Vorticity – the vector measure of the tendency a fluid parcel has to rotate about an axis through its center of mass.

 

Vorticity is directly proportional to angular velocity but is NOT the same thing as angular velocity.  Vorticity is a three dimensional vector.  In synoptic meteorology we are often most interested in the vertical component of the vorticity vector.  That’s given the Greek letter zeta.

 

We will see that vorticity is the “name” given to a kinematic property of the velocity field that appears in kinematic equations.  We will see that it is actually twice the local angular velocity field, 2 X omega (angular velocity) . 

 

Thus, in each instance that 2 X omega (angular velocity) appears in the equations, the symbol for vorticity is substituted. In the case of vorticity associated with the wind flow, the vorticity is relative to the surface of the earth, whihc can have three components (along each of the coordinate axes).

 

What is important at the synoptic scale is the vertical component of relative vorticity. Here are the two equations for the vertical component of relative vorticity.

 

 

What are the units of vorticity?

VKs is known as curvature vorticity.

∂V/∂n is known as shear vorticity.