Cirrus ( Lat. 'wisp of hair') is a type of cloud.Cirrus clouds are composed of ice crystals and shaped like hairlike filaments. They are formed at an altitudes above 5000 metres (16,500 feet). The streaks are made of snowflakes that are falling from the cloud and being caught by the high level winds. The streaks point in the direction of the wind and may appear straight giving the clouds the appearance of a comma ( cirrus uncinus), or may by seem tangled, an indication of high level turbulence. The snowflakes from cirrus clouds invariably evaporate before reaching the ground.Cirrus clouds contribute to the earth's greenhouse effect and its albedo (the amount of sunlight the earth reflects). It is not known for certain if the net effect of cirrus clouds is to warm or cool the earth. Much of the difficulty lies in modelling the albedo effect of clouds composed of various size and shape crystals. Older models tended to underestimate the albedo effect of cirrus. Refinements of these models will improve climate predictions.If there are many cirrus clouds in the sky it may be a sign that a frontal system is approaching. Cirrus clouds can also be the remnants from a thunderstorm.
Gallery - 
