I live near Gatwick airport and am so used to the noise of planes that I rarely notice it. However, during a recent cold spell, the planes were a lot louder than usual. Why would this be?
Nick Baker
Colchester, Essex, UK
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Cold weather is often associated with a temperature inversion where the temperature is lowest at ground level. Sound travels faster in warmer air and this leads to refraction, or a bending of the sound waves. According to the relative position of the source and the listener, this creates a focusing effect, making the noise louder on the ground.
Frank Dempsey
Pickering, Ontario, Canada
In my experience, louder, crisper noise from aircraft occurs when cold Arctic air linked with strong, high-pressure weather patterns moves overhead.
The very low humidity in the cold air allows better propagation of sound, since moisture attenuates its transmission. As well as this, the high pressure is associated with a sinking layer of dense, cold air, causing what is known as a subsidence inversion.
This acts as a low-level, horizontal boundary between cold air (in contact with the cold ground) and warmer air above it. The boundary reflects distant sounds to the observer, resulting in louder noise from an airport than normal, as sounds that would usually radiate upward as well as horizontally get reflected back down to ground level and seem louder.
These atmospheric conditions allow me to hear noise from distant trains and road traffic, as well as other sounds not normally heard in the absence of an inversion.
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