Rainbows are fairly common around here but still beautiful enough to stop most of us dead in our tracks. Last evening, a line of showers popped up and triggered some pretty stunning rainbows across the region. 

Sometimes, colourful bands of light appear high in the sky, when there is no rain in the air.  For the most part, these are halos that form when sunlight interacts with ice crystals in the upper atmosphere. The most common is the basic halo that forms a complete ring around the sun or moon.  Grandma says:  “ring around the sun or moon, rain or snow upon you soon”.

A less frequently observed band of light was spotted this morning in Esdraelon New Brunswick: a circumzenithal or Bravais’ arc! It’s often described as an "upside down rainbow" .  I think it looks like a big smile in the sky.

This optical phenomenon is similar in appearance to a rainbow, but belongs to the family of halos.  It’s becomes visible thanks to the refraction of sunlight through ice crystals, generally in cirrus or cirrostratus clouds.  Not just any old ice in the sky will do; the type of ice crystals is very specific.  The ice must be plate-shaped hexagonal prisms in horizontal orientation- or parallel to the ground.

Contrary to popular belief, the circumzenithal arc or CZA is not a rare phenomenon; it tends to be overlooked because it appears so high above the sun.  If you’re out and happen to see sundogs, look up, way up;  the same type of ice crystal that cause sun dogs is responsible for the CZA.

Happy sky watching!

 

Chief Meteorologist

Cindy Day