Parameterizations of Boundary Layer Mass Fluxes in High-Wind Conditions for Hurricane Analysis and Forecast System

Development of accurate planetary boundary layer (PBL) parameterizations in high-wind conditions is crucial for improving hurricane forecasts. However, Eddy-Diffusivity Mass-Flux (EDMF)-type PBL schemes, which are widely adopted in various global and regional UFS models, are generally designed for low-wind, convective boundary layers. In high-wind conditions, the lack of an appropriate parametrization of the impact of vertical wind shear on damping rising thermal plumes (i.e., surface-driven mass fluxes, MF) in the EDMF-type schemes can lead to excessive vertical turbulent mixing in hurricane boundary layers and thereby lead to forecast errors. As part of a NOAA/WPO funded project, a new approach of tapering surface-driven MF based on the surface stability parameter is proposed, aiming to retain the surface-driven MF only in non-TC boundary layers. Effects of this approach on modeled tropical cyclone structure and intensity are examined by performing three-dimensional idealized simulations. Compared to the experiments retaining the original MF components, using this approach of MF tapering can lead to a stronger and more compact inner core due to enhanced boundary layer inflow. Comparison to observations and further discussions on MF parameterizations in high-wind conditions will be presented.