Jun 30, 2012
This is a cool question that doesn’t have an easy or clear answer. I’m thinking it’s related somehow to the same reason the sky is blue, and the origins of rainbows.
In physics there is a phenomena called backscattering, when the white light from the sun hits our atmosphere, most of the light comes through pretty easily, except blue wavelengths. Oxygen or O2, has a way of scattering blue light so while all the rest of the light hits the ground directly, the blue bounces around in the atmosphere, getting absorbed by oxygen and water molecules, getting re-emitted and bouncing to the next molecule, until it eventually relays down to the ground. All this scattering causes the sky to seem to glow blue… and the lack of blue in the direct sunlight makes sunlight appear a nice yellow colour when it hits the ground. The same is true for ultraviolet and near ultraviolet rays with ozone, or O3.
In the case of green skies, I’m inclined to think it’s a similar process but with a lot more water in the air. I’m not just talking humidity, but the shear size of the raindrops. In the few experiences I’ve had with this type of weather, the colour was accompanied with an almost ridiculous amount of water, so much in fact, that I had to almost stop driving until the rain let up, because I couldn’t see more than 3 feet in front of my car. Perhaps there is a critical size with rain drops that will only allow certain wavelengths of light out, kind of like a rainbow, but the only available light it’s drawing from is the backscattered blue light, that further gets filtered into green through those massive drops.
It’s important to note, I found no conclusive studies have been made on this matter. This just what we think.