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Vortensity is an astrophysics term for the ratio of a fluid's (local) vorticity to the surface density, within a relatively flat volume of fluid such as a disk. Vorticity is a measure of local angular rotation in a fluid flow, i.e., the curl of the flow's velocity field. Vortensity comes into play in the formation of gravitational instability within protoplanetary disks and in disk/planet dynamics.
In also astrophysics, the term potential vorticity (PV) the same quantity, adopted from meteorology and oceanography where it has been used for various ratios between the vorticity and some indication of the height of the fluid parcel. A basic model of atmospheric circulation (like a default, when free from some influences) presumes the potential vorticity is conserved.