A statistical analysis of 2D-video-disdrometer data: impact on polarimetric rainfall estimation

Over the past three years, the National Severe Storms Laboratory in Norman, Oklahoma has collected an extensive, multi-seasonal data set of 2D-video-disdrometer (2DVD) measurments that document the precipitation characteristics of 80 rain events. In total, these data comprise over 210 hours of precipitation and 930 mm of accumulated rain. Rainfall rates range from 0.1 to 175.0 mm/h.

In this study, the 2DVD data are used to examine the frequency of occurrence of DSDs with anomalously large numbers of big drops (determined from calculations of the median volume diameter, D₀). Calculations indicate that DSDs with D₀ > 2.5 mm, while accounting for only 1.4% of the total distributions, are responsible for as much as 11.8% of the total rainfall. These measurements clearly show that 'big drop DSDs' contribute a significant portion of the total rainfall in the southern US Great Plains. We therefore use these data to assess and improve the accuracy of conventional and polarimetric radar-based rainfall estimation algorithms.

Because previous studies have demonstrated that the 2DVD provides more accurate small (D < 1.5 mm) and large (D > 5 mm) drop measurements than impact type disdrometers, we also use this large data set to verify the assumptions and evaluate the accuracy of previously published parameters of gamma DSDs. Finally, possible relationships between DSDs and seasonal storm types are investigated.