Ga-Gm

GAB

Acronym for Great Australian Bight.

GABEX I

Acronym for Georgia Bight Experiment I. See Lee and Pietrafesa (1987).

GABEX II

Acronym for Georgia Bight Experiment II. See Paffenhöfer et al. (1987).

GAGE

Acronym for Guiana Abyssal Gyre Experiment.

[http://www.aoml.noaa.gov/phod/COSTA/abstracts/miamigage.html]

GALE

Acronym for Genesis of Atlantic Lows experiment. See Bane (1989) and Lee et al. (1989).

GAME

Acronym for the GEWEX Asian Monsoon experiment, the goal of which is to understand the role of the Asian monsoon in the global climate system and develop methods for long-range forecasting.

[http://www.ihas.nagoya-u.ac.jp/game/]

GANES

[http://www.pol.ac.uk/oshi/ganes.html]

GARP

Acronym for the Global Atmospheric Research Program, planned and coordinated jointly starting in 1968 by the WMO and the ICSU.

Gaspé Current

A current in the Gulf of St. Lawrence usually recognized as a baroclinic coastal jet driven by runoff and reinforced by transverse currents from the gulf's north shore. It has a peak near surface speed of 50 cm s$^{-1}$, and a substantial fraction of the transport appears to recirculate in the northwest gulf. See Benoit et al. (1985) and Han et al. (1999).

GATE

1. Acronym for GARP Atlantic Tropical Experiment. 2. Acronym for Global Acoustic Transmission Experiment.

GBRUC

Abbreviation for Great Barrier Reef Undercurrent.

GCD

Abbrevation for General Circulation Drifter.

GCM

See general circulation model.

GCOS

Acronym for the Global Climate Observing System, a global observing program planned jointly by ICSU, WMO, UNEP, and IOC of UNESCO. It was established to develop a dedicated observing system designed specifically to meet to observation requirements for monitoring climate, detecting climate change, and for predicting climate variations and change. The objectives of GCOS are to meet the observational needs for climate system monitoring, climate change detection and response monitoring, especially in terrestrial ecosystems; data for application to national economic development; and research toward improved understanding, modeling, and predicting the climate system. A Joint Scientific and Technical Committee (JSTC) and a Joint Planning Office (JPO) were set up to develop the plans and strategy for implementation of the system. See the GCOS Web site for more information.

GDC

Abbreviation for Global Drifter Center.

GDEM

Abbreviation for General Digital Environmental Model, a four-dimensional (latitude, longitude, depth, and time) digital model of temperature and salinity for the North and South Atlantic, the Pacific, the Indian Ocean north of 40$^\circ$ S, the Arctic Ocean, the Mediterranean Sea, and the Black Sea. It consists of coefficients of mathematical expressions describing vertical profiles of temperature and salnity on a half degree latitude-longitude grid for seasonal and annual time frames, with the actual profiles generated by combining the coefficients with the equations. Some regions are being updated to 10 minute resolution. Data for creating the GDEM were obtained from the Master Oceanographic Observational Data Set (MOODS) as well as from the Levitus climatology. It is used by the U.S. Navy for most of its operational systems. See Teague et al. (1990).

GDP

Abbreviation for Global Drifter Program.

GDSIDB

Abbreviation for Global Digital Sea Ice Data Bank.

GEBCO

Acronym for GEneral Bathymetric Chart of the Oceans, a map series established by Prince Albert I of Monaco in 1903. This is at present an activity of the IOC.

[http://www.bodc.ac.uk/projects/gebco/]
[http://www.ngdc.noaa.gov/mgg/gebco/gebco.html]

GEK

Abbreviation for geomagnetic electrokinetograph.

Gelbstoff

Dissolved material in sea water that is resistant to bacterial attack. Its name comes from the yellow color it imparts to the water. Brown algae, the principal algae group growing in coastal waters of temperature and higher latitudes, excrete phenolic compounds. These polyphenols are converted into a brown polymer by secondary reactions with carbohydrates and proteins of algal origin. The properties of the resulting substance are identical with Gelbstoff. Its concentration in sea water is around 1 mg/l and it is removed mainly by precipitation since its phenolic nature renders it resistant to bacterial attack. This is also known as yellow substance or gilvin. See Riley and Chester (1971).

geodesy

A branch of applied mathematics which determines by observation and measurement the exact positions of points and the figures and areas of large portions of the earth's surface, the shape and size of the earth, and the variations of terrestrial gravity. See Torge (1991).

[http://164.214.2.59/GandG/geolay/toc.htm]

GEODYME

Acronym for Geochemistry and Dynamics of the Mediterranean, an MTP Core Sub-project whose aims are to monitor the evolution of the physical and chemical characteristics of western deep water and the detect similar changes in the different Mediterranean basins, to describe and quantify transfer processes at air-land-sea interfaces, and to give a new picture of phytoplankton distribution, new production and chemical transfers. See the GEODYME Web site.

geological oceanography

More later. Compare to biological, chemical and physical oceanography.

geoid

A hypothetical, global, and continuous sea-level surface perpendicular to the direction of gravity at all points.

geophysical model function

A function used in wind scatterometry to relate the actual measured parameter $\sigma_0$i, the normalized radar cross-section, to the near-surface wind speed and direction. At a given frequency, the function can be expressed as:

$${\sigma_0}\,=\,f(\vert U\vert,\chi ,\cdots ;\theta , p )$$

where $\sigma_0$ is the normalized radar backscatter coefficient, $\vert U\vert$ is the wind speed, $\chi$ the relative azimuth angle between the incident electromagnetic wave, $\cdots$ represents the (possibly small) effects of non-wind variables such as long waves, atmospheric stratification, water temperature, etc., $\theta$ the incidence angle, and $p$ the polarization.

There are many existing model functions that differ in various details, although some common features are shared. These include:

• at fixed incidence angle all model functions predict an increase in $\sigma_0$ with wind speed (for moderate wind speeds);
• the wind speed dependence at a fixed incidence and azimuth angle is frequently expressed as a power law; and
• for a given wind speed, $\sigma_0$ exhibits a biharmonic dependence on the wind direction.

See Naderi et al. (1991).

GEOS

Acronym for Geodynamics Experimental Ocean Satellite, a series of satellites designed exclusively for geodetic studies. They were flown as part of the National Geodetic Satellite Program. The instrumentation varied with each mission. The objectives were to:

• locate observation points (geodetic control stations) in a 3-D earth center-of-mass coordinate system within 10 m of accuracy;
• determine the structure of the earth's gravity field to 5 parts in 10 million;
• define the structure of the earth's irregular gravitational field and refine the locations and magnitudes of the large anomalies; and
• compare results of the various systems on board the spacecraft to determine the most accurate and reliable system.

GEOSAT

Acronym for Geodetic Satellite, a U.S. Navy satellite designed to measure sea surface heights to within 5 cm. It was launched on March 12, 1985 with a primary mission of obtaining a high-resolution description of the marine geoid up to latitudes of 72 degrees. This first or geodetic mission (GM) was completed 18 months after data collection began on March 30. During this mission the ground track had a near-repeat period of of about 23 days (330 revolutions in 23.07 days, average orbital period of 6039.84 sec). The GM data were initially classified but released to NOAA for public distribution in 1995.

The satellite orbit was changed at the conclusion of the GM on September 30, 1986, followed by the start of the scientific Exact Repeat Mission (ERM) on November 8, 1986. The ERM produced sea level profiles along tracks that repeated themselves within 1-2 km at intervals of about 17 days (244 revolutions in 17.05 days, average orbital period of 6037.55 sec). It covered 62 complete 17-day cycles before the failure of the second tape recorder on October 1989 terminated the mission. See Douglas and Cheney (1990).

GEOSECS

Acronym for Geochemical Ocean Sections Study, a global survey of the three-dimensional distribution of chemical, isotopic and radiochemical tracers in the ocean. It was designed to establish a baseline database for assessing future chemical changes in the world's oceans and to provide a better understanding of large-scale oceanic transport and mixing processes. The expeditions were in the Atlantic from July 1972 to May 1973 (121 stations); the Pacific from August 1973 to June 1974 (147 stations); and the Indian Ocean from December 1977 to March 1978 (141 stations). The logistics and handling of GEOSECS cruises and analyses were coordinated by SIO and directed by Arnold Bainbridge. The $^{14}$C analyses for all three oceans are summarized in Stuiver and Ostlund (1980), Ostlund and Stuiver (1980) and Stuiver and Ostlund (1983).

[http://ingrid.ldgo.columbia.edu/SOURCES/.GEOSECS/]

GEOSTAR

Acronym for Geophysical and Oceanographic Station for Abyssal Research, a project to develop an innovative deep sea benthic observatory devoted to continuous and long-term geophysical, oceanographic, and geochemical observations.

[http://web.ingv.it/~wwwgeostar/]

general circulation model

Generally a three-dimensional time-dependent model of the atmosphere and/or ocean circulation. The solution to a set of mathematical equations governing the motions of a layer of fluid on a spherical planet is numerically approximated on a three-dimensional discrete grid of points to obtain temperatures, velocities, rainfall, pressure and any of several other dependent variables that collectively comprise the state of the climate. Often abbreviated as GCM. See Washington and Parkinson (1986).

geophysical fluid dynamics (GFD)

An interdisciplinary field of study for understanding fluid flows which occur naturally, e.g. the general circulation of the atmosphere, oceanic circulations, mantle convection, and the motions which drive the geodynamo. This is accomplished through mathematical, numerical and experimental modeling.

geopotential

The potential energy per unit mass of a body due to the Earth's gravitational field as referred to an arbitrary zero reference level. A unit of geopotential is the potential energy acquired by a unit mass on being raised a unit distance in a gravitational field of unit strength.

geopotential distance

See dynamic height.

geopotential height

See dynamic height.

geopotential surface

A surface to which the force of gravity is everywhere perpendicular and equal. No work is necessary for the displacement of mass along a potential surface as long as no other forces act in addition to gravity. This can also be defined as a surface of equal dynamic height below the level of the sea surface, using the ideal sea surface level as a reference surface with the potential value 0. This has also been called a potential surface or a level surface.

geopotential thickness

See dynamic height.

geostrophy

That which is due to geostrophy.

geostrophic adjustment

The mutual adaptation of mass and momentum toward a steady geostrophic state in rotating fluids. The adjustment problem was first considered by Rossby (1938), who derived the geostrophically balanced steady end state for an ocean to which momentum is impulsively imparted. The end state always possesses less energy than the initial state, a fact due to the end state being achieved through decaying inertial oscillations which disperse energy away in pulses of Poincare waves. See Blumen (1972) and Kuo and Polvani (1997).

geostrophic approximation

The use of the geostrophic wind as an approximation to the actual wind in the equations of motion.

geostrophic balance

See geostrophy.

geostrophic current

A current resulting from geostrophy. Analogous to the geostrophic wind concept in meteorology.

geostrophic force

A virtual force used to account for the change in direction of the wind relative to the Earth's surface. It results from the Earth's rotation and the Coriolis force.

geostrophic method

A method for determining the relative geostrophic flow field in the ocean from the distribution of density in the ocean. An absolute geostrophic flow field can additionally be found with the additional assumption of a level of no motion.

geostrophic turbulence

Turbulent flow that exists in flows that are in near geostrophic balance. The physical effects of rotation and stratification provide basic constraints on the flow.

geostrophic velocity

Those velocities exhibited by geostrophic currents due to geostrophy.

geostrophic wind

The result of geostrophy in the atmosphere. Analogous to the geostrophic current in oceanography.

geostrophy

The balance between the Coriolis force and the horizontal pressure gradient that determines the first order circulation patterns in the open ocean. This balance is expected to hold for most latitudes but to break down near the equator where the local vertical component of the Coriolis force vanishes, although comparisons between geostrophic estimates and direct measurements have shown it to hold within fractions of a degree from the equator. Geostrophy allows the large scale flow of the oceans to be determined by mapping the horizontal pressure distribution, although such solutions are degenerate in that they only allow the current fields to be determined relative to an absolute reference level.

Various methods have been used to determine absolute current fields via the assumption of geostrophy. Inverse methods use constraints such as mass conservation or tracer balances to find a reference velocity for each station pair (Wunsch, 1996). A more traditional method is to find the reference velocities using geostrophy and mass conservation along with qualitative determinations of flow reversals based on tracer fields (Reid, 1989,1994,1986). Satellite altimetry is making it possible to determine the absolute height of the sea surface relative to a geoid and thus be usable as a reference level.

Gerard barrel

A barrel used to collect water samples in oceanography. It holds 250 liters of sea water.

German Deep-Sea Expedition

An investigation of the physical and biological conditions of the Atlantic and Indian oceans during 1898 and 1899 by a research team aboard the ``Valdivia.'' This expedition penetrated into the Antarctic as far as the ice would permit. The results were issued as a series of memoirs under the editorship of Chun, the leader of the expedition. See Murray and Hjort (1912), p. 16.

Gerstner wave

A wave theory developed for periodic waves of finite height to surpass the limitations of Stokes wave theory. The equations are simple to use and the solutions are exact and satisfy continuity as well as the pressure conditions at the water surface, and experimental studies have shown that the theory closely approximates the profiles of real waves on a horizontal bottom. Drawbacks include that mass transport is not predicted, the velocity field is rotational, and the particle movements are opposite to that expected in real waves (and found in other theories).

The predictions of both Gerstner and Stokes wave theories agree equally well with measured wave profiles. This is well explained by the fact that if the Gerstner wave equations are expanded into a series the first three terms are identical to those in the Stokes solution. This similarity in predictive ability and greater ease of use lead to the preferential use of Gerstner wave theory in many engineering applications where its limitations are not significant. This has also been called trochoidal wave theory since the elevation profile takes the form of a trochoidal curve. See Komar (1976) and LeMehaute (1976).

GEWEX

Acronym for the Global Energy and Water Cycle Experiment. Initiated in 1988 by the WCRP to observe and model the hydrologic cycle and energy fluxes in the atmosphere, at the land surface, and in the upper oceans. It is an integrated program of research, observations, and science activities leading to the prediction of global and regional climate change.

GEWEX hydrometeorology and land-surface projects include the GRDC, ISLSCP, GCIP, BALTEX, GAME, LBA, and MAGS. Radiation projects include the BSRN, CPRP, GPCP, GVaP, ISCCP, and SRB. Modeling and prediction projects are GCSS, G-NEP and PILPS. See the GEWEX Web site.

GDD

Abbreviation for geophysicalfluiddynamics. GeophysicalFDL.

GHCC

Abbreviation for Global Hydrology and Climate Center.

Gibb's phenomenon

An artifact of attempting to approximate a function or waveform with a discontinuity using a Fourier series or some other global, continuous basis function. The fit is poor in a region near the discontinuity, usually characterized by large oscillations within the region. Increasing the number of components in the approximation decreases the region of poor fit, which theoretically vanishes with an infinite number of components.

Gibraltar Experiment

See Kinder and Bryden (1987).

gilvin

See Gelbstoff.

GIN Sea

Abbreviation for Greenland/Iceland/Norwegian Sea, an area that has also variously been called the Norwegian Sea and the Nordic Seas. The GIN Sea together with the Polar Sea constitute the Arctic Ocean in some classification schemes (with others including the GIN Sea within the confines of the Atlantic). The former may perhaps be preferred for geomorphological as well as hydrographical reasons. The bottom is continuously oceanic in crust and depth through the connecting passage (to the north) of Fram Strait, while the southern connection is over a continental ridge, i.e. the Greenland-Scotland Ridge. Also, the deep thermohaline circulation processes of the GIN and the Polar Sea are closely linked.

The GIN Sea comprises two major basins: the Greenland Basin and the Greater Norwegian Basins (i.e. the Norwegian Basin and the Lofoten Basin) separated by the Mohn Ridge. It has six open boundaries through which important exchanges occur: Fram Strait connecting to the Polar Ocean to the north, three boundaries over the Greenland-Scotland Ridge that connect with the Atlantic Ocean, and two boundaries connecting to continental shelf seas, i.e. the North Sea and the Barents Sea. See Hopkins (1991).

Global Drifter Center (GDC)

An AOML data center located in Miami, Florida that manages the deployment of drifting buoys around the world. Global Lagrangian Drifters (GLD) are placed in areas of interest using research ships, VOS, and U.S. Navy aircraft. Once they are operationally verified, the data is telemetered to the GDS and disseminated to interested parties everywhere. See the GDC Web site.

Global Drifter Program (GDP)

A NOAA AOML program whose objectives are to: (1) described mixed-layer velocity on a 5 degree resolution global basis and produce new charts of seasonal surface circulation; (2) provide an operational data stream for SST, sea level pressure, and surface velocity data; (3) verify global climate models; (4) compute single particle diffusivities, eddy statistics, and interannual to annual variability; (5) construct models of wind-driven currents; and (6) obtain high resolution coverage in special regions for process studies. The program was started in 1978. See the GDP Web site.

Global Energy and Water Cycle Experiment

GEWEX was initiated in 1988 by the WCRP as a program designed to observe and model the hydrologic cycle and energy fluxes in the atmosphere, at the land surface, and in the upper oceans. The International GEWEX Project Office (IGPO) is the focal point for the planning and development of all GEWEX projects and activities. See Chahine (1992) and Chahine (1992) and the GEWEX Web site for further information.

Global Hydrology and Climate Center

A research center, abbreviated GHCC, whose objective is to address global hydrological processes. See the GHCC Web site.

Global Precipitation Climatology Project

A GEWEX-affiliated project, abbreviated GPCP, designed to provide global data sets of area, time-averaged precipitation for a minimum period of 10 years (1986-1995). This data will be produced by merging geostationary and polar-orbiting satellite microwave and infrared data with rain gauge data from more than 6000 stations. More information can be found at the GPCP Web site. See Arkin and Xie (1994).

Global Runoff Data Center

A GEWEX project, abbreviated GRDC, to compile a global data base of stream flow data for the development and verification of atmospheric and hydrologic models. More information can be obtained at the GRDC Web site.

Global Terrestrial Observing System

The GTOS is a global observing program planned jointly by FAO, UNESCO, ICSU, WMO, and UNEP.

GLOBEC

Acronym for Global Ocean Ecosystem Dynamics, a component of IGBP developed and sponsored by SCOR, the IOC, the ICES, and PICES. Its goal is advance our understanding of the structure and functioning of the global ocean ecosystem, its major subsystems, and its response to physical forcing to where we can develop and capability to forecast the marine upper trophic system response to scenarios of global change. GLOBEC concentrates on zooplankton population dynamics and its response to physical forcing in pursuit of this goal. See the GLOBEC Web site or the U.S. GLOBEC Web site.

globigerina ooze

A type of calcareous ooze composed of the shells of unicellular creatures called globigerina that live in the waters of warmer ocean regions. These oozes are seldom found above 5000 m depth and cover about 35% of the surface of the sea floor. See Neumann and Pierson (1966) and Tchernia (1980).

GLOCOPH

Acronym for Global Continental Palaeohydrology Project, an activity of INQUA.

GLORI

Acronym for Global Land-Ocean River Inputs database.

GLOSS

Acronym for the Global Sea Level Observing System, an IOC-coordinated project for the establishment of a strategic gloval core network of about 300 tide gauges around the world for long term climate change and oceanographic sea level monitoring. These gauges are spaced about 1000 km apart along coastlines and on oceanic islands and provide hourly-resolution standardized sea level data. See Tolkatchev (1996) and the GLOSS Web page.

GLOUP

Acronym for Global Undersea Pressure data set, a global data bank for ocean bottom pressure measurements established by a 1999 IAPSO resolution and maintained by PSMSL. The GLOUP data are archived in either high frequency (typically hourly or every 15 minutes) or daily format. The high frequency data contain the total pressure, predicted pressure from a tidal analysis, and residual pressure. The tidal analysis is performed using 63 constituents for records longer than 12 lunar months, and 55 independent and 2 related constituents for records longer than 6 lunar months. Records shorter than 25 days contain no tidal predictions or residuals. Daily values are only produced for records longer than 25 days, and contain two values for each day calculated from residual pressures from the high frequency data. The first value is a simple average of the residual pressures during that day, and the second a value filtered with a Doodson X0 filter to remove any residual signal at tidal frequencies.

[http://www.pol.ac.uk/psmslh/gloup/gloup.html]

GMP

Abbreviation for Gulf of Mexico Program.