Abstract
Extensive comparisons of dual-wavelength (10 and 3 cm) radar data with observations at the ground and penetration aircraft (T-28) measurements of hail in a Colorado storm show that positive hail signals (10 cm reflectivity factor exceeds that at 3 cm) are well correlated with the presence of hail ≳ 1 cm diameter. Widespread areas of negative hail signals (3 cm reflectivity factor exceeds that at 10 cm) found above the melting level are correlated with the presence of subcentimeter graupel. It is possible, therefore, to discriminate two sizes of particles based on dual-wavelength radar measurements. This finding is exploited in Part II of this work to investigate the evolution of graupel into hail.
