Nested WRF And CFD For Numerical Simulation Of Localized Typhoon Wind Field

Dozens of typhoon land China southeast coast each year. Strong winds, heavy rains and high storm surge brought by t yphoons have been a serious threat to the southeast coastal areas in China. The loss is especially high in economically developed areas. In order to improve our capabilit y to prevent this kind o f disasters and reduce the losses caused by t yphoons, typhoon wind field is needed to provide the necessary inputs for typhoon risk analysis and wind resistance design of structures. To actually measure the the typhoon wind field is not possible due to the uncertaint y o f moving track of t yphoon and limited number o f observat ion instruments. The latest generation of mesoscale weather forecast and data assimilat ion system called Weather Research and Forecast(WRF) represent s the most advanced science and techno logy of its kind in nowdays. It has co mprehensive at mospheric physical processes and opt imized dynamic framework, which makes it embrace a wide applicat ion.In this paper, WRF is emplo yed to numerically simulate three historical typhoons in large scale with fine grids, and the outputs of WRF is then inputed to the Co mputational Fluid Dynamic(CFD) model as init ial boundary. In this way, the nested co mputat ion of WRF and CFD is achieved, and it provides a numerical scheme to realize an elaborat ing downscaling typhoon wind field simulation, in which the effect of topography on the local wind field is obtained.The mesoscale weather forecast model, WRF, and the numerical scheme for typhoon wind field simulat ion are introduced in the paper. Jo int ly with CFD model, the nested computational scheme o f WRF and CFD is proposed to simulate the wind field of local areas with topographic feature. Three kinds o f boundary layer solut ions of WRF model, i.e., YSU scheme, MYJ scheme and MRF scheme, and three kinds of cumulus convection parameterizat ion schemes, i.e., new Kain-Fritsch scheme, Betts-Miller-Janjic scheme and Grell-Devenyi schemes, are co mposed into 9 different combinations. The 9 schemes are used to simulate three historical t yphoon cases, including No. 0812 t yphoon "parrot", No. 0814 typhoon "Hagupit" and No. 1003 t yphoon "Chanthu". The capabilit y o f WRF to model t yphoon track, t yphoon intensit y, t yphoon wind speed and direct ion, and surface characteristics under various scheme combinat ions is tested. CFD model of Tanglang Mountain area in Shenzhen is built, and the No. 1003 typhoon "parrot" wind field simulated by WRF is extracted as init ial boundary to the CFD model for local wind field simulat ion. The nested co mputat ion o f local wind field by WRF and CFD is achieved by data transfer between the two models. According to the simulat ion results, it is obviously that wind field characteristics of typhoon near ground cann’t be precisely computed by WRF, while the nested computation o f WRF and CFD can co mmendably simulate wind field characterist ics near ground, and the results own their value to pract ical applicat ion.