September 19, 2011
I’ve written two entries on interesting phenomena that I’ve seen this summer. I have seen Kelvin-Helmholtz waves and a massive superior mirage, and you can see my posts on those. This year, I saw another interesting atmospheric phenomenon – the “green flash.” It is subtle, and if you aren’t specifically looking for it, it can be hard to see, but it is very interesting when you do see it.
If you see a green flash, there is no need to duck for cover; Lord Voldemort isn’t trying to kill you. A green flash is a very rare sliver of green light most usually seen right after sunset or before sunrise.
Let’s use a setting sun as an example, as green flashes are most commonly seen at sunset. Green flashes occur because light is refracted as enters the atmosphere. Light moves more slowly in the denser air nearer the ground than the thinner air aloft. Out of all the colors in the visible spectrum, infrared (the color) has the longest wavelength, and ultraviolet (once again, the color, not the separate type of wave) has the shortest. Shorter wavelengths follow closer to the curvature of the Earth when the sun is right at the horizon. Therefore, as the sun sets, the longer wavelengths (first red, then orange, then yellow) disappear because they don’t follow the curvature as closely as the shorter wavelengths (green, blue, violet) and therefore travel faster since they are higher up, where the air is thinner. Green, meanwhile, stays in the lower atmosphere and travels slower, so green is the last color we see, with it being more yellowish at first and more blueish at the very end before it dies out.
Why don’t we get blue or violet flashes then? These types of light are generally scattered throughout the atmosphere as the sun sets. Otherwise, we’d see violet flashes. On very rare occasions, however, you can see a blue flash, especially if the air near the surface is very dense and the air aloft is much lighter (like an inversion).
There are four types of green flashes. These are the inferior-mirage, the mock-mirage, the sub-duct, and the green ray. The inferior and mock-mirage flashes are by far the most common, making up 99% of all green flashes, with the inferior being the commoner one. I saw an inferior green flash, and the picture at the top is an inferior green flash as well.
Inferior green flashes are formed when the air at the surface is warmer than the air above. They are best seen at sea level.
Three hours later, I’m done and knowledgeable about green flashes! I can’t do super long posts when school starts, but I’ll still be up on the blog. I move in on the 22nd and start classes on the 28th. UW baby!
Thank you SO MUCH for reading my blog!!! I really appreciate it.