A type of fog, composed of suspended particles of ice, partly ice crystals 20 to 100 m in diameter, but chiefly, especially when dense, droxtals 12-20 m in diameter. It occurs at very low temperatures
, and usually in clear, calm weather in high latitudes. The sun is usually visible and may cause halo phenomena. Ice fog is rare at temperatures warmer than -30C, and increases in frequency with decreasing temperature until it is almost always present at air temperatures of -45C in the vicinity of a source of water vapor. Such sources are the open water of fast-flowing streams or of the sea, herds of animals, volcanoes, and especially products of combustion for heating or propulsion. At temperatures warmer than -30C, these sources can cause steam fog of liquid water droplets, which may turn into ice fog when cooled ( see frost smoke). (Also called ice-crystal fog, frozen fog, frost fog, frost flakes, air hoar, rime fog, pogonip.)
A suspension of numerous minute ice crystals in the air, reducing visibility at the earth's surface; the crystals often glitter in the sunshine; ice fog produces optical phenomena such as luminous pil
lars and small haloes.
A type of fog composed of suspended particles of ice or ice crystals 20 to 100 microns resulting from the freezing of tiny supercooled water droplets. Ice fog occurs in clear, calm, stable air when te
mperatures are -30
Sea ice firmly frozen to the shore at the high-tide line and unaffected by tide. This type of fast ice is formed by the freezing of seawater during ebb tide and of spray. It is separated from the floa
ting sea ice by a tide crack; in many areas it offers a fairly level, continuous route for surface travel.
Describes the predicted position of ice boundaries and expected ice phenomena (ice concentration, distribution, stage of development, thickness and direction of drift, number and size of icebergs) for
a specified period and for a specified locality, based on forecast meteorological and oceanographic conditions and the regional ice climatology. An ice forecast is often issued to cover the period between the current ice analysis and the next scheduled ice analysis.
Ice formation can occur on aircraft either on the ground or in flight. Ice accretion in flight may constitute a danger by affecting the aerodynamic characteristics, engine performance, or in other way
s. There are four types of airframe icing: 1) rime: a light, white opaque deposit that forms generally at temperatures well below 0C in clouds of low water content, consisting of small supercooled water droplets; 2) clear ice or glaze: a coating of clear ice that forms in clouds of high water content consisting of large (greater than 40 m in diameter) supercooled water droplets in the form of drizzle or rainfall on aircraft with a temperature near or below 0C; 3) mixed ice or cloudy ice: a rough, cloudy deposit that occurs in clouds containing a large range of drop sizes or a mix of ice crystals, cloud droplets, and snowflakes; and 4) hoarfrost: a white crystalline coating of ice that forms in clear air by deposition of water vapor when an aircraft surface is colder than the frost point of the air; this can occur when an aircraft moves rapidly (usually in descent) from very cold air into a region with warm and relatively moist air.