Retrieval Of Hydrometeor And Vertical Velocity From Radar Reflectivity Factor And Numerical Simulation Experiments

Based on the properties of radar observed data, coordinate conversion and spatial smooth of raw radarvolume-scanning data were completed and simple quality control was adopted at the same time. On the basis of warm microphysical processes and Hypothesized cloud as constant state at a given time, the mixing ratios of water vapor, cloudy water and vertical velocity can be calculated through rain water mixing ratio, while water mixing ratio can be retrieved by radar reflectivity echo through Z-R relations. Nudging technique was introduced to nudge the retrieved variables into model at each time step of the integration by adding an extra term to the prognostic equation, forcing model output towards observation. Simulated experiments were carried out with Hefei doppler radar data and CMA's GRAPES (Global/Regional Assimilation and Prediction System) model on a torrential rain case. Some conclusions were drawn as follows:The CAPPI images gained of this paper's method are just the same as those of radar itself at altitude of 4km. The layout of the mixing ratios of water vapor, cloudy water, rain water and vertical velocity are corresponding to radar image, and the three dimensional spatial structure of convective cloud is presented. Nudging technique is helpful on initialization, it can make model forecast adjust gradually to the observed information and yield a balanced initial field. In addition, it can also remove spin-up phenomenon and achieve model hot start in some extent. Contrast experiment show that this paper's retrieved variables are available to Kessler warm microphysical scheme and NCEP-3Class simple ice scheme, while Liuqijun simple ice scheme's forecast results are worse. Because of insufficient mesoscale information in the background, model could smooth the variables and construct one big convective structure after forecasting for about 2h. Water vapor is vital to precipitation;it is a governing factor to amount and duration of precipitation. Cloudy water, rain water and vertical velocity describe the distribution of convection and cause precipitation at beginning of model forecast. The horizontal wind field directs the drift orientation of the weather system. The forecast precipitation within 6h is successful with obviouslycharacteristics of mesoscale weather system, the updraft vertical velocity in the center of convective structure is about 2.0m/s, the maximum cloud water content is about 1.5g/kg above the level of 400hPa and the maximum rain water content is about 3.0g/kg below 400hPa. At low level of the convective structure is notable convergence of wind stream and upper level is obvious divergence while the weather system moving follows the steering flow.Only reflectivity of one radar factor is used and the weather system is cut arbitrarily, the observed data does not cover the whole model domain and a great difference lies between retrieved data and background data, some experienced parameters are introduced into the retrieve method, so further studies on some results of the paper are expected.