Wind Noise

Bio-Acoustics 105

We all know that wind makes noise. Winds whistle and roar. Morgan and Raspet 1992 show that for a wind increase from 3 to 10 m per second, the wind noise increases 20 dB (nothing to sneeze at). Wind noise at 20 Hz is 10 dB greater than the noise at 200 Hz. So, the wind has a deep voice. Most of the turbulent kinetic energy in the atmosphere produces sounds below 40 Hz.

If it is windy and turbulent and you are an infrasound communicator in search of a mate, it would be best to wait till the winds die down. Even so the low frequency bellower has a real advantage over the high frequency whiner. Low frequency sound is attenuated less by the air than higher frequencies.

During the day, temperatures decline with elevation above the surface (so-called lapse conditions). Under such conditions, sounds are upward-refracting. Sound levels away from the origin decline at the surface, as sound energy is lost to higher altitudes.

Sunset cooling at the surface results in the building of a nocturnal inversion: cool at the surface and getting warmer as you go up. Sound is reflected downward. Canard-Carauna et al. 1990 found enhanced acoustic signal after sunset and through the night. So, wait for the sun to fall below the horizon and cold air to pool on the ground before vocal mate hunting.

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