Effects of Vertical Eddy Diffusivity Parameterization on the Evolution of Landfalling Hurricanes

Abstract

ue to rapid changes in surface conditions when a landfalling hurricane moves from ocean to land, interactions between the hurricane and surface heat and moisture fluxes become essential components of its evolution and dissipation. With a research version of the Hurricane Weather Research and Forecasting (HWRF) model, this study examines the effects of the vertical eddy diffusivity in boundary layer on the evolution of three landfalling hurricanes (Dennis, Katrina, and Rita in 2005).Specifically, the parameterization scheme of eddy diffusivity for momentum (Km) is adjusted with the modification of the mixed-layer velocity scale in the HWRF model for both stable and unstable conditions. Results show that the change in the Km parameter leads to improved simulations of hurricane track, intensity, and quantitative precipitation against observations during and after landfall, compared to the simulations with the original Km.Further diagnosis shows that compared to original Km, the modified Km produces stronger vertical mixing in hurricane boundary layer over land, which tends to stabilize hurricane boundary layer. Consequently, the simulated landfalling hurricanes attenuate effectively with the modified Km while mostly inherit their characteristics over the ocean and decay inefficiently with the original Km.