Wind gradients bend sound waves and explain downwind audibility

Evidence

Wind can also cause refraction effects because the velocity of sound within the medium is unaffected by the velocity of the medium. The velocity of a sound wave in a moving medium, when viewed from a fixed point, is the sum of the two velocities, so that it is increased when the sound is moving with the wind and is reduced when it is moving against the wind. As the velocity of air is generally less at ground level compared with the velocity higher up (due to the effect of the friction of the ground), sound waves are bent upward or downward depending on their direction relative to the wind. The degree of direction change depends on the rate of change in wind velocity as a function of height; a faster rate of change results in a greater direction change. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 340 (#expands, via linked claim)

The wind is an element that grasps the ears forcefully. The sensation is tactile as well as aural. How curious and almost supernatural it is to hear the wind in the distance without feeling it, as one does on a calm day in the Swiss Alps, where the faint, soft whistling of the wind over a glacier miles away can be heard across the intervening stillness of the valleys. — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 79 (#exemplifies, via linked claim)

Categorization

• XREF: connects to: Prevailing wind direction should guide where one lives relative to noise sources; Wind speed gradients, not wind itself, refract sound and break reciprocity; Downwind sound is bent downward and waveguides along the ground, gaining intensity (+7 more)

Related

• Wind gradients refract sound toward slow regions and extend its range (similarity 0.96)
• Downwind sound is bent downward and waveguides along the ground, gaining intensity (similarity 0.95)
• Wind speed gradients, not wind itself, refract sound and break reciprocity (similarity 0.94)
• Prevailing wind direction should guide where one lives relative to noise sources (similarity 0.94)
• Wind bends sound waves because air velocity changes with height (similarity 0.93)
• Atmospheric physics creates striking asymmetries in how sound travels (similarity 0.90)
• Sound bends like light because temperature changes its speed. (similarity 0.88)
• Wind refraction and humidity structure alter sound propagation in air (similarity 0.87)
• The same wind sound expresses one’s happiness or unhappiness. (similarity 0.86)
• Distant wind can be heard across intervening stillness without being felt (similarity 0.84)
• A moving medium shifts sound speed, and speed gradients bend waves by refraction (similarity 0.84)
• Sound refracts toward slower-speed regions over long outdoor distances (similarity 0.81)
• Diffraction arises because air-pressure waves cannot abruptly end at an edge (similarity 0.79)
• Sound bends around obstacles because pressure changes cannot end abruptly at shadow boundaries (similarity 0.79)
• Waves always refract toward regions of slower wave speed (similarity 0.79)

Broader Connections

• Wind bends sound waves because air velocity changes with height #expands (0.95) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 340
• Distant wind can be heard across intervening stillness without being felt #exemplifies (0.80) — Schafer, Murray R, The Soundscape- Our Sonic Environment…, 79