Rare
phenomenon occurs over Idaho
Holly
Newcomer, posted Sept. 28, 2006
Rainbows
are a magnificent colorful sight. But, the one seen in the
sky over northeastern Idaho this summer was a visual phenomenon.
This wonder was a circumhorizontal arc also known as a fire
rainbow. Like other rainbows the fire rainbow is caused by
the refraction of light in ice crystals in the atmosphere.
However, these ice crystals are found only in cirrus clouds,
distinguished by wispy thin strands.
“This phenomenon is rare because it requires certain
conditions,” Anthony Lupo, associate professor of atmospheric
science, said. The conditions are the sun has to be 58 degrees
in the sky or higher, unlike the rainbow everyone is use to
seeing which the sun has to be low.
“The ice crystals have to be relatively aligned in the
same direction,” Lupo said. In other rainbows, the alignment
of the ice crystals are vertical, these ice crystals are horizontal.
This is not the first time these types of arcs have been spotted.
Circumhorizontal arcs can occur anywhere with the right conditions.
However, there have not been any recorded sightings in Missouri.
If cirrus’s crystals are aligned perfectly, the entire
cloud lights up in a spectrum of colors creating an amazing
sight.
