The effects of boundary layer vertical turbulent diffusivity on the tropical cyclone intensity

Abstract

The sensitivity of the simulated intensification of Typhoon Mangkhut (2018) to boundary layer turbulent diffusivity (Km) is investigated through a series of numerical simulations using the modified Km from the Yonsei-University (YSU) planetary boundary layer (PBL) scheme in the Weather Research and Forecasting (WRF) model. Two intensity metrics, namely grid-point and area-averaged metrics, were employed to evaluate the simulations. The results indicate that a smaller Km tends to result in a smaller grid-point minimum central sea level pressure (MSLP), while producing a larger area-averaged MSLP and smaller area-averaged maximum 10 m wind speed (VMAX), which is consistent with a weaker radial inflow averaged over the area of a 500 km radius. Furthermore, the surface latent heat flux exhibits a nearly linear relationship with Km throughout the simulation. Overall, a larger Km tends to produce a greater diabatic heating rate, although this relationship is not as clear as that between Km and latent heat flux due to the presence of spontaneous asymmetric convective eddy features. Moreover, since a larger Km tends to result in a larger 10 m tangential wind, the size of a tropical cyclone (TC) defined by the radius at which 10 m tangential wind speed becomes 10 m s−1 shows a positive linear relationship with Km.