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An artificial seeding experiment was carried out over the Genkai Sea, Japan, using liquid carbon dioxide. The seeded cloud was followed by an aircraft and radar at Kyushu University. A radar-echo intensity of 19 dBZ was formed in the seeded cloud where no radar echo was observed previously. The results of the experiment are analyzed using a numerical model [Weather Research and Forecasting Model (WRF), version 3.1] to evaluate the effects of the artificial seeding. The numerically simulated radar echo has a slightly stronger intensity and wider area than that observed. The results of the experiments were similar to those produced by the numerical model, however. Evaporation of cloud liquid water; growth of snow particles that is due to deposition, autoconversion, aggregation, and collection; and convection caused by released latent heat are shown in the numerical results as effects of the seeding experiment. The falling snow particles cause downward flow, which is compensated for by upward flow that causes the formation of new cloud liquid water as a secondary effect of seeding, although this secondary effect is confirmed only in the numerical results.

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Abstract:In order to bring large amounts of precipitation, the new seeding method using liquid carbon dioxide (LC) was suggested by Fukuta (1996a). The method was applied to the supercooled convective cloud in a post-frontal weather condition in northern Kyushu, Japan, on October 27 1999. In the seeding experiment, LC seeding and the subsequent observation by aircraft were carried out and the features of a seeded echo were observed by radar. Consequently, the aircraft observation confirmed the further development of the seeded cumulus together with a fuzzy aspect of the cloud surface, which indicates the feature consisting of ice particles. Furthermore, the observed cloud top was quite consistent with the cloud top estimated by the thermodynamic analysis following parcel theory. Therefore, the observed results indicate the artificial effects by LC seeding. On the other hand, the radar observation confirmed an artificially induced echo, which showed spreading of the echo area and took a unique mushroom shape in the RHI pictures. The maximum width of the echo reached 24 km and the total amount of estimated radar precipitation of the seeded cumulus was approximately 2.4 million ton, traversing a distance of 60 km in 1 h 40 min. The observed and estimated results are consistent with the hypothesis of the new seeding method, which induces the dynamic and microphysical processes consisting of two fundamental processes. In addition, it was found that dynamical interaction between the seeded and the adjacent natural cumuli was an important factor in the formation of the secondary cumulus. The observational fact will give new viewpoint into the future seeding study.

This experiment of artificial rainfall was carried out by an aircraft seeding operation of liquid carbon dioxide on Feb. 26-27, 2012, near Miyake Island of the Izu Islands in Tokyo, Japan. The development of convective clouds was significant after 0.5 to 1 h of the seeding near Miyake Island and reached to the heights of 3000 m and 4000 m on Feb. 26 and 27, respectively. Artificial clouds appeared and rain was recognized by eye around Mikura Island on Feb. 27 as a direct effect, and it was presumed that the amount of rain increased on the mountainous area. It was clearly successful that the artificial cloud echoes were recognized about 1.5 h later after the seeding on Feb. 27 as a chain-type cloud echo at east-northeast of Mikura Island on the composition radar echo of Japan Meteorological Agency as an indirect effect. The echo height reached from 3000 m to 5000 m when the artificial cloud moved to the leeward side of Miyake Island. It was recognized that the seeding rate of liquid carbon dioxide with about 5 g/s is suitable in a little inside convective cloud with an air temperature below-5℃.