USE OF COPOLAR CORRELATION-COEFFICIENT FOR PROBING PRECIPITATION AT NEARLY VERTICAL INCIDENCE

We present observations of the copolar correlation coefficient between horizontally and vertically polarized echoes \rho(hv)(0)\. These were made with ground-based and airborne weather radars at nearly vertical incidence. A sharp decrease of \rho(hv)(0)\ occurs at the bright band bottom, and is attributed to a varying mixture of hydrometeors with d iverse shape, size, and thermodynamic phase. The largest contribution to decorrelation seems to come from wet aggregates; this is substantia ted by consideration of two simple models. One consists of randomly or iented wet prolate spheroids, and the other considers an ensemble of d istorted spheres. Prolates with axis ratios of 3 or distorted spheres with rms roughness equal to 15% of the diameter decrease the correlati on to 0.8 at S band. At Ku band and for the size range encountered in the bright band, the decrease is a function of equivalent diameter bec ause scattering is in the Mie regime. \rho(hv)(0)\ measurement at 13.8 GHz and from the aircraft are the first ever. Also, differential phas e and differential reflectivity at a 10-degrees off nadir are the firs t of its kind. These last two variables showed a distinct signature in the bright band. This is significant because it might lead to applica tions on airborne or spaceborne platforms.