ESS227
Prof. Jin-Yi Yu
Ertel’s
Potential Vorticity
•The quantity P [units: K kg−1
m2 s−1] is the isentropic coordinate form of Ertel’s
potential vorticity.
•It is defined with a minus sign so that its value is
normally positive in the Northern Hemisphere.
•Potential vorticity is often expressed in the potential
vorticity unit (PVU), where
1 PVU = 10−6 K kg−1 m2 s−1.
•Potential vorticity is always in some sense a measure of
the ratio of the absolute
vorticity to the effective depth of
the vortex.
•The effective depth is just the differential distance
between potential temperature
surfaces measured in pressure units (−∂θ/∂p).
