Helical scenario of tropical cyclone genesis and intensification

Abstract

A helical scenario of tropical cyclogenesis and further vortex intensification is proposed based on results of direct numerical simulation of atmospheric flows. The main idea of the scenario consists in a specific topology of helical flows which are characterized by the linkage of vortex lines. Velocity fields resulting from a high resolution numerical simulation by the Regional Atmospheric Modeling System (RAMS) are used to calculate helical and integral characteristics during a tropical cyclone formation. It is shown how non-zero mean helicity is generated by moist convective atmospheric turbulence, which implies a new flow topology with linked vortex lines. A possible role of vortical hot towers (VHTs) is discussed in generating the linkage. It is shown that the linkage results in a positive feedback between the horizontal and vertical circulation in the formation of a larger-scale vortex and contributes to the instability of the macro vortex.