THE DECAY OF CYCLONIC EDDIES BY ROSSBY-WAVE RADIATION

It is argued that because shallow water cyclones on a P-plane drift we stward at a speed equal to an available Rossby wave phase speed, they must radiate energy and cannot, therefore, be steady. The form of the Rossby wave wake accompanying a quasi-steady cyclone is calculated and the energy flux in the radiated waves determined. Further, an explici t expression for the radiation-induced northward drift of the cyclone is obtained. A general method for determining the effects of the radia tion on the radius and amplitude of the vortex based on conservation o f energy and potential vorticity is given. An example calculation for a cyclone with a 'top-hat' profile is presented, demonstrating that th e primary effect of the radiation is to decrease the radius of the vor tex. The dimensional timescale associated with the decay of oceanic vo rtices is of the order of several months to a year.