Glossary
Glossary | |
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| Term | Definition |
| AAQS | Ambient Air Quality Standards: Health- and welfare-based standards for outdoor air which identify the maximum acceptable average concentrations of air pollutants during a specified period of time. (See also CAAQS and NAAQS and Criteria Air Pollutant.) |
| abatement | The reduction or elimination of pollution. |
| ablation | (1) combined processes (such as sublimation, fusion or melting, evaporation) which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes (2) reduction of the water equivalent of a snow cover by melting, evaporation, wind and avalanches. |
| ablation area | the area of a glacier where more glacier mass is lost than gained. |
| ablation hollows | depressions in the snow surface caused by the sun or warm, gusty wind. |
| ablation moraine | mound or layer of moraine in the ablation zone of a glacier; the rock has been plucked from the mountainside by the moving glacier and is melting out on the ice surface. |
| ablation season | period during which glaciers lose more mass than they gain; usually coincides with summer. |
| ablation zone | area or zone of a glacier where snow and ice ablation exceed accumulation. |
| absolute humidity | (1) the ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air (2) mass of water contained in a unit volume of moist air. |
| Acceptable Daily Intake | The highest daily amount of a substance that may be consumed over a lifetime without adverse effects. |
| accretion | growth of a cloud or precipitation particle by the collision and union of a frozen particle (ice crystal or snowflake) with a super-cooled liquid droplet which freezes on impact. |
| accumulation | all processes by which snow or ice are added to a glacier, this is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack. |
| accumulation area | area of a glacier where more mass is gained than lost. |
| accumulation season | period during which a glacier gains more mass than it loses; usually coincides with winter. |
| accumulation zone | area of a glacier where more mass is gained than lost. |
| accuracy | the extent to which the readings of an instrument approach the true value of the calculated or measured quantities, supposing that all possible corrections are applied. |
| Acid Deposition | A comprehensive term for the various ways acidic compounds precipitate from the atmosphere and deposit onto surfaces. It can include: 1) wet deposition by means of acid rain, fog, and snow; and 2) dry deposition of acidic particles (aerosols). |
| acid precipitation | rain or snow containing acidic substances, resulting from the atmospheric pollution mainly with sulfur and nitrogen; acid precipitation has a lower pH than unpolluted rain. |
| acid rain | Rain which is especially acidic (pH <5.2). Principal components of acid rain typically include nitric and sulfuric acid. These may be formed by the combination of nitrogen and sulfur oxides with water vapor in the atmosphere. |
| active air-cooled thermal pile | a foundation pile on which a cold air refrigeration system has been installed to remove heat from the ground. |
| active construction methods in permafros | special design and construction methods used for engineering works in permafrost areas where permafrost degradation cannot be prevented. |
| active ice wedge | an ice wedge that is growing as a result of repeated (but not necessarily annual) winter cracking. |
| active layer | the layer of ground that is subject to annual thawing and freezing in areas underlain by permafrost; also known as seasonal frost. |
| active liquid refrigerant pile | a foundation pile on which a liquid coolant refrigeration system has been installed to remove heat from the ground. |
| active rock glacier | a mass of rock fragments and finer material, on a slope, that contains either an ice core or interstitial ice, and shows evidence of present movement. |
| active thermokarst | the process by which characteristic landforms are currently developing as a result of thawing of ice-rich permafrost or melting of massive ice. |
| active-layer failure | a general term referring to several forms of slope failures or failure mechanisms commonly occurring in the active layer overlying permafrost. |
| active-layer thickness | the thickness of the layer of the ground that is subject to annual thawing and freeing in areas underlain by permafrost. |
| acute exposure | One or a series of short-term exposures generally lasting less than 24 hours. |
| acute health effect | A health effect that occurs over a relatively short period of time (e.g., minutes or hours). The term is used to describe brief exposures and effects which appear promptly after exposure. |
| add-on control device | An air pollution control device such as carbon absorber or incinerator that reduces the pollution in exhaust gas. The control device usually does not affect the process being controlled and thus is "add-on" technology, as opposed to a scheme to control pollution through altering the basic process itself. |
| adfreeze | the process by which two objects are bonded together by ice formed between them. |
| adfreeze strength | the tensile or shear strength which has to be overcome to separate two objects that are bonded together by ice. |
| ADI | Acceptable Daily Intake: The highest daily amount of a substance that may be consumed over a lifetime without adverse effects. |
| adsorber | An emissions control device that removes VOCs from a gas stream as a result of the gas attaching (adsorbing) onto a solid matrix such as activated carbon. |
| advance | when a mountain glacier's terminus extends farther downvalley than before; glacial advance occurs when a glacier flows downvalley faster than the rate of ablation at its terminus. |
| advection | the horizontal transfer of air mass properties by the velocity field of the atmosphere. |
| advection fog | fog which forms in the lower part of a warm moist air mass moving over a colder surface (land or water). |
| adverse health effect | A health effect from exposure to air contaminants that may range from relatively mild temporary conditions, such as eye or throat irritation, shortness of breath, or headaches to permanent and serious conditions, such as birth defects, cancer or damage to lungs, nerves, liver, heart, or other organs. |
| aerosol | Non-gaseous substances, divided into solid particles or liquid droplets, held in suspension in the atmosphere. Particles of solid or liquid matter that can remain suspended in air from a few minutes to many months depending on the particle size and weight. |
| afterburner | An air pollution abatement device that removes undesirable organic gases through incineration. |
| aggradational ice | the additional ground ice formed as a direct result of permafrost aggradation. |
| agricultural burning | The intentional use of fire for vegetation management in areas such as agricultural fields, orchards, rangelands, and forests. |
| air | So called "pure" air is a mixture of gases containing about 78 percent nitrogen; 21 percent oxygen; less than 1 percent of carbon dioxide, argon, and other gases; and varying amounts of water vapor. See also ambient air. |
| air basin | A land area with generally similar meteorological and geographic conditions throughout. To the extent possible, air basin boundaries are defined along political boundary lines and include both the source and receptor areas. California is currently divided into 15 air basins. |
| air freezing index | the cumulative number of degree-days below 0° C for the air temperature during a given time period. |
| air mass | an extensive body of the atmosphere in which physical properties, particularly temperature and humidity, exhibit only small and continuous differences in the horizontal plane; it may extend over an area of several million square kilometers and over a height of several kilometers. |
| air monitoring | Sampling for and measuring of pollutants present in the atmosphere. |
| air pollutant | Amounts of foreign and/or natural substances occurring in the atmosphere that may result in adverse effects to humans, animals, vegetation, and/or materials. (See also air pollution.) |
| air pollution | Degradation of air quality resulting from unwanted chemicals or other materials occurring in the air. (See also air pollutants.) |
| Air Quality Index | A numerical index used for reporting severity of air pollution levels to the public. It replaces the formerly used Pollutant Standards Index (PSI). Like the PSI, the AQI incorporates five criteria pollutants -- ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide -- into a single index. The new index also incorporates the 8-hour ozone standard and the 24-hour PM2.5 standard into the index calculation. AQI levels range from 0 (Good air quality) to 500 (Hazardous air quality). The higher the index, the higher the level of pollutants and the greater the likelihood of health effects. The AQI incorporates an additional index category -- unhealthy for sensitive groups -- that ranges from 101 to 150. In addition, the AQI comes with more detailed cautions. |
| Air Quality Management District | A group of counties or portions of counties, or an individual county specified in law with authority to regulate stationary, indirect, and area sources of air pollution within the region and governed by a regional air pollution control board comprised mostly of elected officials from within the region. |
| air temperature | the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation, or placed in an instrument shelter 1.5 to two meters above ground; also called surface temperature. |
| air thawing index | the cumulative number of degree-days above 0°C for the air temperature during a given period. |
| air toxics | A generic term referring to a harmful chemical or group of chemicals in the air. Substances that are especially harmful to health, such as those considered under U.S. EPA's hazardous air pollutant program or California's AB 1807 and / or AB 2588 air toxics programs, are considered to be air toxics. Technically, any compound that is in the air and has the potential to produce adverse health effects is an air toxic. |
| Airborne Toxic Control Measure | A control measure adopted by the ARB (Health and Safety Code Section 39666 et seq.), which reduces emissions of toxic air contaminants. |
| airshed | A subset of air basin, the term denotes a geographical area that shares the same air because of topography, meteorology, and climate. |
| alas | a large depression of the ground surface produced by thawing of a large area of very thick and exceedingly ice-rich permafrost. |
| albedo |
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| Alberta low | a low centered on the eastern slope of the Canadian Rockies in the province of Alberta, Canada. |
| Aleution low | the low pressure center located near the Aleutian Islands on mean charts of sea level pressure during the winter; it represents one of the main centers of action in the atmospheric circulation of the northern hemisphere. |
| alpine | refers to high mountain areas above the timber line (where trees cease to inhabit extremely cold environments). |
| alpine glacier | a glacier that is confined by surrounding mountain terrain; also called a mountain glacier.  Muddy River Glacier carves its way through forested mountains near Frederick Sound in southeast Alaska. Typical of mountain glaciers, it is constrained on all sides by mountainous terrain. (Photo courtesy of U. S. Navy. Archived at the World Data Center for Glaciology, Boulder, CO.) |
| alpine layers | annual accumulations of snow and dust on a glacier. |
| alternative fuel | Fuels such as methanol, ethanol, natural gas, and liquid petroleum gas that are cleaner burning and help to meet ARB's mobile and stationary emission standards. These fuels may be used in place of less clean fuels for powering motor vehicles. |
| altitudinal limit of permafrost | the lowest altitude at which mountain permafrost occurs in a given highland area outside the general permafrost region. |
| altitudinal zonation of permafrost | the vertical subdivision of an area of mountain permafrost into permafrost zones, based on the proportion of the ground that is perennially cryotic. |
| altocumulus | a principal middle level cloud type (cloud genus), white or gray, or both white and gray, which occurs as a layer or patch with a wave aspect, the elements of which appear as laminae, rounded masses, rolls, etc; these elements usually are sharply outlined, but they may become partly fibrous or diffuse; they may or may not be merged, and they generally have shadowed parts; most of the regularly arranged altocumulus elements have an apparent width of 1 - 5 degrees. |
| altostratus | a principal middle level cloud type (cloud genus) in the form of a grayish (gray) or bluish cloud sheet or layer of striated, fibrous, or uniform appearance, totally or partly covering the sky; the layer has parts thin enough to reveal the position of the sun; halo phenomena do not usually occur. |
| ambient air | The air occurring at a particular time and place outside of structures. Often used interchangeably with "outdoor air." |
| Ambient Air Quality Standards | Health- and welfare-based standards for outdoor air which identify the maximum acceptable average concentrations of air pollutants during a specified period of time. (See also CAAQS and NAAQS and Criteria Air Pollutant.) |
| ammonia | NH3: A pungent colorless gaseous compound of nitrogen and hydrogen that is very soluble in water and can easily be condensed into a liquid by cold and pressure. Ammonia reacts with NOx to form ammonium nitrate -- a major PM2.5 component in the Western United States. |
| anabatic wind | any wind blowing up a steep incline or mountain; the opposite of katabatic wind. |
| analysis | in synoptic meteorology, a detailed study of the state of the atmosphere over a particular region based on the actual observations. |
| anchor ice | submerged ice which is attached to the bottom. |
| anemometer | an instrument which measures wind speed or wind speed and direction; a cup anemometer measures the wind speed from the speed of rotation of a windmill which consist of 3 or 4 hemispherical or conical cups, each fixed to the ends of horizontal arms attached to a vertical axis; a byram anemometer is a variety of the cup anemometer; a counting anemometer has cups or a fan whose rotation is transmitted to a technical counter which integrates directly the air movement speed; a hand anemometer is small portable anemometer held at arm's length by an observer making a wind speed measurement; a pressure tube anemometer (dines anemometer) is an instrument which derives wind speed from measurements of the dynamic wind pressures - wind blowing into a tube develops a pressure greater than the static pressure, while wind blowing across a tube develops a pressure less than the static, this pressure difference is proportional to the square of the wind speed. |
| anemorumbograph | a Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed. |
| anemorumbometer | a Russian anemograph (recording anemometer) which is equipped with a device to record the wind direction in addition to wind speed. |
| aneroid barometer | an instrument for measuring atmospheric pressure; it is constructed on the following principles: an aneroid capsule (vidie capsule, which is a thin, disk-shaped box or capsule, usually metallic) is partially evacuated of gas, and is restrained from collapsing by an external or internal spring; the deflection of the spring will be nearly proportional to the difference between the internal and external pressures; magnification of the spring deflection is obtained both by connecting capsules in series and by mechanical linkages. |
| anomaly | deviation of a meteorological quantity value in a given region from the normal (mean) value for the same period. |
| antarctic circle | the line of latitude 66° 34′ S (often taken as 66.5° S); along this line the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice. |
| antarctic polar front | also known as the antarctic convergence; the southern front of the antarctic circumpolar current that separates the antarctic zone in the south from the polar frontal zone in the north; taken by many to delineate the actual northern boundary of the antarctic zone; characterized by sea surface temperatures near 5°–6° C and a salinity minimum of 33.8–34.0 psu produced by high rainfall. |
| antarctic zone | the region between the antarctic circle (66° 34′ S) and the South Pole; climatically, the limit of the zone may be set at about 60° S, poleward of which the prevailing westerly winds give place to easterly or variable winds; over most of this region the average temperature does not rise above 0°C (32°F) even in summer. |
| anti-icing | the prevention of ice accumulation of aircraft, ships and other objects; the most common measures are heating or applying a dressing by brush or spray to weaken adhesion and facilitate removal. |
| anti-syngenetic ice wedge | an ice wedge that grows progressively downwards into a receding slope, in a direction normal (perpendicular) to the surface. |
| anticyclone | area of increased atmospheric pressure relative to surrounding pressure field in the atmosphere; it is outlined by closed isobars on a synoptic surface chart, and by closed contours on a constant-pressure chart; this term is used interchangeably with high. |
| anticyclonic circulation | system of air movements (atmospheric circulation) associated with an anticyclone, which is clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere. |
| apparent heat capacity | the amount of heat required to raise the temperature of a unit mass of frozen ground by one degree. |
| approximate freezing index | the cumulative number of degree-days below 0 degrees Celsius for a given time period, calculated from the mean monthly temperatures for a specific station without making corrections for positive degree-days in spring and fall. |
| approximate thawing index | the cumulative number of degree-days above 0 degrees Celsius for a given time period, calculated from the mean monthly temperatures for a specific station without making corrections for negative degree-days in spring and fall. |
| AQI | Air Quality Index: A numerical index used for reporting severity of air pollution levels to the public. It replaces the formerly used Pollutant Standards Index (PSI). Like the PSI, the AQI incorporates five criteria pollutants -- ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide -- into a single index. The new index also incorporates the 8-hour ozone standard and the 24-hour PM2.5 standard into the index calculation. AQI levels range from 0 (Good air quality) to 500 (Hazardous air quality). The higher the index, the higher the level of pollutants and the greater the likelihood of health effects. The AQI incorporates an additional index category -- unhealthy for sensitive groups -- that ranges from 101 to 150. In addition, the AQI comes with more detailed cautions. |
| AQMD | Air Quality Management District: A group of counties or portions of counties, or an individual county specified in law with authority to regulate stationary, indirect, and area sources of air pollution within the region and governed by a regional air pollution control board comprised mostly of elected officials from within the region. |
| arctic | (from Greek arktikos which means northern) northern polar region of the earth which includes almost the whole area of the Arctic Ocean and adjacent areas of Eurasian and North American continents. |
| arctic air mass | mass of very cold air in the arctic regions which invades lower latitudes at irregular intervals. |
| arctic circle | the line of latitude 66 degrees 34 minutes N (often taken as 66.5 degrees N); along this line, the sun does not set on the day of the summer solstice, and does not rise on the day of the winter solstice. |
| arctic front | (1) the semi-permanent, semi-continuous front between the deep, cold arctic air and the shallower, basically less cold polar air of northern latitudes (2) south boundary of the arctic air mass. |
| arctic haze | haze in arctic regions which reduces horizontal and slant visibility and which may extend to a height of about 10 km; it appears blue-grey when viewed away from the sun, and reddish-brown toward it. |
| arctic high | a weak high which appears over the arctic basin during late spring, summer and early autumn; one of the centers of action in the atmosphere. |
| arctic mist | a mist of ice crystals; a very light ice fog. |
| arctic oscillation | an atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes (about 45 degrees N) on time scales ranging from weeks to decades; the oscillation extends through the depth of the troposphere, and from January to March, it extends upward into the stratosphere where it modulates in the strength of the westerly vortex that encircles the arctic polar cap region; the north atlantic oscillation and arctic oscillation are different ways of describing the same phenomenon. |
| Glossary V2.0 | |
