•If the horizontal flow is divergent, the area enclosed
by a chain of fluid parcels
will increase with time and if circulation
is to be conserved, the average absolute vorticity of the enclosed fluid must decrease (i.e., the vorticity
will be diluted).
•If, however, the flow is convergent, the area enclosed
by a chain of fluid parcels
will decrease with time and the vorticity
will be concentrated.
•This mechanism for changing vorticity following the motion is very important in synoptic-scale disturbances.