What makes the wind howl in the first place?
And would a horror story's classic forest of dead trees really make for louder winds than a forest full of leafy branches? Let's start with sounds, which are just vibrations in the air around us that get picked up by our ears.
Faster vibrations translate to a higher pitched sound, slower vibrations translate to a low pitched sound and everything in between, that's in between. So to get a certain sound, all you need is air vibrating at the right rate.
These vibrations are usually measured in units of Hertz or the number of movements back and forth per second. And wind gets air wiggling back and forth when it curves around obstacles like trees or buildings. 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.
But because of natural randomness and things like the air speed and the surface of the tree, one sides wind is gonna be slightly stronger when the winds recombine. So it pushes the other side's wind out of the way. That builds up pressure on the second side, which eventually overpowers the wind from the first side and pushes it out of the way.
And that builds pressure back up on the first side and the cycle starts all over again. As the two trade back and forth, the wind carries a series of high pressure waves and whirlpools past the tree which vibrate the air as they interact with each other. They're called von Kármán vortices. The rate of switching back and forth depends on the wind speeds and the size of the obstacle.
But since sounds are just vibrations, 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. And for us to get kind of creeped out by it. Different trees or buildings with slightly different shapes will make slightly different sounds in the same winds, creating a sort of howling chorus that you can hear in the woods. If those trees are leafy, the leaves will absorb some of the vibrations in the air and dull the sound.
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. But winds can also howl without even hitting something. There are always going to be random pockets of air with higher and lower pressure and wind can bend around or through those patches just like it would bend around a tree. Which is how you can get howling winds even on the flattest plains. And why windy nights in the middle of nowhere can be downright creepy.
