Monterey Bay’s Crazy Labor Day Horizon

A superior mirage along the coast of Monterey Bay as seen from Twin Lakes beach in Santa Cruz, California. Mid-afternoon, September 7, 2015.

A superior mirage along the coast of Monterey Bay as seen from Twin Lakes beach in Santa Cruz, California, mid-afternoon on September 7, 2015.

If you happened to be looking out across Monterey Bay over Labor Day weekend you might have noticed that the coastline looked weirdly distorted. It was as if someone had superimposed a strange, hallucination-inspired 50-foot vertical bar code along the coastline, making the cliffs look huge. The Moss Landing smoke stacks appeared extremely tall and skinny with a lot of “bar code” floating around them. Everyone I pointed it out to said, “Wow, what is that?”

A close up of Moss Landing power plant during the visual distortion. September 7, 2015.

A close up of Moss Landing power plant during the visual distortion. September 7, 2015.

Moss Landing from Seabright Beach, Santa Cruz, California, with no optical distortion present.

Moss Landing from Seabright Beach, Santa Cruz, California, with no optical distortion present.

It’s a Mirage

A mirage is a naturally occurring optical phenomenon in which light rays are bent to produce a displaced image of distant objects or sky. They are caused when two horizontal air masses with large differences in temperatures are right on top of each other. Cold air is denser than warm air and hence has a greater ability to refract (bend) light. If a viewer is observing light traveling at a shallow angle between air masses with different temperatures, the light rays bend towards the colder air.

If the air near the ground is warmer than the air higher up, the light ray bends upward just above the ground. Human eyes are used to intercepting straight rays of light back to their source. When the source ray is bent from its original source we can’t trace it back to the right spot. Instead we trace the light back along a perfectly straight “line of sight” to somewhere the light did not come from. If the light was bent upward your eye traces it downward and produces an “inferior image” of the sky that appears to be on the ground. If the air near the ground is colder than that higher up, the light ray bends downward just above the ground and your eye traces it upward. This is a “superior” image that appears to be coming from above the ground surface and above the original source of the light.

An inferior mirage on the Mojave Desert in April, 2007. Photo by Broken Inaglory.

An inferior mirage on the Mojave Desert in April, 2007. Photo by Broken Inaglory.

Mirages at the earth’s surface do not happen often because the temperature gradients between air masses aren’t usually strong enough. On average temperatures decrease upward at a rate of 0.007 °F per vertical foot. Mirages require a much steeper gradient to start, about 1.3 degrees °F for each vertical foot. A strong mirage needs about 2.75 °F per vertical foot. These conditions occur with strong heating at ground level, for example when the sun shines on sand or asphalt for several hours.

What is the name of this phenomenon? Find out and see and the “explain it in a glance graphic” here at MobileRanger.com.

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Julia Gaudinski


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