THE MEASUREMENTS OF BACKSCATTER DIFFERENTIAL PHASE δ IN THE MELTING LAYER AT X AND S BANDS

The polarimetric variable backscatter differential phase δ is defined as the difference between the phases of horizontally and vertically polarized components of the wave caused by backscattering from objects within the radar resolution volume. δ (measured in [°]) contributes to the total measured differential phase DP [°], along with the propagation differential phase DP [°]. It has been recognized that accurate rainfall measurements using KDP (particularly at X band) are contingent on the effectiveness of a separation of the backscattered and propagation components of DP (e.g., Matrosov et al. 1999, 2002; Otto and Russchenberg 2011; Schneebeli and Berne 2012). However, the practical utilization of the backscatter differential phase δ is not well explored yet. δ is a tell sign for Mie scatterers in the radar volume and bears important information about the dominant size of drops in rain and of wet snowflakes in the melting layer. A relation between δ and ZDR the differential reflectivity (difference between reflectivities of the horizontally and vertically polarized wave components) in rain has been noted. For example, Otto and Russchenberg (2011) suggested a best-fit relationship