Understanding the Influence of Uniform Flow on Tropical Cyclogenesis and Intensification

To obtain an understanding of the influence of a uniform flow on tropical cyclogenesis and intensification in three dimensions, we analyze a suite of idealized numerical simulation experiments with a zonally uniform flow in geostrophic balance above the frictional boundary layer, together with an initially weak circular vortex in gradient wind balance above the boundary layer. To keep the experiments simple, we assume a uniform sea-surface temperature, a standard bulk aerodynamic surface scheme for heat and momentum transfer at the ocean surface and a simple boundary layer parameterization scheme. Because of the frictional interaction between the initial vortex and the uniform flow of the environment, a preferred sector of the vortex flow emerges for initiating deep organized convection in and around the maximum wind region of the developing vortex. This azimuthal asymmetry modulates the ensuing convective-vorticity organization and intensification process and is notably different from the more random convective asymmetries found in companion no-motion experiments. Implications of the motion-induced convective and wind asymmetries on the organization and intensification of the emerging tropical cyclone will be analyzed in relation to forecasting rules of thumb.