Evolution of Raindrop Size Distribution by Coalescence, Breakup, and Evaporation: Theory and Observations

Abstract

Abstract The evolution of raindrop size distribution by coalescence, collisional breakup, and evaporation is studied using the Low and List parameterization for collisions. The authors consider two models of the development of raindrop size distribution; model 1 is a spatially homogeneous, time-dependent model, and model 2 is a ID (vertical) time-dependent model. The authors present the governing equations for the drop size distribution, balance equations for the rainwater content and rainfall rate, and scaling relationships. The authors demonstrate that the two models are intimately related. For model 1, the authors find that under the action of coalescence and breakup the size distribution attains a steady equilibrium form with three peaks at small drop sizes and an exponential tail at large drop sizes with a slope of approximately 65 cm−1. Under the action of coalescence, breakup, and evaporation. the evolution of a size distribution with a high enough rainwater content can be divided into two phases. ...