How do tornadoes form? - James Spann

翻译人员: Sunny Wang 校对人员: Shelley Krishna Tsang

They call me the tornado chaser.

他们称我是“龙卷风追逐者”。

When the wind is up and conditions are right,

当风来了，其他条件又刚好合适的时候，

I get in my car and follow violent storms.

我就会钻进我的车里去追逐暴风。

"Crazy," you say? Perhaps, but really I chase these sky beasts to learn about them.

也许你会说：“疯了吧你？” 但其实我追赶这些空中野兽是为了了解他们。

I want to share with you what I know.

在此，我想跟大家分享一下我所了解的。

Tornadoes are rapidly rotating columns of air that form inside storms

龙卷风是在大风内部形成的 高速旋转的空气柱，

that connect with the ground via a funnel of cloud.

通过一个漏斗形的云状物 和地面连接起来。

When that happens, they tear across the Earth,

当龙卷风形成之后， 它们就会快速席卷地面，

posing a huge threat to life and property.

对生命和财产造成巨大威胁。

Because of this, there's a great deal of research into these phenomena,

正因如此，有大量针对 这种天气现象的研究，

but the truth is, there's still a lot we don't know about how tornadoes form.

但是事实上是，我们还是对 龙卷风的成因知之甚少。

The conditions that may give rise to one tornado

我们所了解的形成龙卷风的条件，

won't necessarily cause another.

即使都满足， 也不一定会形成另一次龙卷风。

But we have learned a lot since people first started recording tornadoes,

但是从人们第一次记录龙卷风以来， 我们已经学到了不少东西。

like how to recognize the signs when one is brewing in the sky.

比如：当它还在天上酝酿形成的时候， 我们怎么识别龙卷风将要来临的信号。

Are you coming along for the ride?

你准备要参与其中了么？

Tornadoes begin with a thunderstorm but not just any thunderstorm.

龙卷风的开始是雷暴， 但是却不止是普通的雷暴。

These are especially powerful, towering thunderstorms called supercells.

非常强大，非常激烈的雷暴， 被称为超级雷暴云。

Reaching up to over 50,000 feet, they bring high force winds,

超级雷暴云有五万多尺的厚度， 它能带来强风，

giant hailstones, sometimes flooding and great flashes of lightning, too.

巨大的冰雹， 有时会引起洪水和雷鸣。

These are the kinds of storms that breed tornadoes,

这就是孕育着龙卷风的暴风雨，

but only if there are also very specific conditions in place,

但是只有在一些特殊条件 也到位的时候龙卷风才会形成。

clues that we can measure and look out for when we're trying to forecast a storm.

当我们想要预测风暴时， 还有一些我们可以用来衡量和寻找的线索。

Rising air is the first ingredient needed for a tornado to develop.

上升气流是形成龙卷风 所需要的第一个要素。

Any storm is formed when condensation occurs,

当凝结发生的时候风暴就形成了，

the byproducts of the clouds.

风暴是云的副产品。

Condensation releases heat,

凝结释放热量，

and heat becomes the energy that drives huge upward drafts of air.

热量成为驱动大量气流上升的能量。

The more condensation and the bigger the storm clouds grow,

凝结程度越大， 并且形成风暴的云团越大时

the more powerful those updrafts become.

那些上升气流也就越强。

In supercells, this rising airmass is particularly strong.

在超级雷暴云中， 这些上升的气团格外的强大。

As the air climbs, it can change direction and start to move more quickly.

当气流上升的时候， 它可以改变方向并且开始以更快的速度移动。

Finally, at the storm's base, if there is a lot of moisture,

最终，在风暴云团的底部， 如果有很多的水分，

a huge cloud base develops, giving the tornado

就会形成一个巨大的云底， 为之后的龙卷风

something to feed off later, if it gets that far.

提供能量， 前提是如果真的到了这一步。

When all these things are in place, a vortex can develop enclosed by the storm,

当所有这些东西都准备就绪的时候， 一个涡旋会在风暴包围中形成，

and forming a wide, tall tube of spinning air that then gets pulled upwards.

继而形成一个宽大高耸的高速旋转空气柱， 之后被向上拉动。

We call this a mesocyclone.

我们称其为“中气旋”。

Outside, cool, dry, sinking air

外部那些又干又冷的下沉气体

starts to wrap around the back of this mesocyclone,

开始在“中气旋”后侧环绕，

forming what's known as a rear flank downdraft.

形成一个“后侧下环流”。

This unusual scenario creates a stark temperature difference

这种特殊的情景使“中气旋” 内外部的气体间

between the air inside the mesocyclone, and the air outside,

产生了非常明显的温差，

building up a level of instability that allows a tornado to thrive.

由此造成的更高一级的不稳定性 使龙卷风更加猖狂。

Then, the mesocyclone's lower part becomes tighter,

接着，“中气旋”靠下的部分会更紧绷，

increasing the speed of the wind.

以此给风加速。

If, and that's a big if, this funnel of air moves down

基于足够的假设， 这个漏斗形的气团向下移动

into that large, moist cloud base at the bottom of the parent storm,

到在母风暴底端的 巨大又潮湿的云的下边界（云底），

it sucks it in and turns it into a rotating wall of cloud,

云底会将其吸入， 并且把它变成一个旋转的云墙，

forming a link between the storm that created it and the Earth.

这个云墙把产生它的母风暴 和地面连接起来。

The second that tube of spinning cloud touches the ground,

在这个旋转的中空的云 与地面接触的一瞬间，

it becomes a tornado.

就形成了龙卷风。

Most are small and short-lived, producing winds of 65-110 miles per hour,

大部分的龙卷风都是小规模的而且短暂的， 产生65到110英里每小时的风。

but others can last for over an hour, producing 200 mile per hour winds.

但是有一些龙卷风能持续超过1小时， 产生200英里每小时的风。

They are beautiful but terrifying,

龙卷风是美丽又令人生畏的，

especially if you or your town is in its path.

尤其是，如果你或者你的村子 在它移动的路线上。

In that case, no one, not even tornado chasers like me,

在这种情况下，没有人， 甚至像我这种“风暴追逐者”

enjoy watching thing unfold.

也不会享受龙卷风一步步的发展。

Just like everything, however, tornadoes do come to an end.

但是又像所有的东西一样， 龙卷风总是有结束的时候。

When the temperature difference disappears and conditions grow more stable,

当温差消失并且 其他条件都稳定下来的时候，

or the moisture in the air dries up,

抑或是是气体中的水分干燥下来的时候，

the once fierce parent storm loses momentum and draws its tornado back inside.

那个原本猛烈的母风暴就会失去它的动力， 然后把它的龙卷风重新拉回去。

Even so, meteorologists and storm chasers like me will remain on the lookout,

即使这样，气象学家和那些像我一样的“风暴追逐者” 也还是会继续守望，

watching, always watching to see if the storm releases its long rope again.

观察，一直观察看风暴是否会再次扬鞭。