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Acronym for Wave Direction Measurement Calibration Project, a program held in the vicinity of the Edda platform in the Ekofisk field in the North Sea during winter 1985-1986. Several wave buoys, platforms and wave staffs were intercalibrated in this project. See Allender et al. (1989).

Walker circulation
A name coined by Bjerknes for two circulation cells in the equatorial atmosphere, one over the Pacific and one over the Indian Ocean. Schematically these are longitudinal cells where, on one side of the ocean, convection and the associated release of latent heat in the air above lifts isobaric surfaces upward in the upper troposphere and creates a high pressure region there. The lack or lesser degree of the same process on the other side of the ocean results in lower pressure there, and a longitudinal pressure gradient is established which, being on the equator, cannot be balanced by the Coriolis force. Thus a direct zonal circulation is driven in the equatorial plane with countervailing winds at the surface and in the upper troposphere, with concomitant rising and sinking branches on the appropriate sides of the ocean.

The normal Walker circulation in the Pacific consists of air rising over Indonesia, west winds in the upper troposphere, sinking air off the west coast of South America, and east winds near the surface. A reversed but weaker Walker circulation (and an enhanced Hadley circulation occurs during ENSO years. In the Indian ocean the circulation cell proceeds in the opposite sense (to the normal Pacific Walker cell), with sinking air over cold waters off the Somali coast and a low-level acceleration from west to east along the equator in the lower atmosphere. See Henderson-Sellers and Robinson (1986) and Kraus and Businger (1994).

Walvis Basin
See Cape Basin.

Acronym for Wave Model Development and Implementation group, an organization created to advanced sea surface state models. See Group (1988).

Acronym for the West African Monsoon Experiment, a component of FGGE designed to study monsoonal circulations. See WAMEX (1990).

Warm Deep Water
See Antarctic Circumpolar Water.

Acronym for Waves And Storms in the North Atlantic, a project whose goal is to verify or falsify the hypothesis of a worsening storm and wave climate in the Northeast Atlantic and its adjacent seas in the 20th century. The main conclusion of the project is that the storm- and wave-climate in most of the Northeast Atlantic and in the North Sea has undergone significant variations on times scales of decades, that is has indeed roughened in the past decades, but that the present intensity seems to cmopare with the intensity at the beginning of the century. Part of the variability was found to be related to the North Atlantic Oscillation. See WASA (1998).


Acronym for WOCE/Atlantic/Tropical-Boundary Eastern Equatorial.

water mass
In physical oceanography, a body of water with a common formation history. A water mass is identified through relationships on a T-S diagram, although additional information about the degree of spatial and temporal variability during its formation as expressed by a standard deviation is almost always needed as well. A single T-S point, i.e. a water type, along with its standard deviation, may be sufficient for identification (especially with deep water masses), although generally a set of T-S combinations, i.e. a function in T-S space, is needed along with a standard deviation envelope. Generally the standard deviation decreases with depth. In practice not enough data is usually available to calculate a standard deviation, so a point or line in T-S space is specified around which the water mass properties are presumed to vary. See Emery and Meincke (1986a).


See Emery and Meincke (1986b) and Wright and Worthington (1970).

water mass analysis
A technique introduced by Jacobsen (1927) as a graphical method for determining mixing coefficients in a T-S diagram. It was extended by Wüst in 1935 who developed his core layer method. This was further extended by Tomczak (1981) who developed a multi-parameter analysis technique by adding oxygen and nutrients as additional quasi-conservative parameters. This idea was further developed into what is currently known as Optimum Multiparameter Analysis (OMP). See Rees and Aiken (1995).

water mass characteristics
A property value or, more often, range of property values by which a water mass can be identified and tracked through the ocean. The most commonly used are temperature, potential temperature, salinity, potential density or the density referenced to a particular depth or pressure. Less often used by still quite valuable for certain applications are oxygen, nitrate, phosphate, silicate, chlorofluorocarbon, carbon 14 and tritium. See also the entry on ocean tracers.

water type
In physical oceanography, a point on a T-S diagram.

water vapor feedback
A positive feedback loop in the atmosphere wherein an increase in temperature increases the water holding capacity. This will lead to an increase in the amount of atmospheric water vapor which, being a greenhouse gas, will in turn lead to another temperature increase. This process is better understood in the lower troposphere where there is reasonable certainty as to the feedback process. The upper atmosphere, while not as well understood in this regard, has a preponderance of evidence pointing to this. The temperature change is not uniform with height and the resulting changes in the vertical temperature gradient can partially compensate for the water vapor feedback.

water vapor mixing ratio
The ratio of the mass of water vapor to the mass of dry air in a specified volume as expressed in grams per kilogram.

water vapor pressure
The part of atmospheric pressure due to the water vapor in the atmosphere.

Acronym for Western Atlantic Ocean Experiment. See Ray et al. (1990).

Acronym for Western Atlantic Thermohaline Transport Study.

wave action
See Andrews and McIntyre (1978).

wave climate
The general condition of sea state at a particular location, the principal elements of which are the wave height, period parameters, and the wave direction. The significant wave height is usually used as the heighter parameter with the period parameter either the significant wave period as determined from time-series analysis, the period corresponding to the spectral peak frequency, or the mean wave period from time-series or spectral analysis. The wave direction is usually expressed with the 16-point bearing system (i.e. NNE, WSW, etc.). The wave climate is described in terms of months, seasons and years. See Goda (1990).

wave-current interaction
See Peregrine (1976) and Johsson (1990).

wave forecasting
Predicting the development and characteristics of ocean surface gravity waves via semiempirical methods. These methods use some theory in their foundation but require basic data for the evaluation of various constants and coefficients. Advances in the state-of-the-art are usually a matter of collecting a larger database of winds and the wave they generate. The two main approaches to wave forecasting are the significant wave method and the wave spectrum method. See Komar (1976) and Bates (1949).

wave model
A general term for numerical models designed to simulate the generation, propagation, shoaling, interaction, refraction, reflection, etc. of wind waves. These are used to predict wave fields for complicated wave fields and bathymetry.

First generation wave models include:

Second generation models include:

Third generation models include:


wave set-down
See wave set-up.

wave set-up
A phenomenon local to the surf zone wherein wave breaking causes a stress or a landward push of the water which causes it to pile up against the shore until the seaward slope of this set-up is sufficient to oppose the wave stresses. This is called wave set-up to distinguish it from storm set-up or storm surge and from wind set-up, both of which occur over a larger scale. Wave set-up can range from 17-50% of the incident wave height on natural beaches which can give values of up to 1 m during large storms, which can result in a shoreward indundation of 50 m on a beach with a 1:50 slope. A related wave set-down is found in the vicinity of the wave breaking point in the surf zone, while the set-up occurs shoreward of this. of the wave breaking point on the beach profile, with a small set-down also found at The mechanism by which waves can exert a stress on the fluid in which they propagate is via a phenomenon called radiation stress. See Holman (1990).

wave spectrum
A method for describing the characteristics of irregular waves in which parameterized formulae are developed by spectral analysis of measured wave data. Several wave spectra have been developed including: See ().

wave spectrum method
A method of wave forecasting that describes the waves generated by storms in terms of a complete spectrum of periods and energies rather than in terms of a single significant wave height or period. An example of a wave spectrum method is the P-N-J method, while a significant wave method is the S-M-B method. See Komar (1976).

A series of wavemodels, i.e. WAVEWATCH III is a third-generation wave model that solves the spectral action density balance equation for wavenumber-direction spectra. It is implicitly assumed that the medium (i.e. depth and current) as well as the wave field vary on time and space scales much larger than the corresponding scales of a single wave. The source code and complete documentation are available for WAVEWATCH III.


Abbreviation for western boundary current.

Abbreviation for World Data Center, a system of facilities established within the framework of the IOC IODE program to receive oceanographic data and inventories from NODCs, RNODCs, marine science organizations, and individual scientists. The data are collected and submitted voluntarily from national programs or arise from international cooperative ventures. The WDCs are also responsbile for monitoring the performance of the international data exchange system. See the See the IODE Web site.

See Warm Deep Water.

Weber number
A dimensionless number that relates the inertial force to the surface tension force. It is given by

$\displaystyle W\,=\,{ {{\nu^2}l\rho} \over {\sigma} }$

where $ \nu$ is the kinematic viscosity, $ l$ a characteristic length scale, $ \rho$ the fluid density and $ \sigma$ the surface tension. It is generally used in momentum transfer calculations such as bubble/droplet formation and breakage of liquid jets.

See Barber (1992) and other papers therein.

Weddell Gyre
See Deacon (1979), Orsi et al. (1993) and Schröder and Fahrbach (1999).

Weddell Gyre Boundary
See Continental Water Boundary.

Weddell Sea
More about which later.

Weddell-Scotia Confluence
The zone separating the waters of the Weddell Sea from those of the Scotia Sea in the Southern Ocean. This is a line extending from the South Shetland Islands near the Antarctic Peninsula in a northeastward direction across the southern Scotia Sea to as far as 30$ ^\circ$ E. The deep waters on either side of the boundary are distinguishable on the basis of their temperature and salinity properties, with those to the north of the line (from the southeast Pacific) being warmer and slightly saltier.

The water column in the western WSC itself is nearly homogenuous due to vertical mixing that is active to one degree or another throughout the year. As one proceeds eastward lateral mixing processes gradually mix this homogenous water with the stratified waters to the north and south until such stratification is restored on the WSC is no longer in evidence. The complex bathymetry in the region is thought to play a major part in inducing the lateral mixing processes. See Patterson and Sievers (1980).

Weddell Sea Bottom Water (WSBW)
A type of water found in the seas surrounding Antarctica with temperatures ranging from -1.4 to 0.8$ ^\circ$ C and salinities of 34.65 ppt. It underlies Antarctic Bottom Water (AABW) and is found on the slopes and southern and western ages of the Weddell Sea basin.

Weddell Deep Water (WDW)
In physical oceanography, a water mass type formed in the Weddell Sea by surface cooling and subsequent convection in the polyna. This water has stable properties with a potential temperature between 0.4-0.7$ ^\circ$ C. WDW mixes with water above the continental slope in the Weddell Sea to serve as one source for Antarctic Bottom Water. See Gordon (1982) and Tomczak and Godfrey (1994).

Wedderburn number
A dimensionless number expressing a balance between surface wind stress and the pressure gradient resulting from the slope of the interface. It is given by:

$\displaystyle {W_n}\,=\,{ {g'h} \over {U_*^2} }{ {h} \over {L} }$

where $ h$ is the depth of the thermocline, $ L$ is the fetch length (the length of the reservoir at the thermocline in the direction of the wind), $ U_*$ is the surface friction velocity, and g' is the reduced gravity. $ U_*$ is given by:

$\displaystyle {U_*}\,=\,{ {{C_d}{{\rho_a}\over{\rho_0}}}^{1/2} }\,{U_{10}}$

where $ U_{10}$ is the wind velocity at 10 meters, $ \rho_a$ is the density of the air, and $ {C_d}$ is the drag coefficient. Meanings for various values of the Wedderburn number have been defined:

well mixed estuary
One of four principal types of estuaries as distinguished by prevailing flow conditions. In this type the water column is (as you might have guessed) well mixed with essentially no variation in salinity in a vertical column. The Thames estuary is an example of this type.

Acronym for Western North Pacific Experiment, a Japanese program taking place on the Hakuho Maru from Jan. 11-Feb. 5, 1991. See Fujiyoshi et al. (1995).

Acronym for Western Equatorial Pacific Ocean Circulation Study, a program taking place from 1985-1988 to examine the complex current structures in a relatively poorly explored part of the tropics. See Lindstrom et al. (1987) and Lukas et al. (1991).

Acronym for the U.S.-U.S.S.R. Weddell Polynya Expedition of 1981 aboard the Soviet icebreaker SOMOV. See Chen (1982).


West African Trough
See Guinea Basin.

West Europe Basin
An ocean basin located in the eastern North Atlantic Ocean off the west coast of Europe (and also called the Northeastern Atlantic Basin). This includes the Porcupine Abyssal Plain west of Britain, the Biscay Abyssal Plain, and is connected to the Iberia Basin to the south by the Theta Gap. See Fairbridge (1966).

West Spitsbergen Current
A current flowing offshore of West Spitsbergen Island in the eastern part of Fram Strait. This current carries comparatively warm water from the Atlantic into the Arctic Ocean. See Perkin and Lewis (1984), Swift (1986), Pfirman et al. (1994) and Richez (1998).

western boundary current (WBC)
The intensification of the western limb of an oceanic circulation gyre. This is inevitable given a rotating earth, a meridional boundary, and a zonal wind stress pattern that reverses direction at some latitude as was shown using a simple dynamical model in the classic paper of Stommel (1948). Common features of such currents include their flowing as swift narrow streams along the western continental rise of ocean basins, their extension to great depth well below the thermocline, and their separation from the coast at some point and continuation into the open ocean as narrow jets that develop instabilities along their paths. The most well-known western boundary currents are the Gulf Stream and the Kuroshio Current. See Hogg and Johns (1995).

Western Mediterranean Circulation Experiment (WMCE)
A program to study the circulation of the western Mediterranean Sea from the Strait of Sicily to the Strait of Gibraltar using scales ranging from basin size to 1 km and depths from the surface to the deepest layers. The specific goals were to study the major features of the circulation and their variation in space and time, the physical forcing mechanisms, the affects of the circulation on the chemical, biological and optical properties of the western Mediterranean, and to implement the knowledge gained into numerical models.

The field study began in November 1985 and ended in March 1987, and consisted of the placement of long-term current meter moorings as well as campaigns for procuring measurements from aircraft. The field campaigns ran concurrently with those of two other experiments: POEM and the Gibraltar Experiment, with some effort being expended to make the three campaigns complementary to each other. See La Violette (1990).


Western Mediterranean Deep Water (WMDW)
See Perkins and Pistek (1990).

Western North Atlantic Central Water (WNACW)
See Poole and Tomczak (1999).

Western North Atlantic Water (WNAW)
A water mass defined by Iselin (1936) and () to define water found in the North Atlantic Current. The WNAW definition can be subsumed into the broader definition of North Atlantic Subpolar Mode Water, and thus can be seen as a variety of the latter. Se Read (2001).

Western North Pacific Central Water (WNPCW)
In physical oceanography, the dominant water mass in the northern subtropical gyre, formed and subducted in the northern STC. This is fresher than NPEW at all temperatures and saltier than ENPCW except at temperatures above about 17$ ^\circ$ C (the upper thermocline). It is separated to the east from ENPCW at around 170$ ^\circ$ W and to the south from NPEW at around 12-15$ ^\circ$ N. See Tomczak and Godfrey (1994), p. 165.

Western Pacific Warm Pool (WPWP)
An ENSO-related phenomenon conventionally defined as SSTs greater than or equal to 28 $ ^\circ$C. It is a large area of heat accumulation in the global ocean and related to the development of El Nino. See Ho et al. (1995).

Western South Atlantic Central Water (WSACW)
See Poole and Tomczak (1999).

Western South Pacific Central Water (WSPCW)
In physical oceanography, a water mass which is one of six distinguishable Central Water masses in the Pacific Ocean. Its T-S properties are almost indistinguishable from those of ICW and SACW, indicative of similar atmospheric conditions during formation. It is formed and subducted in the STC between Tasmania and New Zealand, and is geographically restricted by that and Australia at 150$ ^\circ$ W. It is separated to the east from the fresher ESPCW in a broad transition zone between 145 and 100$ ^\circ$ W, and to the north from SPEW, fresher above 8$ ^\circ$ C and saltier below, at around 15$ ^\circ$ S. See Tomczak and Godfrey (1994), p. 164.

Western Tropical Atlantic Experiment (WESTRAX)
An international field program conducted during 1989-1991 in the western boundary region of the tropical Atlantic between 0$ ^\circ$ and 10$ ^\circ$ N. Moored current meter observations were collected in the North Brazil Current (NBC) near the equator, near 4$ ^\circ$ N, and near 6$ ^\circ$ N to investigate the structure and variability of the NBC. See Brown et al. (1992).

Acronym for Western Tropical Atlantic Experiment.

A 1982 cruise in the western tropical South Pacific Ocean whose goal was to reassess the regional distribution of the water masses in the area, to identify possible fronts in the region, and to get some idea of the frequency of occurrence of water mass layering, intrusions or interleaving. WESTROPAC was performed using the R. V. Sprightly of the CSIRO. It consisted of three individual cruises identified as Sprightly cruises Sp9/82 (from Sydney to Honiara), Sp10/82 (from Honiara to Nouméa), and Sp11/82 (from Nouméa to Sydney). See Tomczak and Gu (1987).

wet-bulb temperature
The temperature obtained by covering the bulb of a dry-bulb thermometer with a silk or cotton wick saturated with distilled water and drawing air over it at a velocity not less than 1000 ft/min. This is often accomplished by swinging the covered thermometer on the end of a string or rope. If the atmosphere is saturated with water vapor, the water in the wick will not evaporate and the dry and wet bulb temperatures will be the same. If the atmosphere is not completely saturated, the water will evaporate from the wick at a rate depedent upon the degree of saturation. The evaporation will cool the bulb and lower the temperature reading over that of the dry-bulb temperature to that of the wet-bulb temperature.

white noise
Noise that results in a spectrum where all frequency components have the same amount of energy. This can also refer the the resulting spectrum as well as the process. Compare to red noise.

White Sea
One of the seas found on the Siberian shelf in the Arctic Mediterranean Sea. It is located to the west of the Barents Sea and is otherwise landlocked. See Zenkevitch (1963).

Abbreviation for Woods Hole Oceanographic Institution.

Abbreviation for WOCE Hydrographic Program Office. See the WOCE entry.


Acronym for World Hydrological Cycle Observing System.

Wilkes, Charles (1798-1877)
See Peterson et al. (1996), p. 72.

A violent squall in the Straits of Magellan. This is a region where the winds are almost constantly strong and westerly.

wind chill temperature
The hypothetical air temperature in calm conditions that would cause the same heat flux from the skin as occurs for the true winds and the true air temperature.

wind scatterometry
A method wherein a specialized radar called a scatterometer is used to measure the near-surface wind speed and direction. The technique is indirect, i.e. the instrument tranasmits microwave pulses and receives backscattered power from the ocean surface. Changes in wind velocity cause changes in ocean surface roughness, modifying the radar cross-section of the ocean and the magnitude of backscattered power. This backscattered power is measured by scatterometers to obtain an estimate of the normalized radar cross-section of the sea surface. The cross-section varies with both wind speed and direction when measured at moderate incidence angles, allowing the development of a transfer function called a geophysical model function relating the former to the latter. Multiple, collocated, nearly simultaneous cross-section measurements acquired from several directions can be used to simultaneously solve for wind speed and direction. See Naderi et al. (1991).


wind stress
The dominant driving source for the surface layer of the world's oceans. The wind stress $ \tau$ represents a complex interfacial momentum exchange process between the wind and the underlying wind waves and surface currents. Historically, the measurement of the wind stress has been a problematic task. It is usually measured above the sea surface from fixed towers, ships or low-flying aircraft. The most direct approach is a technique called the eddy correlation method wherein the directional components of the near-surface turbulent stress covariance in the atmospheric boundary layer are measured.

A popular alternative technique for measuring the magnitude of the wind stress is based on equilibrium turbulent boundary layer modeling. The vertical wind profile is taken to have the form:

$\displaystyle U(z)\,=\,{{u^*}\over \kappa}
\left[\ln\left({z\over{z_0}}\right)\,-\,{\psi_m}\left({z\over L}\right)

where $ U(z)$ is the wind speed at height $ z$ meters above the surface, $ u^*$ is the surface wind friction velocity given by $ {(\tau /{\rho_a})}^{1/2}$, $ \rho_a$ is the density of air, $ z_0$ is the aerodynamic roughness length, $ \kappa$ = 4 is the von Kármán constant, $ \psi_m$ is a thermal stratification function given for unstable conditions $ (z/L\,<\,0)$ by:

$\displaystyle {\psi_m}\left({z\over L}\right)\,=\,
{{\left({{1+x}\over 2}\right)}^2}\right]\,-\,
2\arctan x\,+\,{\pi\over 2}$

where $ x\,=\,{{(1-16z/L)}^{1/4}}$, and for stable conditions $ (z/L\,>\,0)$ by:

$\displaystyle {\psi_m}\left({z\over L}\right)\,=\,-5{z\over L}$

. $ L$ is the Monin-Obukhov stability length scale defined by:

$\displaystyle L\,=\,{ {-{T_\nu}{u^3_*}} \over {g\kappa\overline{w{T_\nu}}} }$

where $ T_\nu$ is the virtual temperature and $ g$ the gravitational acceleration. The associated drag coefficient is:

$\displaystyle {C_d}\,=\,{ {u_*^2}\over{U^2_{10}} }$

where $ U_{10}$ is the wind speed 10 meters above the sea surface.

The roughness length varies according to conditions. At low wind speeds with aerodynamically smooth flow over the surface it is given by:

$\displaystyle {z_0}\,=\,0.11\nu /{u_*}$

where $ \nu$ is the kinematic viscosity of the air. As the winds grow stronger, the roughness length is given by:

$\displaystyle {z_0}\,=\,\alpha{u^2_*}/g$

where $ \alpha$ is known as the Charnock coefficient, which ranges from 0.011 for well-developed ocean conditions to 0.0145-0.018 for coastal sites with less mature waves. High variability among various measurements led to a proposed extension of the Charnock relation in which the roughness length is a function of the wave age, i.e.

$\displaystyle {z_0}\,=\,{ {u^2_*}\over g}\,f({c_p}/{u^*})$

where $ c_p$ is the phase speed of the spectral peak waves. Several forms for this function have been proposed.

Another technique for estimating the wind stress is the inertial dissipation method, which depends on an assumed dependent on the friction velocity $ u^*$ in the spectral level of the inertial subrange of the turbulence spectrum. See Banner et al. (1999).

Winter Intermediate Water (WIW)
A water mass ... See Perkins and Pistek (1990).

Winter Water
See Antarctic Surface Water (AASW).

Winter Weddell Sea Experiment
An experiment taking place in 1986.

Abbreviation for Winter Intermediate Water.

WKB approximation
More later.

Abbreviation for Western Mediterranean Circulation Experiment.

Abbreviation for Western Mediterranean Deep Water.

Acronym for Winter Monsoon Experiment, a program taking place from Dec. 1, 1978 to Mar. 5, 1979 in the Indian Ocean, the western part of the Pacific Ocean, and in adjacent continental areas.


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