Progress Report
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Artificial generation of upstream maritime heavy rains to govern intense-rain-induced disasters over land (AMAGOI)[6] Engineering
Progress until FY2025
1. Outline of the project
Weather intervention to prevent damage from heavy rainfall has never been tackled in human history, and is by no means an easy task, even with the cutting-edge technologies. Even if it is feasible, it requires careful consideration of safety and ethical issues. One method currently proposed is microwave atmospheric heating technology (see Fig.1), in which microwaves are irradiated to a certain point in the sky to promote atmospheric heating and induce the formation of raining clouds away from densely populated areas. It is essential to repeatedly run simulations on a computer prior to engineering indoor and outdoor experiments to fully confirm whether this technique is effective from meteorological and societal viewpoints.
The feasibility of microwave atmospheric heating is verified through studies based on numerical simulations. In FY2024, we carried out numerical simulations to study whether or not it is technically feasible to artificially induce raining clouds by microwave atmospheric heating.
2. Outcome so far
Microwave atmospheric heating utilizes the microwave absorption by water vapor and oxygen molecules in the atmosphere, as well as cloud water and rainwater in the atmosphere. The figure shows the results of a simulation of atmospheric heating using microwave absorption by water vapor molecules as an example. In the calculation, a weather state characteristic over ocean around Japan are assumed with a microwave emitter with 1 megawatt power and an antenna gain of 40 dB.
Fig.2 (top-left) shows that a high heating rate (yellow) is expected in the vicinity of the emitter, but the heating rate rapidly decreases with distance from the emitter (blue). The heated area is somewhat expanded if a second emitter is installed at x=1 km (top-right). To visualize this more quantitatively, Fig.2 (bottom) depicts its cross section at an altitude of 0.5 km, implying a heating of about 1°C per hour directly above the radiator (x=0). This value is comparable to the latent heating released in cumulonimbus clouds. It is hence theoretically possible to induce rain clouds by microwave heating.
Fig.3 shows the simulated evolution of a heated air parcel for different moisture environments. The air begins to ascend rapidly at some point when the environment is very moist, implying the onset of raining clouds. Otherwise the air simply oscillates around a nearly constant height without evolving into clouds. It follows that the potential of microwave heating as a trigger of rain formation depends largely on how moist the ambient atmosphere is.
A microwave beam is, however, very narrow in the vicinity of the emitter. Fig.4 shows the microwave beam width, with smaller values indicating a narrower heating region. Even in the atmosphere at a distance of 1 km from the emitter, the beam width is about 40 m. Considering that the scale of cumulonimbus clouds can be several kilometers, heating is spatially limited to a very small area. This fact casts doubt on the feasibility of microwave heating.
3. Future plans
This research is terminated at the end of FY2025.In addition, as other means of intervention, we have begun examining offshore structures and advanced cloud seeding.