Effects of Boundary Layer Vertical Mixing on the Evolution of Hurricanes over Land

Abstract

fter a hurricane makes landfall, its evolution is strongly influenced by its interaction with the planetary boundary layer (PBL) over land. In this study, a series of numerical experiments are performed to examine the effects of boundary layer vertical mixing on hurricane simulations over land using a research version of the NCEP Hurricane Weather Research and Forecasting (HWRF) model with three landfalling hurricane cases. It is found that the vertical mixing in the PBL has a strong influence on the simulated hurricane evolution. Specifically, strong vertical mixing has a positive impact on numerical simulations of hurricanes over land, with better track, intensity, synoptic flow and precipitation simulations. In contrast, weak vertical mixing leads to the strong hurricanes over land.Diagnoses of the thermodynamic and dynamic structures of hurricane vortices further suggest that the strong vertical mixing in the PBL could cause a decrease in the vertical wind shear and an increase of the vertical gradient of virtual potential temperature. As a consequence, these changes destroy the turbulence kinematic energy in the hurricane boundary layer and thus stabilize the hurricane boundary layer and limit its maintenance over land.