A main stands on the ground at a fixed distance from a siren which emits sound of fixed amplitude. The man hears the sound to be on a clear night than on a clear day.

Explanation

The intensity of sound at a given at a given point is the energy per second received by a unit by a unit area perpendicular to the direction of propagation.
`I = (1)/(2) rhoVomega^(2) A^(2)`
Also in tensity varies as distance from the point source as
I prop (1)/( r^(2)`