As the air turns cooler in the fall, we experience many changes to the environment that signal the change in seasons. Some of these changes are more noticeable than others. One subtle change is in the way sound carries through the air. The cooler, drier air of autumn is also denser than warm and humid air, and so provides a more efficient medium for sound waves to travel. In fall, we hear sounds a little better.
Temperature inversions, which are more common and pronounced in fall, are another reason for better sound. When the ground cools at night, nearby air is also cooled, creating a layer of air near the ground which is cooler than the air just above. This layer might be 100 to a few hundred feet thick. The top of this is called the boundary layer and it can bend sound waves back to the ground, allowing sound waves to travel greater distances.