One might expect a Gaussian distribution centered on the GK values because of turbulence, but significant skewness might result as reported herein for larger drops in intense rainfall (under certain conditions such as embedded line convection). Additionally, the distribution of fall speeds for a given diameter is also relevant. These latter optical disdrometers are capable of measuring both drop shapes and their fall speeds, which in turn allows for determining if there is any coupling between the two, especially in moderate-to-intense rain rates where drop oscillations may be expected to significantly affect the drag force relative to spherical drops in still air. The laboratory data of Gunn and Kinzer (1949 henceforth GK) for fall speed (of water drops in still air), and the fits to their data, continue to be widely recognized as the “standard” against which to compare measurements made with more modern optical techniques (e.g., Löffler-Mang and Joss 2000 Barthazy et al. The fall speed of raindrops as a function of drop diameter is important in cloud physics and forms a fundamental basis for radar-based estimation of rain rate. These findings are consistent with the asymmetric oscillation modes inferred from the 2DVD measurements for event 2 (probably collision induced) within the convective line. Also found were low ρ hv regions within the line convection that were considerably lower than the scattering calculations. The K dp/ Z h versus Z dr variations within the line convection were not consistent with the corresponding variation determined from the scattering calculations using the measured 1-min drop size distributions and using the “reference” drop shapes. The radar data for the second event were analyzed in terms of the self-consistency among the radar-measured quantities. The implications are that for event 1 the dominant mode of drop oscillation is the axisymmetric mode, and that within the convective line of event 2 other fundamental modes were frequent. Drop shape information from the two 2DVD instruments showed that, during the passage of the convection line, around 30%–40% of the drops did not have an axis of rotational symmetry, whereas for event 1, it was only 5%. The “slower” drops in the second event were detected while the convective line was directly over the 2DVD site. For the first event, the fall speed distribution for a given drop diameter interval showed a narrow and symmetric distribution with a mode at the expected value the second event produced a wider distribution with a significant skewness toward lower fall speeds. Both events had moderate-to-intense rainfall rates, but the second event had an embedded convective line. Two rain events are analyzed using two collocated 2D-video disdrometers (2DVD) and a C-band polarimetric radar at 15-km distance.
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