Turbulence is the irregular motion of air caused by obstructions to airflow around the plane.

亂流是由障礙物造成的空氣不規則運動對飛機周圍氣流的影響 。

And this can be caused by many factors, but is most often caused by unstable weather patterns that trigger storms.

而造成這種情況的原因有很多，但最常見的原因是不穩定的天氣模式引發風暴 。

And if you are thinking, "Wouldn't the pilot know there's a storm ahead?" turbulence can usually be detected on the plane's weather radar, if they contain water particles.

如果你在想「飛行員難道不知道前方有暴風雨嗎？」亂流通常可以通過飛機上的天氣雷達探測到，如果它們含有水顆粒的話。

And pilots also receive preflight weather briefings that include information about potential turbulence.

飛行員在飛行前還會收到包括潛在亂流資訊的天氣簡報。

But as the name clear-air suggests, there are no warnings when the plane is about to encounter such sudden and severe swirls of air.

但正如「晴空」這個名字所暗示的那樣，當飛機即將遇到如此突然和嚴重的氣流漩渦時並沒有警告。

Looking at the number of injuries, I believe that the aircraft, the flight, encountered clear-air turbulence.

從受傷人數來看，我認為這架飛機遇到晴空亂流。

A plane of that size, a Boeing 777, can be tossed about violently.

這麼大的飛機一架波音 777 飛機會被劇烈顛簸。

If it's caused by normal turbulence, the cloud-related turbulence, the pilot could have avoided and will have avoided that.

如果它是由正常亂流（與雲有關的亂流）引起的，機師本可以並且將會避免這種情況。

But clear-air turbulence, there's no way of knowing when it's going to happen, where and the severity or intensity of the turbulence.

但是晴空亂流，我們無法知道它何時會發生和亂流的嚴重程度或強度。

According to the National Weather Service in the US, about 75% of CAT incidents happen in clear air, although they're not restricted to cloud-free air.

根據美國國家氣象局的數據，大約 75% 的 CAT 事件發生在晴朗的空氣中，儘管這些事件並不限於無雲的空氣。

Here's what we know about CAT.

以下是我們對 CAT 的瞭解。

It usually happens in high altitudes of 15,000ft above ground level.

晴空亂流通常發生在離地面 15000 英尺的高海拔地區。

SQ321 was cruising at 37,000ft.

SQ321 在 37 000 英尺高空巡航。

CATs can happen when two masses of air meet at different velocities, pressure or temperature, such as when a jet stream interacts with calmer air.

當兩股空氣以不同的速度、壓力或溫度相遇時，例如當急流與平靜的空氣相互作用時，就會發生 CAT。

Other sources of CAT include airflow over mountainous terrain, as well as when planes pass through the vicinity of thunderstorms, such as wind passing horizontally 5,000ft above a cumulonimbus cloud.

CAT 的其他來源包括山區上空的氣流，以及飛機經過雷暴附近時的氣流，例如在積雨雲上方 5,000 英尺處水平經過的風。

There is currently no technology to detect the phenomenon.

目前還沒有技術可以檢測到這種現象。

Let's retrace the flight of SQ321.

讓我們追溯 SQ321 的飛行軌跡。

At 10: 38pm London time on Monday (May 20), SQ321 departed London's Heathrow Airport.

倫敦時間星期一（5 月 20 日）晚上 10 點 38 分，SQ321 從倫敦希思羅機場起飛。

There were 221 passengers and 18 crew members on board the Boeing 777-300ER jet.

這架波音 777-300ER 飛機上共有 221 名乘客和 18 名機組人員。

The London Heathrow to Singapore Changi route is routinely a 13-hour journey.

倫敦希思羅機場至新加坡樟宜機場的航線通常需要 13 個小時的航程。

About 10 hours into the flight, when the crew was serving breakfast, the plane entered an area over the Irrawaddy basin in Myanmar, and that's when things went wrong.

飛行大約10個小時後，當機組人員正在享用早餐時，飛機進入了緬甸伊洛瓦底江盆地上空的一個區域，就在那時出了問題。

SQ321 encountered unexpected extreme turbulence and began tilting upwards.

SQ321遇到了意想不到的極端亂流流並開始向上傾斜。

Altitude data from FlightRadar24 shows the aircraft was thrust up and down over the course of a minute.

FlightRadar24 的高度數據顯示，飛機在一分鐘內上下推力。

At one point, it reached about 400ft or 120 meters above its original altitude, before dramatically dropping back to cruising altitude of 37,000ft.

在某一時刻，它達到了高於原始高度約 400 英尺或 120 米，然後急劇下降到 37,000 英尺的巡航高度。

If you look at the plane's vertical speed, which is the rate at which it ascends or descends, it surged to 1,664ft per minute and then dived to -1536ft per minute, all in a matter of three seconds.

如果你看一下飛機的垂直速度，也就是它上升或下降的速度，它會飆升至每分鐘 1,664 英尺，然後下降到每分鐘 -1536 英尺，整個過程只花了三秒鐘。

Weather forecasting service AccuWeather would later report explosive thunderstorms had been developing nearby just after 4pm Singapore time.

天氣預報服務 AccuWeather 隨後報告說，新加坡時間下午 4 點剛過，附近就出現了爆炸性雷暴。

The flight was diverted to Bangkok and the pilot declared a medical emergency.

該航班改飛曼谷，機師宣佈醫療緊急狀況。

He landed the plane at Bangkok's Suvarnabhumi Airport at 4:45pm Singapore time.

他於新加坡時間下午4點45分將飛機降落在曼谷素萬那普機場。