| 28 Aug 2025
Evaluate the Impact of Power-Law Scattering Amplitude Fitting on Dual-Polarization Radar Data Assimilation—Summertime Cases Study
Abstract. Different configurations within the observation operator cause dual-polarization radar parameters to exhibit various characteristics, which affect the structure of background error covariance as well as the results of data assimilation. Through real case data assimilation experiments, this study evaluates the raindrop-contributed term in the simulated reflectivity (ZHH) and differential reflectivity (ZDR) to describe the effect of different calculation methods within the operator: the fitting and direct integration methods. In the fitting method, dual-polarization variables are calculated using an analytic function, which assumes a gamma-shaped drop size distribution and fits the relationship between the scattering amplitude (SA) and drop size. In the direct integration method, the quantities of the hydrometeor species and SA are integrated with respect to drop size during the calculation. The results indicate that the fitting method effectively simulates the ZHH. However, the limitations of the fitting function may impact the accuracy when represents the structure of ZDR. By contrast, the direct integration method effectively simulates polarimetric variables. Validation of the raindrop mass-weighted mean diameter (Dmr) indicates that assimilation of dual-polarization radar data into the model results in adjustment of the raindrop size distribution regardless of which configuration is used. However, the Dmr- ZDR structure is closer to the observed structure, and the ZDR structure is more reasonable when the direct integration method is employed. In summary, different configurations within the operator directly affect the results of data assimilation, and the direct integration method has more reasonable performance with respect to simulating dual-polarization radar variables.
Competing interests: Dr. Gyuwon Lee and I have one paper published in Atmoshperic Research which I am third author, and Dr. Lee is the sixth author. Dr. Ya-Chien Feng and I have one paper published in QJRMS which I am the second author, and Dr. Feng is the third author. For the rest of referee, I declare that the neither I nor my co-authors have any competing interests.
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