Sound refracts between air masses of different temperatures just as light does between materials.

Evidence

This is analogous to the refraction of light at the boundary of different materials. In the optical case, refraction arises because the speed of light is different in different materials; for example, it is slower in water than it is in air. In the acoustic case, refraction arises for the same reasons, because the velocity of sound in air is dependent on the temperature, as shown in Equation 1. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 331

Categorization

• DEFINE: Clarifies why acoustic refraction exists: sound speed varies with air temperature, so a temperature boundary acts like an optical boundary.
• corroborated: 2 independent passages support this claim — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 331