 Potential vorticity

Potential vorticity combines fluid rotation with stretching and stratification. For an inviscid barotropic shallow-water layer,where $\zeta$ is relative vorticity and $h$ is layer thickness.

Potential vorticity is a fundamental quantity in fluid dynamics, especially in the study of atmospheric and oceanic sciences. It combines the concepts of vorticity, which is a measure of the rotation of a fluid, with stratification effects related to potential temperature or density.