When you look over a hot surface, like blacktop roads in the summer, you see that wavy light thingy. If that is due to the temperature of the air, why isn’t there a similar phenomenon when the air is extremely cold?
Before you ask: yes, I slept through physcis in High School and a year of chemistry nearly caused me to flunk out of college.
I think the basic answer is that cold is not a thing in itself. It is the name we give to lack of heat. Lack of heat equals lack of the phenomenon.
It’s not the temperature of the air, but the movement, that causes the shimmer.
Black tarmac readily absorbs heat from the sun. It therefore becomes much hotter than the air. It warms the air closest to it, which then rises. It’s this rising of the less-dense warmer air, and the resulting different pockets of different density, that causes light to change direction.
I guess it would be possible to create a situation where the reverse happened - you’d have to have a chilled surface suspended above a volume of air, so the cooled air would become more dense and descend. Not something that happens in an everyday situation.
Cold does shape light, if you want to put it that way. Put an ice cube in a glass of wate and look through the glass. You’ll see distant objects look wavy around the streams of cold water that are falling off the ice cube.
But if you’re talking more specifically about the way a hot road reflects distant objects, that’s happening because the index of refraction of the air is lower close to the hot road (because the air is less dense due to being hotter). Light rays trying to go from a higher index of refraction to a lower one will get reflected instead, if the angle is gradual enough. You can see the same thing if you’re underwater in a swimming pool and you look up, not directly above you but at an angle. There’s some angle such that looking any more gradually upward will have you seeing a reflection instead. This is called “total internal reflection” and is a consequence of Snell’s law. An extremely cold road will aim light more directly at the road surface, not bounce them.
Thanks.
Well, doesn’t it anyway, at least a little?
In my experience hiking and driving in various locations around the world - mountains to deserts and a whole lotta stuff in between - you can generally see much farther and the air seems much clearer when it’s cool. The clarity seems to be fairly closely related to the air temperature.
Admittedly, there are many other factors such as air density (altitude) and environmental factors (such as pollution) at work here also, but I can recall many times, when camping on a mountain or ridge, that visibility was significantly better immediately upon rising than it was several hours later.
What you describe is most likely due the water in the are condensating due to the temperture. In the afternoon the humidity rises due to evaporation.
Hmmm, I always assumed it was due to the temp of the air, because it seemed to happen regardless of the season - whether it was hazy summer or dry, crisp winter, I always seem to see a little better in the morning, right after sunrise.
But IAMostDefinitelyNAMetereologist or even a Science guy, so who knows… Where’s QED when you need him?