Nick (my grandson) asks these questions, and I know just where to get an intelligent discussion, so here goes:
Why do sounds carry farther, or seem louder at night? There is an Interstate 3-4 miles from my home, but you wouldn't know it by listening on any day. If you stay up late, however, from 1 or 2 in the morning till dawn, you'll here semi trucks, or rather, semi truck tires, as they whine down the road.
I've figured you are hearing them from much farther than 3-4 miles. Thats because you hear a single truck's passage for four minutes or so. Given that they are moving about 60 miles per hour, that means you are hearing them approach from 2 miles out and going away for about 2 miles. Sometimes you can hear exhaust pipe rumbles also.
The interstate sounds can no longer be heard once the sun is up. Not that other sounds drown them out; because at early sunup, there is still not much bustle yet, not much sound competition as it were.
Once or twice in the last 5 years I've been startled awake by the noise of a freight train coming down our block, passing right in front of our house on Oakwood Avenue. Okay, I'm exagerating. The train tracks are actually about a mile away, and normally we don't hear much noise from them. But on these rare occasions, the screech and rumble just outside our window was about as great as you'd hear if you were standing right at the crossing as the train goes by.
I have read about sound hammers -- curious sound reflections caused by rare atmospheric inversions. I experienced one once in The Boundary Waters Canoe area in Minnesota. We were camped on a lake shore, and it was a misty early morning, just after dawn. The lake was about 3/4 of a mile accross, and there was another group camping on the opposite shore. For about 30 minutes I could hear everything from the far camp as clearly as if I was in its midst... people quietly talking, moving about, pouring coffee, and doing little things. When the sun got high enough to burn away the mists, the effect quickly dissappeared.
So I ask the brains I've come to respect around here, whats the deal with the night sounds? Does anyone have an explanation of the physics involved, or am I just imagining things? How do I answer Nick?
