Study On Simulation Of Radar Bright Band And Its Analysis

Radar bright band is not only an important symbol to the dissipation of thunderstorm, but also one of the main criteria in distinguishing freezing rain. And the band may lead to overestimation of precipitation when weather radar detects stratiform precipitation(including cumulus-stratus mixed precipitation).But quantitative research on the characteristics and mechanisms of radar bright band are relatively rare. Therefore, it is of great significance in further research on radar bright bandFirstly, this paper is devoted to discuss the effects of different structures, melting degrees, size and scale parameters of radar upon scattering of melting particles, it shows that the standardized backscattering cross sections of mixtures would been larger along of the increasing of the particle’s diameter. When the scale parameter of particles was less than0.5, with increasing of melting volume ratio, the standardized backscattering cross sections of mixtures became larger; Since different algorithms of dielectric constants related to differing assumptions of mixtures’structures, the change of standardized backscattering cross sections differed greatly. When the scale parameter of the particles was larger than0.5, with increasing of the degree of melting, the standardized backscattering cross sections of mixtures became oscillation; Under the condition of different algorithms of dielectric constants, the peak values of cross sections’ oscillation curve corresponded to different melting volume ratios; In addition, with increasing of the particle’s diameter, the peak values would move to the smaller melting volume ratios.The program of mixtures’ scattering calculation linked to SimRAD software to improve its simulation ability about the echoes of stratiform clouds included melting layer. By using this software platform to simulate radar bright band under the condition of different structural melted particles, investigated the effect of differences in particle structure on the radar bright band. The results show that there was mixture whose structure assumed by the Bruggeman algorithm in the melting layer besides the coat. In order to test the rationality, we re-adjusted the parameter setting program, carried out validation and gained that the radar reflectivity factor profiles of the simulation and observation were more consistent after considering the melting layer included mixtures.On the basis of improved simulation software and parameter settings, quantitative analysis for six causes of radar bright band have been carried out, we got that the complex refractive index increased made radar reflectivity factor increased18dBZ; collision coalescence made the echoes enhanced3-7dBZ; shape change of melting particles made the echoes increased only0.2dBZ; the shrinking lead to radar reflectivity factor in the lower melting layer decreased1-2.5dBZ; the broken of raindrops caused radar reflectivity factor below the melting layer reduced about10dBZ; the effect of falling speed resulted in radar reflectivity factor below the melting layer reduced1.5dBZ. Thus, complex refractive index, collision coalescence and the broken of raindrops were the main factors with the radar bright band formed; six causes jointly made the radar reflectivity factor profile became significant bent in the melting layer. The position of0℃layer is an important factor of radar bright band. Finally, one dimensional variation(1Dvar) algorithm for retrieving temperature and humidity profiles from the ground-based microwave radiometer had been done, we gained the height of0℃layer.the results show that the retrieval results were close to the real atmosphere, it could solve the problem of low temporal resolution of the conventional data and provided the conditions for the study of time-varying characteristics of radar bright band.