Which Type of Cloud Is Composed Entirely of Ice Crystals?

Identification

• Cirrus clouds appear as thin, usually white, wisplike clouds and can also often feature a curl towards the end. Their name is derived from the Latin word for curl as these clouds have an appearance that could be compared to locks of hair. Cirrus clouds appear at very high levels, around 20,000 feet above the ground, and are fast-moving due to the high wind speeds at this altitude.

Composition

• Clouds of this type are composed entirely of ice. This is due to the temperature at which they form. At altitudes of more than 20,000 feet, the temperature is around minus 36 degrees Fahrenheit. At a temperature this low, water vapor turns into ice crystals. The ice crystals that cirrus clouds are made from are responsible for their shape and appearance and they also prevent precipitation from falling from these clouds at this level.

Formation

• There is a variety of ways in which cirrus clouds may be formed. One method of formation is the freezing of water vapor that results from a warm air and cold air meeting at high altitudes. Cirrus clouds also can be formed when small amounts of lower-level clouds break away and drift into greater heights, cooling and being carried by wind to form the familiar cirrus shape. A further cause of cirrus clouds forming is when the warm condensation trails that air planes produce freeze at the cold temperature of high altitudes, creating a visible trail that can be seen from the ground.

Climate

• Cirrus clouds could potentially contribute to the greenhouse effect. They could have an impact on climate as the levels of sunlight that the Earth receives and the amount of heat that escapes back into space can be disturbed. Cirrus clouds often reflect little of the sun's energy back but trap a larger amount of heat from escaping from the Earth. Currently, organizations such as NASA are researching how far cirrus clouds could affect climate.

Subtypes

• Cirrus clouds also have subtypes, clouds possessing features of cirrus clouds and other types of clouds. One example is the cirrocumulus cloud, which are high-level clouds that are spread thinly like cirrus clouds, but feature small bunches of clouds that resemble cumulus clouds. Another subtype of cirrus clouds is the cirrostratus cloud, which is often translucent and composed of ice like cirrus clouds, but also share characteristics of stratus clouds as they are thick and can signal that snow is imminent.