q Potential
Vorticity
PV = f + z
f = planetary vorticity = 2Wsinf
z
= relative vorticity = ¶v/¶x- ¶u/¶y
q f1 + z1 = f2 + z2
since f1 > f2 à z1 < z2
q If z < 0, the vortex decreases rotation when moves toward lower latitudes and increases rotation when moves toward higher latitudes.