Sound refracts toward slower-speed regions over long outdoor distances

Evidence

Wave energy often progresses in a well-defined direction, but that direction can change more or less slowly. Such refraction often goes unnoticed for sound waves, but refraction is actually quite ubiquitous outdoors over distances of about 100 m and beyond. Refraction results from the variation of the speed of the wave within the medium in which it is traveling; the bending or curving of the wave is always toward regions of slower wave speed. — Eric J. Heller, Why You Hear What You Hear- An…, 172

Categorization

• DEFINE: Defines refraction for sound as bending toward slower wave-speed regions, the key mechanism for outdoor sound propagation.
• XREF: connects to: Wind refraction and humidity structure alter sound propagation in air — Almo Farina, Soundscape Ecology: Principles,…, 1895