Evaluation of a New Polarimetrically BasedZ–RRelation

Abstract

Abstract A new polarimetrically based (or, pol-based) Z–R relation of the form Z = aR1.5 is described and evaluated where the multiplicative coefficient a is continuously adjusted as the drop size distribution evolves in space and time. The methodology is based on previous studies involving estimation of the normalized gamma drop size distribution parameters (DSD) using radar measurements of Zh, Zdr, and Kdp. In moderate-to-intense rainfall, the retrieval of the DSD parameters are formulated to account for the effects of drop oscillations using the “effective” β concept where the axis ratio (r) versus D relation is assumed to be linear and of the form r = 1 − βD in the underlying raindrop shape model. Rayleigh scattering with analytic approximations are used to show that the β estimator in Gorgucci et al. (2000) based on Zh, Zdr, and Kdp is of the correct form. The changes in the effective β in a storm cell is studied as the cell evolves from the growth phase to the mature phase (with microburst and rain ...