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CDIAC - Atmosphere Glossary Category: Meteorology and astronomy > Atmosphere Date & country: 13/09/2007, USA Words: 301

ocean mixing
Processes that involve rates of advection, upwelling/ downwelling, and eddy diffusion and that determine how rapidly excess atmospheric carbon dioxide can be taken up by the oceans.

opacity
The degree of obscuration of light; for example, a glass window has almost 0% opacity, whereas a concrete wall has 100% opacity.

optical thickness (optical depth)
In calculating the transfer of radiant energy, the mass of an absorbing or emitting material lying in a vertical column of unit cross-sectional area and extending between two specified levels. Also, the degree to which a cloud prevents light from passing through it; the optical thickness then depends on the physical constitution (crystals, drops, and/or droplets), the form, the concentration, and the vertical extent of the cloud.

ozone
A molecule made up of three atoms of oxygen. In the statosphere, it occurs naturally and it provides a protective layer shielding the Earth from ultraviolet radiation and subsequent harmful health effects on humans and the environment. In the troposphere, it is a chemical oxidant and major component of photochemical smog.

paleosol
An ancient soil or soil horizon that formed on the surface during the geologic past.

paludification
The expansion of a bog caused by the gradual rising of the water table as accumulation of peat impedes water drainage.

palynology
The science of reconstructing the past flora and past climate from pollen data obtained from lake and bog sediments. The fossil pollen record is a function of the regional flora and vegetation at a given time and location.

particulate matter
Very small pieces of solid or liquid matter, such as particles of soot, dust, aerosols, fumes, or mists.

past climate analogs
The reconstructing of past climates at a given locality from modern climatic conditions in a different elevation or latitudinal zone to infer past climatic conditions.

pCO2
The partial pressure of CO2 in the atmosphere and the ocean. In the atmosphere, the partial pressure of CO2 is defined as the pressure the CO2 would exert if all other gases were removed. The sum of the partial pressure of all the atmospheric gases will equal the atmospheric pressure. The partial pressure of CO2 in the atmosphere is determined by the atmospheric CO2 concentration and atmospheric temperature. In the ocean, the pCO2 is determined by the amount of dissolved CO2 and H2CO3. It varies…

percolation
The movement of water downward and radially through the subsurface soil layers, usually continuing downward to the groundwater.

permafrost
Perennially frozen ground that occurs wherever the temperature remains below 0 degrees C for several years.

phenology
The study of periodic biological phenomena with relation to climate, particularly seasonal changes. These phenomena can be used to interpret local seasons and the climatic zones.

photochemical smog
Air pollution caused by chemical reactions among various substances and pollutants in the atmosphere.

photoelectric
Of or relating to the electrical effects of light, including the emission of electrons, the generation of a voltage, or a change in resistance.

phytoplankton
That portion of the plankton community comprised of tiny plants (e.g., algae and diatoms).

planetary albedo
The fraction (approximately 30%) of incident solar radiation that is reflected by the earth-atmosphere system and returned to space, mostly by backscatter from clouds in the atmosphere.

planetary boundary layer
The transition region between the turbulent surface layer and the normally nonturbulent free atmosphere. This region is about 1 km in thickness and is characterized by a well-developed mixing generated by frictional drag as the air masses move over the Earth's surface. This layer contains approximately 10% of the mass of the atmosphere. Also called the atmospheric boundary layer or frictional layer.

plankton
Passively floating or weakly motile aquatic plants ( phytoplankton) and animals (zooplankton ).

Pleistocene
The earlier of the two epochs of the Quaternary period, starting 2 to 3 million years before the present and ending about 10,000 years ago. It was a time of glacial activity.

positive feedback
An interaction that amplifies the response of the system in which it is incorporated.

precipitation
Any or all forms of liquid or solid water particles that fall from the atmosphere and reach the Earth's surface. It includes drizzle, rain, snow, snow pellets, snow grains, ice crystals, ice pellets, and hail. The ratio of precipitation to evaporation is the most important factor in the distribution of vegetation zones. Precipitation is also defined as a measure of the quantity, expressed in centimeters or milliliters of liquid water depth, of the water substance that has fallen at a given locat…

primary productivity
See gross primary production and net primary production.

primary succession
The natural development of vegetation and soil on a site that had not previously borne vegetation (e.g., a sand dune or lava flow), which vegetation will be replaced by other, successive plant communities.

primitive equations
The Eulerian equations of fluid motion in which the primary dependent variables are the velocity components of the fluid. In meteorology, they can be specialized to apply directly to the cylonic-scale motions.

proxy climate indicators
Dateable evidence of a biological or geological phenomenon whose condition, at least in part, is attributable to climatic conditions at the time of its formation. Proxy data are any material that provides an indirect measure of climate and include documentary evidence of crop yields, harvest dates, glacier movements, tree rings, varves, glaciers and snow lines, insect remains, pollen remains, marine microfauna, isotope measurements: 18O, in ice sheets, 18O, 2H, and 13C in tree rings; CaCO3 in se…

pycnocline
In the ocean, a region where the water density increases rapidly with depth.

pyrgeometer
An instrument that measures radiation from the earth's surface into space.

Quaternary period
The latest period of geologic time, covering the most- recent 2,000,000 years of the Earth's history. It is divided into two epochs: the Pleistocene - 2 million years ago to approximately 10,000 years ago - and the Holocene - the period from approximately 10,000 years ago to the present. The Quaternary period is the artificial division of time separating prehuman and human periods. It contains five ice ages and four interglacial ages, and temperature indicators seem to show sharp and abrupt chan…

radiant flux density
The total flow of radiation received on a unit area of a given real or imaginary surface. Also called the irradiance.

radiation balance
The difference between the absorbed solar radiation and the net infrared radiation. Experimental data show that radiation from the earth's natural surfaces is rather close to the radiation from a black body at the corresponding temperature; the ratio of the observed values of radiation to black body radiation is generally 0.90 - 1.0.

radiative-convective models
Thermodynamic models that determine the equilibrium temperature distribution for an atmospheric column and the underlying surface, subject to prescribed solar radiation at the top of the atmosphere and prescribed atmospheric composition and surface albedo. Submodels for the transfer of solar and terrestrial radiation, the heat exchange between the earth's surface and atmosphere, the vertical redistribution of heat within the atmosphere, the atmospheric water vapor content and clouds are included…

radiatively active gases
Gases that absorb incoming solar radiation or outgoing infrared radiation, thus affecting the vertical temperature profile of the atmosphere. Most frequently being cited as being radiatively active gases are water vapor, CO2, methane, nitrous oxide, chlorofluorocarbons, and ozone.

radiosonde
A balloon-borne instrument for the simultaneous measurement and transmission of meteorological data up to a height of approximately 30,000 meters (100,000 feet). The height of each pressure level of the observation is computed from data received via radio signals.

recharge
The process by which water is added to a reservoir or zone of saturation, often by runoff or percolation from the soil surface.

reflectivity
The ratio of the energy carried by a wave that is reflected from a surface to the energy of a wave incident on the surface.

relative sea level
The height of the boundary between sea and air as measured in relationship to a fixed reference point on land.

reservoir
Any natural or artificial holding area used to store, regulate, or control a substance.

residence time
The size of any specific reservoir or pool of mass (e.g., carbon) divided by the total flux of mass into or out of that pool.

respiration
A biochemical process by which living organisms take up oxygen from the environment and consume organic matter, releasing both carbon dioxide and heat. In plants, the organic matter in photosynthate produced during daylight hours.

Revelle factor
The ratio of the instantaneous fractional change in the partial pressure of CO2 (pCO2) exerted by seawater to the fractional change in total CO2 dissolved in the ocean waters. The buffer factor relates the partial pressure of CO2 in the ocean to the total ocean CO2 concentration at constant temperature, alkalinity and salinity. The Revelle factor is a useful parameter for examining the distribution of CO2 between the atmosphere and the ocean, and measures in part the amount of CO2 that can be di…

rocketsonde
A rocket-borne instrument for measurement and transmission of upper-air meteorological data in the lower 76,000 meters (250,000 feet) of the atmosphere, especially that portion inaccessible to radiosonde techniques.

runoff
That part of precipitation, snowmelt, or irrigation water that flows from the land to streams or other surface waters.

salinity
The degree of salt in water.

salt water intrusion
The invasion of fresh, surface, or groundwater by salt water.

sea surface temperature
The temperature of the layer of seawater (approximately 0.5 m deep) nearest the atmosphere.

sea surface temperature anomalies
Temperature of emitted energy from the sea surface. SST anomaly = (SST - SST mean).

seasonal variation
The change in a set of meteorological parameters averaged over three months. Seasonal variation is the largest climatic variation, and temperature is the most fre- quently observed meteorological parameter. Often, monthly averaged data are grouped into seasons, according to the prescribed definition.

secular carbon dioxide trend
The fairly uniform and accelerating increase of carbon dioxide concentration in the atmosphere, as illustrated by the Mauna Loa record. The secular trend reflects the increase in global atmospheric carbon dioxide concentrations produced by combustion of fossil fuels, kilning of limestone, and possibly a net biospheric release of carbon dioxide resulting from deforestation.

sensible heat
The excess radiative energy that has passed from the Earth's surface to the atmosphere through advection, conduction, and convection processes.

shortwave radiation
The radiation received from the sun and emitted in the spectral wavelengths less than 4 ´m. It is also called solar radiation.

signal-to-noise ratio
A quantitative measure of the statistical detectability of a signal, expressed as a ratio of the magnitude of the signal relative to the variability. For first detection of a CO2-induced climate change, the model signal is the mean change or anomaly in some climatic variable, usually surface air temperature, attributed by a numerical model to increased concentrations of carbon dioxide. Observed noise is the standard deviation or natural variability computed from observations of that variable and…

silviculture
Management of forest land for timber.

smog
Air pollution associated with oxidants.

smoke
Particles suspended in air after incomplete combustion of materials.

soil carbon
A major component of the terrestrial biosphere pool in the carbon cycle. Organic soil carbon estimates, rather than total soil carbon, are generally quoted. The amount of carbon in the soil is a function of historical vegetative cover and productivity, which in turn is dependent upon climatic variables.

solar constant
The rate at which solar energy is received just outside the Earth's atmosphere on a surface that is normal to the incident radiation and at the mean distance of the Earth from the sun. The current value is 0.140 watt/cm2.

solar cycle
The periodic change in sunspot numbers. It is the interval between successive minima and is about 11.1 years.

Southern Oscillation
A large-scale atmospheric and hydrospheric fluctuation centered in the equatorial Pacific Ocean. It exhibits a nearly annual pressure anomaly, alternatively high over the Indian Ocean and high over the South Pacific. Its period is slightly variable, averaging 2.33 years. The variation in pressure is accompanied by variations in wind strengths, ocean currents, sea-surface temperatures, and precipitation in the surrounding areas. El Nino occurrences are associated with the phenomenon.

Southern Oscillation Inde
xAn indicator based on the pressure gradient between the quasi-stationary low pressure region and the center of a subtropical high pressure cell. A positive index corresponds to an anomalously high pressure difference between the two centers of action.

statistical-dynamical models
Computer programs that calculate simplified climate models based on versions of the conservation equations that have been averaged over longitude, with the effects of the synoptic eddies parameterized statistically in the meridional plane.

steric height
The mean dynamic depth (or height) of the ocean for the month minus the annual mean dynamic depth for the same isobaric reference level.

stoma, plant stomata
A minute pore in the epidermis of plant leaves or stems. Stoma, which are bordered by guard cells that regulate the size of the opening, function in gas exchange between the plant and the external environment. The stomatal apparatus or stomate consists of the stoma plus guard cells.

stratification
Separating into layers.

stratosphere
The region of the upper atmosphere extending from the tropopause (8 to 15 km altitude) to about 50 km. The thermal structure is determined by its radiation balance and is generally very stable with low humidity.

Suess effect
The relative change in the 14C/C or 13C/C ratio of any carbon pool or reservoir caused by the addition of fossil- fuel CO2 to the atmosphere. Fossil fuels are devoid of 14C because of the radioactive decay of 14C to 14N during long underground storage and are depleted in 13C because of isotopic fractionation eons ago during photosynthesis by the plants that were the precursors of the fossil fuels. Carbon dioxide produced by the combustion of fossil fuels is thus virtually free of 14C and deplete…

sunspot
A relatively dark, sharply defined region on the solar disk, marked by an umbra approximately 2000K cooler than the effective photospheric temperature, surrounded by a less dark but also sharply bounded penumbra. The average spot diameter is about 3700 km, but can range up to 245,000 km. Most sunspots are found in groups of two or more, but they can occur singly. Sunspots are cyclic, with a period of approximately 11 years. The quantitative description of sunspot activity is called the Wolf suns…

surface air temperature
The temperature of the air near the surface of the Earth, usually determined by a thermometer in an instrument shelter about 2 m above the ground. The true daily mean, obtained from a thermograph, is approximated by the mean of 24 hourly readings and may differ by 1.0 degrees C from the average based on minimum and maximum readings. The global average surface air temperature is 15 degrees C.

surface albedo
The fraction of solar radiation incident on the Earth's surface that is reflected by it. Reflectivity varies with ground cover, and during the winter months it varies greatly with the amount of snow cover (depth and areal extent). Roughness of terrain, moisture content, solar angle, and angular and spectral distribution of ground- level irradiations are other factors affecting surface albedo.

surface water
All water naturally open to the atmosphere.

swamp
A type of wetland that is dominated by woody vegetation and does not accumulate appreciable peat deposits; it may be fresh- or saltwater, and tidal or nontidal.

tephra
Any rock material produced by a volcano.

terrestrial radiation
The total infrared radiation emitted by the Earth and its atmosphere in the temperature range of approximately 200-300K. Because the Earth is nearly a perfect radiator, the radiation from its surface varies as the fourth power of the surface's absolute temperature. Terrestrial radiation provides a major part of the potential energy changes necessary to drive the atmospheric wind system and is responsible for maintaining the surface air temperature within limits for livability.

thermocline
A transition layer of water in the ocean, with a steeper vertical temperature gradient than that found in the layers of ocean above and below. The permanent ther- mocline separates the warm mixed surface layer of the ocean from the cold deep ocean water, and is found between 100- and 1000-m depths. The thermocline first appears at the 55 - 60 degree N and S latitudes, where it forms a horizontal separation between temperate and polar waters. The thermocline reaches its maximum depth at mid-latit…

thermohaline
Refers to the combined effects of temperature and salinity that contribute to density variations in the oceans.

tidal marsh
Low, flat marshlands traversed by channels and tidal hollows and subject to tidal innundation; normally, the only vegetation present are salt-tolerant bushes and grasses.

trace gas
A minor constituent of the atmosphere. The most important trace gases contributing to the greenhouse effect are water vapor, carbon dioxide, ozone, methane, ammonia, nitric acid, nitrous oxide, ethylene, sulfur dioxide, nitric oxide, dichlorofluoromethane or Freon 12, trichlorofluoromethane or Freon 11, methyl chloride, carbon monoxide, and carbon tetrachloride.

transient tracers
Chemical elements (often radioactive) or compounds that have finite lifetimes. Atmospheric testing of nuclear weapons from the mid-1950s to the early 1960s released large quantities of radionuclides to the atmosphere. Atmosphere-ocean exchange processes have transferred some of these elements to the oceans. Studying the behavior and distribution of these specific isotopes and other chemical tracers in the ocean will provide information on: residence times of the water and its dissolved component…

transpiration
The process in plants by which water is taken up by the roots and released as water vapor by the leaves. The term can also be applied to the quantity of water thus dissipated.

tree rings
Annual growth increments of trees that indicate, among other factors, the climatic conditions that enhance or limit growth. Tree ring widths and indexes have been used to search for solar-terrestrial relationships and climatic cycles and to reconstruct past climates. See also dendroclimatology and dendrochronology.

trophic level
A segment of the food chain in which all organisms obtain food and energy in, basically, the same manner (e.g., photosynthesis, herbivory, or carnivory) and in which all organisms are the same number of links from the photosynthetic segment.

tropopause
The boundary between the troposphere and the stratosphere (about 8 km in polar regions and about 15 km in tropical regions), usually characterized by an abrupt change of lapse rate. The regions above the troposphere have increased atmospheric stability than those below. The tropopause marks the vertical limit of most clouds and storms.

troposphere
The inner layer of the atmosphere below about 15 km, within which there is normally a steady decrease of temperature with increasing altitude. Nearly all clouds form and weather conditions manifest themselves within this region, and its thermal structure is caused primarily by the heating of the Earth's surface by solar radiation, followed by heat transfer by turbulent mixing and convection.

tundra
A type of ecosystem dominated by lichens, mosses, grasses, and woody plants. It is found at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and usually very wet.

turnover rate
The fraction of the total amount of mass (e.g., carbon) in a given pool or reservoir that is released from or that enters the pool in a given length of time. The turnover rate of carbon is often expressed as GtC/year.

upwelling
The vertical motion of water in the ocean by which subsurface water of lower temperature and greater density moves toward the surface of the ocean. Upwelling occurs most commonly among the western coastlines of continents, but may occur anywhere in the ocean. Upwelling results when winds blowing nearly parallel to a continental coastline transport the light surface water away from the coast. Subsurface water of greater density and lower temperature replaces the surface water, and exerts a consid…

vapor
The gaseous phase of substances that are liquid or solid at atmospheric pressure (e.g., steam).

varve
A layer of sediment deposited in lakes during one year. Each layer consists of two parts, which are deposited at different seasons and which differ in color and texture; thus, the layers can be counted and measured. In a complete series, the number of layers gives the date on which the ground was vacated by the retreating ice.

Walker cell
A zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell.

water stress effect
The closing of the stomata by a plant in response to excessive water loss through transpiration or in response to drought conditions. The stomatal closing reduces CO2 uptake as well as water loss, thus decreasing the photosynthetic rate. However, under conditions of elevated CO2 concentration, the CO2 gradient between the atmosphere and the leaf is higher than under ambient conditions, and CO2 can pass through partially closed stomates at a rate similar to that under conditions of lower CO2 and …

water table
The level of groundwater.

water vapor
Water present in the atmosphere in gaseous form; the source of all forms of condensation and precipitation. Water vapor, clouds, and carbon dioxide are the main atmospheric components in the exchange of terrestrial radiation in the troposphere, serving as a regulator of planetary temperatures via the greenhouse effect. Approximately 50 percent of the atmosphere's moisture lies within about 1.84 km of the earth's surface, and only a minute fraction of the total occurs above the tropopause.

water vapor feedback
A process in which an increase in the amount of water vapor increases the atmosphere's absorption of longwave radiation, thereby contributing to a warming of the atmosphere. Warming, in turn, may result in increased evaporation and an increase in the initial water vapor anomaly. This feedback, along with carbon dioxide, is responsible for the greenhouse effect and operates virtually continuously in the atmosphere.

water-use efficiency
A measure of the amount of water used by plants per unit of plant material produced. The term can be applied at the leaf, whole-plant, and ecosystem levels. At the leaf level, it is more precisely referred to as the instantaneous transpiration efficiency, the CO2 assimilation rate (photosynthesis) divided by the transpiration rate (the moles of CO2 taken up divided by the moles of water lost through transpiration in a unit of time per unit leaf area). At the whole-plant level, it is more precise…

weather
The instantaneous state of the global atmosphere-ocean- cryosphere system.

West Antarctic Ice Sheet
See ice sheet.

wetlands
An area that is regularly saturated by surface water or groundwater and subsequently is characterized by a prevalence of vegetation that is adapted for life in saturated-soil conditions.

zonally-averaged models
Statistical-dynamical or energy-balance models in which only the latitudinally averaged quantities are determined and the effects of the longitudinally varying transports are determined parametrically. Abbreviated as ZAM.

zooplankton
That portion of the plankton community comprised of tiny aquatic animals eaten by fish.

C3 plants
Plants (e.g., soybean, wheat, and cotton) whose carbon- fixation products have three carbon atoms per molecule. Compared with C4 plants, C3 plants show a greater increase in photosynthesis with a doubling of CO2 concentration and less decrease in stomatal conductance, which results in an increase in leaf-level water-use efficiency.