The vorticity of a fluid particle determined with respect to an absolute coordinate system.

The absolute vorticity vector is defined by 2Ω + ∇ × u, where Ω is the earth's angular velocity vector and u is the three-dimensional relative velocity vector. 2. The vertical component η of the absolute vorticity vector (as defined above) given by the sum of the vertical component of the vorticity with respect to the earth (the relative vorticity) ζ and the vorticity of the earth (equal to the Coriolis parameter) f: