Refraction of Sound
It can be noticed that in night hours we are able to hear sound from a greater distance compared to day time. This can be explained if the concept of refraction of sound is understood.
Sound also travels as a wave motion although the type of wave is different. The velocity of sound also varies with the air temperature. In day time, the temperature of air increases as altitude increases. On the other hand, at night/early morning hours the temperature of air decreases with the increase in altitude. Thus the air layers of different sections act as different mediums for the sound waves and undergoes refraction at each interface. In day time, the direction of wave motion is upwards and with a shorter wave length. In case of night hours it is just the reverse. Therefore, the sound waves have a better horizontal reach in night hours.