Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 6 2009 10.5194/acpd-9-24145-2009 http://www.atmos-chem-phys-discuss.net/9/24145/2009/ http://www.atmos-chem-phys-discuss.net/9/24145/2009/acpd-9-24145-2009.html http://www.atmos-chem-phys-discuss.net/9/24145/2009/acpd-9-24145-2009.pdf 24145 24192 2009-11-12 Effect of hygroscopic seeding on warm rain clouds &ndash; numerical study using a hybrid cloud microphysical model N. Kuba kuba@jamstec.go.jp M. Murakami Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan Meteorological Research Institute (MRI), Tsukuba, Japan The effect of hygroscopic seeding on warm rain clouds was examined using a hybrid cloud microphysical model combining a Lagrangian cloud condensation nuclei (CCN) activation model, a semi-Lagrangian droplet growth model, and an Eulerian spatial model for advection and sedimentation of droplets. This hybrid cloud microphysical model accurately estimated the effects of CCN on cloud microstructure and suggested the following conclusions for a moderate continental air mass (an air mass with a large number of background CCN). (1) Seeding can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount and radius of seeding particles are appropriate. (2) The optimal radius of monodisperse particles to increase rainfall becomes larger with the increase in the total mass of seeding particles. (3) Seeding with salt micro-powder can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount of seeding particles is sufficient. (4) Seeding by a hygroscopic flare decreases rainfall in the case of large updraft velocity (shallow convective cloud) and increases rainfall slightly in the case of small updraft velocity (stratiform cloud). 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