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Weather Wise: Winter Mirages

Weather Wise: Winter Mirages
Posted at 5:01 PM, Mar 06, 2023

Picture a mirage. Do you imagine crossing the Sahara, it's 120 degrees, all that sand, but off in the distance, you swear you see water and some palm trees? You're saved! Well, mirages also happen here in Montana in the dead of winter when the temperature could be below zero.

The classic mirage is a naturally occurring optical phenomenon in which light rays bend to produce a displaced image of distant objects.

Last week, a viewer sent a picture and did not understand what he was looking at. It certainly is odd looking, and why are the mountain tops flat?

This is an arctic mirage, a phenomenon common in higher latitudes in the presence of a temperature inversion. An inversion is colder air closer to the surface with warmer air above it. As light rays pass from the colder, denser air at the surface through the less dense, warmer air above it, they bend producing a distorted image to the eye.

Arctic mirages are different than desert mirages in that the light is bent in the opposite direction. Desert mirages are upside down and lower than the original object. Arctic mirages are the right way up and higher than the original object. Desert mirages are often images of the blue sky while arctic mirages are usually images of distant land mass, and in this case it was the Rocky Mountain Front. The flat top is created by the top of the cold layer in the inversion. The early viking explorers called them hillingars.