Impact of horizontal resolution in CALMET on simulated near-surface wind fields over complex terrain during Super Typhoon Meranti (2016)

Abstract

A Weather Research and Forecasting (WRF) model simulation with 3-km horizontal grid spacing was coupled with five California Meteorological Model (CALMET) simulations with horizontal grid spacing ranging from 100 m to 3 km to investigate the impact of horizontal resolution on the simulated near-surface wind fields of Super Typhoon Meranti (2016). Assessment of the model output was conducted in two specified regions named Shisun Mountain and Shishe Mountain in Fujian Province, China. The WRF/CALMET coupled system exhibited satisfactory performance, as indicated by the reasonably large correlation coefficient (>0.4) between the simulated and observed winds. The best and second-best outcomes for 10-m wind speed were found in the simulations with horizontal grid spacing of 500 and 250 m, respectively. Specifically, the 10-m wind speed appeared sensitive to model resolution after being affected by the gale-force winds of Typhoon Meranti. For the 10-m wind direction, the best outcome at Shisun Mountain was found with 500-m horizontal grid spacing, whereas it improved continuously with higher horizontal resolution at Shishe Mountain. The wind-followed slope angle was proposed to provide new perspective for quantitative evaluation of the impact of complex terrain with different horizontal resolutions on the near-surface wind field. It is found that, irrespective of the location and model resolution, the 10-m downhill winds were generally larger than the uphill winds before and after being affected by the gale-force winds, while the winds decreased with slope angle in both uphill and downhill situation when affected by the gale-force winds of Typhoon Meranti.