17:15 〜 18:45
[AAS05-P08] Idealized numerical simulations for typhoon weakening from the microphysical approach in the Moonshot Goal 8 program
キーワード：台風、熱帯低気圧、気象制御、ムーンショット課題
1. Introduction
The JST Moonshot Goal 8 (MS8) was launched in 2022. The Typhoon Science and Technology Research Center, Yokohama National University is leading "A core research program for Typhoon controlling aiming for a safe and happy society". Various ideas are proposed in the MS8, we are studying to the typhoon weakening from intervening in the cloud microphysical process. Our strategy is based on the hypothesis by Rosenfeld et al. (2012); seeding with hygroscopic aerosols at the outer region of the typhoon will increase the number of cloud droplets in the local cumulus clouds, shift the size distribution of cloud droplets toward smaller size, and facilitate adiabatic heating in the upper layers. This may promote invigoration of cumulonimbus clouds at the outer region of the typhoon, reduce an amount of water vapor transport toward the typhoon center, and weaken the deep convection at the center of the typhoon. Our goal is realization of the typhoon modification method, but we necessary test this idea before considering the development of the technique. To properly understand how cloud droplets formation and ice crystal formation processes can be modified by seeding under the typhoon environment, we are studying a feasibility to weaken the typhoon by using numerical simulations.
2. Model and experimental setup
To investigate the feasibility of seeding methods, we have conducted idealized typhoon experiments. For the idealized experiments, the regional atmospheric model SCALE-RM (Nishizawa et al. 2015; Sato et al. 2015) developing by RIKEN was used. To investigate the maximum efficacy, experiments were conducted assuming infinite seeding conditions by varying the number concentration of cloud condensation nuclei (Nccn) from 100 cm-3 and 1000 cm-3. Horizontal space of the outer domain was 3000 km x 3000 km and horizontal grid spacing of inner domain was 3 km. The double-moment microphysics scheme (Seiki and Nakajima, 2014) was used for microphysics process. No radiation process was included for simplicity. Time integration period was 10 days from a steady state and an initial profile was given by the mean sounding from Jordan (1958).
3. Result and conclusion
The simulated typhoon was developed during the first 5 days and reached to a quasi-balanced state for the latter 5 days. In the temporal mean for the latter 5 days, the minimum sea level pressure (MSLP) tends to be weaker for the larger Nccn number setting than for the smaller Nccn number setting; the difference of the MSLP was 12 hPa. The spatial distribution of cloud area and wind field are no remarkable difference between the large Nccn case and the small Nccn case. That is, while Rosenfeld’s hypothesis supposes to invigorate deep convection at the outer area of typhoon, the invigoration was not found in the distribution of hydrometeors and updrafts. Dominant difference between the large Nccn case and the small Nccn case was found in the diabatic heating rate at the eyewall clouds. We are now investigating the detail processes which cause the difference in diabatic heating rate. Also, while Rosenfeld’s hypothesis supposes existences of shallow clouds around the outer region, the simulated typhoon shows less shallow clouds, especially around the outer region. So, we will approach to idealized typhoon case which have more low clouds by changing the environmental conditions in the idealized simulation.
4. Laboratory experiments
To properly understand how cloud droplets formation and ice crystal formation processes can be modified by seeding in a typhoon environment, we investigate the aerosol competition through laboratory experiments using a cloud chamber at Meteorological Research Institute, and to reflect the results in a numerical model. The cloud chamber is undergoing modification of the air inlet section and installation of a large heating and humidification system to enable experiments to be conducted under warm and humid conditions.
Acknowledgement
This work was supported by JST Moonshot R&D (JPMJMS2282-04).
The JST Moonshot Goal 8 (MS8) was launched in 2022. The Typhoon Science and Technology Research Center, Yokohama National University is leading "A core research program for Typhoon controlling aiming for a safe and happy society". Various ideas are proposed in the MS8, we are studying to the typhoon weakening from intervening in the cloud microphysical process. Our strategy is based on the hypothesis by Rosenfeld et al. (2012); seeding with hygroscopic aerosols at the outer region of the typhoon will increase the number of cloud droplets in the local cumulus clouds, shift the size distribution of cloud droplets toward smaller size, and facilitate adiabatic heating in the upper layers. This may promote invigoration of cumulonimbus clouds at the outer region of the typhoon, reduce an amount of water vapor transport toward the typhoon center, and weaken the deep convection at the center of the typhoon. Our goal is realization of the typhoon modification method, but we necessary test this idea before considering the development of the technique. To properly understand how cloud droplets formation and ice crystal formation processes can be modified by seeding under the typhoon environment, we are studying a feasibility to weaken the typhoon by using numerical simulations.
2. Model and experimental setup
To investigate the feasibility of seeding methods, we have conducted idealized typhoon experiments. For the idealized experiments, the regional atmospheric model SCALE-RM (Nishizawa et al. 2015; Sato et al. 2015) developing by RIKEN was used. To investigate the maximum efficacy, experiments were conducted assuming infinite seeding conditions by varying the number concentration of cloud condensation nuclei (Nccn) from 100 cm-3 and 1000 cm-3. Horizontal space of the outer domain was 3000 km x 3000 km and horizontal grid spacing of inner domain was 3 km. The double-moment microphysics scheme (Seiki and Nakajima, 2014) was used for microphysics process. No radiation process was included for simplicity. Time integration period was 10 days from a steady state and an initial profile was given by the mean sounding from Jordan (1958).
3. Result and conclusion
The simulated typhoon was developed during the first 5 days and reached to a quasi-balanced state for the latter 5 days. In the temporal mean for the latter 5 days, the minimum sea level pressure (MSLP) tends to be weaker for the larger Nccn number setting than for the smaller Nccn number setting; the difference of the MSLP was 12 hPa. The spatial distribution of cloud area and wind field are no remarkable difference between the large Nccn case and the small Nccn case. That is, while Rosenfeld’s hypothesis supposes to invigorate deep convection at the outer area of typhoon, the invigoration was not found in the distribution of hydrometeors and updrafts. Dominant difference between the large Nccn case and the small Nccn case was found in the diabatic heating rate at the eyewall clouds. We are now investigating the detail processes which cause the difference in diabatic heating rate. Also, while Rosenfeld’s hypothesis supposes existences of shallow clouds around the outer region, the simulated typhoon shows less shallow clouds, especially around the outer region. So, we will approach to idealized typhoon case which have more low clouds by changing the environmental conditions in the idealized simulation.
4. Laboratory experiments
To properly understand how cloud droplets formation and ice crystal formation processes can be modified by seeding in a typhoon environment, we investigate the aerosol competition through laboratory experiments using a cloud chamber at Meteorological Research Institute, and to reflect the results in a numerical model. The cloud chamber is undergoing modification of the air inlet section and installation of a large heating and humidification system to enable experiments to be conducted under warm and humid conditions.
Acknowledgement
This work was supported by JST Moonshot R&D (JPMJMS2282-04).