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Fundamental Study of Cloud Seeding (Rainmaking) Technology Using Liquid Carbon Dioxide

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[Figure 1] Cloud seeding technique using liquid carbon dioxide

ABSTRACT:
As part of our long-term research aimed at obtaining future water resources, we have carried out studies on the development of cloud seeding techniques using liquid carbon dioxide in cooperation with the National Defense Academy. Since 1999, our cloud seeding experiments have succeeded in triggering artificially-induced precipitation by stimulating natural cumulus clouds of about 1 km thickness in winter season. These experimental results are significant as a starting point for obtaining water resources in future winter seasons. Thus, one of our research aims is to create a roadmap for the practical use of rainmaking technology by accumulating valuable information on cloud seeding.

DETAILED:
Studies of cloud seeding activities aimed at obtaining water resources directly from clouds have been carried out around the world for more than half a century. However, in spite of the significant amounts of information that have been accumulated, cloud seeding techniques have not reached the stage of practical use. This is because it is extremely difficult to evaluate the efficiency of cloud seeding due to large natural variations inside of each cloud and to the many complicated meteorological field patterns. Thus, long-term research is required to enable better access to future water resources.

In this study, cloud seeding techniques (Figure 1) using liquid carbon dioxide have been used for cloud seeding experiments in Northern Kyushu in the west of Japan since 1999. This technique is designed to induce a large amount of precipitation through two basic processes. In the first process, after seeding, ice particles form instantaneously through the process of homogeneous nucleation, and the resultant artificially induced thermal continues to go upward, while expanding its volume due to the phase change of vapor into ice. The ice particles basically grow by diffusion, which means depositional growth of evaporated water vapor onto the surface of the ice crystal. In the second process, after the thermal reaches a stable layer, the falling ice particles move horizontally toward both sides of the thermal due to lateral spreading. Finally, the ice crystal can grow into precipitable size as a snowflake. This is one form of rainmaking for cold clouds.

Here, we introduce some past results of cloud seeding using liquid carbon dioxide. Figure 2 shows a cloud seeding experiment carried out in Northern Kyushu after the passage of a cold front on Oct 27, 1999, in cooperation with the National Defense Academy. In this experiment, a P3C airplane operated by the Marine Self-Defense Force seeded some thick, band-like cumulus clouds. The seeding reaction spurred upward development of a target cloud that stood out from the surrounding clouds, as shown in the picture (the left of Figure 2). This seeded cloud also displayed a strong radar echo (indicating strong precipitation). Figures 3 and 4 respectively show cloud seeding experiments carried out in Northern Kyushu (in cooperation with the National Defense Academy, Fukuoka, Feb. 4, 2006) and in Northern Nagasaki (Sasebo, Jan. 17, 2008). The seeding experiments succeeded in the formation of artificially-induced precipitation from 'thin' cumulus clouds of about 1~1.2 km thickness in the winter season. It can be expected that these results will provide significant clues and a starting point for obtaining water resources in future winter seasons. One of our research aims is to create a roadmap for the practical use of rainmaking technology by accumulating valuable information on cloud seeding.

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[Figure 2] Cloud seeding experiment carried out in Northern Kyushu in Japan on Oct. 27, 1999, in cooperation with the National Defense Academy under the assistance of the Maritime Self-Defense Force

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[Figure 3] Cloud seeding experiment carried out in Northern Kyushu in Japan on Feb. 4, 2006, in cooperation with the National Defense Academy under the assistance of the Maritime Self-Defense Force


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[Figure 4] Cloud seeding experiment carried out in Northern Nagasaki (located in the western edge of Japan) on Jan. 2008, in cooperation with the National Defense Academy under the assistance of the Maritime Self-Defense Force. The figure on the left shows the numerical results of the trajectory of ice crystals generated by cloud seeding with liquid carbon dioxide.


Hydro-Environmental Engineering, Department of Urban and Environmental Engineering,
Faculty of Engineering, Kyushu University
Associate Professor Yoshinari Hiroshiro
Assistant Professor Koji Nishiyama
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