What is "potential vorticity"

n. (context meteorology English) a quantity which is proportional to the product of vorticity and stratification. When applied to air parcels, aids the understanding of cyclogenesis

Potential vorticity (PV) is a quantity which is proportional to the dot product of vorticity and stratification that, following a parcel of air or water, can only be changed by diabatic or frictional processes. It is a useful concept for understanding the generation of vorticity in cyclogenesis (the birth and development of a cyclone), especially along the polar front, and in analyzing flow in the ocean.

In meteorology, the potential vorticity unit (PVU) is defined as ${10^{-6} \cdot K \cdot m^2 \over kg \cdot s} \equiv 1 PVU$.

It is also useful in tracing intrusions of stratospheric air deep into the troposphere in the vicinity of jet streaks, a concentrated region within a jet stream where the wind speeds are the strongest. It acts as a flow tracer in the ocean as well. It can also be used to explain how a range of mountains like the Andes can make the upper westerly winds swerve towards the equator and back.

Baroclinic instability requires the presence of a potential vorticity gradient along which waves amplify during cyclogenesis.