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It's a dark and stormy night. There's a strange creaking noise coming from somewhere.
在一个狂风暴雨的漆黑夜晚，从某处传来了怪异的嘎吱嘎吱声。
The wind is howling through the trees, and you just know the main character in the story is in some Dire Straits.
穿梭于树间的狂风呼啸着，你刚好知道某些恐怖海峡故事中的主唱。
But what makes the wind howl in the first place?
但是什么使得风发出呼啸声呢？
And would a horror story's classic forest of dead trees really make for louder winds than a forest full of leafy branches?
恐怖故事森林中的死亡之树真的能够营造出比枝繁叶茂的森林还响亮的声音么？
Let's start with sounds, which are just vibrations in the air around us that get picked up by our ears.
让我们先来研究声音，声音是我们的耳朵从周围的空气中所获取的振动。
Faster vibrations translate to a higher pitched sound,
更加快速的振动能够转化为更高的高音调声，
slower vibrations translate to a low pitched sound and everything in between, that's in between.
稍缓慢的振动则转化为低音调声，而介于高低之间的振动所能转化的音调也介于之中。
So to get a certain sound, all you need is air vibrating at the right rate.
因此要获取某种声音，你所需的就是正确频率下的空气振动。
These vibrations are usually measured in units of Hertz or the number of movements back and forth per second.
这些振动通常以赫兹为测量单位或是以每秒反复的运动次数为单位。
And wind gets air wiggling back and forth when it curves around obstacles like trees or buildings.
当风沿着树或建筑物做曲线运动时会使得空气来回摆动。
When wind goes around a tree for example, it has to split up as it goes past and then come back together on the other side.
例如，当风流动在树木周围，当它穿过树木时必须分开，然后在一边重新汇合。
But because of natural randomness and things like the air speed and the surface of the tree,
但受自然的随机性和空气速度以及树木表面的影响，
one sides wind is gonna be slightly stronger when the winds recombine.
一边的风会比另一边重新汇合的风要稍微强一些。
So it pushes the other side's wind out of the way.
因此，另一边的风被迫移开。
That builds up pressure on the second side, which eventually overpowers the wind from the first side and pushes it out of the way.
这就在第二边形成了压强，最终压倒了来自第一边的风并迫使它移开。
And that builds pressure back up on the first side and the cycle starts all over again.
如此便为第一边压强的形成提供支持，然后形成循环反反复复。
As the two trade back and forth, the wind carries a series of high pressure waves and whirlpools past the tree
随着两股压力的反复，风会带着一系列的高压力波和旋涡穿过树木
which vibrate the air as they interact with each other.
当它们彼此相互作用时使得空气振动。
They're called von Kármán vortices.
它们被称为卡门漩涡。
The rate of switching back and forth depends on the wind speeds and the size of the obstacle.
回转的频率取决于风的速度和障碍物的大小。
But since sounds are just vibrations,
由于声音只是振动，
fast winds going past trees or buildings can lead to vortices that make vibrations at just the right rate for us to hear it as howling wind.
速度快的风穿过树木或建筑物可以导致旋涡，从而以刚好的频率制造出振动，形成我们所听到的风的呼啸声。
And for us to get kind of creeped out by it.
而我们就是被这呼啸声吓到。
Different trees or buildings with slightly different shapes will make slightly different sounds in the same winds,
不同形状的树木或建筑在同样的风中也会发出稍微不同的声音，
creating a sort of howling chorus that you can hear in the woods.
制造出某种呼啸大合唱，也就是你可以在树林中所听到的声音。
If those trees are leafy, the leaves will absorb some of the vibrations in the air and dull the sound.
如果那些树木枝繁叶茂，树叶会吸收空气中的一些振动并使声音变得缓和。
But without leaves, like if it's in the middle of the winter or the entire forest is dead, the howling will travel a lot farther.
但是没有了树叶，比如是在冬季或者整片森林中的树都死了，那么呼啸声会传的更远一些。
But winds can also howl without even hitting something.
但是风仍然可以在不击打任何事物的情况下发出呼啸声。
There are always going to be random pockets of air with higher and lower pressure and
常有带高压和低压的随机空气囊，
wind can bend around or through those patches just like it would bend around a tree.
风可以绕过或穿过这些空气囊，就像穿过树木一样。
Which is how you can get howling winds even on the flattest plains.
这就是为什么即使在平坦的平原上你还能听到呼啸声的原因。
And why windy nights in the middle of nowhere can be downright creepy.
这也解释了为什么在偏僻的地方刮风的夜晚会如此诡异。
Thanks for asking. And if you're interested in learning more about how wind works cause like, why wouldn't you be,
谢谢提问。如果你想了解更多关于风的知识，
you can check out our video where I explain what wind is, what factors influence it and how fast it can go.
你可以点击我们的视频，其中解释了风是什么、什么会影响风以及风的速度能有多快。
