Study On The Quantitative Precipitation Estimation Algorithm Utilized With The Operational Dual-polarization Radar Network And Automatic Stations And Its Effect Analysis

With more and more dual-polarization radars setting up for operation,it is urgent to establish an operational dual-polarization radar quantitative precipitation estimation?QPE?algorithm.In the present study,drop size distributions?DSDs?observed at Suzhou City,Jiangsu province;Yangjiang City,Guangdong province;and Naqu City,Tibet province are analyzed.The optimal fitting method of rainfall estimator is discussed based on the DSD data.The estimators are fitted and a localized dual-polarization radar QPE algorithm that accounts for hydrometeor phase classification is established.The algorithm is applied to the multiple rainfall events in Guangdong province to evaluate the QPE performance and the reasons of errors are anlyzed.A QPE algorithm which uses the dual-polarization radar data and automatic stations data is established based on the QPE algorithm for one dual-polarization radar.The effect of the automatic station density on precipitation estimation is also discussed.Considering the continual development of the dual-polarization radar network,the operational dual-polarization radar mosaic QPE algorithm is discussed.Major conclusions are as follows.?1?More small raindrops?D<1 mm?are found in Suzhou and more large raindrops?D>1 mm?are found in Yangjiang.There are obvious regional differences in the polarimetric radar varibles simulated with the three regions'DSD data.The differences of the polarimetric radar varibles over the three regions indicate the differences of the rainfall estimators.Therefore,the specific rainfall estimators and QPE algorithm should be developed using data of the specific region.The subsequent experiments demonstrated the necessary of the localized estimators and algorithm.Under the condition of considering the observed data deviation,the simulation test based on DSD data and the test using the actual observation data have proved that the nonlinear Piecewise Fitting Method?PFM?is the best method for fitting the rainfall estimator.?2?The algorithm performs well for conventional rainfall events,in which hourly rainfall accumulations are less than 50 mm.However,it severely underestimated the heavy rain?hourly accumulation>50 mm?when it estimated an extremely heavy rainfall event.Compared with the DSD data in Yangjiang?estimators are derived from these data?,this extremely heavy rainfall event was characterized by smaller average ra indrop diameters and higher number concentration.These large DSD differences lead to the underestimation of precipitation.In the improved algorithm,R?A_H?replaces R(K_DP,Z_DR)to estimate precipitation and the estimation effect was improved obviously.?3?The dual-polarization radar data and automatic station rainfall data are jointly used to estimate precipitation.On one hand,the rainfall estimator is revised in real time by using the rainfall data of the automatic stations,so that the estimator can adapt to the DSD variation at any time.Therefore,it mitigates the obvious variation of the estimation error with hourly rainfall accumulations.On the other hand,the spatial correction of the estimation results is carried out by using the rainfall data of automatic stations according to the optimal interpolation method.After all the correction,the estimation effect and stability are both improved obviously.Compared with the single-polarization radar,the dual-polarization radar does not have a high dependence on the automatic station when using the method proposed in this paper.When an automatic station at a 20km×20km region is used,it can meet the optimization requirements for the dual-polarization radar to estimate the precipitation.?4?Yangjiang radar data are seriously affected by the terrain.After necessary quality control of the two radars'data,the data in co-coverage area which are less affected by the terrain are selected and compared.It is found that the data consistency of the two radars is good and the mosaic can be implemented.Dual-polarization radar mosaic can partly solve the problems existed in areas blocked by terrain and areas far from the radar for the single radar QPE,and obtain the more accurate QPE result than the single radar.After the improvement of the hybrid scan strategy and the correction of Z_H and Z_DR in the bright band,the estimation effect of radar mosaic is further improved.