Investigation of effective intervention operation for generating offshore heavy rain
Due to the recent progress of global warming, occurrence of heavy rainfall is becoming more frequent around the world. In recent years, Japan has experienced an increasing number of “linearly elongated precipitation zone,” which is long in shape, stays in the same area for a long time, and cause heavy rainfall. Against this background, the project “Artificial generation of upstream maritime heavy rains to govern intense-rain-induced disasters over land (AMAGOI)” aims to reduce heavy rainfall on land downstream by artificially enhancing heavy rainfall over the sea. Specifically, the idea is to generate rainfall upstream over the sea to reduce the water vapor that serves as the seed for rain.
During the Baiu season, the East China Sea upstream has an environment conducive to the development of cumulonimbus clouds due to evaporation from the warm sea surface and the transport of large amounts of water vapor from the southwest. In fact, one can see that precipitation tends to develop downstream, triggered by small islands west of Kyushu. Based on these facts, Item 5 “Investigation of effective intervention operations for generating off shore heavy rain,” considers that it may be possible to generate and enhance precipitation over the ocean with even a small human-induced stimulus. The goal is to clarify in which situations and with which methods effective interventions are possible. This involves reproducing heavy precipitation events with numerical weather models to test and confirm the effectiveness of realistic meteorological intervention methods.
Item 5-1Evaluation of intervention effectiveness using weather model
Principal investigator: Kazuaki Yasunaga
Outline
Using the numerical weather prediction model (SCALE), this study confirms the effectiveness of weather intervention methods, such as dome formation over the sea, cold pool formation, sea surface cooling, microwave heating, cloud seeding. Particularly from a meteorological perspective, we clarify effective intervention operations for generating offshore heavy rain. In the later stages of the research, we plan field experiments involving airplane, ship, and weather radar. This will include arrangements for coordination, methodological considerations, and case selection.
Methods
We incorporate the proposed weather intervention methods -dome formation over the sea or cold pool formation, sea surface cooling, microwave heating and cloud seeding- into the numerical weather prediction model (assuming SCALE) in manner that closely resembles actual interventions. We quantitatively evaluate their effectiveness based on specific heavy rain events. For the intervention methods considered as promising, we construct a virtual observation system on a computer and evaluate its behavior numerically. This enables the development of plans for conducting field experiments.
At the start of the research, no specific numerical targets will be established, because the scale of heavy rainfall over the sea and the reduction in rainfall over land for disaster mitigation are expected to vary depending on the specific disaster events. By the FY 2024, we select cases with high potential to generate heavy rainfall over the sea based on the results of Item 5-2. Flood inundation and economic damage estimates for the selected cases will be calculated by Item 8-1 and 8-2 to investigate the extent to which the heavy rainfall generation over the sea and rainfall reduction over land are required. Then, we set target values for the rainfall reduction to be achieved for each selected cases at an early stage, to serve as our goals.
Importance
In terms of weather intervention, if we can apply an energy input that surpasses the flow associated with heavy rainfall, we should be able to effectively mitigate rainfall in specific areas. However, feasibility is a key word in this project, and accurately representing intervention methods close to real ones in a numerical model is one of the keys for promoting this study.
Even if promising intervention methods are found, conducting actual field experiments requires a lot of human and material resources. Creating a virtual observation system on a computer and using it for implementation plan is significant for efficient resource use.
Expected problems and solutions
To demonstrate the effectiveness of artificial intervention, a sufficient number of experiments is necessary to allow for probabilistic discussions, even when focusing on specific heavy rainfall events. On the other hand, due to the strong nonlinear processes involved in cloud and precipitation, “a sufficient number of experiments for probabilistic discussions” is not clear. Moreover, the degree of freedom that the internal system can vary depending on the numerical experiment settings, which means that the results may also depend on factors such as the size of computational domain, resolution, and parameterization of physical processes.
For the time being, we focus on the speed of promoting project and conduct experiments as comprehensively as possible. At the same time, we aim to establish methods for setting up and structuring numerical experiments using low-dimensional models, in collaboration with the mathematical research group. We initially plan to focus on specific heavy rain events. However, effective intervention methods may vary depending on the event. Therefore, we organize intervention methods in collaboration with Item 5-2, whose study is to index heavy rainfall events using appropriate parameters.
Members
Item 5-2Selection of events with high potential for maritime heavy rainfall generation
Principal investigator: Atsushi Hamada
Outline
This study utilizes analysis data from organizations such as the Japan Meteorological Agency to select events where intervention operations are likely to be effective in generating heavy rainfall over the sea. Specifically, before selecting events, we investigate the spatial distribution and temporal changes of factors such as convective inhibition energy and the height of free convection to identify suitable events. We find the meteorological mechanisms that can be a trigger of heavy rainfall while examining potential weather intervention operations that are expected to be effective.
Methods
We utilize the mesoscale analysis provided by the Japan Meteorological Agency and ERA5 reanalysis data from European Center for Medium-Range Weather Forecasts (ECMWF) to select events of heavy rainfall that have previously caused significant disasters, and where weather intervention operations are expected to be effective. Currently, the weather intervention operations we are considering include dome formation over the sea, cold pool formation, sea surface cooling, microwave heating, and cloud seeding. Many of these methods are designed to force warm and moist air in the atmospheric boundary layer to uplift. Therefore, the effectiveness of the intervention operations is expected to be related to the atmospheric stability around the boundary layer and the water vapor flux. In selecting events where intervention operations are expected to be effective, we quantitatively evaluate the impact of convective inhibition energy and water vapor flux at the land location of heavy rainfall and upstream over the sea on precipitation. Based on this evaluation, we develop an index that combines these physical quantities to show the effectiveness of the intervention operations.
Importance
In order to evaluate the effects of the intervention operations using a meteorological model, it is important to accurately reproduce the past heavy rainfall events. Heavy rainfall events that cause disasters are diverse, and the intervention operations proposed in this project may not necessarily be effective for all events. By introducing the result of the detailed analysis of a few events into an objective and quantitative index based on physical quantities, we expect to efficiently identify events from a wide range of past heavy rainfall events where intervention operations are likely to be effective.
Expected problems and solutions
For the selection of heavy rainfall events where intervention operations are effective and the organization of an index showing their impact, it is essential to conduct detailed analyses of numerous events to stock knowledge. However, this process may take more time than expected. Therefore, we begin to select one or two events with propriety to some extent and, in close collaboration with Item 5-1, aim to create an index that is highly related to intervention effects.
Members
Item 5-3Ensemble weather prediction experiments
Principal investigator: Yusuke Hiraga
Outline
This study utilizes the Weather Research and Forecasting (WRF) model to identify the effectiveness of weather intervention methods (dome formation over the sea, cooling pool formation, sea surface cooling, microwave heating, cloud seeding). By conducting ensemble sensitivity experiments with changing boundary conditions and initial values, we adopt an inductive approach to find the effective interventions. This will allow us to identify intervention operations that can reduce precipitation on land by generating heavy rainfall over the sea.
Methods
We conduct numerical experiments on weather intervention using the WRF model, which is widely used internationally as a non-hydrostatic meteorological model. We introduce the proposed weather intervention patterns (dome formation over the sea, cooling pool formation, sea surface cooling, microwave heating, cloud seeding) into the WRF model in a manner that closely resembles actual interventions. By conducting simulations on specific heavy rainfall events, we quantitatively evaluate their effectiveness in terms of reducing heavy rainfall on land.
At the start of the research, no specific numerical targets will be established, because the scale of heavy rainfall over the sea and the reduction in rainfall over land for disaster mitigation are expected to vary depending on the specific disaster events. By the FY 2024, we select cases with high potential to generate heavy rainfall over the sea based on the results of Item 5-2. Flood inundation and economic damage estimates for the selected cases will be calculated by Item 8-1 and 8-2 to investigate the extent to which the heavy rainfall generation over the sea and rainfall reduction over land are required. Then, we set target values for the rainfall reduction to be achieved for each selected cases at an early stage, to serve as our goals.
Importance
To achieve the goal of this project, it is essential to thoroughly assess the potential for generating maritime heavy rainfall, as well as its effectiveness. While conducting weather intervention experiments in real world requires much costs, it is possible to conduct various patterns of intervention experiments in a numerical model virtual environment. This allows us to accumulate knowledge on the most effective intervention methods, locations, and timing for generating maritime heavy rainfall, providing essential insights for efficiently conducting field experiments in the future.
Expected problems and solutions
There have been few examples of ensemble experiments aimed at weather intervention using WRF mode, this study is pioneering. For example, when implementing artificial weather intervention, it may affect the stability of numerical computations and the computation may not proceed as planned. In such cases, the principal investigator of this study has been in contact with Prof. Shu-Hua Chen at the University of California, who is a member of the WRF model developers, and we can ask for his opinion and try to solve the problem.
Members
