across this ambitious all-sky panorama. 说明：我们宏伟的银河系蜿蜒穿过这幅高企图心之全天影像。 来自互联网

6 overcast   

adj.阴天的，阴暗的，愁闷的；v.遮盖，（使）变暗，包边缝；n.覆盖，阴天

参考例句：

• The overcast and rainy weather found out his arthritis.阴雨天使他的关节炎发作了。
• The sky is overcast with dark clouds.乌云满天。

7 smoker   

n.吸烟者，吸烟车厢，吸烟室

参考例句：

• His wife dislikes him to be a smoker.他妻子不喜欢他当烟民。
• He is a moderate smoker.他是一个有节制的烟民。

8 diffused   

散布的，普及的，扩散的

参考例句：

• A drop of milk diffused in the water. 一滴牛奶在水中扩散开来。
• Gases and liquids diffused. 气体和液体慢慢混合了。

9 wavy   

adj.有波浪的，多浪的，波浪状的，波动的，不稳定的

参考例句：

• She drew a wavy line under the word.她在这个词的下面画了一条波纹线。
• His wavy hair was too long and flopped just beneath his brow.他的波浪式头发太长了，正好垂在他的眉毛下。