Cirrostratus cloud
A high, thin, sheetlike cloud composed mainly of ice crystals. It often covers much of the sky and produces halos around the Sun or Moon.
Ice crystal: A solid water particle with a crystalline structure. Cirrostratus consists mainly of these crystals, which scatter and refract light.
Cloud classification: A system for grouping clouds by their form, altitude, and other observable characteristics. Cirrostratus is identified by its high altitude and thin, veil-like form.
Cirrostratus fibratus: A cirrostratus species with fine, fibrous streaks that may cover much of the sky. Its fibrous texture is one recognized appearance of cirrostratus.
Warm front: A boundary where a warm air mass advances over a colder air mass. A spreading veil of cirrostratus can appear ahead of an approaching warm front.
Halo (optical phenomenon): A ring or arc of light produced when sunlight or moonlight interacts with ice crystals in the atmosphere. Hexagonal ice crystals in cirrostratus commonly refract light into 22-degree halos.
High-level cloud: A cloud that forms in the upper troposphere, where temperatures are generally below freezing. Cirrostratus belongs to the high-level cloud group and is largely ice-crystal based.
Cirrostratus nebulosus: A uniform, featureless sheet of cirrostratus with little visible internal structure. This species shows the smooth veil-like form commonly associated with the genus.
Cloud forecasting: The use of cloud types and changes to infer present or approaching weather. Increasing cirrostratus can signal a broad, advancing weather system, though it is not conclusive alone.
Refraction: The change in a wave’s direction as it passes between materials with different refractive properties. Refraction through ice crystals bends light into the angles that form halos.
Troposphere: The lowest layer of Earth’s atmosphere, where most weather and clouds occur. Cirrostratus forms in the troposphere’s cold upper region.