The impacts of planetary boundary layer schemes on maximum potential intensity of idealized tropical cyclone

Abstract

Tropical cyclones (TCs)' development relies on boundary layer processes. With climate change increasing extreme TCs, predicting their intensity under different planetary boundary layer (PBL) schemes is crucial. This study utilizes idealized TC experiments at cloud-resolving resolution within the Weather Research and Forecasting (WRF) model, employing PBL schemes of low-order or high-order closure, and local or nonlocal types, to investigate the impacts of these schemes on TC's maximum potential intensity (MPI).

The findings indicate that the MPI is remarkably sensitive to the choice of PBL schemes, with disparities in simulated MPI reaching up to 67 hPa. While schemes with different closure methods often compute turbulent diffusion coefficients differently, some, like YSU and MYNN3, simulate similar MPI due to shared low boundary layer heights (PBLH) and efficient latent heat utilization. Conversely, schemes with similar diffusion coefficient definitions, such as MYNN3 and BouLac, can produce differing MPI due to variations in mixing mechanisms.

Analysis of strong versus weak TC simulations reveals that strong TCs have lower boundary layer heights and turbulent diffusion coefficient peaks further from the surface, leading to greater near-surface gradient wind imbalance and stronger radial inflow. Weak TCs, on the other hand, have higher boundary layer heights and peaks closer to the surface, resulting in weaker inflow. Stronger inflow in strong TCs promotes moisture convergence in the core region, enhancing inner-core diabatic heating and forming a pronounced upper-level warm core, which accelerates TC intensification. The study highlights how PBL schemes significantly affect TC MPI by linking dynamic and thermodynamic processes.