Improvement Of Simulation In Precipitation And Near Surface Wind Over Arid Region In Northwest China With Nudging

Nudging method in WRF(Weather Research and Forecasting)model is used to circularly assimilate FNL(Final Operational Global Analysis)data,and the simulation improvement effect and reasons of Nudging assimilation method on three precipitation process in summer and near surface wind speed in spring in arid areas of northweat China are analyzed.By comparing with the reanalysis data of MERRA2(The Modern-Era Retrospective analysis for Research and Applications,version 2),the simulation performance of Spectral Nudging and Grid Nudging on near surface wind speed and precipitation in northwest arid region was further compared and analyzed.The main conclusions are followed:(1)Compared with the result of precipitation with WRF model.Spectral Nudging approach has a significant improvement for the simulation of the areas for short time precipitation and center of maximum rainfall especially for the complex topography.Spectral Nudging has a better performance than Grid Nudging scheme both for the magnitude and region of the simulating accuracy.(2)After added Spectral Nudging and Grid Nudging methods,the simulation of near surface wind speed by model is improved.The simulation of 700 hPa temperature and relative humidity is the main reason for the improvement of model simulated precipitation.Spectral Nudging method is larger than Grid Nudging method in simulating relative humidity,and more water vapor convergence is simulated.(3)Wind speed simulated by WRF model is larger than the observed data in northwest arid region.After adding nudging assimilation method,the simulated wind speed is significantly reduced,the wind speed and the Weibull by Grid Nudging test are closer to the observed data.The RMSE,deviation and mean absolute error also decrease.Grid Nudging approach performed better than Spectral Nudging for the wind speed simulation.(4)From the diurnal variation of the error of 10 m wind for the WRF,wind changed following temperature.The error is large when the temperature changes strongly,the simulation effect of WRF model is poor.When the temperature is low and cloudy,the error is small and the simulation ability of model is strong.The error of Grid Nudging test is smaller than Spectral Nudging test,that means the effect on the model by Grid Nudging test is obvious.(5)Simulating performance is fair and the error is large on the condition of the intense temperature variation.Based on the Richard number,model has a better performance for the unstable stratification afternoon,and the forecasting is not impressive on the neutral or stable stratification condition.For comparison,the simulation error of Grid Nudging approach is less than Spectral Nudging,Grid Nudging scheme has a better improvement compared to Spectral Nudging.(6)The simulation of wind with the model has a high accuracy compared to the MERRA2 reanalysis data.Meanwhile,model performance is better in cloudy day than sunny day.On both situations the performance of model is improved combined with Nudging assimilation approach.