2024 Volume 34 Issue 1 Pages 1-16
Artificial rainfall experiments by seeding of liquid carbon dioxide (LCD) were carried out 6 times over the Izu Islands, Tokyo, and 1 time each at Karatsu, Saga, Kyushu and Saijo, Ehime, Shikoku in 2012 to 2013.
On Feb. 27, 2012 at Miyake I., a seeded cloud developed and a SW wind moved it to an area NE of Miyake Island (I.), and a NE-NNE wind moved a virga under the artificial cloud to the west of Mikura I. at a low altitude, where it was lifted by a WSW wind and then the clouds developed again, and a chain cloud was formed in the ENE direction. The artificial clouds shown by radar echoes reached to the level of 3000-5000 m. The total amount of rain was estimated as 20 million tons (mt.).
On Mar. 14, 2013 at Miyake I., a strong inversion layer was at 2000-2200 m. A disappeared cloud area of 50 km diameter due to rain was found 2 h after the seeding between Mikura and Miyake I. The estimated amount of rain was 2.0 mt.
On Dec. 16, 2013 at Nii I., three line-type clouds developed by the seeding and were recognized on the satellite image of Tera at 20 min after the seeding. Three spaces of cloud disappeared and 2 h later they were recognized on a satellite image of Aqua east of Mikura I. The amount of artificial rain was estimated to be 0.1 mt.
On Dec. 26, 2013 at Karatsu, the seeding cloud reached 3500 m and the cloud depth increased by 150 m from 1250 m to 1400 m. The final distance affected by artificial clouds was over 100 km after 2 h. The amounts of artificial and natural rainfalls were both estimated to be 0.15 mt. after 2 h. The estimations of artificial rainfall by radar echo and surface rainfall agreed with each other.
On Dec. 27, 2013 at Saijo, the natural clouds almost disappeared and were stimulated and developed by the seeding. Rains at 20 locations seemed to be artificial rain due to the seeding time, location, wind direction of WNW, and wind speed. The main zone of artificial rain was 90 km from Saijo to Sugeoi. The amount of artificial rain was estimated to be 1.3 mt.
The seeding rate was about 5 g/s. Convective or stratus clouds are efficient. The seeding air temperature was around –5°C. The depths of clouds were 1000-3000 m. This is important for the topographical effect, convective air layer, upstream and wind speed. The results showed that this method can be successfully used to create artificial rainfall anywhere if the meteorological and topographical conditions are suitable.
