Vorticity

A measure of the rotation of a fluid. Mathematically, the vorticity is the curl of the velocity field. The vorticity gives a measure of the rotation about a single point whereas the circulation gives a measure of the rotation of a fluid over a finite area.

A measure of the local rotation in a fluid flow. In weather analysis and forecasting, it usually refers to the vertical component of rotation (i.e., rotation about a vertical axis) and is used most often in reference to synoptic scale or mesoscale weather systems. By convention, positive values indicate cyclonic rotation .