Diagnosis And Evaluation Of Grapes Global Model Cloud Scheme

On the basis of analyzing the differences among these diversified materials such as GRAPES cloud microphysical predictand of global model,ERA5,Cloud Sat,etc.,this paper diagnoses and evaluates the cloud plan forecast performance of GRAPES in global model and studies the weaknesses of cloud plan in terms of forecasting cloud macro and micro physical quantities,cloud cover,radiation and precipitation.In view of the above,this paper also optimizes and improves the original cloud plan.In this paper,the calculation process of lattice point cloud cover is optimized,large-scale macro cloud plan is adjusted,the influence of pressure changes on the cloud condensation process is improved and relevant calculation errors are reduced.The influence of cloud cover is also considered in all microphysical processes,making the cloud plan consistent prior to and after cloud cover processing.In addition,the restrictions on raindrop evaporation are set higher in order to adjust the precipitation forecast model.The improvement effect of cloud plan is verified by considering the results of individual cases and batch tests and finally,the following conclusions are obtained:Too low water content predictand of tropical hydrometeor of GRAPES in global model and too high ice water content predictand of mid-high latitude.Low predictand of cloud cover forecast,particularly for the tropic high cloud forecast;small precipitation forecast,which becomes prominent in the case where the large-scale precipitation has a small predictand in the low latitude area;small tropic convection precipitation(the precipitation area is less than ERA5);the external long wave radiation is also less than ERA5.The improvement of the cloud plan plays a positive role in enhancing such aspects as tropical cloud cover,water content of hydrometeor and precipitation forecast,especially the effect of precipitation forecast,such as higher forecast value of water content of tropical hydrometer and broader forecast scope.The cloud cover forecasted becomes higher and closer to ERA5 cloud cover forecast in the same period.Convective precipitation and large-scale precipitation in tropical regions also increase,and the problem of a too small proportion of large-scale precipitation is alleviated.In addition,by analyzing the tendentious item of temperature and hydrometeor water content of GRAPES?GFS,this paper concludes that the tendentious vertical distribution complies with the physical law of convection temperature increase and humidity reduction.With the achievements above,the law of mutual conversion between water vapor and liquid / ice water can be better represented.