“My very first thought was, where did that wall come from?”
So says Chris Ratzlaff, an Alberta photographer and stormchaser, of the strange, shimmering apparition he saw on Jan. 19 from his home in Airdrie, Alta.
“I was just doing some work around the house when I looked out the window and saw a line across the horizon that certainly wasn’t there previously.”
Ratzlaff tweeted a photo and a couple of videos of the phenomenon, which he identified as a fata morgana — also known as a superior mirage.
Derived from the Latin mirari, meaning “to be astonished,” a mirage is an optical phenomenon that causes objects to appear on the horizon that aren’t really there. According to the American National Snow and Ice Data Center at the University of Colorado, a superior mirage such as the one Ratzlaff observed occurs when cold air lies close to the ground with warmer air above it, causing the image of an object to appear above the actual object. In Ratzlaff’s video, the mirage appears to reflect the image of houses on the horizon.
Superior mirages are sometimes called fata morgana after the sorceress Morgan le Fay of Arthurian legend, who was said to be able to cause optical illusions in bodies of water.
Ratzlaff says the mirage may have occurred due to the arrival of a Chinook, which brought relief from the extreme cold temperatures southern Alberta experienced last week.
From Jan. 14 to Jan. 19, temperatures across Alberta hovered around -45C, prompting Environment Canada to issue an extreme cold warning. By the weekend, conditions had improved, with parts of Alberta going from -30 C to -16 C.
“Over the weekend we had a very strong Chinook—a lot of warm air which basically saw our temperature rise significantly in a span of 48 hours,” Ratzlaff says.
Chinook winds are a type of warm, dry wind that originate from the Pacific Coast. They are cool as they blow up the Canadian Rockies, and warm as they drop down the eastern slopes in Calgary and other parts of Alberta.
Ratzlaff says he has not seen a superior mirage in his hometown before, but was excited when he recognized it this past weekend.
“It looked like a wall on the horizon, a really tall wall. Of course, I knew there wasn’t one there, but it took me a few seconds to notice that,” he says. “Once it clicked—what I was looking at—then it was just about running around and getting my camera gear set up.”