Potential Vorticity
For adiabatic motion ( i.e., is a constant) the density is = P(Cv/Cp). For motions between layers of constant
In the Shallow Water Model, where is a constant ( i.e., incompressible), the conserved quantity is usually written as:
example : flow over a mountain
<u> is eastward (westerly) then flow turns towards equator as it passes mountain, then oscillates around original latitude.
<u> is westward (easterly) then flow turns equatorward (note flow turning poleward `bucks' the flow causing it to turn equatorward. System is returned to original latitude after it passes mountain. No oscillations.