Kinematics of a warm‐core dipole ring

The remote sensing and in situ data used by Hooker and Brown [1994] to establish the dipole identity of warm core ring (WCR) 82‐B is reexamined. It is found that a rotating barotropic modon [ Mied et al. , 1992] can be constructed with the same dipole rotation rate, center‐to‐center vortex separation distance, and peak anticyclonic vorticity as those of WCR 82‐B. The model‐derived velocity field is used to deform an array of material lines during a rotation period when the dipole is evident in the imagery and agreement between the model and the imagery is good. Specifically, it is observed that at the end of the imaging period, the surface tracer assumes a skewed dipole appearance, in which the line of centers is not perpendicular to the separatrix. Moreover, the separatrix morphology is qualitatively reproduced. Finally, the cyclone assumes an axisymmetric form. An attempt to derive qualitatively similar signatures using only monopole forcing yields results dissimilar from both the advanced very high resolution radiometer imagery and those obtained with the dipole, further confirming the underlying dipole character of WCR 82‐B.