Potential vorticity
The potential vorticity or potential vorticity is important as a measure of the shear of currents, especially in oceanography and meteorology . It combines the conservation of vorticity (vorticity) with the conservation of mass and is a special case of ertel rule vortex set .
The potential vorticity is defined as:
With
- the relative vorticity
-
the planetary vorticity
- the angular velocity
- the density
- the Nabla operator
- a scalar quantity that only depends on the pressure and the density, for example the potential temperature or the potential density .
The PVU ( potential vorticity unit ) is commonly used in meteorology as the unit of measurement for potential vorticity :
The source or sink of potential vorticity are baroclinic effects and friction .
If the following restrictions apply to the flow:
- no friction
- is the conservation quantity , d. H.
- Barotropy , d. H. or
then the potential vorticity is also a conserved quantity:
It follows that the relative vorticity must decrease as the planetary vorticity increases, e.g. B. when moving a column of water to the north. This is analogous to the conservation of angular momentum in mechanics.
When is a function of density and pressure, i. H. , this is synonymous with adiabasia . Then the obtained potential vorticity can also be represented as:
With
- the latitude
- the water depth .
literature
- Joseph Pedlosky: Geophysical Fluid Dynamícs. Springer Verlag 1987. ISBN 3-540-96387-1
- Adrian E. Gill: Atmosphere-Ocean Dynamics. International Geophysics Series. ISBN 0-12-283522-0
- Jose P. Peixoto: Physics of Climate. Springer Verlag 1992. ISBN 0-88318-712-4
Web link
- Michael E. McIntyre: Potential vorticity ( PDF )