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# On-Oz

ontogeny
In biology, the origin and development of the individual organism, as opposed to phylogeny. See also Biogenetic Law.

Oort Cloud
A spherical zone surrounding and bound to the solar system between 20,000 and 100,000 AU from the Sun. It is hypothesized to contain 10**12 comets whose orbits, perturbed by passing stars or molecular clouds, can occasionally reach to within Jupiter's orbit. The existence of the Oort Cloud is a key element of the Nemesis theory.

OPERA
Acronym for Observatoire Permanent de l'Atlantique Tropical.

Operation Cabot
A multiple-ship cruise to survey the Gulf Stream in 1950. See Fuglister and Worthington (1951) and Stommel (1966).

operator splitting
In numerical ocean circulation modeling this is a technique for splitting the fast and slow dynamics into separate subproblems. When the partial differential equations governing large-scale ocean dynamics are discretized to achieve numerical solutions, dynamical phenomena with many temporal and spatial scales are usually included in the discretized equations. Most prominent in discretizations of the primitive equations are external and internal gravity waves, where the characteristic wave speeds are, respectively, 200 m/s and 1-2 m/s.

The size of the discrete time step used to integrate the equations is limited by the fastest motion that has to be resolved, in this case the external gravity waves. One way to get around this limitation is to separate the fast and slow motions into separate subproblems. The fast external motions are essentially 2-D due to approximate independence from depth, which leads to the common option of obtaining the 2-D velocity field from a vertical average of the horizontal velocity field in the original 3-D equations.

This procedure can give rise to computational instabilities since the operator splitting method is inexact except for the case of a linearized flow with a horizontal bottom and a rigid lid. In this case one solution is exactly independent of depth and the horizontal velocity field obtained corresponds exactly to the vertically averaged velocity. However, if any of the restrictions are relaxed the fast and slow motions can be mixed by variable bottom topography or nonlinearities and can result in numerical instabilities if an explicit method with a long time step is used to advance the slow motion component in time. See Higdon and Bennett (1996).

Ophiuroidea
A class of marine invertebrates in the phylum Echinodermata. The more than 1600 species of these are commonly known as brittle stars. See the Introduction to the Ophiuroidea at the U.C. Museum of Paleontology.

opposition
In tidal mechanics, that instant when the Earth-centered longitude of the Moon differs from that of the Sun by 180 degrees. This is also the time of the full moon and of one of two monthly spring tides. See also conjunction.

optical depth
See optical thickness.

optical oceanography
More later.

optical thickness
A measure of the attenuation of solar radiation by the atmosphere that allows the convenience of considering as a single unit the losses due to scattering and absorption processes. The greater the thickness, the greater the attenuation of incoming solar radiation. This is also referred to as the optical depth.

OPTOMA
Acronym for Ocean Prediction Through Observation, Modeling, and Analysis, a program that consisted of a lengthy set of surveys of the eddy field in the California Current. See Rienecker et al. (1985).

OPUS
Acronym for Organization of Persistent Upwelling Structures, a program taking place in 1983 that studied the inner part of a filament near Point Conception, California. See Atkinson et al. (1986).

OPYC
Abbreviation for an isopycnic ocean circulation model developed and used at the DKRZ.

orbital elements
The six pieces of mathematical data needed to completely determine a planet's orbit and its position in that orbit. These data are: (1) longitude of the ascending node, (2) inclination of the orbit, (3) longitude of perihelion, (4) semi-axis major, (5) eccentricity, (6) epoch, or date of planet's passing perihelion. Analogous elements are used for satellites.

ORCA
Acronym for Oceanographic Remotely Controlled Automaton, a diesel powered semi-submersible designed to survey water depths from 10 to 300 meters. This instrument was designed for the cost effective collection of hydrographic and oceanographic data. See the ORCA Web site.

Ordovician
The second period of the Paleozoic era, lasting from 505 to 438 Ma. It precedes the Silurian period and follows the Cambrian period, and is comprised of the Early (505-478 Ma), Middle (478-458 Ma), and Late (458-438 Ma) epochs. Named after the Ordovices, an ancient Celtic tribe in Central Wales. Widespread volcanic activity and the vast mountain-building movement known as the Caledonian Orogeny took place during this era.

organic matter pump
Then name given to the cycle of organic matter and nutrients in the ocean. Since photosynthesis exceeds respiration only in the euphotic zone, there is a net sink of CO2, phosphate and nitrate in the euphotic zone and a net source in the aphotic zone. Thus a downward flux of organic matter and an upward flux of nutrients connects the euphotic zone sink and the aphotic zone source of nutrients. This has also been called the soft tissue pump, but the present name was suggested in recognition of the possible role of dissolved organic species in the transport cycle. See Najjar (1991).

ORNL
Abbreviation for Oak Ridge National Laboratory.

orogeny
Mountain building when a belt of the Earth's crust is compressed by lateral forces to form a chain of mountains.

OSCR
Abbreviation for Ocean Surface Current Radar, a measuring system that uses high frequency radio pulses to probe the ocean surface to deduce near-surface currents. The shore-based system consists of two units which are deployed several kilometers apart. Each unit makes independent measurements of current speed along radials emanating from its phased-array antennae system. The data are then combined via UHF or telephone communication to produce accurate vector currents, store them to disk, and display them in near real time. Measurements can be made simultaneously at up to 700 grid points at either 1 km or 250 m resolution. The OSCR samples for about 10 minutes and then processes radar returns for about 10 minutes to create a quasi-synoptic surface current map every 20 minutes. See the OSCR Web site.

OSLR
Abbreviation for Intergovernmental Committee for Ocean Science and Living Resources, an IOC committee.

OTEC
Acronym for Ocean Thermal Energy Conversion, the use of the temperature difference between surface and deep sea water to generate electric power. This is done by taking a working fluid with a low boiling point, turning it to vapor by heating it up or depressurizing it, and then using the pressure of the expanding vapor to turn a turbine. The liquid used may be either the sea water or ammonia. The OTEC is called open-cycle if the ocean water itself functions as the refrigerant, transferring heat energy by changing between the liquid and gaseous phases. It is called closed-cycle if ammonia is used.

The idea was first propounded by a French engineer named Jacques D'Arsonval in 1881, although it was a student of his named Georges Claude who first tested the idea. Claude used warm seawater to create a low pressure vacuum system, i.e. an open-cycle system. D'Arsonval's original idea was to use another fluid such as ammonia, i.e. a closed-cycle system. At present the only operating OTEC plant is at the Natural Energy Laboratory of Hawaii.

OTH
Abbreviation for over-the-horizon radar, a type of radar originally developed to detect military targets far beyond the optical horizon. Radio waves in the 5 to 28 MHz range are reflected from the ionosphere and reach up to 3500 km in one hop. Properties of the ocean surface are extracted from the energy backscattered from the ocean surface. Properties that can be measured include surface wind direction, radial surface currents, sea state, surface wind speed, and more. See the OTH Web site.

OTRANTO
A research project whose goal is to improve the knowledge about the hydrodynamics of the Straits of Otranto and the evaluate the water and particulate fluxes across this strait at synoptic, seasonal, and interannual time scales. This MTP Core Project took place from Dec. 1993 to May 1996. See the OTRANTO Web site.

OTTER
Acronym for the Oregon Transect Ecosystem Research Project, a study of a climatic and elevational gradient extending from the Pacific coast 200 kilometers to the east. See the OTTER Web site.

otter trawl
A device used in biological oceanography to trawl for pelagic organisms. As opposed to the beam trawl, the opening to this is kept open not by a rigid rectangular frame but rather by otter boards attached to either side of the net opening. These boards are forced apart by the force of the water when the trawl is towed and close when it is not being towed, an eventuality convenient for retaining the organisms caught. The open may be 20 to 26 m wide and the net up to 40 m in length. See Sverdrup et al. (1942).

OTU
Abbreviation for operational taxonomic units. See numerical taxonomy.

outer sublittoral zone
See circalittoral zone.

overall Richardson number
A dimensionless number expressing the ratio of the removal of energy by buoyancy forces to its production by the shear in a flow. It is expressed by

where g' is the reduced gravity and L and U are, respectively, length and velocity scales imposed by the boundary conditions of the problem. The name comes from the fact that this is an overall parameter describing a whole flow as opposed to the gradient and flux Richardson numbers. See Turner (1973).

OVERFLOW '60
An ICES investigation of cold, sub-arctic, deep water overspill into the North Atlantic Ocean from the Iceland-Faroe Ridge. It was carried out from May 30 to June 18 in 1960 under the leadership of J. B. Tait and was an optimal coordination of 9 research ships in a small region to reach a maximum of synoptic work. This experiment is considered to be the starting point of current measurements in deep water by self-recording anchored instruments. The data collected in the experiment is available at the OVERFLOW '60 Web site.

OVERFLOW '73
An ICES expedition whose core period of observation was between August 15 and September 15 in 1973. The principal objective of this experiment was to describe in detail the kinematic and dynamical processes which lead to the renewal of the sub-Arctic bottom water of the northern North Atlantic across the Iceland-Faeroe Ridge and the Denmark Strait. This experiment, a follow-up to OVERFLOW '60, consisted of over 1700 hydrographic stations and 52 current meter moorings as well as numerous XBTs, tide measurements and drogue tracking. The chief scientist was J. Meincke of the University of Hamburg. The data collected in this experiment is available at the OVERFLOW '73 Web site.

overmixing
A condition that can exist in strongly stratified estuaries with net circulation out in the upper layer and net circulation in in the lower layer. This limits the amount of salt water available for mixing inside the estuary. This condition begins as mixing proceeds within the estuary by whatever processes are dominant. The mixing causes more salt water to be added to the net circulation and volume flow out of the estuary up to a critical condition past which any more increased mixing has no further effect on the discharge flow or the exiting salinity. See Officer (1976).

Oxfordian
The first of three ages in the Late Jurassic epoch, lasting from 163 to 156 Ma. It is preceded by the Callovian age of the Middle Jurassic epoch and followed by the Kimmeridgian age.

oxygen
See Richards (1957).

oxygen isotope analysis
The use of stable oxygen isotopes to extract paleoclimatic information from ice cores. The theoretical basis Bradley (1985) of the method is that two paleoclimatically important heavy isotopes (one containing deuterium and the other 18O) have vapor pressures lower than that of pure H20. Thus, evaporation leads to water vapor depleted in deuterium and 18O as well as a water body enriched in the same. Further, condensation of the vapor preferentially removes even more of these heavy isotopes, leaving the vapor even more depleted in deuterium and 18O. Therefore, to a first approximation isotopic concentration in the condensate can be considered as a function of the temperature at which the condensation occurred, although other considerations come into play.

A major use of this method is to gauge the waxing and waning of glacial periods since the deposition of large amounts of water on land in the form of glaciers leaves the water enriched in and the water depleted of the heavy isotopes.

oxygen isotope ratio
The ratio of oxygen-18 to oxygen-16, used as an indicator of paleotemperatures since it is related to ocean temperature.

Oyashio Current
The western boundary current of the subpolar gyre in the North Pacific Ocean. Divergence in the center of this gyre causes the Oyashio to carry cold water rich in upwelled nutrients and full of marine life - hence the meaning of the name as ``parent current''. The Oyashio is formed by the confluence of the Alaskan Stream and the Kamchatka Current west of the Kamchatka Peninsula at about 55 N. It flows southward and splits into two paths called the First and Second Oyashio Intrusion just south of Hokkaido, after which the First Intrusion proceeds southward along mainland Japan (Honshu) where it turns west at about 38 N to rejoin the First Intrusion, which has proceeded more or less directly south from the splitting point. They merge at about 39 N and 145 E where the southern boundary of the Oyashio defines the Polar Front. This boundary and the northern edge of the Kuroshio maintain their identities at least through the Kuroshio Extension, although it is not well known how much further east they continue to be distinguishable and distinct from the broader eastward flow of the North Pacific Current. Thus the Oyashio forms the western and part of the southern limb of the North Pacific subpolar gyre. See Tomczak and Godfrey (1994).

oyster
A marine invertebrate of the phylum Mollusca and the class Pelecypoda. Related animals include clams and mussels.

ozone
An allotropic form of oxygen, a bluish toxic gas, O , with a characteristic sharp odor, produced from molecular oxygen by electrical discharge and in the upper atmosphere by ultraviolet light. Ozone is climatically significant for this ability to absorb ultraviolet light in the ozonosphere, which is being reduced by its being broken down by anthropogenic chlorofluorocarbon in the atmosphere.

ozonesonde
See the Ozonesonde Web site.

ozone depleting substance
Any compound that contributes to ozone depletion in the stratosphere. These include halons, methyl bromide, CFCs, HCFCs and carbon tetrachloride.

ozone depletion potential (ODP)
A measure of the amount of ozone depletion caused by a substance. It is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11, with the ODP of the latter defined as unity.

ozone layer
See ozonosphere.

ozonosphere
The region of the stratosophere, at an altitude of 10-15 to 40-50 km (6 to 30 miles), containing significant amounts of ozone, which aborbs short ultraviolet light. The region of maximum ozone concentration is between 20 and 25 km (12 and 15 miles). This is also called the ozone layer.

Next: Pa-Pm Up: The Glossary Previous: Oa-Om

Steve Baum
Mon Jan 20 15:51:35 CST 1997