Evaluating the Impact of Parameterized Turbulent Mixing and Boundary Layer Structure on Hurricane Intensification

This talk presents results from the authors’ recent work on evaluating the role of turbulence and boundary-layer parameterizations on hurricane intensification. We show that observation-based modification of these physical parameterizations significantly improved the HWRF intensity forecast. Turbulent mixing in both the vertical and horizontal directions are found to be crucial for hurricane spin-up dynamics in 3D numerical simulations and HWRF forecasts. Vertical turbulent mixing regulates the inflow strength and the location of boundary-layer convergence that in turns regulates the distribution of deep convection and the intensification of the whole hurricane vortex. Convergence of angular momentum in the boundary layer that is a key component of the hurricane spin-up theory is also found to be regulated by vertical turbulent mixing in connection to the boundary layer inflow. Horizontal turbulent mixing, on the other hand, mainly influences the eddy momentum flux inside the radius of the maximum wind speed in the angular momentum budget. The effect of horizontal turbulent mixing on the convergence of angular momentum is on smoothing the radial gradient of the angular momentum when the horizontal mixing length is large. In a sheared storm, both the vertical and horizontal turbulent mixing affect vortex and shear interaction in terms of the evolution of vortex tilt and boundary-layer recovery processes.