The vortex structure and near-surface winds of Typhoon Faxai (2019) during landfall. Part II: Evaluation of WRF simulations

This two-part study presents a comprehensive analysis of (1) the vortex structure, (2) the inner core planetary boundary layer (PBL) wind profile, and (3) the overland surface winds of Typhoon Faxai(2019) during landfall observationally (Part I) and in high-resolution Weather Research and Forecasting Model (WRF) simulations (Part II). Part II presents a framework for evaluating the wind field in the WRF simulations of Typhoon Faxai (2019) by comparing them with the observations presented in Part I. First, WRF simulations with two different surface roughness z(0) tables are presented. The simulation with the default z(0) table in WRF is shown to largely overestimate the surface wind speed. The overestimation is largely mitigated by using larger z(0) based on the climatology for urban and forest areas in Japan. Next, using the modified z(0) table, WRF simulations with three different PBL parametrizations, namely, Mellor-Yamada-Janji & cacute;, Yonsei University, and Mellor-Yamada-Nakanishi-Niino schemes are presented, and their impacts on the simulated vortex structure, inner core PBL wind profile, and overland surface winds are evaluated. In particular, the simulated surface winds are in good agreement with the observations outside the inner core of Typhoon Faxai. However, during the passage of the eyewall, the maximum surface winds are underestimated in the simulations. We show that the underestimation of the inertial stability, associated with the excessively large inner core of Typhoon Faxai in the simulations, led to the overestimation of the eyewall PBL jet height. This, in turn, caused the underestimation of the peak surface winds, as based on the empirical model of the wind reduction factor z(2 km) proposed in Part I.