Sensitivity of 5-cm wavelength polarimetric radar variables to raindrop axial ratio and drop size distribution

The sensitivity of polarimetric variables at a 5-cm wavelength to raindrop size and axial ratio is examined using T-matrix modeling of the scattering process for gamma raindrop size distributions fitted to tropical rainfall c ollected at Darwin, Australia. These simulations demonstrate that, while sp ecific differential phase (KDP)-based estimates of rainfall, attenuation (A (H)), and differential attenuation are less affected by drop size distribut ion (DSD) variations, large drop occurrence can have significant impacts. A ttenuation is sensitive to the occurrence of large drops, which can produce anomalously high values associated with resonance effect scattering. The p olarimetric variables are sensitive to the relation between the equivolume diameter and axial ratio. Variations in the assumed form of the raindrop ax ial ratio can result in significant biases in rainfall and attenuation. Com bined rainfall estimators, which include differential reflectivity (Z(DR)), such as R(K-DP, Z(DR)) and R(A(H), Z(DR)) are more robust to both DSD and raindrop axial ratio variations. The results also demonstrate that polarime tric techniques employed to classify the phase of hydrometeors are sensitiv e to the assumed raindrop axial ratio.