Storm‐Scale and Fine‐Scale Boundary Layer Structures of Tropical Cyclones Simulated With the WRF‐LES Framework

Abstract

AbstractPrevious studies demonstrated that the tropical cyclone (TC) boundary layer (TCBL) contains small‐scale coherent structures, such as roll vortices and tornado‐scale vortices (TSVs), and they play important roles in energy transport and intensity changes in TCs. However, little is known about how horizontal resolutions can affect storm‐scale and fine‐scale structures in the TCBL with the grid spacing decreasing from the turbulent gray zone (100 m–1 km) to the large‐eddy scale (<100 m). In this study, numerical experiments with the large eddy simulation technique are used to investigate the effect of the model horizontal resolution on the simulated TC‐scale and fine‐scale structures in the TCBL. The simulated TC tends to have a shallower BL, a lower BL jet associated with stronger near‐surface vertical wind shear in the TCBL when the grid spacing decreases from 333 to 111 m or 37 m. When the grid spacing decreases to 111 m or 37 m, the fine‐scale coherent structures and near‐surface wind streaks associated with roll vortices and TSVs can be simulated, and the characteristics of the simulated turbulent kinetic energy in the TCBL are in good agreement with observational studies. With the grid spacing of 111 and 37 m, no significant differences in TC intensity are found in terms of instantaneous maximum and azimuthal‐mean maximum wind speeds. This study suggests that simulations with the horizontal grid spacing of 100 m or less can simulate the small coherent structures in the TCBL and their effect on TC intensity.