Interactions between a barotropic vortex and an idealized subtropical ridge. Part II: structure changes

The interactions between a barotropic vortex and an idealized subtropical ridge environment on a beta plane are examined and compared to the well-documented case of a single vortex with no environmental flow. First, the problems and advantages of several potential partitioning methods are discussed and then a three-part partition is chosen. Substantial variations are found from the single vortex case. In particular, the familiar gyres associated with the propagation of a single vortex are markedly distorted and relocated by the environment. A vorticity budget is presented to help isolate the physical mechanisms. This analysis indicates that the major processes are associated with interactions with the gradients of absolute vorticity in the environment. Other nonlinear mechanisms can also be of significance in specific cases. -Authors