An-Az

 

anabatic wind

A local wind which blows up a slope heat by sunshine, as opposed to its converse the katabatic wind

 

Anadyr Current

A surface current that flows along the northwestern side of the Bering Sea and on through the Bering Strait. It is mostly seasonally invariant with a velocity of about 0.3 m/s. See Tomczak and Godfrey (1994).

 

analog

In signal processing this refers to a continuous physical variable which bears a direct relationship to another variable so that one is proportional to the other. An example would be the mercury level in a thermometer and its relation to the temperature, both of which vary continuously on the macroscopic level. Contrast with digital.

 

anastomosis

A cross-connection between two channels, vessels, branches, etc.

 

Andaman Sea

A body of water in the northeastern corner of the Indian Ocean that lies to the west of the Malay Peninsula, the north of Sumatra, the east of the Andaman Islands, and the south of the Irrawaddy Delta in Burma. It stretches about 650 km from west to east and 1200 km from north to south. The Andaman communicates with the westward lying Bay of Bengal through several channels between the chain of islands that stretches along 93 deg. E., including the Preparis (200 m deep), Ten Degree (800 m deep) and Great (1800 m deep) Channels. It is connected with the Australasian Mediterranean Sea via the Malacca Strait between Thailand and Sumatra. It has been variously estimated to have an area of 600,000 to 800,000 km2 and an average and maximum depth of, respectively, 870-1100 m and 4200 m.

The temperature of the surface waters fluctuates mildly from a monthly average of about 30 deg. C in the summer months to one of about 27.5 in the winter months. They drop off with depth to about 5 deg. C and 2000 m. The surface salinities exhibit strong seasonal variations due to an extremely large freshwater influx from the Irrawaddy and Salween rivers during monsoon season. In the northern part the salinities range from about 20 during the monsoon months from June to November to about 32 from Demember to May. These grade to a fairly constant 33.5 in the southwest end and to a maximum of about 35 near 1500 m depth.

The steadiest current is the inflow through the Malacca Straits, averaging around 1/3-2 knots through the year. The monsoons controls the currents elswhere, driving inflow waters from the Bay of Bengal through the western channels from June to August during the southwest monsoon. This also pushes the Malaccan inflow against the Sumatran coast and forces some Andaman sea water through the Straits. When these winds die southwestward currents gradually form that are maintained and enhanced by the northeast monsoon from December through February. A more sudden shift is seen from March through May when the southwest monsoons begins anew. See Fairbridge (1966).

 

anelastic approximation

A filtering approximation for the equations of motion that eliminates sound waves by assuming that the flow has velocities and phase speeds much smaller than the speed of sound. In its purest form, it requires that the reference state be isentropic as well as hydrostatic, although in practice the reference state is often taken to be nonisentropic which can have deleterious effects on the energy conservation properties of the full set of equations. The anelastic approximation is one of the set of approximations used for the somewhat similar Boussinesq approximation. See Ogura and Phillips (1962), Durran (1989), and Houze (1993), pp. 35-37.

 

anemogram

A continuous record of wind speed (and sometimes direction) made with an anemograph.

 

anemograph

A recording anemometer which gives a continuous record of wind speed (and sometimes direction). These were once mechanical devices (e.g. the Dines tube anemograph), but are now constructed using solid-state electronic devices.

 

anemometer

A device that measures the velocity and direction of the wind. This usually takes the form of a series of cups attached to a vertical axis, the rotation rate of which is measured and calibrated to obtain the wind speed.

 

aneroidograph

A self-recording aneroid barometer.

 

angiosperm

A vascular plant possessing true flowers with seeds in ovaries.

 

Angola-Benguela Front

A front, often abbreviated as ABF, caused by the confluence of the southward flowing Angola Current and the northward flowing Benguela Current near 16 deg. S off the African coast. This can be identified in the temperature of the upper 50 m and in the salinity to at least 200 m. See Tomczak and Godfrey (1994).

 

Angola Current

The eastern part of a cyclonic gyre centered around 13 deg. S and 4 deg. E that is driven by the South Equatorial Countercurrent in the Atlantic Ocean. This subsurface circulation gyre extends from just below the surface to around 300 m depth with velocities of about 0.5 m/s in the section nearest the African coast. The confluence between this southward flowing current and the northward flowing Benguela Current near 16 deg. S off the African coast is called the Angola-Benguela Front. See Tomczak and Godfrey (1994).

 

Angola Dome

A small cyclonic gyre, centered near 10 S and 9 E, driven by the South Equatorial Undercurrent in the eastern Atlantic Ocean. It is called a dome due to the elevation or doming of the thermocline in the middle of the gyre. See Peterson and Stramma (1991) and Tomczak and Godfrey (1994).

 

angular frequency

The repetition rate of a cyclic process measured in radians/sec. If the frequency in cycles/sec is f, then the angular frequency  =  f.

 

angular momentum

The product of mass times the perpendicular distance from the axis of rotation times the rotation velocity. The angular momentum about the Earth's axis of rotation can be expressed as the sum of the angular momentum of the solid Earth's rotation plus the angular momentum of zonal air motion relative to the surface of the Earth. Were this quantity to be absolutely conserved, a parcel of air with the angular momentum of the Earth's surface at the Equator would have a westerly zonal wind speed of 134 m/s at 30 deg. latitude. See Hartmann (1994).

 

anisotropic

Descriptor for a physical property (e.g. density, etc.) that varies depending on the direction in which it is measured.

 

anomalistic month

The interval between two successive passages of the Moon in its orbit through perigee. This is equal to 27.55455 days.

 

anomalistic year

The interval between two successive passages of the Sun, in its apparent motion, through perigee. It is equal to 365.25964 mean solar days.

 

anomalous absorption paradox

In the study of solar radiation in the atmosphere, this is a paradox whereby measurements of the absorption of solar radiation by clouds generally suggest that clouds absorb more solar energy than theoretical predictions can explain for clouds composed solely of liquid water and water vapor. One explanation offered to resolve this is that absorbing aerosols are responsible for the excess absorption. See King (1993) for a summary.

 

anomaly

In celestial mechanics, the angle between the radius vector of an orbiting body and the major axis of the orbit as measured from perihelion in the direction of motion.

 

Antarctic Air

An air mass, originating over the Antarctic continent, which is cold and dry in all seasons.

 

Antarctic Bottom Water

A type of water in the seas surrounding Antarctica with temperatures ranging from 0 to -0.8 deg. C, salinities from 34.6 to 34.7, and a density near 27.88. This is the densest water in the free ocean, with the only denser waters being found in regional sill basins such as the Norwegian Sea or the Mediterranean. It is overlain by AACW at a depth of 1000 to 2000 m [3000 m (Tchernia)] and overlies Weddell Sea Bottom Water (WSBW) in some locations. See Tomczak and Godfrey (1994), p. 153, 223, 281 and Tchernia (1980).

 

Antarctic Circle

 

Antarctic Circumpolar Current

Nothing yet.

 

Antarctic Circumpolar Water

A type of water in the seas surrounding Antarctica with temperatures ranging from 0 to 0.8 deg. C, salinities from 34.6 to 34.7 ppt, and a depth range from a few hundred meters to about 1000-2000 m [3000 m (Tchernia)] It is formed from a mixture of overlying NADW and underlying (at 1000-2000 m) AABW. It has a temperature maximum around 500-600 m and a salinity maximum between 700-1300 m. This was originally called Warm Deep Water by Deacon, but renamed AACW by Sverdrup. See Tomczak and Godfrey (1994), pp. 83, 287 and Tchernia (1980).

 

Antarctic Convergence

A region of convergence and subduction in the Southern Ocean that circles Antarctica at latitudes ranging from 47-62 deg. S. It can be identified as a relatively rapid transition is surface temperature from 1-3 deg. C in winter and 3-6 deg. C in summer. It coincides with the maximum velocity axis of the ACC and marks the change from relatively temperature climate to polar climate, and is also the limit of distribution of some marine species. See Tchernia (1980).

 

Antarctic Divergence

In physical oceanography, a region of rapid transition located in the Antarctic Zone of Southern Ocean between the Continental Water Boundary to the south and the Polar Front to the north. It can be distinguished hydrographically by a salinity maximum below about 150 m caused by the upwelling of water of high salinity, i.e. North Atlantic Deep Water. Above this the maximum is blurred by high precipitation and the melting of ice. Its position corresponds reasonably well to the demarcation between the east and west wind drifts which, in the light of Ekman dynamics, at least partially explains its divergent nature. See Tomczak and Godfrey (1994), pp. 76-79.

 

Antarctic Front

In meterology, a front which develops and persists around the Antarctic continent at about 60-65 deg. S, and divides Antarctic Air from the maritime Polar Air to the north.

 

Antarctic Intermediate Water

In physical oceanography, a type of water mass that is thought to originate mainly through convective overturning of surface waters during winter west of South America, after which it is injected into the subtropical gyre and fills the southern subtropics and tropics from the east. There is also evidence for some formation via subduction of surface waters along the Polar Front. It is characterized by a temperature near 2.2 deg. C and a salinity of about 33.8 near its formation region, but erodes by the time it reaches the Subtropical Convergence to values closer to 3 deg. C and 34.3. It can be also identified by a salinity minimum near 800-1000 m depth, which weakens and finally disappears as it progresses northwards. See Tomczak and Godfrey (1994), p. 161, 228, 287.

 

Antarctic Polar Front

See Polar Front.

 

Antarctic Surface Water

In physical oceanography, a water mass in the Antarctic Zone of the Southern Ocean SouthernOcean. It is characterized hydrographically by very low temperatures ranging down to the freezing point of -1.9 deg. C and low salinities as the result of ice melting in the summer in the upper 100-250 m of the water column. See Tomczak and Godfrey (1994), p. 82.

 

Antarctic Zone

A name given to the region in the Southern Ocean between the Polar Front to the north and the Southern ACC Front to the south. The AZ is one of four distinct surface water mass regimes in the Southern Ocean, the others being the Continental Zone (CZ) to the south and the Polar Frontal Zone (PFZ) and Subantarctic Zone (SAZ) to the north. See Orsi et al. (1995).

 

anthropogenic

Originating from human rather than natural sources.

 

anticyclone

An atmospheric pressure distribution in which there is a high central pressure relative to the surroundings. This term was selected to imply the possession of characteristics opposite to those found in a cyclone or depression. As such, the circulation about the center of an anticyclone is clockwise (counter-clockwise) in the northern (southern) hemisphere, and the weather is generally quiet and settled.

 

anticyclonic

The direction of rotation around a center of high pressure. This is clockwise in the northern hemisphere and counter-clockwise in the southern.

 

Antilles Current

More later.

 

antitriptic wind

A type of wind that occurs when the pressure gradient is balanced by the force of friction. These are the atmospheric analogs of Poisseuille flow. See Dutton (1986).

 

ANZFLUX

Acronym for the Antarctic Zone Flux experiment, the objective of which was to measure the magnitude of heat flux through the air-sea-ice interface and to describe the mechanisms that drive and control the fluxes of heat, salt and momentum. See the ANZFLUX Web site.

 

AODC

Abbreviation for Australian Oceanographic Data Centre, more about which can be found at the AODC Web site.

 

AOML

Abbreviation for the Atlantic Oceanographic and Meteorological Laboratry, a part of NOAA. See the AOML Web site.

 

AOU

Abbreviation for Apparent Oxygen Utilization, defined as the difference between the observed oxygen content and the saturation oxygen content of a sample of sea water. This is a method of estimating the amount of dissolved oxygen utilized by organisms via respiration, although it is called "apparent" for a reason. Surface waters may more than likely carry more than the saturation amount of oxygen due to the nonlinearity in the solubility of oxygen with temperature. The effects of this nonlinearity are small, though, and the AOU is usually quite close to TOU, the True Oxygen Utilization. See Broecker and Peng (1982).

 

APAR

Acronym for Absorbed Photosynthetically Active Radiation.

 

APE

1. In the thermodynamics of geophysical fluid flows, an abbreviation for available potential energy. The difference between the total potential energy when the atmosphere or ocean is baroclinically stratified and that when it has been driven into barotropic stratification by an adiabatic redistribution of mass. 2. In bioclimatology, an abbreviation for annual potential evapotranspiration. This quantity is calculated differently in various bioclimatic classification schemes.

 

APETR

An abbreviation for annual potential evapotranspiration ratio, a variable used in the Holdridge scheme for bioclimate classification. It is defined as APE/APPT, where in this scheme the APE is defined as 58.93 times ABT.

 

aphelion

That point of the orbit of a planet or comet which is farthest from the sun.

 

apogee

That point of the orbit of a satellite, natural or artificial, which is farthest from the Earth.

 

apparent polar wander

The motion of the paleomagnetic pole relative to a continent or plate. Until recently, this was hypothesized to be due solely to plate motion relative to the mesosphere, the relatively stronger and slowly deforming mantle beneath the asthenosphere, but now it is generally regarded that polar wandering affects true polar wander paths. See Gordon (1987).

 

apparent solar day

The interval between two successive transits of the true Sun over the meridian. This is not constant due to the Earth's elliptical orbit around the Sun.

 

apparent solar time

Time as measured by the apparent position of the Sun in the sky, i.e. time as would be measured by a sundial.

 

APPT

Abbreviation for average total annual precipitation, a variable used in the Holdridge scheme for classification of bioclimates. It is defined as the annual mean of monthly precipitation amounts (in mm).

 

apse line

The diameter of an elliptical orbit which pases through both foci and joins the points of greatest and least distance of the revolving body from the center of attraction.

 

Aptian

The fifth of six ages in the Early Cretaceous epoch, lasting from 119 to 113 Ma. It is preceded by the Barremian age and followed by the Albian age.

 

aquifer

A subterranean body of unconsolidated material such as sand, gravel, and soil that is saturated with water and sufficiently permeable to produce water in useful quantities.

 

Aquitanian

The first of six ages in the Mioocene epoch (the first of two in the Early Miocene), lasting from 23.7 to 21.8 Ma. It is preceded by the Chattian age of the Oligocene epoch and followed by the Burdigalian age.

 

Arabian Sea

A regional sea, centered at approximately 65 deg. E and 15 deg. N, that is bounded by Pakistan and Iran to the north, Oman, Yemen and the Somali Republic to the west, India to the east, and the greater Indian Ocean to the south. The southern boundary, from an oceanographic point of view, runs from Goa on the Indian coast along the west side of the Laccadive Islands to the equator, and thence slightly to the south to near Mombasa on the Kenyan coast. It covers an area of about 7,456,000 km .

The flow pattern in the Arabian Sea is seasonal, changing with the monsoon winds. In the northeast monsoon season (from November until March) the winds are light and the surface circulation is dominated by a weak westward, counter-monsoon flow (as an extension of the North Equatorial Current) with velocities usually under 0.2 m/s. This pattern starts in November with water supplied by the East Indian Winter Jet flowing around the southern tip of Indian and heading northwestward along the western Indian shelf.

Westward flow dominates in the southern parts until late April with the north gradually shifting into a weak anticyclonic pattern. With the advent of the southwest monsoon in April, the Somali Current and its northward extension, the East Arabian Current, both develop into strong, northeastward flowing currents by mid-May. The anticyclonic pattern in the eastern Arabian Sea is simultaneously being gradually replaced by a moderate eastward flow composed of extensions of the Somali Current and the Southwest Monsoon Current. This pattern lasts for 4-5 months, peaking in June and July at about 0.3 m/s and weakening rapidly in October as the eastward flow around southern India once again pushes northwestward.

From May to September there is strong upwelling in the East Arabian Current along Oman, accompanied by a 5 deg. C or more lowering of coastal temperatures due to the cold upwelling water. This upwelling isn't as conducive to primary production as elsewhere due to the rapidly moving current removing much of the upwelled additional biomass before it can be utilized.

 

Arafura Sea

Part of the southeastern Australasian Mediterranean Sea centered at about 10 deg. S and 137 deg. E. It is bounded by Irian Jaya and Papua/New Guinea to the north and northeast, the Timor Sea to the west, and Australia and the Gulf of Carpenteria to the south and the southeast. It is mostly a large shelf (covering about 650,000 km ) ranging from 50 to 80 m deep, although it can get as deep as 3650 m to the northwest in the Aru Basin.

There is a steady westward flow along the southern side of the Sunda Islands that is part of the larger pattern of throughflow through the Australasian Mediterranean from the Pacific to the Indian Ocean. South of this the circulation varies with the monsoon and trade winds that drive it. The deep water is renewed from the northwest via the Timor Trough.

Sea surface temperatures range from a maximum of 28.4 in Dec.-Feb. to a minimum of 26.1 in Jun.-Aug., while salinities annually range from 34.2-34.8 in the deeper parts to the north to 34.2 to 35.0 on the Arafura Shelf. See Fairbridge (1966) and Tomczak and Godfrey (1994).

 

ARC

Acronym for atmospheric radiative cooling.

 

ARCSS

Abbreviation for ARCtic System Science, an NSF global change program. The goals of ARCS are to understand the chemical, physical, biological and social processes of the arctic system that interacts with the total earth system and thus contributes to or is influenced by global change in order to advance the scientific basis for predicting environmental change on a decade to centuries time scale. See the ARCSS Web site.

 

Archean

The first of two eons in the Precambrian period, lasting from as far back as you want to go to 2500 Ma. It is preceded by a great bloody void and followed by the Proterozoic eon, and comprised of the Early (whenever-3400 Ma), Middle (3400-3000 Ma), and Late (3000-2500 Ma) eras.

 

Arctic Bottom Water

In physical oceanography, a water mass type which fills the deep basins in the Arctic Sea at depths less than 3000 m. Its formation process involves the interplay of two sources, GSDW and water from the Arctic shelf regions. The salinities of ABW are generally close to 34.95 but highest in the Canada Basin. The potential temperature in most basins is between -0.8 deg. C and -0.9 deg. C, although the Lomonossov Ridge prevents ABW colder than -0.4 deg. C from entering the Canada Basin. Its main impact in the overall ocean circulation is its contribution to the formation of NADW in the depth range between 1000 m and 4000 m. See Tomczak and Godfrey (1994), pp. 99, 282.

 

Arctic Circle

More later.

 

Arctic Ocean

More later.

 

AREP

Acronym for the Atmospheric Research and Environment Programme of the WCRP, which coordinates and fosters research on the structure and the chemical composition of the atmosphere and its related physical characteristics; the physics of weather processes and weather forecasting. The four major components of AREP are the Global Atmospheric Watch (GAW), Weather Prediction Research, Tropical Meteorology Research, and Physics and Chemistry of Clouds and Weather Modification Research. See the AREP Web site.

 

Argon-39

An isotope of argon that is useful as a tracer in ocean studies. It is a radioactive inert gas with a half life of 269 years and is produced in the atmosphere by cosmic ray interactino with Argon-40. It is well-mixed through the troposphere and its variation in concentration over the last 1000 years has been estimated to be no more than about 7%. This means that its distribution in the atmosphere and ocean is in steady state.

It enters the ocean by gas exchange with the equilibrium time between the surface mixed layer and the atmosphere being about a month. The equilibrium concentration in surface water is calculated from the solubility of argon, a well known function of temperature and salinity, and the also well known concetration of Ar-39 in the atmosphere. The surface concentration in regions of deep water formation, where the surface water may not equilibrate with the atmosphere due to rapid convection processes, can be determined from measurements. Measurement is at present an onerous process requiring 1500 liters of water, and the concentration measured is reported in % modern, i.e. the Ar-39:Ar:40 ratio of the sample divided by the Ar-39:Ar:40 ratio of the troposphere. The minimum detectable limit is about 5% modern (with an error of 3-5% modern) which corresponds to an age of 1100 years with a resolution of about 50 years.

Argon-39 is an ideal tracer for investigating mixing and circulation in the deep ocean and in the mid to lower thermocline. Its distribution is in steady state and the boundary conditions are well known, i.e. there is no flux across the ocean bottom and the surface water concentration is known everywhere. Its distribution in the ocean interior is affected only by circulation, mixing and radioactive decay process, and since the decay rate is know it serves as a clock for circulation and mixing processes. See Loosli (1983), Sarmiento (1988) and Broecker and Peng (1982).

 

ARIC

Acronym for the Atmospheric Research and Information Centre located at the Manchester Metropolitan University, a multidisciplinary center for the study and resolution of atmospheric pollution issues. See the ARIC Web site.

 

ARISTOTELES

Acronym for Applications and Research Involving Space Techniques for the Observation of the Earth's fields from Low-Earth-orbit Spacecraft.

 

ARM

Acronym for Atmospheric Radiation Measurement Program, a major program of atmospheric measurement and modeling intended to improve the understanding of processes and properties that affect atmospheric radiation, with a particular focus on the influence of clouds and the role of cloud radiative feedback. See Stokes and Schwartz (1994) and the ARM Web site.

 

ARMA

Abbreviation for autoregressive moving average, a method for constructing simple dynamical models from data.

 

ARME

Acronym for the Amazon Region Micrometeorological Experiment. See Shuttleworth (1988).

 

arrested salt wedge estuary

One of four principal types of estuaries as distinguished by prevailing flow conditions. This is a type in which there is a relatively stationary interface between an underlying stable salt wedge of sea water and an overlying strong flow of fresh river water.

 

ARTEMIS

Acronym for Africa Real Time Environmental Monitoring Using Imaging Satellites, an operational environmental monitoring program that provides real and near-real time precipitation and vegetation assessment for African, the Near East and southwest Asia based on the integrated use of high frequency Meteosat and NOAA AVHRR data. See the ARTEMIS Web site.

 

ASAD

Acronym for a Self-contained Atmospheric chemistry coDe, a package developed for integrating chemical schemes into atmospheric GCMs. It was developed by the ACMSU group of the UGAMP project. See the ASAD Web site.

 

ascending node

The point on Earth at which a satellite crosses the equatorial plane traveling from south to north.

 

ASF

Abbreviation for Atmospheric Stabilization Framework.

 

ASHOE

Acronym for Antarctic Southern Hemisphere Ozone Experiment.

 

ASLO

Acronym for the American Society of Limnology and Oceanography. Their goals are to promote the interests of limnology, oceanography and related sciences, to foster the exchange of information across the range of aquatic science, adn to facilitate investigations dealing with these subjects. More information can be found at the ASLO Web site.

 

assemblage

An aggregation of species that live together at some locality but do not relate to each other ecologically. Contrast with community.

 

assemblage biozone

In biostratigraphy, a type of biozone in which the recognition of different taxa with varying vertical ranges forms the basis for the definition, and in this case the name of the biozone itself is generally based on one of the more common members. See Briggs and Crowther (1990), pp. 466-467.

 

ASTER

Acronym for Advanced Spaceborne Thermal Emission and Reflection Radiometer, an imaging instrument that will fly on the satellite EOS AM-1. ASTER consists of three separate subsystems that operate in different spectral regions, with each system having its own telescope. The subsystems are the Visible and Near Infrared subsystem (VNIR), the Shortwave Infrared (SWIR) subsystem, and the Thermal Infrared (TIR) subsystem. See the ASTER Web site.

 

ASTEX

Acronym for the Atlantic Stratocumulus Transition Experiment. See Albrecht et al. (1995).

 

asthenosphere

The layer of the Earth below the lithosphere, characterized by lower strength, lesser rigidity and greater density than the overlying layer. These qualities lead to the process of isostatic adjustment taking place here as well as the generation of magma and the attenuation of seismic waves. It is approximately 200 km thick.

 

ASTRAIA

See ELDORA.

 

ASW

See Arctic Surface Water.

 

ATEX

Acronym for the Atlantic Trade-wind Experiment. See Albrecht (1981).

 

Atlantic Ocean

Much more later.

 

Atlantic-Indian Basin

One of three major basins in the Southern Ocean. It extends from its western border with the Pacific-Antarctic Basin at the Scotia Ridge and Drake Passage (at about 70 deg. W) to its eastern border with the Australian-Atlantic Basin at the Kerguelan Plateau (about 75 deg. E). It consists of the Enderby and Weddell Abyssal Plains and is bounded to the north below 4000 m by the Mid-Atlantic and South-West Indian Ridges except for deeper connections into the Argentine Basin in the western Atlantic and into the deep basins of the western Indian Ocean.

 

Atlantic period

A post-LGM European climate regime. This refers to the period from about 6000-3000 BC that spans most of the warmest postglacial times. It is also known as the Postglacial Climatic Optimum. It was preceded by the Boreal period and followed by the Sub-Boreal period. See Lamb (1985), p. 372.

 

ATM

Abbreviation for Atmospheric Transport Model.

 

ATMOS

The Atmospheric Trace Molecule Spectroscopy experiment is an infrared spectrometer (a Fourier transform interferometer) designed to study the chemical composition of the atmosphere. This instrument is carried and used on the Space Shuttle. Measurements are made at the times in each orbit during which the atmosphere is between the Sun and the ATMOS instrument. Rapid successive measurements are taken to distinguish changes in the composition of specific molecules with altitude. This is accomplished by analyzing the absorptions due to each molecule in each successive spectrum. See the ATMOS Web site.

 

atmospheric electrical circuit

A proposed method for measuring global temperatures that uses the relationship between global thunderstorm activity and the mean global temperature. Thunderstorms lead to an electrification of the fair-weather atmosphere, and it is known that thunderstorm activity is nonlinearly related to temperature. It has been suggested that a 1% increase in global temperature may lead to a 20% increase in the ionospheric potential. Such measurements may be complicated by changes in atmospheric composition and by changes in atmospheric dynamics, e.g. El Nino and ancillary phenomena. See Karl et al. (1995).

 

atmospheric radiative cooling

The combination of the net radiative energy flux at the top-of-the-atmosphere (TOA) with the net radiative energy flux at the Earth's surface. This is the net effect of infrared emission by the atmosphere, the absorption by the atmosphere of infrared emitted by the Earth's surface, and the absorption by the atmosphere of solar radiation. To a first approximation, the ARC is balanced by latent heat release, which suggests that the globally averaged precipitation rate is determined by radiative processes. See Wielicki et al. (1995).

 

atmospheric tide

Those oscillations in any atmospheric field whose periods are integral fractions of either a lunar or a solar day. These differ from ocean tides in several ways, one of which is that atmospheric tides are excited not only by the tidal gravitational potential of the sun and moon but also (and to the larger extent) by daily variations in solar heating. Another difference is that the atmosphere is a spherical shell and thus there are no coastal boundaries to worry about. Finally, the response of the atmosphere to tidal forcing is by means of internal gravity waves rather than the barotropic surface waves of the sea. See Lindzen (1971).

 

ATOC

Abbreviation for Acoustic Thermometry of Ocean Climate.

 

atmospheric stabilization

A term used to describe the limiting of the concentration of the greenhouse gases at a certain level.

 

atoll

One of three geomorphologically distinct types of coral reefs, the other two being fringing reefs and barrier reefs. An atoll is an annular reef formed around a subsiding volcanic island. See Barnes and Hughes (1988).

 

ATSR

Abbreviation for Along-Track Scanning Radiometer microwave sounder, a satellite-borne instrument designed to measure land and ocean surface temperatures. The ATSR is a passive two-channel radiometer that scans the near-infrared and middle-infrared bands with a spatial resolution of 1 km x 1 km and a swath width of 500 km. It views the Earth from an orbit of about 800 km and can measure ocean temperature to within 0.3 deg. C. The ATSR can be used to detect exceptional local incidents, large scale changes, and general trends in the Earth's climate. See the ATSR Web site.

 

attribution problem

The problem of establishing a causal link between changing greenhouse gas emissions and changes in climate, i.e. of establishing that changes in anthropogenic emissions are required to explain satisfactorily a detected change in climate. There is a nonzero chance that a change thus detected could indeed be due to non-anthropogenic causes, and the only way to decrease this possibility is via a systematic numerical investigation of the system's response to various combinations of possible climate forcing changes. Unique attribution of a detected climate change to anthropogenic causes would require the explicit specification of the climate change signals of all possible competing mechanisms (individually and in combination), and statistical determination that none of these mechanisms could satisfactorily explain the detected change.

 

austausch coefficient

A German term for a quantity equivalent to the eddy viscosity coefficient.

 

Australian-Antarctic Basin

One of three major basins in the Southern Ocean. It extends from its eastern boundary with the Pacific-Antarctic Basin at the longitude of Tasmania (at about 145 deg. E) to the Kerguelan Plateau (at about 75 deg. E). The South-East Indian Ridge separates it from the Indian Ocean at depths greater than 4000 m except for a gap in the Ridge at 117 deg. E.

 

Australasian Mediterranean Sea

The region on either side of the equator between the islands of the Indonesian archipelago. This has the most complicated topography of any of the regional seas of the world, consisting of a series of deep basins with limited interconnections, each characterized by its own type of bottom water of great age. The basins comprising this include the Banda, Sulawesi (formerly Celebes), Molucca, Halmahera, Serman, Sulu, Flores, Java and Sawu Seas, with the Banda being the largest and deepest.

The net transport is believed to be westward at all times, from the Pacific to the Indian Ocean, with a maximum in August (estimated at 12-20 Sv) and a minimum in February (estimated at 2-5 Sv). It takes the form of a western boundary current that is strongest along Mindanao and and Kalimantan. The transport also occurs mainly in the upper layers with little transport below 500 m and about 75% above 150 m. Most of the high salinity input occurs across the sill between the Pacific and the Sulawesi Sea, while most of the low salinity output is through various narrow passages between the south Indonesian islands, with both input and output occurring over the entire water depth over the sills.

The freshening of the throughput occurs due to both high freshwater input from seasonal precipitation and to strong turbulent mixing that effects water mass conversion in the upper 1000 m of the water column, with the turbulence probably due to locally strong tidal currents. This mixing process imparts a unique character to the Australasian Mediterranean in that the salinity field in the upper 1000 m is nearly homogeneous while the temperature field is still stratified. This occurs because even though both temperature and salinity are strongly mixed the intense solar heating in the region serves to maintain the temperature stratification. See Tomczak and Godfrey (1994).

 

authigenic

One of three major components of deep sea sediments, the other two being detrital and biogenic. Authigenic minerals are those formed by spontaneous crystallization within the sediment or water column, and make up only a small fraction of the total sediment volume. The most important of this type of sediment is the iron-manganese oxide material formed by reduction of these metals deep in the sediment column. The resultant material migrates upwards and is deposited in the oxygenated upper layers of sediment. It can also be produced as a by-product of hydrothermal activity near ridge crests. See Broecker and Peng (1982).

 

autoconversion

In cloud microphysics, the rate at which cloud water content decreases as particles grown to precipitation size by coalescence and/or vapor diffusion. See Houze (1993).

 

autocorrelation

The mathematical process of calculating the correlation coefficient between a time series and the same series with a lag of a number of sampling intervals. The variation of this correlation coefficient as a function of the lag provides information on the existence of periodic fluctuations in the series.

 

autoecology

The ecology of an individual species.

 

autotrophic

Descriptive of a phytoplankton species that is able to satisfy its dietary requirements from purely inorganic sources.

 

autotrophic respiration

The form of respiration by which CO2 is released by the metabolic processes of plants.

 

autovariance

A term used in respect to climate change to denote the capacity of the global climate to fluctuate of its own accord without the need for extraterrestrial (e.g. solar variations, orbital variations, etc.) influences.

 

autumnal equinox

See equinox.

 

auxotrophic

Descriptive of a phytoplankton species unable to grow without a supply of a specific organic compounds, e.g. vitamin B12, which they are unable to produce for themselves.

 

available potential energy

The part of the total potential energy of the atmosphere available for conversion into kinetic energy by adiabatic redistribution of its mass so that the density stratification becomes everywhere horizontal.

 

AVHRR

Abbreviation for Advanced Very High Resolution Radiometer, a five channel scanning radiometer with channels in the visible, visible near infrared, and infrared water vapor window. These were selected for production of quantitative sea surface temperature products and visible and IR imagery depicting clouds and thermal features, e.g. the Gulf Stream. The AVHRR produces 1 km resolution data.

 

AVIRIS

Acronym for Airborne Visible Infrared Imaging Spectrometer, an instrument that flies aboard a NASA ER-2 airplane (a U2 modified for increased performance). It is an optical sensor that delivers iamges of the upwelling spectral radiance in 224 contiguous spectral channels in wavelengths ranging from the infrared (400 nm) to the ultraviolet (2500 nm). It flies at about 20 km at about 730 km/hr. The main scientific objective of the instrument is to identify, measure, and monitor constituents of the Earth's surface and atmosphere based on molecular absorption and particle scattering signatures. See the AVIRIS Web site.

 

AVNIR

Acronym for Advanced Visible and Near-Infrared Radiation, a visible and near-infrared radiometer designed to measure land and coastal zones with high spatial resolution. It measures solar light reflected by the Earth's surface in order to monitor such environmental phenomena as vegetation and desertification. It has a spatial resolution ranging from 8 to 16 m and a swatch width of about 80 km and will fly on the ADEOS mission.

 

AWI

Abbreviation for Alfred Wegener Institute.

 

azimuth

The horizontal angle between the observer's meridian and the line joining observer and object. This is conventionally measured from north through east in astronomical computations and from south through west in triangulation and precise traverse work.

 

azoic zone

Term used to describe the part of the deep sea thought lifeless in the mid-19th century. It was thought that the abyss was filled with a thick layer of 4 deg. C (since sea water was thought to be densest at that temperature), motionless water which, combined with the tremendous pressures and absence of sunlight, virtually guaranteed an absence of life. The term was coined by the naturalist Edward Forbes in the 1840s who, after dredging for life forms in various regions, postulated eight bands or depth zones, each characterized by a particular assemblage of animals. These zones extended to a lower limit he set at about 300 fathoms below which he existence of life was highly unlikely. His results (and therefore perceptions) on this issue were skewed by an 1841 cruise in the eastern Mediterranean where he dredged for life forms at depths up to 230 fathoms in what is now known to be a relatively barren area. The contrast of this with the rich hauls he made in shallower waters around England led to his thinking the abyss devoid of life. See Schlee (1973).

 

Azores Current

The northern branch of the subtropical gyre in the North Atlantic Ocean. This carries around 15 Sv of water along 35-40 N to the western part of the gyre, i.e. the Canary Current.

 

Azores High

A center of action centered near the Azores Islands (near 35 deg. N and 25 deg. W). It extends from near the western end of the Mediterranean Sea westward almost to Florida in the summer months, with the western section in summer sometimes referred to as the Bermuda High. See Angell and Korshover (1974).

 

Azov, Sea of

A large gulf or lagoon, centered at about 46 deg. N and 37 deg. E, connected to the Black Sea by the narrow and shallow (around 5 m sill depth) Kerch Strait. The Sea of Azov covers around 38,000 sq. km which comprises 9% of the area of the Black Sea system but only 0.5% of the volume.