What in the wild, wild, world of weather?!
Have you ever been driving around on a warm day when you look up the road to see what appears to be water, where the road should be? Most of us refer to that optical illusion as a mirage, and we’re right to do so. In addition to the common mirage, there’s another optical effect caused by cold weather called the Fata Morgana.
Did you know that when light passes through layers of the atmosphere, that it becomes bent, reflected, refracted, and distorted in different ways? This effect is compounded when the densities of each layer of the atmosphere is varied. For instance, we all know light bends when it hits water. Why should a moisture laden atmosphere be any different? Now imagine the earth’s atmosphere as a multi-layered shell that is viscous, fluid, dry and gassy. If you put a light through each of those layers, the light is destined to come out distorted at the earth’s surface. (This explanation also applies to the, “why is the sky blue?” question. It’s simply a refraction of the light that causes our eyes to perceive the light as blue.)
In the case of a common mirage, surfaces that absorb much of the sun’s solar radiation become quite hot, while the air just above that surface remains relatively cooler. Light from the sun above the road is refracted into our eyes, and the surface then appears wet. Really what you’re seeing is a reflection of the sky, on the road.
A Fata Morgan is a touch more complicated. To explain it, I must explain the term, looming. When warm air exists over a cold surface, images below are inverted in the air. It may appear that a town in the distance, below the horizon is visible, (although upside-down) in the air above the horizon. Now… when conditions are just right… you can see multiple images, one on top of the other, or also known as, a Fata Morgana.
To see last week's installment of Shelley's What in the wild, wild, world of weather?, click here.
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