A Simulation Study on Raindrop Orientation Variation to Dual Linear Polarimetric Radar Observation with Different Transmitting and Receiving Model

On the basis of scattering and attenuation theory of raindrop, the coupling relation between vertical and horizontal polarimetric wave is analyzed with numerical simulation methods in the same transmission and receiving waves (STSR) and alternate transmission and receiving horizontal and vertical waves (ATAR) model. While radar beam passes through uniform rain area, the variety of horizontal reflectivity Z_H and its error ΔZ_H, differential reflectivity Z_DR and its error ΔZ_DR, the differential propagation phase shift Φ_DP and specific differential propagation phase shift K_DP and its difference ΔK_DP brought by raindrop slant are compared respectively along with distance between the two polarimetric models. The results indicate that the Z_H of STSR are bigger and Z_DR are smaller than ATAR model while raindrop is slant, so the errors of Z_H and Z_DR in STSR model are bigger when attenuation are not considered. While attenuation is considered, the errors of Z_H in STSR are small, the errors of Z_DR of 3.2 cm are small too, and that of 5.7, 10.7 cm are big. However, the difference of Z_H and Z_DR between models is little because the raindrop slant is small in real air. Influenced by raindrop slant K_DP is bigger in ATAR model than in STSR, it decreases less than in STSR model, so the difference of ΔK_DP between models is more while the slant angle increases. The shorter the wave length, the bigger the K_DP, and the larger the ΔK_DP are impacted by slant. In addition, two real value definitions of Z_H and Z_DR are addressed, by which the scattering effect of raindrop slant is considered or not. The actual microphysical structure of raindrop can be better represented by the value of not considering slant, the influence of propagation effect is eliminated, and the full size is reflected accurately, which are better representatives on the application of radar data such as quantitative estimation precipitation. It is more reasonable that the none-slant-consideration Z_H, Z_DR values are regarded as the real definitions.