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gradient wind

the same as geostrophic wind, but blowing parallel to curved isobars or contours; the curved airflow pattern around a pressure center results from a balance among pressure-gradient force, coriolis force, and centrifugal force.

granic cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form discrete loosely packed units.

granoidic cryogenic fabric

a distinct soil micromorphology, resulting from the effects of freezing and thawing processes, in which soil particles form more or less discrete loosely packed units.

graupel

snowflakes that become rounded pellets due to riming; typical sizes are 2 to 5 millimeters in diameter (0.1 to 0.2 inch); graupel is sometimes mistaken for hail.
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gravimetric (total) water content

the ratio of the mass of the water and ice in a sample to the dry mass of the sample, commonly expressed as a percentage.

gravity wave

a wave disturbance in which buoyancy (or reduced gravity) acts as a restoring force on parcels displaced from hydrostatic equilibrium; there is a direct oscillatory conversion between potential and kinetic energy in the wave motion.

gravity wind

a cold wind blowing down an incline; a kind of katabatic wind.

grease ice

a very thin, soupy layer of frazil crystals clumped together, which makes the ocean surface resemble an oil slick.
Grease ice (thin, light-grey area) with thick ice floes. (Photo courtesy of Ted Maksym, United States Naval Academy.)
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Greenland high

the anticyclone that appears to overlie Greenland; analogous to the antarctic anticyclone.

grey-white ice

a category of young ice 15 to 30 centimeters (6 to 12 inches) thick, named for its color.
Thin grey-white ice showing the effects of ridging and rafting. (Photo courtesy of the Antarctic Sea-Ice Processes and Climate program (ASPeCt).)
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grid

a finite collection of points to which the meteorological variables used in a numerical model, or interpolated from observations, apply; a field of such regular values (points) is termed gridded field.

ground ice

a general term referring to all types of ice contained in freezing and frozen ground.

ground moraine

continuous layer of till near the edge or underneath a steadily retreating glacier.
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growler

an iceberg less than 2 meters (6.6 feet) across that floats with less than 1 meter (3.3 feet) showing above water; smaller than a bergy bit.

hail

precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 millimeters (0.2 to 2.0 inches), or sometimes bigger, falling either separately or agglomerated into irregular lumps; when the diameter is less than about 5 millimeters (0.2 inch), the balls are called ice pellets.

halo

group of optical phenomena, in the form of rings, arcs, pillars or bright spots around the sun or moon, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere (cirrus clouds, diamond dust, etc.).

hanging glacier

a glacier that terminates at or near the top of a cliff.
Mt. Kefton, Antarctica
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hanging valley

a valley formed by a small glacier that has a valley bottom relatively higher than nearby valleys formed by larger glaciers.
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hard frozen ground

frozen ground (soil or rock) which is firmly cemented by ice.

haze

fine dust or salt particles dispersed through a portion of the atmosphere; the particles are so small that they cannot be felt or individually seen with the naked eye, but they diminish horizontal visibility and give the atmosphere a characteristic opalescent appearance that subdues all colors; a type of lithometeor.

headwall

a steep cliff, usually the uppermost part of a cirque.
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heat balance

equilibrium between the gain and loss of heat at a specific place or for a specific system.

heat balance of the earth-atmosphere system

the equilibrium that exists between the radiation received by the earth and atmosphere from the sun and that emitted by the earth and atmosphere.

heat budget

relation between fluxes of heat into and out of a given region or body and the heat stored by the system; in general, this budget includes advective, evaporative, and other terms as well as a radiation term.

heat capacity

the amount of heat required to raise the temperature of a unit mass of a substance by one degree.

heat flux

the amount of heat transferred across a surface of unit area in a unit time.

heat sink

process, or region, in which energy is removed from the atmosphere in the form of heat.

heat source

process, or region, in which energy is added to the atmosphere in the form of heat.

heaving pressure

upward pressure developed during freezing of the ground.

high

area of high pressure in the atmosphere; used interchangeably with anticyclone.

high-center polygon

an ice-wedge polygon in which melting of the surrounding ice wedges has left the central area in a relatively elevated position.

high-level clouds

typically thin, white clouds above 6,000 meters (20,000 feet); at these altitudes, temperatures are so cold that clouds are composed primarily of ice crystals; includes cirrus, cirrocumulus and cirrostratus clouds.

hoarfrost

a deposit of interlocking ice crystals (hoar crystals) formed by direct sublimation on objects, usually those of small diameter freely exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc.; the surfaces of these objects are sufficiently cooled, mostly by nocturnal radiation, to cause the direct sublimation of the water vapor contained in the ambient air.

horn

a peak or pinnacle thinned and eroded by three or more glacial cirques.
The Matterhorn in Switzerland was carved away by glacial erosion. (Photo courtesy of the World Data Center for Glaciology, Boulder, CO.)
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hostile ice

from the point of view of the submariner, an ice canopy containing no large ice skylights or other features which permit a submarine to surface.
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humidity

(1) water vapor content of the air. (2) some measure of the water-content of air; see also absolute humidity, relative humidity, specific humidity, dew point.

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