Comparison of Remote Measurements by Single- and Dual-Wavelength Meteorological Radars

Dual-wavelength radar was used routinely to observe and record, in digital form, severe convective storms in northeastern Colorado in 1972-1974. By postprocessing, the precipitation-caused attenuation of the attenuating wavelength of the dual-wavelength pair is determined while the other wavelength remains essentially unattenuated. Precipitation rate computed from this attenuation is more accurate than that computed from the radar reflectivity factor Z, the quantity popularly associated with meteorological measurements of storms. The attenuation-derived precipitation over an artificial catchment shows the greatest improvement over that derived from Z at the highest precipitation rates. The attenuation technique has particular strength in that it discounts regions of hail that occur in the heaviest storms which greatly perturb the simple radar reflectivity estimates. The hail signal H is the ratio (expressed in decibels) of the S-band and X-band normalized echo powers from a point in a storm less the attenuation. Using the assumption of spherical hail with exponential size spectra randomly truncated at the upper limit, the equation D0 = 0.31 + 0.12H is a reasonable relationship between this hail signal and the median volume diameter, in centimeters, of the hail. Theoretical relationships relating the hail mass deposition rate and the vertical hail energy flux density are derived and are shown to be correlated with hail totals over the artificial catchment with correlation coefficients exceeding 0.8 for mass and 0.65 for energy.