Cloud Seeding Experiments for Precipitation Augmentation with Aircraft In Situ Measurements

As one of the physical evaluation techniques of seeding effects, cloud seeding experiments were conducted utilizing an instrumented aircraft, with the use of dry-ice pellets in cold clouds and hygroscopic flares and salt micro-powders in warm clouds as a seeding agent.

On the north-western side of central mountain range in Japan, orographic snow clouds occasionally exist in a quasi-steady state during winter. The airborne seeding experiments had been conducted since 1998. The experiment data were combined as a dataset from about 50 flights during seven field campaigns. The seeded portions were confirmed with seeding line position and its time period, identified with significantly high concentration of ice crystals, and tracked by a wind-based pointer system. We demonstrate from statistical analysis of the in-situ measurements that dry-ice pellet seeding of mixed-phase orographic clouds were effective, based on the comparison of estimated radar reflectivity factor, ice water content, or precipitation intensity from the 2D images of ice particles between seeded portions and their surroundings.

On the western part of Japan, the airborne seeding experiments had been conducted in early summer season during 2008 and 2010. Size distributions of cloud droplets within updraft core were compared between affected and unaffected regions by hygroscopic seeding. The observational results we obtained so far showed that hygroscopic seeding of warm clouds might be effective under limited conditions. We are conducting an airborne field campaign over the eastern part of United Arab Emirates in the mid-summer of 2017. The effectiveness of hygroscopic seeding will be investigated in comparison with previous findings.