The evocative sound of wind in the trees, called psithurism or sough, occurs when the smooth, “laminar” flow of air becomes turbulent around branches, twigs and leaves. The different scales of obstruction give rise to a mix of different frequencies of sound, resulting in something like white noise. Wind through pine trees is higher pitched because of the smaller size of pine needles, making a hissing or whispering sound.
When indoors you may sometimes hear the wind howling. That sound is the airflow interacting with the sharp edges, gaps and openings of buildings, producing a note in the same way as blowing over the top of an empty bottle does. These are known as Aeolian tones after Aeolus, the Greek god of winds.
When this effect, technically known as vortex shedding, matches the resonant frequency of an object such as a taut wire or line, the wire vibrates and hums in turn. It becomes an Aeolian harp string.
Even where there are no other objects, what appears to be the sound of the wind is actually distorted airflow around the external structure of your ears.
A pedant might argue that the wind itself is silent. What we hear is the just sound of various objects blowin’ in the wind.
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