Beachgoer captures rare, colorful phenomenon decorating the afternoon sky
This awesome rainbow was spotted in the sky over Brazil. It's cloud iridescence, and it happens when solar rays diffract in water droplets and ice crystals that make up the cloud. The light spreads through the cloud and reflects the colors of the rainbow.
Normally when we spot a gorgeous rainbow glittering across the sky, a shower or downpour usually precedes it. That’s not always the case, however, especially when it comes to the relatively rare occurrence of fire rainbows—scientifically known as circumhorizontal arcs.
“I’ve never seen a rainbow like this. What is it?,” inquired Packy McCormick via Twitter as he shared his unique image of the phenomenon from a beach in Avalon, New Jersey, near 64th Street on the afternoon of May 26. His camera had captured high in the sky above tanning beachgoers a wispy cloud that was decorated with the colors of the rainbow.
“I was with my family and a few friends and neighbors, and no one had seen anything like it before,” McCormick, a New York resident and vice president of experience at Breather, told AccuWeather.
Twitter user Packy McCormick took this image of a fire rainbow, also known as a circumhorizontal arc, over a beach in Avalon, New Jersey, on May 26. (Twitter photo/@packyM)
“People mentioned that it rained hard the night before, and that what we saw might be related to that,” he said. His curiosity led him to turn to Twitter for answers, which is how he discovered that what he and others had seen was a circumhorizontal arc.
They’re defined as near-horizon arcs that extend parallel to the horizon, according to the World Meteorological Organization (WMO). The National Weather Service (NWS) stated that as light passes through cirrus clouds, it refracts the light.
“These can only form with high cirrus clouds, because they are made out of purely ice crystals,” said AccuWeather Senior Meteorologist Dave Samuhel.
Cirrus clouds are typically found at 20,000 feet in the atmosphere or higher, according to the University of Illinois. “Most clouds are made of water droplets. The ice crystals in the clouds scatter the sunlight to produce the rainbow-colored arc,” Samuhel said.
In order for circumhorizontal arcs to occur, the angle of the sun must be quite high, which is why they are usually seen in areas closer to the equator, according to Samuhel.
“However, they can be seen farther north in the summer, since the sun angle is higher,” he said. “They are 46 degrees from the sun, about twice as far as the more typical halo that is 22 degrees from the sun.”
For the most part, these phenomena happen on precipitation-free weather days, Samuhel added.
A fire rainbow was spotted on May 22, 2019, during the City of Philadelphia Office of Emergency Management's annual Field Day training session outdoors in sunny conditions. (Twitter photo/@PhilaOEM)
They can only occur when the elevation of the light source is more than 58 degrees, when the sun reaches an elevation of around 68 degrees, the circumhorizontal arc reaches its maximum intensity, according to the WMO.
McCormick’s image quickly attracted attention online, with other Twitter users and friends sending him and his wife images of very similar occurrences, both recent and from a couple of years ago, from locations including Japan and Italy—a testament to just how unusual it is to spot circumhorizontal arcs in the sky.
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