ice that is not attached to the shoreline and drifts in response to winds, currents, and other forces; some prefer the generic term drift ice, and reserve pack ice to mean drift ice that is closely packed.
pieces of new ice approximately circular, up to 10 centimeters (4 inches) thick and 0.03 to 3 meters (0.1 to 9.8 feet) in diameter, with raised edges that form from rubbing against each other; formed from the freezing together of grease ice, slush or shuga, or the reaking up of ice rind or nilas.
(Photo courtesy of the National Oceanic and Atmospheric Administration/Department of Commerce.)
(1) a term used loosely by many meteorologists for almost any meteorological quantity or element (2) an arbitrary constant or variable appearing in a mathematical expression; changing it can give various outcomes for the phenomena represented.
predominant characteristic of the weather which had existed at an observing station during a given period of time (during the preceding hour or six hours), specified in the international synop code.
a general term for any ground surface exhibiting a discernibly ordered, more or less symmetrical, morphological pattern of ground and, where present, vegetation.
A photograph taken from the air reveals patterned ground surrounding thaw lakes in Alaskas Arctic National Wildlife Refuge. Credit: U.S. Fish and Wildlife Service
a generally flat-topped expanse of peat, elevated above the general surface of a peatland, and containing segregated ice that may or may not extend downward into the underlying mineral soil.
a layer of frozen ground which forms as part of the seasonally frozen ground (in areas free of permafrost or with a lowered permafrost table); remains frozen throughout one or several summers, and then thaws.
layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C for at least several years; it exists where summer heating fails to reach the base of the layer of frozen ground.
the lower boundary surface of permafrost, above which temperatures are perennially below 0 degrees Celsius (cryotic) and below which temperatures are perennially above 0 degrees Celsius (noncryotic).
a region in which the temperature of some or all of the ground below the seasonally freezing and thawing layer remains continuously at or below 0 degrees Celsius for at least two consecutive years.
a region that is covered with sea ice year-round; most of the sea ice in the permanent ice zone is multiyear ice, but younger ice and open water may still be present; the permanent ice zone is what remains in summer after all melting has occurred (often called the summer minimum extent).