An Investigation of the Impact of Different Turbulence Schemes on the Tropical Cyclone Boundary Layer at Turbulent Gray‐Zone Resolution

Abstract

AbstractAccurately resolving turbulence in the tropical‐cyclone boundary layer (TCBL) is crucial for realistic simulations of tropical cyclones (TCs), but how well the fine‐scale structure of the simulated TCBL can be reproduced at gray‐zone resolutions by state‐of‐the‐art planetary boundary layer (PBL) parameterization schemes, and why the simulated fine‐scale structure is so sensitive to the PBL scheme, are yet to be evaluated and understood. To address these issues, a series of numerical experiments under idealized conditions were conducted using the advanced research weather research and forecasting (WRF‐ARW) model at 500 and 166 m grid spacing. An 18‐hr WRF‐ARW large‐eddy simulation (LES) with a 55‐m grid spacing based on the nonlinear backscatter and anisotropy subfilter‐scale (NBA‐SFS) stress scheme was used as reference (RLES). Results from experiments using five different PBL schemes, that is, two conventional schemes—the Yonsei University (YSU) and the original MYNN (termed MYNN1)—two scale‐aware schemes—the Shin‐Hong (S‐H) and the revised MYNN (termed MYNN2)—and the coarse‐resolution LES (CLES), were subsequently compared with the RLES. The YSU and S‐H not only produced better simulations of TC intensity and structure than the other three PBL schemes, but also produced a fine‐scale turbulent structure reasonably well compared with the RLES. Discrepancies in the simulated fine‐scale structure among the PBL schemes result primarily from the different strength of vertical mixing, which could be reduced by the scale‐aware option. Results from a series of sensitivity experiments with a 166‐m grid spacing demonstrate that the scale‐aware S‐H can significantly improve the finer resolution simulations than the conventional YSU at relatively finer grid spacing at gray zone.