Summary of Japanese Cloud Seeding Experiments for Precipitation Augmentation (JCSEPA)

MRI, in cooperation with 10 other research organizations, carried out the five-year research project (2006-2011) “Japanese Cloud Seeding Experiments for Precipitation Augmentation (JCSEPA)” to aim drought mitigation and water resources management. As for the dry-ice pellet seeding of orographic snow clouds, in-situ aircraft and simultaneous ground-based radar observations showed that the seeding enhanced radar reflectivity and precipitation rate in clouds. A combination of NHM and land surface model, which were validated with observation results, showed that dam water storage increased from 70 % to 100 % at the end of June with the dry ice seeding of about 1,000 hr in total during a whole winter. Thus the effectiveness and usefulness of the dry-ice seeding of orographic snow clouds is demonstrated. On the other hand, as for the hydroscopic (hygroscopic flare and salt micro-powder) seeding of warm cumulus and stratocumulus clouds, cloud simulation chamber experiments, hybrid cloud microphysics model simulation and aircraft seeding experiments showed that the hydroscopic seeding could cause some broadening of cloud droplet size distribution toward larger sizes. However, the chamber experiments and model simulation showed that hygroscopic flare seeding suppressed rain drop formation due to a decrease in mean size of cloud droplets resulting from the increase of cloud droplets number concentrations. The cloud microphysics model and 3D NHM with a simplified seeding scheme showed that salt micro-powder seeding of about 540 hr in total during a whole summer could produce about 20% of increase in seasonal rainfall amount and may increase dam water storage by 50 megatons and prevent the dam from getting empty. However, the amount of salt micro-powder needed for 540 hr seeding would be unrealistically huge and we have to consider the cost-benefit and environmental issues.