Assuming there is a separation in scale between the mean flow and fluctuations, the linearized potential vorticity equation is solved using the WKB method. Attention is focused on wave properties such as action and enstrophy which in some circumstances are conserved. In the most general case of Rossby waves supported by an arbitrary mean potential vorticity field,q=f/h, and propagating through a forced mean flow neither action nor enstrophy is conserved. It is shown that action is produced by the forcing which drives mean flow acrossqcontours, while enstrophy is produced both by complicatedqcontours and by horizontal divergence of the mean flow.