circumhorizontal

Circumhorizontal arc is a type of ice halo that appears in the sky when the sun is high in the sky, typically between 58 and 68 degrees above the horizon. It is a rare optical phenomenon that forms when sunlight passes through plate-shaped ice crystals in cirrus clouds. These crystals are oriented horizontally, with their flat faces parallel to the ground. The light refracts through the crystals at a 90-degree angle, creating a bright, colorful arc that appears horizontally across the sky. The colors of the arc are typically red on the outside and blue on the inside, with a greenish tint in the middle. The arc is often accompanied by other ice halos, such as a parhelic circle or a 22-degree halo. Circumhorizontal arcs are most commonly observed in the summer months and are often seen in the mid-latitudes. They are a beautiful and rare sight, but they can also be a sign of severe weather, as they are often associated with thunderstorms.