On the shape-slope relation of drop size distributions in convective rain

The relation between the slope and shape parameters of the raindrop size distribution parameterized by a gamma distribution is examined. The comparison of results of a simple rain shaft model with an empirical relation based on disdrometer measurements at the surface shows very good agreement, but a more detailed discussion reveals some difficulties - for example, deviations from the gamma shape and the overestimation of collisional breakup.