Reflectivity Factor Assimilation Algorithm Combining Background Field With Dual Polarization Radar Phase Classification And Its Preliminary Application In CMA-MES

The traditional temperature-determination indirect assimilation method for radar reflectivity factors is to retrieve the mixing ratio of hydrometeors through a given temperature threshold and temperature-related calculation rules,which has empirical problems in the process of hydrometeor retrieval.Compared with conventional radars,dualpolarization radars can provide rich hydrometeor information and accurately identify the phase types of hydrometeors in the atmosphere.In order to make the indirect assimilation of radar reflectivity factors more reasonable,this paper refers to an indirect assimilation method of radar reflectivity factors that combines the background field and dual-polarization radar phase classification and improves on it.The hydrometeor phase classification algorithm based on dual-polarization radar is used to realize the determination of the hydrometeor phase type and the adjustment of the corresponding weight ratio in the process of indirect assimilation.Then this method was applied to WRFDA and CMA-MESO,and relevant assimilation test research was carried out.The main work and summary are as follows:(1)This paper refers to and improves a radar reflectivity factor indirect assimilation method that combines the background field and dual-polarization radar phase classification.By using the dual-polarization radar phase classification algorithm rules,the accuracy of hydrometeor type judgment and dynamic adjustment of corresponding weight ratio in the indirect assimilation process is realized.After processing the dual-polarization radar data,a preliminary assimilation comparison test was carried out between this method and the commonly used temperature-determination method in WRFDA.Experiments show that this scheme has significantly improved the ice phase particles in the upper layers of the assimilation analysis field,and significantly adjusted the content of each hydrometeor in the melting layer,which makes the hydrometeor structure in the initial field similar to the dual polarization phase classification results.(2)In order to further test the method,this study transplanted the temperaturedetermination method and the background field combined with the dual-polarization phase state classification method into the CMA-MESO system independently developed by China Meteorological Administration,and cyclic assimilation experiments for three cases of strong convective weather are carried out.The results show that the phase types and weights of each hydrometeor are adjusted during the retrieval process due to the introduction of dual polarization phase classification.The hydrometeor retrieval and assimilation results of the new method are closer to the hydrometeor identification results than that of the temperaturedetermination method,and the adjustment of snow particles in high-level are particularly obvious.(3)In order to find out the influence,which was made from initial hydrometeor field changes,on the thermal,dynamic and water vapor fields of the model,this study continues to carry out cyclic assimilation experiments in the CMA-MESO system and conducts comparative analysis.The results show that: the changes to the initial field of hydrometeors are transmitted to the thermodynamic force and water vapor field during the cycle assimilation process in both methods.Compared with the traditional temperaturedetermination method,the new method has more significant characteristics of thermodynamic conditions and stronger strength in convective system,these changes are more conductive to the development of convective system.