P9r.3 a New Polarimetric Method for Correcting the Effects of Attenuation at C-band

Molecular absorption by the precipitation media is known to reduce values of horizontal reflectivity (ZH) and differential reflectivity (ZDR) for precipitation radars operating at relatively short wavelengths. This attenuation effect is most pronounced behind intense convective echoes. With the advent of polarization diversity, differential propagation phase measurements (ΦDP) offer the advantages of being immune to radar calibration errors, attenuation effects, hail contamination, and partial beam blocking (Ryzhkov and Zrnic 1995). Moreover, Holt (1988) and Bringi et al. (1990) discovered that coefficients used to correct both ZH and ZDR were linearly related to ΦDP measurements. Fig. 1 shows actual observations of ZDR and ΦDP. It is evident that low values of ZDR are coincident with high values of ΦDP. Several methods have emerged which utilize ΦDP as a basis to correct for the reduction in ZH and ZDR due to attenuation. This paper demonstrates a new methodology, called the advection-correction technique, that is independent of an assumed raindrop size-shape model, b) may accommodate temperaturedependent attenuation, and c) is semi-empirical. The technique presented here essentially tracks echoes from one image to the next and then assumes that any changes in ZH and ZDR are due to attenuation effects alone. Correction factors based on ΦDP measurements are produced for several cases of intense convection. Comparisons of corrected versus uncorrected reflectivity measurements are made using data collected at neighboring radars.