Progress Report
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Typhoon Control Research Aiming for a Safe and Prosperous Society[1] Meteorological Approach
Progress until FY2025
1. Outline of the project
We will develop a more accurate numerical prediction model that can represent typhoon internal structure in detail and use it to investigate methods for effectively controlling typhoons. Specifically, we will examine possible intervention methods, including cloud seeding, to modify typhoon intensity. We will also investigate methods that induce changes in typhoons through sustained weak interventions.
Assuming aircraft-based seeding, we will conduct laboratory experiments to investigate the detailed cloud microphysical processes within convective clouds. In parallel, we will identify potentially disastrous typhoon cases using advanced prediction systems and assimilate observational data into high-resolution numerical models. This will improve prediction accuracy to a level at which the effects of human intervention can be quantitatively evaluated, while also enhancing the overall accuracy of typhoon forecasts.
2. Outcome so far
In FY2025, we explored efficient methods of human intervention, primarily through numerical simulations of cloud seeding. Figure 1 shows the results of an intervention experiment using condensation nuclei seeding with the global nonhydrostatic model NICAM (14-km resolution) for Typhoon Jebi in 2018. In the experiments, cloud droplet number concentrations were increased for 24 hours within a 50 km radius at altitudes of 6–8 km at different times before and during typhoon genesis, to investigate the response of the typhoon system.
The results showed that interventions conducted before typhoon genesis could potentially induce substantial changes in both typhoon track and intensity. This is likely because, during the early developmental stage of a typhoon, even small changes in cloud microphysical processes can strongly influence subsequent convective organization and circulation formation. In contrast, once the typhoon became fully developed, even very large amounts of seeding produced little change in the track, suggesting that the structure of a mature typhoon is relatively stable against small external perturbations.
These results suggest that interventions in cloud microphysical processes before typhoon genesis may exert nonlinear and amplified impacts on future typhoon track and intensity. At the same time, they indicate that the timing of intervention is critically important, and that typhoons may exhibit particularly high sensitivity during their early developmental stages.
Figure 2 shows the results of supercooled water freezing seeding experiments conducted for an idealized typhoon. The experiments used the cloud-resolving model CReSS (2 km resolution) to investigate the effects of artificially inducing freezing in supercooled droplets within the typhoon. Specifically, forced freezing of supercooled water was applied within a region with a radius of approximately 50 km, corresponding to an equivalent silver iodide seeding amount of about 10 tons.
The results showed that the typhoon's maximum wind speed decreased by approximately 10 m/s, while its central pressure increased by approximately 40 hPa, indicating a temporary weakening. These results suggest that typhoon intensity may be sensitive to cloud microphysical processes, particularly ice-phase processes, and indicate that such interventions could be a viable candidate for an efficient typhoon modification method.
Furthermore, we conducted experiments using NHM-CHEM (3 km resolution), which can represent in detail cloud microphysical processes associated with seeding. In experiments targeting Typhoon Hagibis in 2019, we investigated the effects of artificially dispersing sulfate aerosols on typhoon intensity. The seeding amount was set to several tens of tons, representing intervention conditions that could realistically be feasible. The results showed that, depending on the seeding conditions, the central pressure increased by up to approximately 4.5 hPa, indicating a significant change in typhoon intensity. In particular, the response characteristics differed depending on whether the intervention was applied in the northeastern quadrant or on the radius of aerosol dispersion, suggesting that typhoons may exhibit high sensitivity even to relatively small external perturbations.
3. Future plans
In FY2025, we explored efficient methods of human intervention, focusing primarily on cloud seeding techniques. We will further advance numerical simulation experiments to quantitatively evaluate intervention methods that reduce overall or localized typhoon damage. By integrating numerical experiments, aircraft observations, laboratory experiments, and engineering studies, we will assess the feasibility of typhoon modification approaches aimed at disaster mitigation. In addition, we will investigate the mechanisms by which typhoons respond to small-scale interventions that are realistically achievable by humans, and we will establish the scientific and technical foundations necessary for future outdoor experiments.