Thine eyes deceive: A cold-weather mirage on a hot summer day

Driving north on a hot summer day earlier in July, Alaska's Parks Highway cut beneath blue skies past marsh and mountains, strip malls, roadside lakes and forests of birch and spruce.

Around Mile 69, the highway climbs a small hill, revealing at its crest a panoramic view of Denali and its companion peaks, with the Alaska Range stretching wide beneath.

It can be a glorious view; a promise signaled to anyone headed even farther north that they are venturing somewhere special. Against a crisp sky, the mountain stands tall, its angled, white ridges well-defined in perfect juxtaposition to the canvas of summer sky that surrounds it.

But on this drive, the scenic view from the top of the hill was noticeably distorted. It's not unusual for Denali to hide on an otherwise cloudless day; the mountain self-generates storm clouds which can obscure its grandeur, as can summer haze caused by humidity.

This was something different. In the distance, a series of rectangular white masses jutted upward from the horizon, as if a bored, mythological toddler had used hills like Lego blocks to craft a crude cityscape.

After some moments of bewilderment and awe, my wife and I realized we were witnesses to a phenomenon known as Fata Morgana, a type of mirage that reflects images directly above themselves.

I knew the term thanks to a former colleague who'd covered the Iditarod Trail Sled Dog Race with me in 2011. Commuting by small plane between checkpoints. Stephen Nowers, my race coverage partner, noticed that mountains in the distance, near the ghost town of Iditarod, looked unusually large, blocky and tall. He'd recalled the illusion's unusual name.

That he'd spotted this one near a ghost town is fitting. The phenomenon is otherworldly. Part awe-inspiring, part eerie, watching it is to witness something that is not a thing at all, but a trick on the eyes.

Indeed, witchcraft is at the root of its etymology. The legends of King Arthur and Queen Guinevere include tales of the sorceress Morgan le Fay, a powerful fairy known to live in the sea who cast spells to lure sailors to their deaths. La Fata Morgana, "the fairy Morgan," is her Italian name.

The optical illusion is more commonly a wintertime event. In a 1978 article for the Alaska Science Forum, seismologist T. Neil Davis noted that winter in Alaska creates prime conditions for temperature inversions in large valleys, and Fairbanks, home to the University of Alaska Fairbanks' Geophysical Institute, is an inversion mecca.

As light passes through alternating layers of warm and cold air, it bends toward the denser air, altering the image, not unlike viewing an object placed in a clear glass of water.

Bands of air of varied density refract and reflect light in different ways, leading to stacked, superimposed images that can deceive a distant viewer. Buildings, spires and castles may appear to exist where they do not.

Nicole Molders, founding chair of UAF's Department of Atmospheric Sciences, is no stranger to the transformations. Her office window overlooks the Alaska Range.

"It's like half of the mountain is mirrored in the sky, like you see your mirror in the water. When I (first) came here, I thought 'That's amazing!'" Molders said in an interview from her office Wednesday. "I was excited about it."

Nowadays, the amazement has worn off. Molders sees the illusion so often her reaction has toned down to become simple observation, rather than awe.

"It's just there," she said.

Transient and ethereal, Fata Morganas are shape-shifters, morphing frequently.

The visions are thought to explain some UFO sightings, as well as ghost ships that appear to sail above the horizon and floating cities in the sky.

Ben Bartos, a meteorologist with the National Weather Service, offered another definition, from the American Meteorological Society's Glossary of Meteorological Terms. Fata Morgana, the glossary states, are mirages that "… occur over a surface when density decreases with height but are most striking when a temperature increases with height."

In other words, typically, temperature and pressure decrease with height, thus also decreasing air density. With a temperature inversion, a layer of warm air sits above a layer of cold air.

Generally, this happens in winter, when the Earth's surface is cooler than the air above it.

There can also be something called a "lifted temperature inversion," in which warmer air flows over water, and through cooler air, essentially creating a temperature inversion within the atmospheric bands themselves. In this scenario you could have: warm surface (land mass), cool air, warm air, cool air.

Bartos theorized this may be what happened on that summer drive earlier this month. A lifted temperature inversion drifting above the snow, ice and glaciers of the Alaska Range — all forms of water — could explain the stacked mirage we saw, he said.

Weather balloon data for Anchorage, Fairbanks and McGrath did not capture a lifted temperature inversion on July 5 or July 6, the dates around which we saw the mirage. But that doesn't mean it didn't happen, Bartos said. Alaska is large enough that it would not be surprising for a local weather event to occur which instruments did not record.

Rare, delicate, surreal.

Potent magic, indeed.

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