SKEWNESS AND KURTOSIS OF MEASURED RAINDROP SIZE DISTRIBUTIONS

Skewness and kurtosis are used to investigate particle size distributions. A quantitative method is introduced to distinguish between a gamma distribution and an exponential (e.g. Marshall-Palmer) distribution. For this method, two "deviation coefficients" are introduced, which are the skewness and the square root of the kurtosis of the measured distributions divided by their values for an exponential distribution. The method is illustrated with data for raindrop size distributions from four case studies and demonstrates that the data are inadequately described by the Marshall-Palmer distribution, although it does appear to be an "equilibrium" distribution toward which steady precipitation appears to tend.