Establishment And Preliminary Application Of Forward Modeling Method For Doppler Spectral Density Of Ice Particles

Owing to the various shapes of ice particles,the relationships between fall velocity,backscattering cross-section,mass,and particle size are complicated,which affects the application of cloud radar Doppler spectral density data to retrieve the microphysical properties of ice crystals.In this paper,under the assumption of six particle shape types,the relationships between particle mass,fall velocity,backscattering cross-section,and particle size were established based on existing research.Variations of Doppler spectral density with the same particle size distribution(PSD)of different ice particle types are discussed.The effects of air speed,turbulence and radar sensitivity on the radar Doppler spectrum and inversion of PSDs are evaluated,and the radar-retrieved liquid and ice PSDs,water content,and mean volume-weighted particle diameter are compared with airborne in situ observations in Xingtai,Hebei Province,China,in 2018.In addition,in order to use a single radar to invert the complete size spectrum of ice crystals,a model of particle shape and number concentration distribution was established,and the observed data from Naqu,Xizang province in 2014 were used for inversion verification.The results showed the following:(1)for particles with the same equivalent diameter(De),the fall velocity of aggregates is the largest,followed by hexagonal columns,hexagonal plates,sector plates,and stellar crystals,with ice spheres falling two to three times faster than ice crystals with the same De.Hexagonal columns have the largest backscattering crosssection,followed by stellar crystals and sector plates,and the backscattering crosssections of hexagonal plates and two kinds of aggregates are very close to those of ice spheres.,The size of ice particles corresponding to the same fall velocity will be much smaller than actual ice particles of different shapes if suppose that all ice particles in a cloud are spherical.This will cause a deviation from the real situation when retrieving PSD spectra using radar data.(2)The width of the simulated radar Doppler spectral density generated by various ice crystal types with the same PSD is mainly affected by how fast the particle's falling velocity increased with the particle size.Turbulence has different degrees of influence on the Doppler spectrum of different ice crystals,and it also brings large error to the inversion of the PSD.(3)PSD comparisons showed that each ice crystal type retrieved from the cloud radar corresponded well to aircraft observations within a certain scale range when assuming that only a certain type of ice crystals existed in the cloud,which can fully prove the feasibility of retrieving ice PSDs from reflectivity spectral density.The liquid water content obtained by radar inversion was compared with the aircraft observation,the change trend of the two is basically the same with the altitude,and the value of the aircraft is slightly smaller than the radar inversion results.(4)With the established model of the distribution of ice particles,the complete PSD of ice crystal can be well retrieved.The inversion results of the microphysical parameters of the rain stratus cloud and the deep convective cloud in Naqu,Tibetan,show that the ice water content(IWC)and effective particle radius of the rain stratus cloud are relatively uniform,while the deep convective cloud is relatively inhomogeneous.The reflectivity observed by radar has a good correlation with the IWC,and the effective radius of particles in the cloud is mostly small than 60 ?m.