Mr. Gao presented a seminar “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 mid-troposphere where baroclinicity reaches the maximum have little impact on the vortex mean flow near the surface, rather, they show a strong upward and radially outward propagation till the stagnation height and radius where energy is absorbed into the mean flow. The substantially different locations of wave-mean-flow interaction resulting from disturbances excited at different heights in baroclinic vortices have an important implication on TC intensification.
The recording of the presentation is available on the anonymous ftp site: