Instrumentation Effects on Estimated Drop Size Distribution and Radar Parameters

Drop size distribution (DSD) is fundamental and important in studying precipitation microphysics and interpreting remote measurements. Accurate measurement and characterization of rain DSDs have been difficult and have encountered a number of issues. Several studies have addressed sampling and processing issues regarding the estimation of drop size distribution (DSD) attributes with disdrometer measurements. A more fundamental issue may be the quality of the measurements themselves.

In this paper, the data quality issue is examined by comparing measurements from a Joss-Waldvogel impact disdrometer and a two-dimensional video disdrometer. Small drops missed by and large drops miscataloged by the Joss-Waldvogel disdrometer yield narrower DSDs characterized by steeper slopes, larger median volume diameters, and lower estimates of rainfall rate, evaporation, drop accretion, and radar reflectivity and differential reflectivity. The differences represent, in part, the uncertainty that exists in our understanding of DSDs. Definitive field studies and perhaps new instruments are needed to establish the true nature of drop populations.