科学揭秘"暴风雨前的宁静"

 　　Have you ever spent an afternoon in the backyard, maybe grilling¹ or enjoying a basketball game, when suddenly you notice that everything goes quiet? The air seems still and calm—even the birds stop singing and quickly return to their nests.

　　你可曾有过这样的经历：某天下午正在后院烧烤或者打篮球的时候，突然发现一切瞬间变得安静下来，空气似乎凝结了，连鸟儿也不再歌唱而转身躲回窝里去了？

　　After a few minutes, you feel a change in the air, and suddenly a line of clouds ominously² appears on the horizon—clouds with a look that tells you they aren't fooling around. You quickly dash in the house and narrowly miss the first fat raindrops that fall right before the downpour. At this moment, you might stop and ask yourself, "Why was it so calm and peaceful right before the storm hit?"

　　几分钟后，你感觉到空气中有所变化，忽然之间一排乌云出现在地平线上，让人有种不祥的预感——乌云的样子好像是在告诉你它们可不只是做做样子而已。你急冲进屋里，险些被瓢泼大雨前掉下的大雨点砸个正着。此时，你也许会停下来问自己：“为什么暴风雨来临前是那么宁静安详呢？”

　　It's an intriguing³ phenomenon that people have recognized for centuries, but what on earth causes this calm? And there is an old phrase "calm before the storm", often used in its figurative meaning—a quiet period just before a great activity or excitement. According to our own experience, we know there is literally⁴ calm before the storm. But what causes this calm? And is it always calm before the storm? Let's hear what scientists have to say.

　　人们在几个世纪前就已经发现这个神秘的现象了，但究竟是什么原因造成暴风雨前的这番宁静呢？古谚有云“暴风雨前的宁静”，这通常用在比喻的修辞中，描述热闹的活动以及情绪亢奋前的一段安静时间。根据自身的经验，我们也知道事实上暴风雨来临前也确实是宁静的。但这是什么原因造成的呢？暴风雨前总是平静么？让我们来听听科学家们的解释。

　　The answer is sometimes there is; sometimes there isn't. Under the right conditions, an eerie⁵ or peaceful calm will befall your picnic before a storm moves in. Other storms skip the calm and proudly announce their presence by instantly unleashing⁶ bad weather.

　　答案是：有时如此，有时则不然。在特定的情况下，暴风雨来临前会出现令人恐惧的或是祥和的寂静，降临在你野餐的时候。其他种类的暴风雨则直接跳过寂静的步骤，犹如在骄傲地宣布自己的存在一般，瞬间风雨大作。

　　A period of calm happens in a particular kind of storm, the simplest kind of storm—a single-cell thunderstorm . In this type of thunderstorm, there is usually only one main updraft, which is warm, humid air and drawn⁷ from places near the ground. Storms need warm and moist air as fuel, so they typically draw that air in from surrounding environment. Storms can draw in the air that fit their need from all directions—even from the direction in which the storm is traveling.

　　平静时期出现在一种特定的暴风雨中，即最简单的暴风雨——单细胞雷暴。在这种类型的雷暴中，通常只有一种主要的上升气流，即暖湿气流从地面升起。温暖湿润的空气是暴风雨形成的必要条件，所以通常会把它们从周围的环境中吸进来。雷暴能够从周围任何一个方向吸进自己所需的暖湿空气——甚至是处在雷暴运动方向上的空气也被吸了进来。

　　As the warm, moist air is pulled into a storm system, it leaves a low-pressure vacuum in its wake. The rising air meets the cold dry air that has already existed in the storm clouds, thus the temperature of the warm air drops, and the water vapor⁸ in it condenses into tiny droplets⁹ that are a precondition of rain. These droplets clump¹⁰ up and build on larger particles like dust, until they grow large enough to form raindrops.

　　由于暖湿空气被吸进雷暴中，雷暴经过之处就形成了低气压真空带。正在上升的暖湿气流遇到雷暴云层中原本就存在的干燥冷空气，此时热空气的温度下降，里面的水分凝结成小的水滴——这是形成雨水的前提。这些水滴不断聚集，包裹住一些大的颗粒（如灰尘），当水滴凝聚到足够大时就会形成降雨。

　　This warm, moist air keeps moving upwards¹¹, but it becomes colder and drier during its trip through cloud which involves cooling and condensation¹². When it reaches the top of the cloud mass, the air gets spit out at the top. This air is sent rolling out over the big, anvil¹³ — shaped head of the thunderclouds. From there, the air descends—drawn back toward lower altitudes by the very vacuum its departure created in the first place. Warm and dry air is relatively¹⁴ stable, and once it blankets a region, it stabilizes¹⁵ that air in turn. This causes the calm before a storm.

　　暖湿气流持续上升，但当穿越云层时经历气温下降水汽凝结的过程，暖湿气流开始冷却并变得干燥。当暖湿气流达到云层顶部时，会被挤出云层，这股气流会翻过巨大的铁砧形雷雨云。此时，气流开始下沉——被其自身上升时所形成的真空带吸回低处。干热的气流相对稳定，一旦它覆盖了某一个地区，就会使该区域的气流稳定下来，这就造成了暴风雨前的平静。

　　Most thunderstorms, though, don't start with a calm. That's because most are actually clusters of storms with complex wind patterns. There's so much air moving up and down in the vicinity of these storm clusters that the calm before the storm never happens. And instead, before the storm, it might be really windy!

　　尽管如此，大多数的雷暴来临前并不是一片宁静。这是因为它们大多是风向复杂的暴风雨团。在暴风雨团的周围，有很多气流频繁上下流动，这就使得这种类型的暴风雨来临前毫无平静可言。相反，这种类型的暴风雨来临前往往会狂风大作。

1 grilling   

v.烧烤( grill的现在分词 )；拷问，盘问

参考例句：

• The minister faced a tough grilling at today's press conference. 部长在今天的记者招待会上受到了严厉的盘问。
• He's grilling out there in the midday sun. 他在外面让中午火辣辣的太阳炙烤着。 来自《简明英汉词典》

2 ominously   

adv.恶兆地，不吉利地；预示地

参考例句：

• The wheels scooped up stones which hammered ominously under the car. 车轮搅起的石块，在车身下发出不吉祥的锤击声。 来自《简明英汉词典》
• Mammy shook her head ominously. 嬷嬷不祥地摇着头。 来自飘（部分）

3 intriguing   

adj.有趣的；迷人的v.搞阴谋诡计(intrigue的现在分词)；激起…的好奇心

参考例句：

• These discoveries raise intriguing questions. 这些发现带来了非常有趣的问题。
• It all sounds very intriguing. 这些听起来都很有趣。 来自《简明英汉词典》

4 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

5 eerie   

adj.怪诞的；奇异的；可怕的；胆怯的

参考例句：

• It's eerie to walk through a dark wood at night.夜晚在漆黑的森林中行走很是恐怖。
• I walked down the eerie dark path.我走在那条漆黑恐怖的小路上。

6 unleashing   

v.把（感情、力量等）释放出来，发泄( unleash的现在分词 )

参考例句：

• Company logos: making people's life better by unleashing Cummins power. 公司理念：以康明斯动力建设更美好的生活！ 来自互联网
• Sooner or later the dam will burst, unleashing catastrophic destruction. 否则堤坝将崩溃，酿成灾难。 来自互联网

7 drawn   

v.拖，拉，拔出；adj.憔悴的，紧张的

参考例句：

• All the characters in the story are drawn from life.故事中的所有人物都取材于生活。
• Her gaze was drawn irresistibly to the scene outside.她的目光禁不住被外面的风景所吸引。

8 vapor   

n.蒸汽，雾气

参考例句：

• The cold wind condenses vapor into rain.冷风使水蒸气凝结成雨。
• This new machine sometimes transpires a lot of hot vapor.这部机器有时排出大量的热气。

9 droplets   

n.小滴( droplet的名词复数 )

参考例句：

• Droplets of sweat were welling up on his forehead. 他额头上冒出了滴滴汗珠。 来自辞典例句
• In constrast, exhaled smoke contains relatively large water droplets and appears white. 相反，从人嘴里呼出的烟则包含相当大的水滴，所以呈白色。 来自辞典例句

10 clump   

n.树丛，草丛；vi.用沉重的脚步行走

参考例句：

• A stream meandered gently through a clump of trees.一条小溪从树丛中蜿蜒穿过。
• It was as if he had hacked with his thick boots at a clump of bluebells.仿佛他用自己的厚靴子无情地践踏了一丛野风信子。

11 upwards   

adv.向上，在更高处...以上

参考例句：

• The trend of prices is still upwards.物价的趋向是仍在上涨。
• The smoke rose straight upwards.烟一直向上升。

12 condensation   

n.压缩，浓缩；凝结的水珠

参考例句：

• A cloud is a condensation of water vapour in the atmosphere.云是由大气中的水蒸气凝结成的。
• He used his sleeve to wipe the condensation off the glass.他用袖子擦掉玻璃上凝结的水珠。

13 anvil   

n.铁钻

参考例句：

• The blacksmith shaped a horseshoe on his anvil.铁匠在他的铁砧上打出一个马蹄形。
• The anvil onto which the staples are pressed was not assemble correctly.订书机上的铁砧安装错位。

14 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。

15 stabilizes   

n.（使）稳定， （使）稳固( stabilize的名词复数 )v.（使）稳定， （使）稳固( stabilize的第三人称单数 )

参考例句：

• The broadbased attachment of the mesenteric root stabilizes the small bowel. 肠系膜根部基底宽阔的附着面使小肠得以稳定。 来自辞典例句
• The available supply of industrial product and produce stabilizes growth. 工业品与农产品的有效供给稳定增长。 来自互联网