# Vorticities

From Glossary of Meteorology

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## vorticity

A vector measure of local rotation in a fluid flow, defined mathematically as the curl of the velocity vector, where ζ is the vorticity,

**u**the velocity, and**∇**the del operator.The vorticity component normal to a small plane element is the limit of the circulation per unit area as the area of the element approaches zero (

*see*Stokes's theorem). The vorticity of a solid rotation is twice the angular velocity vector. In meteorology, "the vorticity" usually refers to the vertical component of the vorticity.*See also*relative vorticity, absolute vorticity, geostrophic vorticity, thermal vorticity, vorticity equation, curl;*compare*deformation, divergence.