Artificial rainfall experiment by seeding liquid carbon dioxide above the Izu Islands of Tokyo on March 14 in 2013

Experiments of cloud seeding using liquid carbon dioxide (LCD) were carried out on March 14, 2013 near Miyake Island and Mikura Island in the Izu Islands, Tokyo, Japan. Convective clouds near the islands developed 0.5 to 1 h after the seeding. Artificial convective clouds accompanied by rain stream, i.e., virga, were observed, and rain was seen around the islands. Photos from aircraft and satellite images revealed trails and holes of disappeared clouds about 1 h and 2 h later, respectively. Within 1 h, the amount of precipitation was presumed to be about 0.1 million tons, with the precipitation intensity of 1 mm/h, based on a disappeared area 2 km × 50 km, constituting the first direct effect. Within 2 h, the total amount of precipitation from the disappeared cloud was presumed to be 1.8 million tons, based on a disappeared cloud area of diameter 50 km, constituting the secondary indirect effect. The main objective is whether the experiment of artificial rain is a success or not in a meteorological condition. Other objectives were shown successfully by photos taken of virga and the disappeared cloud, and by a satellite image based on the combination of convective cloud and the air temperature inversion layer. We found that LCD seeding at about 5 g/s within convective clouds near their bases is feasible when the air temperature is below 0°C, i.e., suitable around -5°C. The excellence of LCD seeding technique is supported by the results of this study, and we believe this technique will spread worldwide.