On the role of asymmetric convective bursts to the problem of hurricane intensification. Radiation of vortex Rossby waves and wave-mean flow interactions

The role of asymmetric convection to the intensity change of a weak vortex, is investigated with the aid of a "dry" thermally forced model. Numerical experiments are conducted, starting with a weak vortex forced by a localized thermal anomaly. The concept of wave activities, the Eliassen-Palm flux, and eddy kinetic energy are then applied to identify the nature of the dominant generated waves and diagnose their kinematics, structure and impact on the primary vortex. The physical reasons for which disagreements with previous studies exist, are also investigated utilizing the governing equation for potential vorticity (PV) perturbations and a number of sensitivity experiments.

From the control experiment, it is found that the response of the vortex is dominated by the radiation of a damped sheared vortex Rossby wave (VRW) that acts to accelerate the symmetric flow through the transport of angular momentum. An increase of the kinetic energy of the symmetric flow by the VRW is shown also from the eddy kinetic energy budget. Additional tests performed on the structure and the magnitude of the initial thermal forcing confirm the robustness of the results and emphasize the significance of the wave-mean flow interaction to the intensification process.

From the sensitivity experiments, it is found that for a localized thermal anomaly, regardless of the baroclinicity of the vortex, the radial and the vertical gradients of the thermal forcing, the resultant PV perturbation follows a damping behavior, suggesting therefore that deceleration of the vortex should not be expected.