Verification And Improvement Of WRF Model Cloud Parameter Scheme For A Typhoon Precipitation Case Simulation

The strong precipitation caused by the typhoon Fung-Wong landing in 2008 was simulated by using WRF WDM6 double-moment cloud microphysics scheme.The model simulations are evaluated by statistical methods using cloud top brightness temperature TBB and precipitation radar reflectivity data from MTSAT-1R,TRMM satellite and the Satellite Data Simulator Unit.Reduce the difference between simulation results and satellite observations through sensitivity experiments including autoconversion rate of cloud water to rain,ice nucleation,the terminal velocity and the slope parameter of snow and graupel.The results show that:(1)The location and range of the heavy rain from the typhoon Fung-Wong simulated by the WDM6 scheme are basically same with the actual sit uation,but the intensity of the simulated precipitation is locally strong.The overall simulation effect of the WDM6 scheme for brightness temperature is in good agreement with the satellite reality.The WDM6 scheme successfully simulated the strong convec tive cloud system observed by satellites,and the simulated strong convective cloud system's distribution and moving is close to the observation.However,there is still a shortage of the simulated strong convective cloud system and the simulated cloud top brightness temperature is higher in some areas.The regional average TBB of the long-term sequence indicates that the trend of observed and simulated TBB is in a positive phase relationship,and the trend of change is basically same.The simulated convective radar echo is consistent with the observation,and the position of the convection is close to the observation,but the echo intensity and the echo top height are higher.(2)The joint histogram of cloud top brightness temperature and the precipitation top height show that the WDM6 scheme simulated more shallow convective clouds and underestimates the frequency of convective cloud systems.The comparison of contoured frequency by altitude diagrams of radar reflectivities for different cloud types shows that the vertical distribution of convective cloud radar echoes is close to observation.(3)The sensitivity experiments results show that the production rate for autoconversion of cloud water to rain in the modified WDM6 scheme effectively improves the simulation results,it reduces the difference between the simulated cloud top brightness temperature TBB to the observation,at the same time,the simulated radar echo intensity and echo top height are closer to the observation,the area of the echo-free area is reduced.It is found that the concentration of initial cloud droplets affects the production rate for autoconversion of cloud water to rain and finally affects the simulation results of cloud structure and radar reflectivity.High concentration of initial cloud droplets will make the simulation result worse.The improved production rate for autoconversion of cloud water to rain can improve the simulation effect of the WDM6 scheme.