Background: When attempting to appropriately intervene in severe weather to mitigate its threats, it is critically important to consider what kind of intervention methods should be used. Phenomena that develop over the ocean, like tropical cyclones, ideally should be intervened over ocean. It is necessary to develop new intervention methods that do not currently exist, in collaboration with theoretical research.
Objective: Based on the other theoretical R&D Item, we will develop novel and realistic intervention methods which can significantly alter the future of extreme weather events, including tropical cyclones.
Method: We will focus on the individual cumulonimbus clouds which are generated in tropical cyclones over ocean. By taking a multifaceted approach to these cumulonimbus clouds and the moist convection which produces them, we aim to suppress these clouds (see Fig. 1). We will explore methods that can be implemented over ocean.

① This R&D Item was launched in January 2024. In collaboration with other R&D Items, as shown in Fig. 1, we have formulated a strategy to intervene in the weather systems which produce individual clouds over ocean from both the top and bottom of the atmosphere.

② To realize the effective intervention from the top of the atmosphere, we are exploring ice-nucleating substances derived from plants and fungi. In the atmosphere, water may not freeze—even at temperatures as low as -30°C—if there are no particles to act as ice nuclei. As a result, clouds may not form. By dispersing these substances from aircraft and other means, we aim to control cumulonimbus clouds. Compared to similar approaches, our goal is to design solutions which have minimal environmental impacts and are more effective. Fig. 2 summarizes the ice-nucleating activity inside blueberry branches. It has been found that ice can form inside blueberry branches even at relatively high temperatures (e.g., -1.6°C), which typically do not support ice formation. In fiscal year 2024, we studied ice-nucleating substances found in forsythia branches and similar materials. We found that they have ice-nucleating activity comparable to silver iodide, which is commonly used in cloud seeding.

③ In FY2025, we focused particularly on ice-nucleating substances derived from fungi. Through repeated experiments and measurements, we obtained robust results. Detailed analyses of ice-nucleating activity in test tubes confirmed that these substances exhibit sufficient ice-nucleating activity, even in comparison with silver iodide. However, the behavior of these substances in aqueous systems in test tubes is not necessarily the same as their behavior when dispersed into the atmosphere. We therefore began measurements using a specialized experimental apparatus called a cloud chamber, which can simulate cloud formation in the real atmosphere under laboratory conditions. Based on the findings obtained so far, we judged this fungus-derived substance to be a promising candidate. We examined methods for identifying the protein responsible for its activity and for achieving large-scale production.