The Cirrus

We are going to talk about one of the high clouds par excellence, the cirrus or cirrus. They are separate clouds in the form of delicate white filaments, or narrow white or almost white banks or bands. These clouds have a fibrous appearance, similar to the hair of a person, or of a silky shine or of both characteristics at the same time.

They are made up of tiny ice crystals, since they are formed at a high altitude (8-12Km.). At these levels the temperature ranges from -40º to -60ºC, so that a mass of air, with a high content of water vapor and that is cooled to saturation, produces ice crystals instead of water droplets. The formation of this type of cloud is due to the fact that these crystals, driven by the strong winds, which prevail at high levels, form the characteristic shreds with which they appear in the skies. Be careful not to confuse them with the Cirrostratus. The latter always produce a halo phenomenon.

Regarding the state of the weather to which they are associated, it can be said that when they appear isolated they are a sign of good weather, but if they advance organized and progressively increasing towards the horizon (as in the photo) they indicate an imminent time change, some front or squall. Transverse to the wind indicate a jet stream in height.

We will give a few tips in case any reader wants to photograph this type of cloud. You have to know that they offer their best light at an angle of 90º with the sun. Use polarizing filter to bring out the white of the Cirrus and darken the sky blue. Include earth references. At sunset, the rays of the sun below the horizon make, by refraction, the Cirrus first turn yellow, then orange, then red, pink, to end up being gray. This order is exactly the reverse at sunrise.

In the Cirrus they are distinguished 4 species (Fibratus, Uncinus, Spissatus and Floccus) and 4 varieties (Intortus, Radiatus, Vertebratus and Duplicatus).

Source: AEMET