Effect of baroclinicity on vortex axisymmetrization

A two-layer baroclinic model is constructed to investigate the axisymmetrization process in a hurricane-like vortex. Three types of basic-state vortices with different baroclicity are examined. The first one is a barotropic vortex with the same strong cyclone at both the lower and upper levels. The second one is a weak baroclinic vortex with a strong cyclone at the lower level but a weak cyclone at the upper level. The third one is a strong baroclinic vortex with a strong cyclone at the lower level and a strong anticyclone at the upper level. The initial barotropic (baroclinic) wave-number-two vorticity disturbances are specified near the eyewall of the symmetric vortex.

Under the barotropic symmetric vortex, more asymmetric energy is transferred to the symmetric flow from a baroclinic initial perturbation than a barotropic initial perturbation due to the slower (faster) radial propagation of the baroclinic (barotropic) vortex Rossby wave energy. As a result, the axisymmetrization process is faster in the presence of an initial baroclinic perturbation than an initial barotropic perturbation. With the increase of baroclicity of the symmetric vortex, the energy transfer from asymmetric disturbances to symmetric flows decreases, leading to a slower axisymmetrization process.