Variational Analysis Method Of Radar Observations Based On LAPS And Its Application On The Numerical Simulation And Characteristics Analysis Of Rainstorms

Study on the characteristics and numerical forecast method of heavy rainfall is a major demand for improving the ability to prevent and mitigate disasters in China.High temporal and spatial resolution operational weather radar observations available in real time may provide a possibility for improving the numerical forecast of heavy rainfall.However,there are differences in operational radars of China,which causes radar data observation errors and affects the assimilation effect of radar data in numerical models.Reasonable study of mesoscale and small scale characteristics of rainstorms relies on more accurate observation data and better numerical simulation.In view of these difficulties and problems,to study the analysis and assimilation methods of different types of radar observations in the numerical prediction models is helpful to solve the difference of various radar observations to improve the ability of rainstorm prediction and better reveal the mesoscale characteristics of rainstorm structure.In this paper,the method of variational analysis of radar reflectivity data based on LAPS(Local Analysis and Prediction System)is developed.It can correct the errors of radar observation.Numerical experiments are carried out to study the impact of the variational analysis method on heavy rainfall forecast.Based on more accurate numerical simulation results using this method,the characteristics of mesoscale structure of rainstorms are analyzed.The main conclusions are as follows.A new variational analysis method is developed to correct three-dimensional radar reflectivity data using ground precipitation observations based on LAPS.The method can improve the quality of observations of various types of radar and effectively assimilate operational Doppler radar observations.The effect of the radar reflectivity data assimilation in LAPS cloud analysis is improved,and the cloud water distribution structure in the precipitation area is corrected.It is helpful to reveal the evolution of cloud microphysical processes during the heavy rainfall events.Local rainstorms are simulated by WRF model with assimilation of corrected radar data using LAPS.The results show that this method can improve the assimilation effect of radar reflectivity factors in LAPS cloud analysis,and increase the observed precipitation information in the initial field to improve rainstorm forecast.The variational analysis method is used to the batch numerical test of the rainstorm events.By assimilating plateau radar data with the variational analysis method,the heavy rainfall forecast in the downstream region can be improved.According to the results of the optimal model simulation with variational corrected radar data assimilation,the initiation,development,and dissipation mechanism of Meiyu frontal rainstorm system is studied to analyze the impact of radar data assimilation on the Meiyu frontal rainstorm evolution mechanism.The results show that the configuration of the large-scale weather system provided favorable conditions for the subsequent development of heavy rainfall.The convective cells continue to cross the key rainstorm area during the heavy rainfall,which is the reason for the heavy rainfall in the area.Convective instability,dramatic uplift,and abundant water vapour exist in the lower layers above the key rainstorm area,which is helpful to the occurrence and development of heavy rainfall.The low-level jet provides sufficient energy for the development of the heavy rainfall system,and the convergence of the underlying air is enhanced,which is an important reason for the continuous and strongest development of precipitation in the key rainstorm area.During the mature stage,there exists an inclined vertical structure and a dramatic upward movement over the key rainstorm area,which is conducive to the generation of the strongest precipitation.During the period of precipitation decline,the unstable energy decreases,the low-level jet rapidly weakens,the middle-lower stratification tends to be stable,and the ascending movement weakens,which causes the convective system to weaken and dissipate.