物理海洋学名词-V 449

Glossary of Physical Oceanography and Related Disciplines

Steven K. Baum Department of Oceanography Texas A&M University

May 26, 2004

 

VENTS A NOAA PMEL program established in 1984 to focus research on determining the oceanic impacts and consequences of submarine hydrothermal venting, with most of the effort directed towards achieving an understanding of the chemical and thermal effects of venting along northeast Pacific Ocean seafloor spreading centers. See the VENTS Web site (http://www.pmel.noaa.gov/vents/home.html).


Veronis effect See Gough and Lin [1994].


VERTEX A multidisciplinary study of VERtical Transport and EXchange of material in the upper ocean performed in the California Current. It was organized to investigate the vertical exchange of materials between the photic zone and deeper waters in the Pacific Ocean. VERTEX was one of the first larger scale programs to focus on the couplings between new production and export. Components involved the use of particle traps and subsequent analyses of trapped particles for major elements, trace elements, radionuclides, fecal pellets and microbial populations to estimate vertical particulate fluxes. See Martin et al. [1987] and Broenkow et al. [1992].


vertical coordinates Currently there are three main types of vertical coordinate systems in use in ocean models, each representing specific generalized vertical coordinate systems. These types are z, σ or ρ vertical coordinates.
The simplest type is z coordinates, where z represents the vertical distance from a resting ocean surface (i.e. a static ocean under hydrostatic balance) at z = 0, with z positive upwards and z = -H(x,y) the topography. Griffies et al. [2000] list the advantages of z coordinates as:
• allowing the simplest of numerical discretization approaches;
• easy representation of the horizontal pressure gradient for a Boussinesq fluid;
• clean and accurate representation of the equation of state for seawater; and
• natural parameterization of the surface mixed layer using a z–coordinate.
The disadvantages are:
• cumbersome representation of tracer advection and diffusion along inclined density surfaces in the ocean interior;
• unnatural representation and parameterization of the bottom boundary layer; and
• difficult representation of bottom topography.
Another choice for vertical coordinate is the potential density ρ referenced to a given pressure. This is a close analogy to the use of the entropy or potential temperature in atmospheric models. In a stably stratified adiabatic ocean, potential density is materially conserved and defines a monotonic layering of the ocean fluid. The advantages are:
• well–suitedness for representing the dynamic of tracer transport in the ocean interior since it has a strong tendency to occur along directions defined by locally referenced potential density;
• representation of the bottom topography in a piecewise linear manner;
• better representation of the physics of overflows;
• easy representation of the horizontal pressure gradient in an adiabatic fluid; and
• conservation of the volume (Boussinesq fluid) or mass (non-Boussinesq fluid) between isopycnals.
The disadvantages are:

• cumbersome representation of the effects of a realistic, nonlinear equation of state; and
• an inappropriate framework for representing the surface mixed layer or bottom boundary layer.
The third popular vertical coordinate choice is the terrain following or σ coordinate, originally introduced in atmospheric modeling in 1957 and usually defined as:
σ =(z − η)/(H + η)
where η(x, y, t) is the displacement of the ocean surface from its resting position z = 0, and z =−H(x, y) is the ocean bottom. The usual convention is that σ = 0 is the ocean surface and σ = −1 the ocean bottom. Sine σ is monotonic, the relation defines a unique mapping between the depth z and σ. The advantages of this coordinate are:
• a smooth representation of the ocean bottom topography with isolines concentrated where bottom boundary layer processes are most important; and
• good representation of the thermodynamic effects associated with the equation of state.
The disadvantages include:
• variable representation of the surface mixed layer, i.e. more surface layers in shallow than in deeper water;
• cumbersome representation of advection and diffusion along inclined density surfaces in the ocean interior;
• difficulty in accurately representing the horizontal pressure gradient, which is the difference of two relatively large numbers.

 

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