Hi,
Just a quick note. I know that as relative humidity--the presence of water vapour in the air--changes, the movement of sound waves is affected. Winter (cold) air is denser, which acutally affects the "lift" of an aircraft wing and the efficiency of its propeller. Shorter take-offs are possible in winter than in summer (I know this because I fly remote control model planes in both seasons). Ian would know more because he is a licensed pilot and owns a real plane!
The speed of sound is also affected by temperature and humidity. Whether any of these factors affect audibility--it's possible--I will have to research. Interesting question. . .
Regards,
