The effect of raindrop size distribution variability on the estimation of attenuation

A key problem in determining rain attenuation from rainfall rate is the considerable variability of the raindrop size distribution. Based on analysis of disdrometer and numerical weather prediction model data, the aim of this work is to constrain the parameters of the raindrop size distribution and generate probabilistic attenuation forecasts. Disdrometer data were analysed by fitting a normalized gamma distribution to derive three parameters that were used to define the raindrop size distribution and calculate both rainfall rate and specific attenuation. The parameters of the raindrop size distribution demonstrated no definitive pattern to perfectly define the raindrop size distribution with rainfall rate. Variability in attenuation due to raindrop size distribution was determined by analysing histograms of attenuation over rainfall rate intervals. The results provide a mean attenuation and standard deviation that could be used to calculate the most likely value of attenuation and variance.