With linear shallow water theory (LSW) we find del(omega)/del(t) = 0, that is vorticity is preserved, whereas if we consider non-linear shallow water theory (NLSW) it is the potential vorticity that is conserved following each fluid particle. In oceanographic context potential vorticity is a very important parameter. I wish to distinguish the vorticity and potential vorticity terms physically? How can I do this?
By the word 'physically' I mean some real life examples by which this distinctions seems obvious.