Atmospheric icing

Atmospheric icing occurs in the atmosphere when water droplets freeze on objects they come in contact with. Icing conditions can be particularly dangerous to aircraft, as the built-up ice changes the aerodynamics of the flight surfaces, which can increase the risk of a stall. For this reason, on-board ice protection systems have been developed.

The effect of atmospheric icing on a tree in the Black Forest of Germany.

Water does not always freeze at 0 °C (32 °F). Water that persists in liquid state below this temperature is said to be supercooled, and supercooled water droplets cause icing on aircraft. Below −20 °C (−4 °F), icing is rare because clouds at these temperatures usually consist of ice particles rather than supercooled water droplets. Below −48 °C (−54 °F), supercooled water cannot exist, therefore icing is impossible.[1]

Icing also occurs on towers, wind turbines, boats, oil rigs, trees and other objects exposed to low temperatures and water droplets. Unmanned aircraft are particularly sensitive to icing.[2] In cold climates on land, atmospheric icing can be common as elevated terrain interacts with cold clouds.[3] Ice loads are a major cause of catastrophic failures of overhead electric power lines. Their estimation is, therefore, crucial in the structural design of power line systems[4] and can be done by numerical icing models that include meteorological data.[5]