Numerical investigations for the impacts of triple-moment and double-moment condensation schemes on the warm rain formation

Abstract

ABSTRACTThe initiation and intensity of warm rain are processes dominated by the evolution of cloud droplet spectra. To treat the cloud condensation process properly is a fundamental step for the simulation of warm rain formation. Double-moment bulk schemes with a limited number of prognostic variables cannot simulate the evolution of droplet spectra properly. A triple-moment bulk scheme, however, should overcome the problem of spurious cloud droplet spectrum broadening induced by double-moment schemes. To compare the effects of a newly developed triple-moment scheme with double-moment schemes on warm rain formation, the authors conducted WRF-LES numerical simulations to investigate the impacts of the two types of condensation scheme on rain initiation and intensity. In the early stage of raindrop formation, the simulation with the triple-moment scheme delays the raindrop initiation and produces droplet spectra with smaller average radii than those with the double-moment scheme. In the developing stage, t...