Characteristics of hydrometeor orientation obtained from radar polarimetric measurements in a linear polarization basis

Knowledge of the orientation of atmospheric particles is important for reliable hydrometeor classification and discrimination between liquid and frozen particles. This has implications for interpretation of the specific differential phase K_DP and differential phase Z _DR data that are used for rainfall measurement. There is a widespread opinion that for rain media mean canting angle ⟨ψ⟩ is usually very close to zero and the width of canting angle distribution σ_ψ is about few degrees. This assumption needs to be carefully reexamined. Characteristics of hydrometeor orientation such as ⟨¯ψ> and σ_ψ have so far been obtained with radar polarimetric measurements in a circular polarization basis. However, the polarimetric variables for the circular polarization basis are substantially affected by propagation through a medium of anisotropic scatterers. Sometimes it is very difficult to separate forward scatter and backscatter effects in radar returns for circularly (or elliptically) polarized waves. Measurements in the linear polarization basis are much less biased by propagation and are better suited for rainfall estimation. The authors suggest a method to obtain the mean canting angle and the spread of canting angle distribution using linearly polarized waves. The estimates of ⟨ψ⟩ and σψ have been obtained using measurements from the S-band NCAR/SPOL and CSU/CHILL dual-polarization radars that have dual-channel receivers