A group headed by Taichi Maki, a visiting professor of Tsukuba University who belongs to the Agricultural environment engineering session of Science Council of Japan, unveiled its success in the experiments of “Artificial Rain” taking advantage of liquefied carbon dioxide.

The experiment was carried out for two consecutive days for the purposes of drought management and anti-desertification. From 2000 meters high up in the sky, liquefied carbon dioxide gas of 5 – 6 gram/s was dispersed for about 15 minutes to the cloud base areas three or four times respectively, and an estimated amount of 1 to 5 million tons of rain was precipitated successfully with about 30 kg of liquefied carbon dioxide.

Artificial precipitation is a technology in which the clouds having a difficult chance to change into rain naturally are eased to cause precipitation artificially, according to the group headed by visiting professor Taichi Maki. The technology is applied to such a cloud as is just likely to rain (like the one under a winter pressure pattern), and a variety of precipitation methods were attempted. Among them the liquefied carbon dioxide method proved to be close to the most practical means from the viewpoints of cost-effectiveness and environmental contribution.

Practically, they dispersed liquefied carbon dioxide horizontally straight to the gaseous layer around the base of cumulus cloud below 0℃ using an aircraft. An intensive cooling effect at about -80℃ resulted from the dispersion generates 10 trillion pieces of ice crystal with only 1 gram of liquefied carbon dioxide.

Before reaching the cloud top by the rising air current inside the cloud, the ice crystal grows into a size to enable precipitation (the RETHIT effect), and effectively makes a wide-volume cloud through the diffusion process to scatter and grow over the cloud (the FILAS effect), which eventually brings precipitation.

In respect of application making the most of utilization of cooling effect, liquefied carbon dioxide would be theoretically replaced by liquefied nitrogen gas for precipitation, but they adopted more inexpensive method because no temperature problem can be involved only if it is below zero.

It takes quite a long period of time to collect data because the experiment can be started only after clearing so many conditions like suitable timing, climatic and cumulus conditions or airspace adjustment for experiment. In addition, there lies some problems like patent or comparison of precipitation volume between natural and artificial clouds. Namely, it is one of the issues that the evaluation of rain increasing effect is difficult.

However, they have already made a procedure and completed standardization. When it comes to practical applications, it can be extended to new businesses like precipitation insurance for agriculture or sightseeing or carbonic rain forecasters. Furthermore, it could also be applied to military purposes by means of intentional change of rain clouds to cause drought over the involved area.