Cryosphere glossary
nilas
a thin sheet of smooth, level ice less than 10 centimeters (4 inches) thick; appear darkest when thin.
Image
Nilas are the dark sheets of ice near the bottom of the photo.
Ted Maksym, United States Naval Academy
nimbostratus
a principal cloud type (cloud genus); gray and often dark; rendered diffuse by more or less continuously falling rain, snow, sleet, etc. of the ordinary varieties and not accompanied by lightning, thunder, or hail; precipitation in most cases reaches the ground; may or may not merge with low, ragged clouds that frequently occur below.
nip
ice is said to nip when it forcibly presses against a ship which is beset; a vessel so caught, though undamaged, is said to have been nipped.
noncryotic ground
soil or rock at temperatures above 0 degrees Celsius.
nonsorted circle
a patterned ground form that is equidimensional in several directions, with a dominantly circular outline which lacks a border of stones.
nonsorted net
a patterned ground with cells that are equidimensional in several directions, neither dominantly circular nor polygonal, and lacking borders of stones.
nonsorted polygon
a patterned ground form that is equidimensional in several directions, with a dominantly polygonal outline which lacks a border of stones.
nonsorted step
a patterned ground feature with a step-like form and a downslope border of vegetation embanking an area of relatively bare ground upslope.
nonsorted stripe
form patterned ground with a striped and nonsorted appearance, due to parallel strips of vegetation-covered ground and intervening strips of relatively bare ground, oriented down the steepest available slope.
North American high
the relatively weak general area of high pressure which, as shown on mean charts of sea-level pressure, covers most of North America during winter; this pressure system is not nearly as well-defined as the analogous Siberian high.
North Atlantic Oscillation
an oscillation in the strength of the Icelandic Low and Azores High, the two dominant surface pressure features in the North Atlantic. When both are unusually strong, the North Atlantic Oscillation (NAO) is in its positive phase; when both are unusually weak, it is in its negative phase. The NAO has climate impacts not just in the Arctic, but in North America and Europe. The NAO, identified by Sir Gilbert Walker in the 1920s, is similar to the Arctic Oscillation.
north pole
90° N latitude; one of the two points where the Earth's axis of rotation meets the Earth's surface (the other being the south pole, diametrically opposite).
nunatak
a rocky crag or small mountain projecting from and surrounded by a glacier or ice sheet.
observation
a weather or meteorological observation is an evaluation of one or more meteorological elements that describes the state of the atmosphere either at the earth's surface or aloft.
observational network
a group of stations (surface meteorological, upper-air, or other) spread over a given area for making regular observations.
ogives
alternate bands of light and dark ice seen on a glacier surface.
Image
Ogives, Juno Icefield, Alaska
old ice
sea ice more than 2-years-old, up to 3 meters (10 feet) or more thick; hummocks on old ice are even smoother than in second-year ice, and the ice is almost salt-free; when old ice is bare of snow, it is blue and lacks the greenish tint of second-year ice.
old snow
deposited snow whose transformation into firn is so far advanced that the original form of the ice crystals can no longer be recognized.
onshore permafrost
permafrost occurring beneath exposed land surfaces.
open lead
a lead that connects two open bodies of water; ships can traverse between them through this lead; it also refers to a lead where open water is found, or a lead that has not completely frozen.