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TOBI
Acronym for Towed Ocean Bottom Instrument, a deep-towed multi-sensor sonar sytem that comprises a two-sided 30 kHz sidescan sonar, a 7.5 kHz sub-bottom profiler sonar, a magnetometer, a temperature probe, a transmissometer, and a range of vehicle handling instruments. TOBI is towed on a 200 meter umbilical behind a 600 kg depressor weight attached to the surface ship via the main 0.68 in. armored coaxial cable, which reduces ship-induced heaving that influences the stability of the vehicle. The sidescan sonar has a range of 6 km and a seabed footprint ranging from 4 by 7 meters close to the vehicle to 42 x 2 meters at longer ranges, and the profiler sonar can penetrate up to 60 meters into soft sediments with a vertical resolution of better than 1 meter. This instrument was developed by the IOSDL. See Flewellen et al. (1993) and the TOBI Web site.

TOCS
Acronym for Tropical Ocean Climate Study, a project commenced by JAMSTEC in 1993 as a follow-up to the JAPACS program as a Japanese contribution to TAO. The objective of TOCS is to achieve a better understanding of the western Pacific warm pool and its effects on ocean circulation, the ENSO phenomenon, and global climate change.

TOGA
Acronym for Tropical Ocean and Global Atmosphere program, a WCRP program beginning in 1985. The objectives of TOGA were:

The objectives were addressed by:

Significant results from the TOGA program include:

See McPhaden et al. (1998).

[http://www.ncdc.noaa.gov/coare/toga.html]
[http://www.ncdc.noaa.gov/coare/]
[http://www.pmel.noaa.gov/pubs/outstand/mcph1720/TMP938460841.htm]

TOGAMA
Acronym for TOGA Marégraphies Atlantique.

TOPEX
Acronym for Typhoon Operational Experiment, a WMO 3-year project for testing the typhoon warning system under real typhoon conditions.

[http://www.wmo.ch/web/www/TCP/Projects.html]
[http://www.unescap.org/enrd/water/disaster/watdis6.htm]

TOPEX/POSEIDON
A cooperative project between the U.S. (NASA) and France (CNES) which was the first space mission specifically designed and conducted for studying the circulation of the world's oceans. TOPEX is the collective name for the instruments comprising the U.S. portion of the mission and POSEIDON that for the French portion. The satellite uses a state of the art altimetry system to measure the precise height of sea level from which information about the ocean circulation can be obtained. It was launched on August 10, 1992 and began making measurements in late September of the same year. The unprecedented accuracy required for obtaining useful information about the ocean circulation from altimetry measurements led to a number of innovations. These included the first dual-frequency space-borne radar altimeter capable of retrieving the ionospheric delay of the radar signal, a three-frequency microwave radiometer for retrieving the signal delay caused by water vapor in the troposphere, an optimal model of the Earth's gravity field, and multiple satellite tracking systems for precision orbit determination. These innovations produce single-pass sea level measurements with a root-sum-square accuracy between 4.7-5.1 cm, better than the requirement for useful data of 13.7 cm. The mission is designed to last for at least 3 years with a possible extension to 6 years.

The orbit configuration was chosen to avoid aliasing tidal signals into the frequencies of ocean current variabilities. The chosen inclination of 66 degrees avoids this as well as the aliasing of different tidal constituents to the same frequency. A 9.916 day repeat period allows an equatorial cross-track separation of 316 km. An orbital height of 1336 km satisfied several constraints including maximizing the accuracy of orbit determination and minimizing the power needed to achieve the required level of signal to noise ratio. The satellite circles the world every 112 minutes between latitudes 65$ ^\circ$ N and S, allowing it to measure sea surface height over 90% of the world's ice-free oceans.

The mission payload consists of six scientific instruments. The four operational sensors are:

The two experimental sensors are the single-frequency solid-state radar altimeter (SSALT) and the Global Positioning System (GPS) demonstration receiver (GPSDR). See Fu et al. (1994).

[http://topex-www.jpl.nasa.gov/]
[http://podaac.jpl.nasa.gov/toppos/]

topographic form stress
The integrated horizontal pressure force on the bottom. See McWilliams (1996).

topographic Rossby wave
To be completed. See Hendershott (1981), p. 309.

topographic steering
The deflection or steering of flow required to keep the potential vorticity constant. For large scale processes in the interior of the ocean, we can neglect the relative vorticity and the potential vorticity reduces to $ f/D$. As such, if a water column stretches, i.e. D increases, (shrinks, i.e. D decreases) to accomodate a greater (lesser) depth, then it must move toward (away from) the nearest pole to increase (decrease) $ f$ to keep its ratio to $ D$ constant.

TOPS
Acronym for Total Ocean Profiling System.

Torres Strait
See Gulf of Carpenteria.

TOU
Abbreviation for True Oxygen Utilization. See AOU.

TOURBILLON
A study of mesoscale eddies in the northeast Atlantic Ocean. See Le Group Tourbillon (1983).

TOWARD
Acronym for Tower Ocean Wave and Radar Dependence Experiment, an experiment conceived to provide a data base to resolve the disparity among different Synthetic Aperture Radar (SAR) ocean surface imaging theories. The specific objectives were to investigate the hydrodynamics of short waves and their modulation by long waves, to assess the assumptions stipulated in radar backscatter theory that are used in SAR ocean surface imaging, and to develop a verifiable theory for SAR imaging of the ocean surface. See Shemdin (1990).

TPOP
Abbreviation for the TOGA Program on Prediction. See the TPOP Web site for more information.

TPPN
Abbreviation for Trans-Pacific Profiler Network, a joint NOAA/University of Colorado project.

TPS24
Abbreviation for the series of Trans-Pacific expeditions along 24$ ^\circ$ N in 1985.

TPS47
Abbreviation for the series of Trans-Pacific expeditions along 47$ ^\circ$ in 1985.

TPTMS
Abbreviation for Tropical Pacific Thermal Monitoring System.

TRACMASS
Acronym for Tracing the Water Masses of the North Atlantic and the Mediterranean, a project to use a Lagrangian trajectory method to investigate the North Atlantic and Mediterranean water mass circulation as they result from numerical simulations of the global ocean. The major goals of the project are to investigate: The OCCAM, OPA and GIM circulation models will be used in the investigation.

[http://www.knmi.nl/onderzk/oceano/special/mast.html]

trade winds
The trade winds, or tropical easterlies, are the winds which diverge from the subtropical high-pressure belts, centered at 3-40$ ^\circ$ N and S, towards to equator, from north to east in the northern hemisphere and south to east in the southern hemisphere.

transfer efficiency
In marine ecology, the ratio of the production of one trophic level to that of the next. This is a reasonable estimate of the ecological efficiency if it is assumed that the energy extracted from a given trophic level is proportional to its production. See Barnes and Hughes (1988).

transfer function
A device used in paleoclimate data analysis to obtain proxy data. An equation, or transfer function, is developed using mathematical techniques of regression that relates the actual data (.e.g. planktonic fossil assemblages) to some desired physical variable (.e.g. water temperature). See Imbrie and Kipp (1971), Kipp (1976) and Crowley and North (1991).

transfer velocity
See piston velocity.

Transitional Mediterranean Water (TMW)
A transition water mass found between the overlying Levantine Intermediate Water (LIW) and the underlying Eastern Mediterranean Deep Water (EMDW) in the eastern Mediterranean Sea. The TMW is relatively colder (14.25$ ^\circ$C) and slightly less saline (38.88-38.90) than LIW. See Theocharis et al. (1999).

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

transmissometer
An instrument for the measurement of the transmission of light of a given wavelength over a known distance in a seawater sample. The wavelengths are usually chosen based on the particles being studied, with about 660 nanometers the wavelength most often used. The changes in transmission are primarily related to changes in the abundance and type of particles present, with most variations resulting from particles less than 20 microns in diameter.

transmittance
In radiation transfer, the fraction of incoming radiation that is transmitted into or through a medium. The sum of this, the absorptance, and the reflectance must equal unity.

TRANSPAC
Acronym for TRANS-PACific experiment. See White and Bernstein (1979).

TRE
Abbreviation for Tracer Release Experiment.

TREMORS
Acronym for Tsunami Risk Evaluation through Seismic Moment from Real-Time System.

trench wave
See Mysak et al. (1979).

TRISTAR
A type of drifter. See Niiler et al. (1995).

tritium
A hydrogen isotope useful as a tracer in ocean studies. It is the heaviest isotope of hydrogen, and emits a low energy beta particle in its decay to helium-3. Being hydrogen, it exists almost exclusively as water and is thus transported only by fluid motion and vapor exchange, making it an ideal hydrologic tracer. Tritium is produced naturally in the upper atmosphere by cosmic ray spallation, with pre-nuclear concentrations in precipitation around 5-10 Tritium Units (TU) and surface water concentrations ranging from 0.1 to 0.5 TU. The pre-nuclear natural inventory was around 3.6 kg.

Atmospheric nuclear weapons testing in the 1950s and 1960s produced tritium in quantities that dwarfed the natural inventory which, given the subsequent cessation of such testing, offered a unique opportunity to study the long-term transport through the ocean of a large spike of an important and readily identified tracer. About 500 kg of tritium was produced by the weapons testing programs, boosting the concentration in precipitation to as high as 10,000 TU in places, with surface seawater concentrations reaching 20-30 TU in the northern hemisphere. The latitudinal distribution of weapons tritium delivery to the ocean is characterized by mid-latitude maxima (near 45-50$ ^\circ$) with about a five-fold asymmetry between northern and southern hemisphere. The time history of surface delivery is a spike for the northern hemisphere and more extended for the southern hemisphere.

The usefulness of tritium as a tracer is due to its time history not monotonically increasing (i.e. the weapons source is no more) which gives independent time information, the strong hemispheric asymmetry in its delivery which is valuable in the study of cross-equatorial flow and, finally, its nature as an ideal fluid tracer since, being part of the water molecule, it is unaffected by biological and chemical processes. The long-term evolution of its large-scale distribution will provide much useful information about ocean circulation processes. See Sarmiento (1988), Broecker and Peng (1982), and Broecker et al. (1986).

Tritium Unit
A unit defined as 10**18 times the atom ratio of tritium to normal hydrogen.

TRITON
Acronym for Triangle Trans Ocean Buoy Network, a a buoy for measuring surface meteorology and upper ocean data. These Japanese moorings are used in the TAO/TRITON array west of 165E.

[http://www.jamstec.go.jp/jamstec/TRITON/]

trochoidal wave
See Gerstner wave.

TROPEX
Acronym for Tropical Experiment.

TROPIC HEAT
Acronym for Tropical Pacific Upper Ocean Heat and Mass Budgets, a process-oriented study within the TOGA observing system for examining the processes controlling SST in the equatorial eastern Pacific. It was designed to explore the characteristics and dynamics of the mixing in the equatorial Pacific Ocean in greater detail and to establish the basis for realistic parameterizations of the mixing. A two ship study was conducted southeast of Hawaii in November and December 1984 in which intensive fine- and microscale observations were made. See Eriksen (1985) and Heert et al. (1991).

tropical cyclone
A non-frontal, synoptic scale, low pressure system originating over tropical or subtropical waters with organized convection and definite cyclonic wind circulation.

tropical depression
A tropical cyclone with maximum sustained winds of 33 knots or less near the center.

tropical instability waves
Waves that derive their energy from the large-scale, seasonally varying zonal equatorial currents through shear instability (and possibly through SST frontal instabilities). They were first observed in the Pacific in 1977 in satellite SST imagery, and have since been detected in ocean currents, temperature and salinity fields, and in satellite altimetry data. They typically appear as well-organized, cusplike features that propagate westward with zonal wavelengths of 800-2000 km and periods of 20-30 days. They are seasonally and interannually modulated, being weakest during the boreal spring and during the warm phase of ENSO.

These waves provide a significant source of drag on the South Equatorial Current (SEC) and the Equatorial Undercurrent (EUC). They heat the cold tongue via large downgradient (i.e. equatorward) eddy heat transports. They can also affect the stability of the atmospheric boundary layer, the distribution of cloudiness, latent heat fluxes, and the distribution of nutrients and chemical species in the eastern equatorial Pacific. Instability waves have also been detected in the Atlantic during the boreal summer. They potentially provide a large source of aliased energy which can add noise contamination to measurements of lower frequency signals. See McPhaden et al. (1998).

tropical SST paradox
This refers to an apparent contradiction between tropical SSTs as inferred from various proxy data and as calculated by the present generation of computer models for past warm periods. The measurements for the Pliocene, Eocene and Cenomanian suggest that tropical SSTs were not significantly greater than those at present, while model simulations for these times show significant differences. See Crowley and North (1991).

tropical storm
A tropical cyclone with maximum sustained winds of 34 to 47 knots near the center.

troposphere
The narrowest of the atmospheric layers, extending from the surface of the Earth to about 10 km at the Equator and 6 km at the poles near the 200 mbar level. This layer contains about 80-85% of the atmosphere's total mass and almost all of the water vapor and clouds. Temperatures fall with height at the rate of about 0.5$ ^\circ$ F per 100 feet. It is bounded above by the tropopause which varies with latitude and season. This layer is characterized by strong vertical mixing associated with latent heat effects and clouds.

tropospheric aerosols
See Haywood and Boucher (2000).

truncation error
That which occurs when a function, theoretically represented exactly as the summation of an infinite (or otherwise bloody huge) number of terms, is represented by a smaller subset of these terms. The difference between the exact function and the function represented by the finite number of terms is called the truncation error. This is one of several kinds of errors inherent in representing a continuous world discretely on computers.

T-S curve
See T-S diagram.

T-S diagram
A graph showing the relationship between temperature and salinity as observed together at, for example, various depths in a water column. A T-S diagram for a given station is typically prepared by plotting a point for the temperature/salinity combinations at a range of depths and then joining them by straight lines in order of depth. The resulting line is called the T-S curve. Isopleths of constant density are often also drawn on the same diagram as a useful additional interpretation aid. In the ocean certain T-S combinations are preferred which leads to the procedure of identification via the definition of water types and water masses and their distributions.

T-S-t diagram
An extension of the T-S diagram concept to include information about the temporal evolution of the properties of ocean waters in specific areas. It is created by plotting, on a standard T-S diagram, the temperature and salinity of a given area at regular time intervals (say, monthly or quarterly values).

T-S-V diagram
An extension of the concept of a T-S diagram to display the distribution of temperature and salinity in the world ocean waters in proportion to their total volume. This is created by dividing a T-S diagram into a grid of squares with each square containing a number indicating the volume of water whose properties lie within it. A 3-D graphic of the results can also be created by replacing each number with a proportionally long vertical bar. See Montgomery (1958) and Worthington (1981).

Tsuchiya jet
Narrow eastward currents in the Pacific that bracket the equator just below the equatorial thermocline. They form the poleward boundaries of the 13$ ^\circ$C equatorial thermostad. The northern jet begins west of 141$ ^\circ$E at 325 m depth, and the southern jet near 155$ ^\circ$E at 300 m depth. Both start 3$ ^\circ$ from the equator, then gradually diverge and shoal to the east until they are 6$ ^\circ$ from the equator and 150 m below the surface at 110$ ^\circ$W. The typical core speeds are 35 cm s$ ^{-1}$, and the transport 5-10 Sv each. There is some evidence for a secondary southern jet south of the main southern jet in the eastern Pacific. These are also known as subsurface countercurrents (SCC).

One model of their dynamics considers a linear, vertically diffusive model which simulates the Tsuchiya jets as lobes of the Equatorial Undercurrent (EUC) which are formed at the poleward edge of a broad diffusive equatorial boundary layer (McPhaden (1984). Downward vertical diffusion of cyclonic relative vorticity is balanced by the poleward advection of planetary vorticity within the boundary layer, with the advection of planetary vorticity balanced by vortex stretching creating a pycnostad outside of it. The jets are the result of a geostrophic balance across the pycnostad. An inertial jet model has the conservation of the Bernoulli function and potential vorticity combining with th eastward shoaling of the tropical pycnocline to determine its structure. See Tsuchiya (1972), Tsuchiya (1975), Johnson and Moore (1997) and Rowe et al. (2000).

Tsugaru Current
A current flowing east from the Japan Sea through the strait between mainland Japan and Hokkaido and on into the Pacific Ocean. This is also known as the Tsugaru Warm Current. The Tsugaru originates in the Tsushima Current, which splits off from the Kuroshio Current and enters the Sea of Japan through Tshushima Strait where it is modified before exiting through the Tsugaru Strait. In summer and autumn, the Tsugaru tends to expand eastward and into a small anticyclonic gyre as it meanders eastward past the northern tip of Honshu, and then turns southward along the Sanriku coast. In winter and spring, it usually turns directly southward along the coast. See Tomczak and Godfrey (1994) and Talley et al. (1995).

Tsugaru gyre
See Nof and Pichevin (1999).

Tsugaru Warm Current
Another name for the Tsugaru Current.

tsunami
A Japanese word meaning ``harbor wave''. This is often used (along with the even more incorrect ``tidal wave'') as a name for what is more correctly called a seismic sea wave. A true harbor wave is a type of seiche and can be excited by, among other things, seismic sea waves. Tsunami originally applied to all large waves including storm surges but is now more or less restricted to seismic sea waves, and has mostly supplanted both seismic sea wave and tidal wave in the literature.

Tsunamis are primarily created by vertical movements of the sea floor caused by tectonic activity. This causes rapid vertical movements in the sea surface over a large area which leads to the formation of a train of very long period waves, with periods exceeding one hour not unusual. Secondary mechanisms for tsunami formation are landslides and volanic activity, with the effects of the resultant waves more localized than those of the tectonic variety which may travel across ocean basins. See Camfield (1990).

Tsushima Current
A branch of the Kuroshio Current that flows into the Japan Sea via the Korea Strait. This brings in warm water which is ultimately exported to the Pacific via a continuation of the Tsushima called the Tsugara Current. The Tsushima splits into two branches near 35$ ^\circ$ N when it encounters the Tsushima Islands, with the western branch following the Korea coast and eventually turning east to join the Polar Front and the eastern branch closely following the Japanese coast until it becomes the Tsugara Current. The transport varies seasonally, with August transport about 1.3 Sv (at up to 4 m/s) and January transport only 0.2 Sv (below 0.1 m/s). Most of the increased August transport passes through the western branch as the eastern branch is weak year round. Both branches are prone to major pathway shifts and the western branch tends to shed large eddies where it separates from the Korean coast. The western branch has also been called the East Korea Current. See Lie and Cho (1994) and Tomczak and Godfrey (1994).

TTO
Abbreviation for Transient Tracers in the Ocean. This comprised two separate studies: the TTO North Atlantic Study (TTO/NAS) and the TTO Tropical Atlantic Study (TTO/TAS). The 1981 North Atlantic Study (NAS) experiment cruise consisted of seven legs and visited 250 hydrographic stations across the North Atlantic in 200 days. About 9000 water samples were taken for analysis of salinity, oxygen, and nutrients; 3000 samples were taken for tritium analysis; and 1000 samples for radiocarbon analysis. The TTO/NAS data is available from the CDIAC.

turbidity current
See Johnson (1964).

turbulence
As defined by a subpanel of SCOR working group 69 in 1987:
Turbulence is a condition of fluid flow in which:

Kantha and Clayson (2000) list the characteristics of turbulent flows as:

Small-scale, active turbulence is defined as a nearly isotropic, eddy-like state of fluid motion where the inertial forces in the eddies are larger than the buoyancy and viscous forces. It consists of random motions, with Reynolds and Froude numbers that exceed critical values. The length scales of such three-dimensional turbulent motion are smaller than about 0.6$ L_R$ and larger than about 11$ L_K$, where $ L_R$ is the Ozmidov length scale and $ L_K$ is the Kolmogorov length scale.
Small scale fluctuations that satisfy the first three requirements but not those of active turbulence are sometimes described as fossil turbulence, i.e. remnants of previously active turbulence. See McDougall et al. (1987) and ocean turbulence.

turbulence kinetic energy (TKE)
The energy contained within the turbulent portion of a flow.

turbulent stress tensor
See Reynolds stress tensor.

Turner angle
A quantity delineating the stability of a water column to double diffusion and salt fingering. It is given by:

$\displaystyle {T_u}\,=\,{\tan^{-1}} \left({{R_\rho}+1}\over{{R_\rho}-1}\right)$

where $ R_\rho$ is a density ratio defined as:

$\displaystyle {R_\rho}\,=\,{ {{\beta_T}\delta T} \over {{\beta_S}\delta S} }$

where $ \beta_Tt$ and $ \beta_S$ are the coefficients of thermal and saline expansion, and $ \delta T$ and $ \delta S$ the vertical gradients of temperature and salinity. The angle obtained is interpreted as: See Ruddick (1983).

turnover time
A time scale defined as the ratio of the mass of a reservoir to the rate of its removal from that reservoir. In the context of the climate this can be seen as the total amount of carbon dioxide in the atmosphere and its rate of removal via land and ocean processes.

TWATE
Acronym for Two-Way Acoustic Transmission Experiment. See Worcester (1977).

TWIST
The Turbulence and Waves over Irregularly Sloping Topography Experiment is a WHOI program to discover what dictates the magnitude, frequency and spatial scales of internal waves in continental slope regions. The study area is on the continental slope of the North Atlantic Ocean near Norfolk Canyon. The area is centered at 37.25$ ^\circ$N and 74.66$ ^\circ$ W and was chosen for the evenly spaced topographic waves that run orthogonal to the slope. In the deployment phase, planned to last from May 10 to June 8, 1998, three Moored Profilers (MP) will be deployed in a closely spaced array (about 500 m separation). This should allow the assessment of horizontal internal wave scales. High Resolution Profiler (HRP) dives will also be made to quantify the smallest scale components of vertical mixing. See the TWIST Web site.

TWP
Abbreviation for tropical western Pacific.

typhoon
A tropical cyclone with maximum sustained winds of 64 knots or more near the center.

Tyrrhenian Sea
One of the seas that comprise the western basin of the Mediterranean Sea. It is separated from the Balearic Sea to the west by Sardinia and Corsica and from the eastern basin by the StraitsofSicily. It has a central abyssal plain along with some smaller plains located witin slope basins. The central plain is pierced by a large seamount that rises 2850 m above the sea floor to within 743 m of the surface. See Fairbridge (1966).

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