Effects of Surface Fluxes on Ventilation Pathways and the Intensification of Hurricane Michael (2018)

Abstract

This study investigates the effects of surface fluxes on ventilation pathways and the development of Hurricane Michael (2018), and is a real-case comparison to previous idealized modeling studies that investigate ventilation. Two modeling experiments are conducted by altering surface exchange coefficients to achieve a strong and weak experiment. Ventilation pathways are evaluated to understand how the vortex responds to dry-air infiltration. Pathways for dry-air infiltration are split into downdraft and radial ventilation. Results show that downdraft ventilation at low levels is maximized left of shear, exists between the surface and a height of 3 km, and is associated with rainband activity. Trajectories from downdraft ventilation demonstrate slower thermodynamic recovery for the weaker experiment. The slower recovery contributes to the initial intensity bifurcation between experiments. Radial ventilation has two pathways. At low levels, it is coupled with downdraft ventilation. Aloft, between heights of 5 and 10 km, it is maximized upshear and associated with storm-relative flow. This pathway is similar for each experiment initially, suggesting that the initial bifurcation of intensity is not a consequence of radial ventilation aloft. Trajectories from radial ventilation during a later time period show the destructive impact of lower-θe air in the near environment on convection upshear and right of shear for the weaker experiment. This study demonstrates how ventilation pathways at low levels and aloft are affected by surface fluxes, and how ventilation pathways operate, at different times, to affect tropical cyclone development.