Music. Tea. Justice. (Bitey mad lady with a love of physics, food, and fiction, and a hyper-literate prog rock soundtrack.)
Circumhorizontal Arc
Known in the weather world as a circumhorizontal arc, this rare sight was caught on film on June 23 as it hung over Boise, Idaho. It lasted about 1/2 hour.
The arc isn’t a rainbow — it is caused by light passing through wispy, high-altitude cirrus clouds. The sight occurs only when the sun is very high in the sky (more than 58° above the horizon). What’s more, the hexagonal ice crystals that make up cirrus clouds must be shaped like thick plates with their faces parallel to the ground.
When light enters through a vertical side face of such an ice crystal and leaves from the bottom face, it refracts, or bends, in the same way that light passes through a prism. If a cirrus’s crystals are aligned just right, the whole cloud lights up in a spectrum of colors.
Copyright: Brad Viets
Hole-Punch Clouds
A fallstreak hole, also known as a hole punch cloud is a large circular gap that can appear in cirrocumulus or altocumulus clouds. Such holes are formed when the water temperature in the clouds is below freezing but the water has not frozen yet due to the lack of ice nucleation particles. When a portion of the water does start to freeze it will set off a domino effect, due to the Bergeron process, causing the water vapor around it to freeze and fall to the earth as well. This leaves a large, often circular, hole in the cloud.*
