Angular momentum transports by moving spiral waves

Theoretical results based on the shallow water equations show that outgoing spiral waves generated by a nonaxisymmetric vortex can effectively remove angular momentum from the vortex, and the removal rate is sensitive to the strength of the vortex. When the model is applied to tropical cyclones, the results suggest that radiation of spiral waves may play a noticeable role in the total angular momentum budget of the core and affect the intensification of a tropical cyclone. An Eliassen-Palm relation is derived for the shallow water equations. It shows that the total angular momentum carried by shallow water waves does not change during their propagation through an axisymmetric mean flow.