Modeling of Melting Layer in Cross-Platforms Radar Observation Operator ZJU-AERO: Multi-Stage Melting Particle Model, Scattering Computation, and Bulk Parameterization

This study presents an implementation of a new melting layer model in the ZJU-AERO radar observation operator (Accurate and Efficient Radar Operator designed by ZheJiang University). The proposed model utilizes a coated spheroid to represent melting snow and graupel. It consists of three stages–coating, soaking, and melting–to account for the dielectric and density effects of melting particles. The scattering properties of the melting particles are computed with the Invariant-Imbedding T-Matrix (IITM) method, and the results are tabulated as look-up tables for the radar operator. Regarding the parameterization of bulk optical properties, a flux-conservation scheme is employed to estimate the size distribution of melting particles. To demonstrate its flexibility and superiority, the single and bulk scattering properties of our multi-stage melting model are compared against the traditional homogeneous model, which uses the effective medium approximation (EMA). The effectiveness of the multi-stage melting model has also been assessed by mapping model states in the regional mesoscale model of the China Meteorology Administration (CMA-MESO) to radar observations. In the microphysics package of CMA-MESO, the melting process is not explicitly represented, and we assume that melting hydrometeors occur where solid and liquid phases overlap. When compared with observations, the present multi-stage melting model successfully reproduces melting layer signatures, highlighting its potential for microphysic validation, quantitative precipitation estimations, and data assimilation studies.