Vortex Rossby wave propagation and wave-mean-flow interaction in 3D baroclinic TC-like vortices

Vortex Rossby wave propagation (VRW) and wave-mean-flow interaction in 3D baroclinic TC-like vortices are investigated using both theoretical analyses and numerical simulations by WRF. Based on the asymmetric balance (AB) model, the dispersion relation, group velocities, and stagnation radius and height of VRWs propagating in 3D baroclinic TC-like vortices are derived. The theoretical derivation and analyses show that basic-state baroclinicity has a profound impact on the radial and vertical propagation of VRWs. Unlike barotropic vortices in which vertically propagating VRWs do not change their vertical wavenumbers, the vertically propagating VRWs in baroclinic vortices increase their wavenumbers as wave packets propagate upward, similar to the shearing effect that causes the increase of radial wavenumbers. Compared with the VRWs in barotropic vortices, baroclinicity limits the radial propagation but promotes the vertical propagation of VRWs. Numerical simulations by WRF confirm the main findings of theoretical analyses and show a substantial vortex structure change induced by baroclinicity. In addition, the simulations show that perturbations excited near the surface in baroclinic vortices behave in a similar manner to barotropic VRWs in that vertical propagation is limited and wave energy is axisymmetrized into the mean flow at the stagnation radius, a classic view of wave-mean-flow interaction of VRW theory obtained in 2D nondivergent and 3D barotropic AB model. However, perturbations excited in the low- to mid-troposphere and in the inner core region of the vortex can most effectively propagate upward but their radial propagation is substantially suppressed. WRF dry simulations by turning off all model physics confirm the main findings of the theoretical analyses. The numerical simulations also show for wave activity excited at the surface, the wave-mean interaction associated with wave outward propagation just follows what was depicted in 2D barotropic model and 3D barotropic vortices. The wave-mean interaction induced maximum acceleration occurs outside the radius of the center of the initial perturbation, leading to a storm expansion. On the other hands, for wave activity excited in the low- to mid-troposphere and in the inner core region, baroclinicty suppress wave outward propagation but promotes wave upward propagation, which tends to result in storm contraction. The reason is the wave-mean interaction induced maximum acceleration occurs inside the initial perturbation center in 3D baroclinic vorticity. This result can be an important implication on TC intensification.