It's a mirage! Northwest heat wave warps sense of comfort… and reality

HANSVILLE, Wash. -- The heat wave baking the Pacific Northwest isn't just warping locals' sense of normalcy when it comes to temperature; it's warping the sense of reality.

The chilly waters of Puget Sound were combining with the sizzling heat to create mirages along the coastlines, tricking the mind into thinking the coastline was undergoing radical shifts.

The mirages appear when cold, dense air near the Earth’s surface -- in this case air cooled by Puget Sound waters -- is trapped beneath a layer of significantly warmer air aloft of lighter density, known as a temperature inversion. 

"So on a hot summer day next to the cold Puget Sound waters, you get a shallow layer of air near the water that is made much colder than the air above it, and thus, making it denser," said Michael Kavulich with the National Center for Atmospheric Research. 

This causes light rays from distant objects to refract, or bend, downward toward an observer standing on the ground.

"As light moves from a region of less dense substance to more dense substance, no matter what the substance, it will bend away from a straight line path!" Kavulich said. "If you have a layer of significantly denser air near the surface, light will tend to bend downwards, meaning you see things as ‘higher up’ than they are in reality."

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This tricks our brains into seeing the objects as if their refracted light traveled in a straight line rather than bending as it passed through the layers of varying temperature within the inversion.

Distant landmarks or shorelines will appear warped or stretched, making them seem both taller and closer than they actually are because the observer is typically viewing several such mirages stacked on top of each other.

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You can watch this process play out in this 2012 time lapse from nearly the same location as the photo above, as the temperature variations near the water create chaotic visual scenes and giving appearances of extended earthquakes.

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