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In-Iz

INAMHI
Abbreviation for Instituto Nacional de Meteorología e Hidrología, located in Ecuador.

INDEA
Acronym for Inlet and Nearshore Dynamics Experiment: Algarve. See the INDEA Web site.

INDEX
Acronym for Indian Ocean Experiment, which took place from 1976-1979.

independent variable
See dependent variable.

Indian Central Water (ICW)
See Poole and Tomczak (1999).

Indian monsoon
The seasonal reversal of the wind direction along the shores of the Indian Ocean, especially in the Arabian Sea. The winds blow from the southwest during half of the year and from the northeast during the other half. The reversal of direction (from that due to the normal zonal circulation pattern) is due to the effects of differential heating as the Himalayan plateau heats up during the summer, causing the air to rise and be replaced by the warm, moist air from over the Indian Ocean.

Indian Ocean
Much, much more later. See Sparrow et al. (1996), Stramma and Lutjeharms (1997), Shetye and Gouveia (1998) and Ganachaud et al. (2000).

INDIGO
Acronym for the Indien Gaz Ocean project, a series of three cruises taking place aboard the RV Marion Dufresne from 1985-1987. The INDIGO 14C activities are available from the CDIAC.

INDOEX
Acronym for Indian Ocean Experiment, a project whose goal is to study natural and anthropogenic climate forcing by aerosols and feedbacks on regional and global climate. It will incorporoate field studies where pristine air masses from the southern Indian Ocean including Antarctica and not-so-clean air from the Indian subcontinent meet over the tropical Indian Ocean to provide a unique natural laboratory for studying aerosols.

[http://www-indoex.ucsd.edu/]

INDOMED Expedition
A research expedition taking place from 1977-1979. See Scripps Institution of Oceanography (1979b).

Indonesian throughflow
See Godfrey (1996).

INDOPAC Expedition
See Scripps Institution of Oceanography (1978).

Indo-Pacific Deep Water
See Yu et al. (1996).

inertial circles
The paths followed by inertial waves.

inertial dissipation method
An observational technique for inferring the ocean surface wind stress magnitude. See Fairall and Larsen (1986) and Geernaert (1990).

inertial frequency
The frequency f of rotation of inertial waves.

inertial motion
See inertial wave.

inertial oscillation
See inertial wave.

inertial wave
A limiting form of a long Poincare wave that oscillations at the inertial frequency. In this limit the effects of gravity are negligible and the fluid particles are moving under their own inertia, whence the name. See Webster (1968) and Gill (1982).

infragravity wave
More later.

infralittoral zone
The third (from the top) of seven zones into which the benthos has been divided. This has also been called the inner sublittoral zone. See Fairbridge (1966).

infrared
That part of the electromagnetic radiation spectrum from approximately 0.75 to 1000 $ \mu$m. This is between the visible and microwave regions of the spectrum. It is further divided into the near (0.75 to 1.5 $ \mu$m), intermediate (1.5 to 20 $ \mu$m), and far (20 to 1000 $ \mu$m) ranges. Most of the energy emitted by the Earth and its atmosphere is at infrared wavelengths, and it is generated almost entirely by large-scale intramolecular processes. The tri-atomic gases such as water vapor, CO2, and ozone absorb infrared radiation and play important roles in the propagation of infrared radiation in the atmosphere.

inland sea
A sea surrounded by land and connected to the open ocean by one or more narrow straits. Examples include the Baltic Sea, the Red Sea, and the Black Sea. Compare to epeiric sea and epicontinental sea.

INMARSAT
Acronym for International Maritime Satellite Organization.

inner sublittoral zone
See infralittoral zone.

INO
Abbreviation for Institute for Naval Oceanography.

INOUT
A part of JONSDAP 76.

INPOC
Acronym for Subarctic North Pacific Hydrographic Surveys, a cooperative program among Russia, the U.S. and Canada from 1991-1993 that addressed the variability of the circulation in the subpolar and northern subtropical gyres of the North Pacific.

[http://sam.ucsd.edu/inpoc/inpoc.html]

inshore
The zone or portion of a beach profile extending seaward from the foreshore to just beyond the breaker zone. See Komar (1976).

Inshore Countercurrent
One of the two narrow, poleward-flowing boundary currents in the California Current system (the other being the California Undercurrent). The IC has been reported as a seasonal flow, appearing in fall and winter. It is found over both the shelf and slope and transports shallow, upper ocean waters derived largely from CC waters with some modification by coastal processes. This is sometimes called the Davidson Current or Davidson Inshore Current at locations north of Point Conception. See Collins et al. (2000).

Inshore Peru Current
The name sometimes given to the combination of the Chile Coastal Current (CCC) and the Peru Coastal Current (PCC).

in situ data
Data associated with reference to measurements made at the actual location of the object or material measured, by contrast with remote sensing (i.e., from space).

insolation
The radiation received from the Sun.

INSROP
Acronym for International Northern Sea Route Project, a program organized by the Fridtjo Nansen Institute in Norway.

instrument error
An error that is a function of the instrument design and the ambient conditions under which it must operate. For example, the mercury barometer for surface (not mean sea level) pressure measurements has an expected instrument error of about 0.25 mb for a single reading due to ambient temperature and wind effects. See Daley (1991).

instrumental data
This refers to data, e.g. temperatures, rainfall amounts, atmospheric pressure, etc., that have been gathered via direct measurement as opposed to proxy data. Most of these records (at least the reliable ones) are on the order of a hundred years or less in duration, with perhaps the longest being a temperature record for central England prepared by Manley (1974) that extends back to 1659.

INTECMAR
Acronym for Instituto de Tecnología y Ciencias Marinas, located in Venezuela.

intensive parameter
A determining parameter of a system that does not depend on the size and mass of the system, e.g. temperature, pressure, and concentration, as opposed to an extensive parameter.

interbasin exchange
In physical oceanography, the active exchange of waters and/or water mass properties between basins. Evidence for this process is provided by the similarities in water masses in the three major oceans despite quite different water mass conversion processes in each. The three avenues for this in the world ocean are: the Bering Strait, which provides a conduit for North Pacific-North Atlantic exchange via the Arctic Ocean; passes in the Indonesian Archipelago, which connect the Indian and Pacific Oceans at low latitudes; and the Southern Ocean, in which the ACC flows through several broad passages between Antarctica and the other southern hemisphere continents. The conveyor belt paradigm was the first attempt to tie these together into a unified theory of interbasin circulation.

The most up-to-date scenario for these interbasin circulation processes starts with 14 Sv of upper and intermediate level water being converted to NADW in the North Atlantic and flowing southward across the equator to join the ACC. This loss from the Atlantic is compensated by 10 Sv of upper level entering via the Drake Passage and 4 Sv entering from the Indonesian throughflow through the Australasian Mediterranean and around Africa. The Indian Ocean receives 24 Sv of lower level cold water from the ACC, returning 14 Sv as cold water and transforming 10 Sv to upper level water. This latter 10 Sv flows south of Australia, across the South Pacific, and through the Drake Passage into the Benguela Current regime. This joins the afore mentioned Indonesian Throughflow, crosses the equator, and flow with the Gulf Stream into the North Atlantic to replace the lost NADW. The Pacific takes 20 Sv of cold water from the ACC and returns it as less cold water, with about half of it traversing the North Pacific.

This is a simplified two-layer version of a more complicated four-layer circulation scheme developed by Schmitz (1995) which includes intermediate and upper layer compensations flows as well as abyssal and deep interbasin thermohaline circulation layers. The greatest uncertainties remain in the Indian and Pacific Oceans, especially with the flows associated with vertical exchange, which in itself is perhaps the least well established feature of ocean circulation.

interferometer
A device, e.g. imaging radar, that uses two different paths for imaging and deduces information from the coherent interference between the two signals. Paths with spatial and temporal differences have been used to measure, respectively, terrain height and ocean currents.

intermediate models
A class or group of equations that have been formulated in an attempt to extend the formal validity of the quasi-geostrophic equations while also avoiding the complications of the full primitive equations. The usual approaches attempt to extend the quasigeostrophic or planetary geostrophic equations. This is done by either proceeding to a higher order in an asymptotic expansion (or similar procedure) in the Rossby number (or some other small parameter) or by attempting to extend the validity of the equations at their lowest order. A disadvantage of the former approach is that it does not extend the regime of validity of the new equations beyond that of the lowest order system. The latter approach, usually less mathematically formal, attempts to include terms neglected or inaccurately approximated in the original equations which restrict their range of applicability. These include terms involving large variations in depth, Coriolis parameter, and the advection of relative vorticity. The ultimate goal is to develop a set of equations valid for both planetary and synoptic scales. See Mundt et al. (1997).

internal Froude number
See Froude number.

internal tide
Internal waves somehow excited at or near tidal periods. It is generally accepted that these are generated by energy scattered from surface to internal tides by bottom roughness. See Hendershott (1981), p. 329.

internal wave
A gravity wave propagating in the interior of the ocean with typical spatial and temporal scales of kilometers and hours. The amplitudes are on the order of 10 meters, much larger than their surface counterparts.

Internal waves can be classified according to the density distribution of the fluid in which they propagate:

Peter Rhines reviewed recent progress in understanding internal waves (at the APROPOS conference). His remarks give some of the overall flavor of internal wave research from 1970-2000:

Internal wave research reached a feverish pitch in the 1970s as an appreciation for the spectrum of observed waves was gained, and weak interaction theory produced useful results about the production of turbulent mixing, and induction of mean currents. The theory of critical-layer absorption and reflection (where the mean flow speed U equals the phase speed, c, of the wave in the direction of mean flow) showed us how such interactions can also be "strong", and localized in space. Generally, the power of geometrical optics (ray theory) was demonstrated in wholly new classes of problems. Attention then drifted toward nonlinear waves that are outside of the random-phase approximation of triad interaction theory: solitary waves and undular bores for example. Inverse-scattering theory allowed one to trace uniquely the distribution of solitons emerging from complex initial conditions. This gives one of many examples where a significant GFD discovery (here traceable back to Scott-Russell riding along canals in Victorian England on horseback ) radiated outward into many areas of physics and engineering.

See LaFond (1962), Cox (1962), Baines (1986), Roberts (1975), Briscoe (1975a) and Munk (1981).

International Hydrographic Bureau
More later.

International Hydrographic Organization
More later.

International Indian Ocean Expedition (IIOE)
A research program under which scientists of twenty-two nations collected data in the Indian Ocean from 1959-1965. This was done under a plan coordinated by the Scientific Committee on Oceanographic Research (SCOR) of UNESCO. See Currie (1966).

International Year of the Ocean (IYO)
The United Nations declared 1998 to be the International Year of the Ocean with the overall objective being to focus and reinforce the attention of the public, governments and decision makers at large on the importance of the oceans and the marine environment as resources for sustainable development.

[http://ioc.unesco.org/iyo/]

Irish Marine Institute
A national agency of Ireland whose mission is to undertake, coordinate, promote and assist in marine research and development and provide such services related to ma rine research and development that, in the opinion of the institute, will promote economic development and create employment and protect the environment. See the IMI Web site.

Iselin, Columbus O'Donnell (1904-1971)
See Stommel (1993) (reprinted in first volume of Stommel's collected works).

ISMARE
Acronym for Irish Marine Data Center, a part of the Irish Marine Institute that collects, manages, processes, quality controls, and archives data collected by Irish institutions. See the ISMARE Web site.

International Ship Operators (ISO)
An open international forum of research ship operators from 14 countries and representatives of EC, FAO and OCEANIC who meet annually to discuss research fleet barter/exchange arrangements and research fleet status as well as report on staff exchanges and lost equipment. See the ISO Web site.

Intertropical Convergence Zone
A narrow low-latitude zone in which air masses originating in the northern and southern hemispheres converge and generally produce cloudy, showery weather. Over the Atlantic and Pacific it is the boundary between the northeast and southeast trade winds. The mean position is somewhat north of the equator, but over the continents the range of motion is considerable. Often abbreviated as ITCZ.

intransitive
In dynamical systems theory, a system is said to be intransitive if different sets of initial conditions evolve to more than one alternative resultant state. Compare to transitive and almost intransitive. See Lorenz (1979).

INTIMATE
Acronym for INTegration of Ice-core, MArine and TErrestrial data for the North Atlantic region from 25 to 9 ka BP. The goal of this INQUA project is to integrate data sets from ice-core, marine and land records to produce a series of paleoenvironmental maps for the interval between the Last Glacial Maximum and the Early Holocene. The primary objective is to study the ice-sea-land-atmosphere interactions and the feedbacks operating during a glacial-interglacial transition. See Walker et al. (2001).

[http://www.geog.uu.nl/fg/INTIMATE/]

intrinsic frequency
See buoyancy frequency.

inventory-box model technique
A method for analyzing transient tracer data where a time dependent box model is used to simulate the inventory or mean concentration of a tracer in a prescribed reservoir. The model is driven by the time dependent surface water concentration and parameters representing exchange times or volume transports are determined by fitting the model to observations. See Sarmiento (1988).

inverse methods
More later.

inverted echo sounder (IES)
An instrument used to monitor oceanic fronts since Rossby (1969) first introduced the concept of using variations in acoustic travel time to measure changes in the depth of the main thermocline. They were initially deployed in the MODE project and have been used extensively in many other regions. The use of an IES requires calibration of travel time measurements into other scientific quantities of interest, with calibration requiring knowledge of the variations in temperature and salinity stratification and the resulting density and sound speed profiles in the region where the IES is to be deployed. See Watts and Rossby (1977).

IOC
Abbreviation for Intergovernmental Oceanographic Commission, a UNESCO commission that focuses on promoting marine scientific investigations and related ocean services, with a view to learning more about the nature and resources of the oceans. The four themes on which the IOC focuses are: The IOC is composed of an Assembly, an Executive Council, a Secretariat, and a number of Subsidiary Bodies. The Assembly meets every two years and consists of one seat for each member state, of which there are currently 125. The Executive Council meets every year and is elected by the Assembly. The Secretariat is the executive arm and is headed by an Executive Secretary elected by the Assembly. It ensures the implementation of activities decided upon by the Assembly.

The presently (1998) constituted Subsidiary Bodies are divided into scientific/technical and regional categories. The former category includes:

The latter includes:

IOC services available online include:

See the IOC Web site.

IOCARIBE
Acronym for IOC Sub-commission for the Caribbean and Adjacent Regions.

IOC-TEMA
Abbreviation for IOC Committee for Training, Education, and Mutual Assistance in the Marine Sciences, formerly known as TEMA.

IOC-VCP
Abbreviation for IOC Voluntary Cooperation Program.

IODC
Abbreviation for the ICES Oceanographic Data Center, a bank of oceanographic data supplied by ICES member countries that dates back to the early 1900s. See the IODC Web site.

IODE
Acronym for International Oceanographic Data and Information Exchange, an IOC project established in 1961 to ``enhance marine research, exploration and development by facilitating the exchange of oceanographic data and information between participating member states.'' The IODE system is composed of a committee which governs the development and operations of the system and a number of data centers that carry out the activities established by the committee. The data center structure is composed of three components: NODCs, RNODCs, and WDCs.

[http://ioc.unesco.org/iode/]

IOF
Abbreviation for the International Oceanography Foundation, whose mission is to encourage scientific investigation of the sea amongst other things. See the IOF Web site.

ION
Acronym for International Ocean Network, a committee established in June 1993 with the goal of facilitating international cooperation in the development of ocean botton observatories. While originally created for the purposes of seismology, in 1995 it was enlarged to include all geosciences.

[http://www.seismo.berkeley.edu/seismo/ion/]

Ionian Sea
One of the seas that comprise the eastern basin of the Mediterranean Sea. It is surrounded by Italy, Hellas, Libya and Tunisia, and has a volume of 10.8 $ \times\,{10^4}$ km$ ^3$. It connects to the Cretan Sea via the Kithira (160 m deep, 33 km wide) and Antikithira (700 m deep, 32 km wide) Straits, the Levantine Sea via the Cretan Passage, the western Mediterranean via the Strait of Sicility, and the Adriatic Sea via Otranto Strait (780 m deep, 75 km wide).

The major water masses of the Ionian Sea are Modified Atlantic Water (MAW), Levantine Intermediate Water (LIW), and Eastern Mediterranean Deep Water (EMDW). The MAW spreads eastward from the Sicily Straits in the surface layer and is identified as a subsurface salinity minimum between 30 and 200 m depth. It overlies the LIW that enters through the Cretan passage and is identified by a salinity maximum between 200 and 600 m depth. Below this, the colder and less saline EMDW, the main source of which is Adriatic Deep Water (ADW), occupies the layers below 1600 m. A transitional mixture of LIW and EMDW occupies the range between 700 and 1600 m. In the summer Ionian Surface Water can be differentiated from the MAW as saltier and warmer.

Prominent circulation features in the upper thermocline and intermediate layer include the Atlantic-Ionian Stream (IAS), the Ionian Anticyclones (IA), the Pelops Anticyclone (PA), the Mid-Mediterranean Jet (MMJ), and the Cretan Cyclone (CC). The AIS enters the Ionian Sea from the northwest via the Sicily Straits, meanders west and then south, and then turns northeast to flow between Sicily and the IA. At around 17$ ^\circ$ E and 37$ ^\circ$ N it bifurcates, with a southward flowing branch combining with the IAS to the west to form the IA region. The northeastward flowing branch continues to the heel of Italy where it turns to the south and flows past the PA, continuing past there until it passes to the south of the CC and turns west through the Cretan passage, becoming the MMJ. See Fairbridge (1966) and Malanotte-Rizzoli et al. (1997).

Ionian Surface Water (ISW)
A water mass formed at the surface in the Ionian Sea. See Malanotte-Rizzoli et al. (1997).

IO-PAS
Abbreviation for Institute of Oceanology of the Polish Academy of Sciences, founded in 1983 as the successor to the Marine Station of the Academy in existence in Sopot since 1953. The institute is divided into departments for marine physics, hydrodynamics, marine chemistry and biochemistry, and marine ecology. See the IO-PAS Web site.

IOS
Abbreviation for Institute of Ocean Sciences, a research facility of the Canadian Department of Fisheries and Oceans (DFO). The IOS is located in Sidney, British Columbia and is one of a network of nine major scientific facilities across Canada run by the Science Sector of the DFO. See the IOS Web site.

IOSDL
Abbreviation for the Institute of Oceanographic Sciences, Deacon Laboratory, an institute whose mission is to advance understanding of the ocean environment and processes of environmental change in the oceans and to predict future change by carrying out multidisciplinary studies on the oceans and their boundaries with the air and seabed. More information can be found at the IOSDL Web site.

IOUSP
Abbreviation for Instituto Oceanografico da Universidade de Sao Paulo.

IPAB
Abbreviation for International Program for Antarctic Buoys.

IPAR
Acronym for Intercepted Photosynthetically Active Radiation.

IPAST
Acronym for IGOSS Pilot Project on Altimetric Sea Surface Topography Data.

IPDW
Abbreviation for Indo-Pacific Deep Water.

IPSLN
Abbreviation for Indo-Pacific Sea Level Network.

IPTS-48
See ITS-90.

IPTS-68
See ITS-90.

Iribarren number
A surf similarity parameter developed by Battjes in 1974. It is expressed as:

$\displaystyle {I_N}\,=\,{ {\tan \beta} \over {\sqrt{{H_\beta}/{L_0}}} }$

where $ H_\beta$ is the breaker height measured at the toe of the slope, $ \beta$ is the beach slope angle, and $ L_0$ the deep water wavelength, i.e.

$\displaystyle {L_0}\,=\,g{T^2}/2\pi$

where $ T$ is the wave period. The Iribarren number is used to generally predict when various beach states are likely to occur. The states are spilling ( $ {I_N}\,<\,0.4$), plunging ( $ 0.4\,<\,{I_N}\,<\,2.3$), collapsing ( $ 2.3\,<\,{I_N}\,<\,3.2$) and surging ( $ 3.2\,<\,{I_N}$).

Irish Sea
A marginal sea located between Ireland and Wales. It extends from the Mull of Galloway in the north to a line connecting St. David's Head (in Wales) to Carnsore Point (in Ireland) in the south. See Bowden (1955), Fairbridge (1966) and Howarth (1984).

Irminger Current
A branch of the North Atlantic Current that curves north near Iceland, where a minor part of it splits to flow north along the west coast of Iceland and the major part curves to the west and joins the southward flowing East Greenland Current. Both branches ultimately rejoin the North Atlantic Current. The transport of this current has been estimated ar about 8-11 Sv. See Fairbridge (1966) and Tomczak and Godfrey (1994).

Irminger Sea
A body of water in the North Atlantic recognized as such for oceanographic if not official purposes. It lies roughly between the east coast of Greenland and the west coast of Iceland, with the Labrador Sea on its southwest corner and the Greenland Sea to the northeast. The southern boundary is marked by hydrographical rather than geographical features. The basin of this sea is mostly occupied by the eastern part of the Labrador Basin which ranges up to 4600 m in depth. The chief circulation feature is the Irminger Current.

IronEx I
An experiment taking place in October 1993 that marked the first attempt to experimentally manipulate an ocean ecosystem. A single pulse of iron was added to a 64 square kilometer patch of water in the eastern equatorial Pacific HNLC zone. The fertilized patch was tracked using a Chl fluorescence and a sulfur-hexafluoride (SF6) inert tracer. After 2 to 3 days researchers measured a doubling of phytoplankton biomass, a tripling of Chl, and a fourfold increase in net primary productivity (NPP), with no measureable drawdown of either NO3 or CO2. See Martin et al. (1994) and Coale et al. (1998).

IronEx II
The follow-up to IronEx I in which a 64 square kilometer area of the ocean in the eastern equatorial Pacific was fertilized three times over a week with a total of 225 kg of FeSO4. The repeated pulsing was used to prevent the rapid sedimentation that occurred in IronEx I. The patch was again tracked with Chl fluorescence and SF6, and a drogued drifter was deployed in the center of the patch to make it easier to follow. The patch persisted for 19 days, drifting 10 to 100 km per day. The observed consequences included: See Coale et al. (1996) and Frost (1996).

IronEx III
This has apparently been renamed SOFeX.

iron hypothesis
The hypothesis that iron plays a major regulatory role in phytoplankton productivity. While the potential role of iron as a limiting factor in phytoplankton productivity was appreciated by researchers as early as the 1930s, it wasn't until John Martin convincingly pieced together several lines of evidence in the late 1980s that the oceanographic community gave notice to the point of planning major experiments to test it. The threads of Martin's argument included that: See Chisolm (1995).

[http://earth.agu.org/revgeophys/chisho00/chisho00.html]

irradiance
The radiant energy that passes through a unit horizontal area per unit time coming from all directions above it. The irradiance $ F_i$ is defined by

$\displaystyle {F_i}\,=\,{\int_0^{2\pi}}I\,\cos\,\theta\,d\omega$

where $ I$ is the radiance, $ \theta$ the zenith angle, and $ d\omega$ the infinitesimal solid angle. The rate at which radiation is incident upon a unit area.

irrotational
In geophysical fluid dynamics this refers to fluid motion in which there is no vorticity.

ISABP
Abbreviation for International South Atlantic Buoy Program, a DBCP program.

isallobar
A contour line on a weather map that signifies the location of equal changes of pressure over a specified period.

isallobaric wind
A theoretical wind component originating from the spatial non-uniformity of local rates of change of pressure.

isentropic coordinates
The replacement of the z coordinate in an x-y-z coordinate system with the potential temperature. This can be done when horizontal scales are large compared to vertical scales, i.e. when the hydrostatic approximation can be made. See Gill (1982), p. 180.

ISHTAR
Acronym for Inner Shelf Transfer And Recycling, a program for investigating ocean processes in and near the Bering Strait.

ISHTE
Abbreviation for In-Situ Heat Transfer Experiment, a project of the APL of the University of Washington School of Oceanography.

ISLP-PAC
Abbreviation for IGOSS Sea Level Program in the Pacific, a program established for the purpose of making monthly mean sea level data available to a wide circle of users in a timely fashion and to generate products that would be valuable for scientific analysis of climate-related processes. See the ISLP-PAC Web site.

ISO
Acronym for International Ship Operators.

isobar
In physical oceanography, a contour of constant pressure.

isobaric
Descriptive of a surface that is an isobar.

isobaric coordinates
The replacement of the z coordinate in an x-y-z coordinate system with the pressure. This can be done when horizontal scales are large compared to vertical scales, i.e. when the hydrostatic approximation can be made. This set of coordinates is widely used in meteorology. See Gill (1982), p. 180.

isobaric surface
A surface on which the pressure is everywhere the same.

isogram
See isopleth.

isohaline
In physical oceanography, a contour of constant salinity.

isopleth
A general term referring to lines drawn on a map or chart to display the distribution of any element, each line being drawn through places at which the element has the same value. See, for example, isohaline, isobar, etc. Isogram is sometimes used as a synonym.

isopycnal
In physical oceanography, a contour of constant density.

isopycnal form stress
A horizontal pressure force averaged in longitude and time over a material surface of constant potential density. This is associated with a combinatino of transient (mesoscale) and standing (time-mean, longitudinally varying) eddies. See McWilliams (1996).

isopycnal method
A scheme to systematize the classification of the hydrography of the oceans developed by Montgomery in the late 1930s. He developed this to overcome limitations he saw in the earlier core layer method of Wust. In this method variable properties (e.g. salinity, temperature, etc.) are examined on surfaces of constant potential density along which it is assumed that maximum mixing and flow occur. The variations in depth of such surfaces can also be used as a diagnostic tool for locating geostrophic currents since rapid changes in depth are indicative of their presence.

The isopycnal method was originally applied such that all densities were calculated relative to the ocean surface, i.e. as either sigma-t or sigma-$ \theta$. This was later modified when it was found that, due to the nonlinearity of the equation of state for seawater, maximum values could exist well above the ocean bottom - ostensibly signifying a hydrostatic instability. The problem was rectified by the use of potential densities calculated relative to different pressures as was required by the situation, i.e. sigma-1 for densities relative to 1000 decibars (db), sigma-2 for 2000 db, etc., a procedure that is still followed today.

ISOS
Acronym for International Southern Ocean Studies, a program to study the Southern Ocean, especially the fronts and energetics in the regions of Drake Passage and southeast of New Zealand. The monitoring of the transport of the Antarctic Circumpolar Current also had high priority.

isostasy
The tendency of the crust of the earth (i.e. the lithosphere) to maintain a near equilibrium state in relation to the denser, underlying asthenosphere or upper mantle. For example, a continental block might sink or rise due to the presence or absence of an ice sheet in a process called glacial isostatic adjustment.

isostere
In meteorology, a line on a chart joining points of equal specific volume, the volume of unit mass.

isotach
In meteorology, a line or contour of constant wind speed. An alternative is isovel.

isotherm
In physical oceanography, a contour of constant temperature.

isotope
Each of two or more varieties of a particular chemical element which have different numbers of neutrons in the nucleus, and therefore different relative atomic masses and different nuclear (but the same chemical) properties.

isotope dilution analysis
A technique for determining the unknown quantity of an element of known isotopic composition. A spike, i.e. a known quantity of the same element with a known different isotopic composition, is mixed with the sample and the composition assessed via the resulting isotopic composition of the mixture.

isotope fractionation
See Fairbridge (1966).

isotope reference standards
Neither absolute abundances of minor isotopes nor absolute values of isotope ratios can be determined accurately enough for geochemical purposes. As such, differences in such absolute isotopic ratios between two substances are substituted. These comparisons are made between the laboratory samples and various internationally accepted standards known as isotope reference standards. Examples of these are SMOW (standard mean ocean water) and V-SMOW (a SMOW artificially prepared in Vienna) for oxygen and PDB (a Cretaceous belemnite) and V-PDB (the same prepared in Vienna) for oxygen in carbonates. See Bowen (1991) for a thorough discussion.

isotope stage
A division of a deep-sea core on the basis of oxygen isotope ratios. There have been 19 isotope stages since the reversal of the Earth's magnetic field 700,000 years ago.

isovel
See isotach.

ISOW
Acronym for Iceland-Scotland Overflow Water.

Istrian Coastal Countercurrent (ICCC)
See Supic et al. (2000).

ISW
Abbrevation for Ionian Surface Water.

ITCE
Abbreviation for the International Turbulence Comparison Experiment, performed in Australia in 1976. See Kraus and Businger (1994).

ITCZ
See Intertropical Convergence Zone.

ITIC
Abbreviation for International Tsunami Information Center, established in Nov. 1965 by the IOC. The ITIC monitors the activities of the Tsunami Warning System in the Pacific, making use of 31 seismic stations, 79 tidal stations, and 101 dissemination points scattered across the Pacific. It also has a public education program directed towards coastal residents and other interested parties. See the ITIC Web site.

ITPO
Abbreviation for International TOGA Project Office.

ITRIS
Abbreviation for Integrated Tsunami Research and Information System.

ITS-90
Abbreviation for International Temperature Scale of 1990, a temperature scale approved by the International Committee for Weights and Measures at its annual meeting in September 1989. It replaces the International Practical Temperature Scale of 1968 (IPTS-68) and took effect on Jan. 1, 1990. ITS-90 takes advantage of technological advances and more closely approximates the thermodynamic temperature scale than previous scales.

The features of oceanographic interest were outlined by Saunders (1990):

Of particular interest to oceanographers are the properties of ITS-90 in the range -2$ ^\circ$C to +35$ ^\circ$. The single most important property is that the triple point of water remains unchanged at 273.16 K or 0.010$ ^\circ$C; however at standard atmospheric pressure the boiling oint of water falls to 99.974$ ^\circ$C. Consequently in the interval 0-100$ ^\circ$C temperatures measured on the ITS-90 scale are lower than values measured on the IPTS-68 scale. But below 0$ ^\circ$ they are higher. The differences are expressed in the following table.

Over this range (although slightly nonlinear) the relation between the temperature scales can be adequately represented by the expression

$\displaystyle {t_{90}}\,=\,0.99976 {t_{68}}$

Initially it is expected that oceanographers will employ the above expression to correct temperatures measured on the IPTS-68 scale but new calibration procedures will be introduced in National Standards Laboratories commencing 1990 and it is hoped these practices will rapidly spread to oceanographic calibration facilities. The value for the fixed points on the ITS-90 scale and the instruments and interpolation equations to be employed for the measurement of temperature are described in a text to be published in the Journal Metrologia, early in 1990.

Although the impact of the new temperature scale on ocean temperature measurements and their climatology is likely to be small (or even negligible), unfortunately this is not true for its knock-on effects. Corrections will be required for the computation of salinity and other state properties of sea water.

The conversion between IPTS-48 and IPTS-68 is given by () as:

$\displaystyle {t_{68}}\,=\,{t_{48}}\,-\,4.4\times 10^{-6}\,\cdot\, {t_{48}}(100\,-\,{t_{48}})$

IWEX
Acronym for Internal Wave Experiment. See Briscoe (1975b) and Müller et al. (1978).

IWP
Abbreviation for Intergovernmental WOCE Panel, a subsidiary body of the IOC and the WMO established to meet the scientific, managerial, implementation, and resource needs of WOCE. See the IWP Web site.

IWSOE
Abbreviation for International Weddell Sea Oceanographic Expedition.

IYFS
Abbreviation for ICES International Young Fish Survey, a project that has been undertaken in every year in January/February in the North Sea since about 1970. This survey includes station observations of hydrochemical measurements which has resulted in a comprehensive North Sea data set of over 20 years duration. Maps of the temperature and salinity distributions measured during these surveys can be obtained at the IYFS Web site.

IYO
Abbreviation for International Year of the Ocean.

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Manbreaker Crag 2001-08-17