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"Fire rainbow" spotted near Toronto


A circumhorizontal arc is a rare, but not unheard of, phenomenon
A circumhorizontal arc is a rare, but not unheard of, phenomenon

Cheryl Santa Maria, staff writer

July 10, 2012 — A ''fire rainbow" danced across the horizon Sunday afternoon -- and it left some people wondering: "What does this mean?"

The effect occurs when the sun enters the atmosphere at at least 58 degrees
The effect occurs when the sun enters the atmosphere at at least 58 degrees

Matthew Haskill was driving near Toronto Sunday afternoon when something in the sky caught his attention.

"It looked like a strange rainbow. At first I thought it was a phenomenon related to St. Elmo's fire," he says, referring to an event that usually occurs during a thunder storm, "but I knew that couldn't be right. It was so weird to see rainbow clouds that looked like they were on fire."

The phenomenon - dubbed a ''fire rainbow'' by a Washington journalist in 2006 - is formally known as a circumhorizontal arc, and while rare in Canada, it isn't unheard of.

Dayna Vettese, a meteorologist at The Weather Network, says the conditions have to be ''just right'' for the arcs to appear.

"When the sun travels through tiny ice crystals in the atmosphere you tend to see this effect," she says, "but the sun has to be high in the sky -- at least 58 degrees."

Circumhorizontal arcs most commonly occur in cirrus clouds -- but only when they're aligned horizontally.

"You're more likely to see this type of rainbow during the summer here in North America," Dayna says. "But in places like Europe, the arcs are much rarer." 

Photos courtesy of Matthew Haskill

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