Saturday, January 24, 2009
"Sea Ice Data.....Around Newfoundland"
More to ice than meets the eye may be an understatement. As I was reading up on sea ice I discovered new terminology and the "Egg Code" which is used to describe ice concentration, the stage of ice and the size of ice floes using coded numbers. At first I found it a bit difficult but wih some practise I was able to gain a very, very basic understanding of the concept. I found it an extremely interesting exercise none-the-less.
Sea-ice types New: A general term for recently formed ice which includes frazil ice, grease ice, slush and shuga. These types of ice are composed of ice crystals which are only weakly frozen together (if at all) and have a definite form only while they are afloat.
Grey: Young ice 10-15 cm thick. Less elastic than nilas and breaks on swell. Usually rafts under pressure.
Grey-white: Young ice 15-30 cm thick. Under pressure it is more likely to ridge than to raft.
Thin first-year: First-year ice of not more than one winter's growth, 30-70 cm thick.
Medium first-year: First-year, ice 70-120 cm thick.
Thick first-year: First-year ice over 120 cm thick.
Old ice: Sea ice which has survived at least one summer's melt. Topographic features generally are smoother than first-year ice. May be subdivided into second-year ice and multi-year ice.
Second-year ice: Old ice which has survived only one summer's melt.
Multi-year ice: Old ice which has survived at least two summer's melt.
New: Recently formed ice less than 5 cm thick.
Thin: Ice of varying colours, 5-15 cm thick.
Medium: A further development of floes or fast ice, 15-30 cm thick.
Thick: Ice 30-70 cm thick.
Very Thick: Floes or fast ice developed to more than 70 cm thickness.
Arrangement of the ice
Ice drift: Caused by the combined action of the wind and water current's drag on the ice. Expressed in units of kilometres per day (km/d). Terms used are descriptive: slow or light, moderate, rapid, and variable.
Ice growth: Caused by the freezing of water by cold air, and its rate will depend on the air temperature, wind conditions, and water salinity. Terms used are descriptive: little or no ice growth, slow or light, moderate, and rapid.
Ice melt: Caused by the melting of ice by warm water or warm air. Terms used are descriptive: slow or light, moderate, and rapid.
Ice pressure: Caused by compaction of ice floes under the influence of wind or water currents, forming ice deformation of several forms (fractures, hummocks, ridges, rafting). Terms used are descriptive: light, moderate, strong.
The ratio expressed in tenths describing the amount of the water surface covered by ice as a fraction of the whole area.
Ice free: No ice present. If ice of any kind is present, this term shall not be used.
Open water: A large area of freely navigable water in which ice is present in concentrations less than 1/10. No ice of land origin is present.
Drift ice/Pack ice: Term used in a wide sense to include any area of ice, other than fast ice, no matter what form it takes, or how it is disposed. When concentrations are high, i.e., 7/10 or more, drift ice may be replaced by the term pack ice.
Very open drift: Ice in which the concentration is 1/10 to 3/10 and water dominates over ice.
Open drift: Floating ice in which the concentration is 4/10 to 6/10, with many leads and polynyas. Floes generally not in contact with one another.
Close pack: Floating ice in which the concentration is 7/10 to 8/10, composed of floes mostly in contact with one another.
Very close pack: Floating ice in which the concentration is 9/10 to less than 10/10.
Compact ice: Floating ice in which the concentration is 10/10 and no water is visible.
Consolidated ice: Floating ice in which the concentration is 10/10 and the floes are frozen together.
The following terms are used in ice messages and forecasts to describe the distribution of ice in a given area.
Ice cake: Any relatively flat piece of ice less than 20 m across.
Ice Openings: Includes all forms of fractures and cracks.
Crack: Any fracture of fast ice, consolidated ice, or a single floe which may have been followed by separation ranging from a few centimetres to 1 m.
Strips: Long narrow area of drift ice, about 1 km or less in width, usually composed of small fragments detached from the main mass of ice, which run together under the influence of wind, swell or current.
Ice edge: The demarcation at any given time between the open water and sea, lake or river ice whether fast or drifting. May be termed compacted or diffuse.
Iceberg concentrations and limits
Isolated: No more than one iceberg per degree of latitude and longitude.
Scattered: Two to four icebergs per degree of latitude and longitude.
Many: Five to ten icebergs per degree of latitude and longitude.
Numerous: More than 10 icebergs per degree of latitude and longitude.
Limit of all known icebergs: The limit at any given time between iceberg infested waters (with or without sea ice) and ice-free waters.