How do tornadoes form? - James Spann

龍捲風怎麼形成？- 詹姆士‧史班

譯者: Aaron Shoo 審譯者: Adrienne Lin

They call me the tornado chaser.

大家都叫我「追風少年」。

When the wind is up and conditions are right,

當起風、和其他條件成立時，

I get in my car and follow violent storms.

我就會跳上車 跟著那些龍捲風跑。

覺得我瘋了嗎？ 也許吧！

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

但我只是想多了解它們一點。

I want to share with you what I know.

我想分享一下我的發現。

Tornadoes are rapidly rotating columns of air that form inside storms

龍捲風是高速迴旋的空氣柱，

在暴風中以漏斗狀的雲， 自天空延伸到地面。

that connect with the ground via a funnel of cloud.

When that happens, they tear across the Earth,

它們會橫掃經過的地方，

posing a huge threat to life and property.

造成生命財產的重大損傷。

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

為此有很多 針對這個天然災害的研究。

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

但對它形成的原因， 仍有許多未解之謎。

The conditions that may give rise to one tornado

一個龍捲風成形的條件，

won't necessarily cause another.

未必能讓另一個龍捲風也成形。

但我們從前人的紀錄， 對龍捲風了解更多，

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

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

比如說怎麼辨認 龍捲風在空中醞釀的徵兆。

Are you coming along for the ride?

想知道是什麼嗎？

Tornadoes begin with a thunderstorm but not just any thunderstorm.

龍捲風的前兆是雷雨， 但不是每次雷雨後都有龍捲風。

These are especially powerful, towering thunderstorms called supercells.

要充滿能量、巨大的「超級雷雨胞」。

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

高五萬英呎以上， 會帶來強風、大冰雹，

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

有時甚至會淹水、大閃電等。

These are the kinds of storms that breed tornadoes,

這就是孕育龍捲風的基本需求。

但還要再滿足一些特定條件，

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

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

那些我們可以測量、察覺到， 幫助我們預測龍捲風的指標。

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

「上升氣流」是首要條件。

Any storm is formed when condensation occurs,

任何風暴形成前， 水氣都會先凝結，

the byproducts of the clouds.

這是製造雲的過程之一。

Condensation releases heat,

凝結時會放出熱量，

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

熱量會變成 推動龐大上升氣流的能量。

The more condensation and the bigger the storm clouds grow,

水氣凝結越多， 就會製造越大的積雨雲；

the more powerful those updrafts become.

又會推動更多上升氣流。

In supercells, this rising airmass is particularly strong.

在超級雷雨胞中， 這些的空氣變得特別有力。

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

空氣上升後可能會改變方向， 開始快速移動。

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

最後在雲的底部， 如果水氣夠的話，

a huge cloud base develops, giving the tornado

會發展成巨大的「雲底」，

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

如果龍捲風形成， 就能所需提供能量。

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

當一切就緒， 雲團中心會形成渦流，

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

再發展成向上吸引的 巨大管狀旋風。

We call this a mesocyclone.

我們稱為「中氣旋」。

Outside, cool, dry, sinking air

外面的乾冷下沉空氣，

starts to wrap around the back of this mesocyclone,

開始從中氣旋的後方捲入，

forming what's known as a rear flank downdraft.

形成所謂的「後側下沉氣流」。

This unusual scenario creates a stark temperature difference

這樣的現象會造成 中氣旋裡外強烈的溫差，

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

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

溫差造成的不穩定， 進一步助長龍捲風壯大。

Then, the mesocyclone's lower part becomes tighter,

之後中氣旋底部會收緊，

increasing the speed of the wind.

風速因此增加。

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

如果，我是說假如， 這個漏斗狀的氣旋往下移，

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

接觸到雷雨胞下層 潮濕豐沛的雲底，

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

就會吸收雲底變成快速旋轉的雲牆，

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

最後再向下觸及地面。

The second that tube of spinning cloud touches the ground,

一旦這道快速旋轉的雲柱，

it becomes a tornado.

碰觸到地面就成了「龍捲風」。

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

龍捲風大多小又短命， 風速約每小時65到110英里，

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

但有些風速可達每小時200英里， 而且維持一個小時左右。

They are beautiful but terrifying,

雖然很美但很恐怖。

especially if you or your town is in its path.

尤其是當你本人 或你家在它的行進路線時。

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

這時候沒有人， 包括我這樣的觀察家在內，

enjoy watching thing unfold.

會想看接下來的後果。

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

就跟萬物一樣， 龍捲風也有消失的時候。

When the temperature difference disappears and conditions grow more stable,

當溫差消失、各項條件趨於穩定，

or the moisture in the air dries up,

或是空氣中的溼度降低，

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

雷雨胞能量耗盡，

龍捲風就會慢慢消散。

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

儘管到了這個階段， 氣象學家或追風少年如我，

還是會繼續盯著它， 看它會不會死灰復燃。

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