Description
Cirrus clouds are characterized by thin, wispy strands. Cirrus is a Latin word which means a ringlet or curling lock of hair. Cirrus clouds form at altitudes above 5000 metres where the atmosphere is so cold that they are made entirely from ice crystals and contain on average 30 ice crystals per litre. Strong winds can blow the crystals into wispy “mares’ tails,” the common name given to cirrus clouds since the long threads of cloud resemble a mare’s tail. Ci vertebratus is a type of cirrus cloud that looks like ribs or a fishbone. Optical phenomena such as sun dogs and haloes are produced when visible light interacts with the ice crystals in cirrus clouds. Cirrus clouds are often an indication of the leading edge of a warm front and an approaching depression (area of low atmospheric pressure that produces cloudy and windy weather with precipitation). However, if cirrus clouds appear irregular and patchy, slowly shifting and often dissolving, they are indicating increasing high pressure and dry, sunny weather.