pilvöpiirroot

Pilvöpiirroot is a rare atmospheric optical phenomenon that occurs when sunlight passes through ice crystals in the atmosphere at a specific angle. It is a type of cloud illumination, similar to halos and circumhorizontal arcs.

During a pilvöpiirroot event, the sun appears as a diffuse ring with a bright center. The ring's brightness decreases towards the edges, creating a crescent-shaped appearance. The color of the sun is not changed, but the ring of light surrounding it has a characteristic white or grayish hue.

Pilvöpiirroot is often confused with other optical phenomena, such as circumhorizontal arcs or ice halos. However, the unique ring-shaped appearance of the pilvöpiirroot sets it apart from these other effects. Pilvöpiirroot can occur when the sun is low on the horizon and ice crystals in the atmosphere are aligned at the same angle, typically between 22 and 42 degrees.

This optical phenomenon is relatively rare, as it requires very specific atmospheric conditions. The elongated ice crystals must be evenly spaced and oriented in a particular direction. Visual observations of pilvöpiirroot require a low sun angle and a terrain with the right characteristics to view the phenomenon clearly. Pilvöpiirroot has been observed in regions with frequent ice crystal formation, but no comprehensive record of its frequency is available.