Error Structure of Multiparameter Radar and Surface Measurements of Rainfall Part II: X-Band Attenuation

Abstract

In Part II of this study, simulations of multiparameter radar observables to include X-band specific attenuation (A) are performed in order to study the relationship between A, Z, and ZDR. We also compute the triplet (A, Z, ZDR) from simulations of disdrometer raindrop spectra. As in Part I, our simulations include the fluctuations due to both measurement errors and physical variations of the gamma raindrop spectra parameters (N0, D0, m). We examine the correlation between (A/Z) and ZDR derived from both disdrometer and radar simulations, and show that the disdrometer-based data yields a negative collation (? ?0.9) between (A/Z) and ZDR, whereas for radar data the correlation ≈ 0. We emphasize that these correlations are due only to measurement fluctuations, and not to physical variations. The large magnitude for the negative correlation compresses the scatter in plots of (A/Z) versus ZDR based on disdrometer RSD samples whereas the same scatter plots using multiparameter radar data show very large scatter. We also simulate A, Z and ZDR from three separate disdrometers (all sampling the same gamma RSD) and show that the scatter is more realistic and much larger than when using a single disdrometer.