32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Wednesday, 6 August 2003
Drop-Size Distribution Retrieval from Polarimetric Radar Measurements Using the Constrained-Gamma Model: Verification and Application
Edward A. Brandes, NCAR, Boulder, CO; and G. Zhang and J. Vivekanandan
Poster PDF (352.6 kB)
Polarimetric radar measurements are used to retrieve properties of raindrop distributions. The procedure assumes that drops are represented by a gamma distribution and retrieves the governing parameters from an empirical relation between the distribution shape and slope parameters and measurements of radar reflectivity and differential reflectivity. The proposed paper will briefly describe the method, verify the method with disdrometer observations, and demonstrate its utility through application to several storms. Retrieved DSDs in the core (high reflectivity) regions of thunderstorms were broad (near exponential). Largest drop median volume diameters were at the leading edge of the storm core and displaced slightly downwind from updrafts. Rainy downdrafts exhibited what are believed to be equilibrium DSDs in which breakup and accretion appear to be roughly in balance. DSDs for stratiform precipitation were dominated by relatively large drops. Median volume diameters at ground were closely related to the intensity of overlying bright bands. The radar measurements suggest that, although DSDs in stratiform rain were also broad and nearly constant in the rain layer, they were not at equilibrium but merely steady. DSD invariance is attributed to small total drop numbers resulting in few collisions.

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