See vorticity

1. The vorticity of a fluid particle determined with respect to an absolute coordinate system. The absolute vorticity vector is defined by 2Ω + ∇ × , where Ω is the earth's angular velocity vector and 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)

The sum of the relative vorticity ( ) and the planetary vorticity, i.e. .