Atmospheric icing occurs in the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

when water droplets suspended in air freeze on objects they come in contact with. It is not the same as

freezing rain Freezing rain is rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow or ice pellets, freezing rain is made entirely of liquid droplets. The rain ...

, which is caused directly by precipitation.

Icing conditions In aviation, icing conditions are atmospheric conditions that can lead to the formation of water ice on an aircraft. Ice accretion and accumulation can affect the external surfaces of an aircraft – in which case it is referred to as ''airframe ...

can be particularly dangerous to

aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...

, as the built-up ice changes the

aerodynamics Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...

of the flight surfaces and airframe, which can increase the risk of a stall and potentially accidents. For this reason, on-board ice protection systems have been developed on aircraft intended to fly through these conditions.

Water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

does not always freeze at . Water that persists in liquid state below this temperature is said to be

supercooled Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crysta ...

, and supercooled water droplets cause icing on aircraft. Below , icing is rare because clouds at these temperatures usually consist of ice particles rather than supercooled water droplets. Below , supercooled water always freezes; therefore, icing is impossible. Icing also occurs on

tower A tower is a tall structure, taller than it is wide, often by a significant factor. Towers are distinguished from masts by their lack of guy-wires and are therefore, along with tall buildings, self-supporting structures. Towers are specific ...

wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. ...

boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats. Small boats are typically found on i ...

s, oil rigs, trees and other objects exposed to sub-freezing temperatures and water droplets. Unmanned aircraft are particularly sensitive to icing. In cold climates on land, atmospheric icing can be common in winter as elevated terrain interacts with cold clouds as these can freeze en masses on mountain slopes. Ice loads are a major cause of catastrophic failures of overhead electric power lines when icing accumulates and breaks them from shear weight. Their estimation is, therefore, crucial in the structural design of power line systems to withstand ice loads and can be done by numerical icing models and examples that include meteorological data.Makkonen, L. (2000) Models for the growth of rime, glaze, icicles and wet snow deposits on structures. Philosophical Transactions of the Royal Society of London A, 358 (1776): 2913-2939.

References

;Sources
FAA (U.S.) Advisory Circular 20-113
Pilot Precautions and Procedures to be taken in Preventing Aircraft Reciprocating Engine Induction System and Fuel System Icing Problems
FAA (U.S.) Advisory Circular 20-117
Hazards Following Ground Deicing and Ground Operations in Conditions Conducive to Aircraft Icing
FAA (U.S.) Advisory Circular 20-147
Turbojet, Turboprop, and Turbofan Engine Induction System Icing and Ice Ingestion

Icing on wind turbines

External links

Airline Regulators Grapple With Engine-Shutdown Peril

WSJ ''The Wall Street Journal'' is an American business-focused, international daily newspaper based in New York City, with international editions also available in Chinese and Japanese. The ''Journal'', along with its Asian editions, is published ...

April 7, 2008 *
Supercooled liquid water and airframe icing
{{Authority control Precipitation

See also

References

External links