Effects of Baroclinicity and Different Initial Asymmetries on Vortex Axisymmetrization

A non-linear two-layer model is constructed to investigate the effects of baroclinicity and different initial asymmetries on the vortex axisymmetrization process. Only stable hurricane-like symmetric profiles are considered and the asymmetric disturbances have a wavenumber-two structure in the azimuthal direction. There is more than one track for the outward radial propagating of the asymmetric kinetic energy (KE) in the linear axisymmetrization process for both barotropic and baroclinic vortices, but only one track during the non-linear axisymmetrization. The asymmetric KE in the inner core region in the linear barotropic process is larger than that in the linear baroclinic axisymmetrization process. The initial baroclinic asymmetries can generate a barotropic asymmetry, but the barotropic asymmetric KE is one order smaller than the corresponding baroclinic asymmetric KE, as such the baroclinic asymmetric KE can directly exchange energy with the barotropic symmetric component. Overall, the hurricane-like vortex is weaker during the nonlinear barotropic evolution process than that in the nonlinear baroclinic process.

Two different initial vorticity asymmetries are considered, with the maximum center of the first type located at the radius of maximum wind (RMW) and the second one situated outside the RMW. For the first type initial disturbance, the asymmetric KE decreases with time, and the symmetric vortex intensifies during the first eight hours followed by a weakening stage. In comparison, the second-type asymmetric disturbance grows during the first three hours near the RMW at the expense of the symmetric vortex and weakens at later time with the energy feeding back to the symmetric vortex.