Variability of raindrop size distribution as characterized by the generalized gamma formulation

Advantages of using the generalized gamma (GG) model to represent raindrop size distribution (DSD) are discussed, especially when near-complete DSD spectra are considered. Measurements from three climatically different locations in the United States are used. The central approach is the use of double-moment normalization of the measured DSDs using two reference moments, together with an underlying or intrinsic shape, h(x), based on two shape parameters. Stability of h(x) is examined and illustrative examples are presented. It is shown that the modal GG-fitted h(x) representing semiarid and subtropical regimes (combined) provides equally good fits to those from outer rain bands (after landfall) of a Hurricane, a tropical storm, and a tropical depression event. We also show similarities with some recent studies which had used GG model and address the goodness-of-fit aspects of the model, especially when compared with the (much) more widely used standard gamma model. Finally, some applications of the modal GG-fitted h(x) in remote sensing and numerical modeling of microphysical processes are briefly considered.