The Shape–Slope Relation in Observed Gamma Raindrop Size Distributions: Statistical Error or Useful Information?

The three-parameter gamma distribution n(D ) N 0 D exp(D) is often used to characterize a raindrop size distribution (DSD). The parameters and correspond to the shape and slope of the DSD. If and are related to one another, as recent disdrometer measurements suggest, the gamma DSD model is simplified, which facilitates retrieval of rain parameters from remote measurements. It is important to determine whether the - relation arises from errors in estimated DSD moments, or from natural rain processes, or from a combination of both statistical error and rain physics.