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In [[fluid mechanics]], the '''Okubo–Weiss parameter''', (normally given by "W") is a measure of the relative importance of [[Deformation (mechanics)|deformation]] and [[rotation]] at a given point. It is calculated as the sum of the squares of normal and [[shear strain]] minus the [[relative vorticity]].  This is widely applicable in fluid properties particularly in identifying and describing [[Eddy (fluid dynamics)|oceanic eddies]].  

For a horizontally non-divergent flow in the ocean, the parameter is given by:

:<math>W = s_n^2 + s_s^2 - \omega^2</math>

where:
* <math>s_n</math> is the normal strain.
* <math>s_s</math> is the shear strain.
* <math>\omega</math> is the relative vorticity.

==References==
* Okubo, A., 1970: Horizontal dispersion of floatable particles in the vicinity of velocity singularities such as convergences. Deep-Sea Res., 17, 445–454
* Weiss, J., 1991: The dynamics of enstrophy transfer in two-dimensional hydrodynamics. PhysicaD, 48, 273–294


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[[Category:Fluid dynamics]]
[[Category:Continuum mechanics]]


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