Radar measurements of ZDR are compared with ZDR deduced from aircraft graupel spectra during the Cooperative Convective Precipitation Experiment. On August 4, 1981, the University of Wyoming's Super King Air made two penetrations (at altitudes of 3 km and 1.8 km above mean sea level) through a convective cell located 90 km NE of the CHILL radar. The aircraft was equipped with two two-dimensional PMS probes located orthogonally so as to view the falling hydrometeors along their symmetry axis (V probe) and along an axis orthogonal to it (H probe). Elliptical raindrop images were observed below cloud base (1.8 km altitude), and conical graupel images were observed at 3 km altitude. Because of beam blockage at the lowest elevation scans, radar data were not available in the rain region. Aircraft raindrop spectra were analyzed in detail, and it is shown that ZDR deduced from such spectra should be an excellent estimator of D0 provided the correct form for the drop size distribution is assumed. ZDR and ZH deduced from the graupel spectra are shown to be in the range measured by the radar.
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