Studies On The Fine-Scale Near-Surface Winds Over Complex Terrain Of Landfalling Typhoon

Limited by temporal-spatial resolution of the observations,insufficient understanding still exists concerning the fine-scale wind structure over complex terrain under the influence of the typhoon,which has become a bottleneck problem restricting the improvement of typhoon disaster warning.The dynamical downscaling scheme,which combines mesoscale meteorological model with microscale diagnostic model,has become a new trend of typhoon fine-scale wind research,providing a promising technical approach for further research on fine-scal wind over complex terrain under typhoon conditions.In this paper,the mesoscale model Weather Research and Forecast Model?WRF?,combined with the diagnostic model California Meteorological Model?CALMET?,was selected to simulate5-days fine-scale wind of landfalling super-typhoon Meranti?1614?.The sensitivity analyses of both land use datasets and physical parameterization schemes of CALMET were conducted.The improved kinematic scheme was then proposed.Furthermore,by improving the horizontal resolution of CALMET,the influence characteristics of complex terrain on the fine-scale wind under the influence of typhoon were studied.The WRF model was configured with three nested domains with horizontal grid spacing of27,9 and 3 km,respectively.While the CALMET model was set up with 500 m grid spacing.The results show that the simulated track and intensity of Meranti are in consistence with China Meteorological Administration?CMA?best track data.Moreover,verifying with the observations data from 981 national automatic stations shows that WRF/CALMET model significantly improves the simulated wind by 20³0%.Both 1-km resolution land use datasets from Global Land Cover Characterization?GLCC?and 30-m resolution land use datasets from GlobeLand30?GL30?were used in the sensitivity analysis of land use datasets in CALMET model.The result shows that the fine-scale near-surface wind is not sensitive to the land use data resolution.The possible reason is that the resolution of CALMET in this study is 500 m,which cannot fully reflect the impact of 30-m resolution GL30land use datasets.Besides,the sensitivity analysis of physical parameterization schemes was carried out.The results indicate that the blocking effect can cause up to 12 m s^-1 wind speed deviation outside the radius of gale wind?R17?,whereas it takes no effect within R17.The slope flows effect tells the diurnal variation characteristics of mountainous areas,with mountain wind at nighttime and valley wind at daytime,causing wind speed deviation up to 2.5 m s^-1 and 1.5 m s^-1,respectively.The original kinematic effects scheme in CALMET does not apply to typhoon so that the improved scheme KETT?Kinematic Effects of Terrain for Typhoons?was proposed.Based on KETT and other physical parameterization schemes in CALMET,both 3-km and 500-m resolution wind fields were simulated.After raising the CALMET's horizontal resolution,results show that wind direction deviation outside R17?±45°?is larger than that inside R17?±36°?.Moreover,wind speed of downslope flows is larger than upslope flow before being affect by gale wind.When gale wind comes,wind speed in gentle slope?less than 5°?is larger than that in steep slope,whether downhill or uphill.Wind speed deviation is about 5⁶ m s^-1 outside R17 while is about 10 m s^-1inside R17.In addition,compared with the wind field in the region with different terrain features,it is found that the bimodal region is more prone to"channeling effect"and"wind shelter"than single-peak region.