Why does sound travel farther at night than it does during the day?

The cooler-colder air of night is denser and propagates sounds much better. In this hot, dry desert climate, the air is often so 'light' that jets passing over are soundless.

The lowest layer of the atmosphere is shallow because it's capped by a temperature inversion at night. This creates a duct through which propagating sound waves are compressed in the vertical making them sound louder and travel farther.

During the day, the lowest layer of the atmosphere is deeper and well-mixed. The sound waves are dispersed over a larger areas in the horizontal and vertical.

Sound waves travel faster when the density of air is less.Moist air is lighter than dry air.Hence sound travels faster on rainy days and foggy days. In the night the humidity becomes more and that can be the reason.