16:30 〜 16:45
[AAS02-10] How much the vertical mixing effect is enhanced by the intervention such as the released deep sea water using the cooling parameter
キーワード：台風、クーリングパラメータ、鉛直混合
A project of Moonshot Goal 8 supported by Japan Science and Technology Agency is to study the possibility to reduce typhoon intensity by artificial interventions. Ocean thermal energy conversion (OTEC) is considered to be one of the artificial interventions. The OTEC technology mixes cold deep sea water at a depth of 800 m with warm sea water at a depth of 20 m and discharges the mixed water to a depth of 20 m, resulting in not only a decrease in the sea surface temperature (SST), but also an enhanced vertical mixing. There is few studies that quantitively estimate effects of vertical mixing. Miyamoto et al. (2017) developed an index “cooling parameter (Co)” that is theoretically formulated by considering the effects of vertical mixing, and Iida et al. (2022) showed that the amounts of SST decrease after the passage of Typhoon FAXAI and HAGIBIS in 2019 can be captured by Co. The purpose of this study is to investigate how much the vertical mixing effect is enhanced by the intervention such as OTEC using sensitivity experiments with Co.
Co is a dimensionless number, indicating the degree of vertical mixing from the characteristics of typhoons and oceans. This study used the long-term ocean reanalysis (FORA-WNP30) and the Best Track data created by the Regional Specialized Meteorological Center Tokyo-Typhoon Center to obtain the vertical profile of sea water temperature directly below the typhoon center position. Maximum winds and radius of strong winds, and moving speed of typhoons were used to estimate Co. For 865 typhoons that occurred in the Northwest Pacific from 1982 to 2015, Co was calculated at a total of 30,300 points every 6 hours. The ”TC-Co” was calculated by averaging Co over time during the development period of each typhoon, from the genesis time to the time of maximum intensity.
A single OTEC peaks at a depth of about 30 m and decreases the temperature by about 0.25°C. Assuming that the water temperature can drop further if the number of OTEC is increased to several tens, an OTEC sensitivity experiment was conducted to estimate Co from a temperature profile that peaks at a depth of about 30m and decease to 0.1-1.0°C. As a result, from the median value of TC-Co in 0.0°C experiment (CTL), the increase rate of the mixed layer after the passage of typhoons was theoretically about 4.4 times, but in the 0.25°C decrease experiment, it was about 4.5 times. In the 1.0°C drop experiment, it is 4.8 times. The amount of SST decrees after the mixing that effectively affects the typhoon’s intensity will be investigated. This research was supported by JST Moonshot R&D Grant Number JPMJMS2282.
Co is a dimensionless number, indicating the degree of vertical mixing from the characteristics of typhoons and oceans. This study used the long-term ocean reanalysis (FORA-WNP30) and the Best Track data created by the Regional Specialized Meteorological Center Tokyo-Typhoon Center to obtain the vertical profile of sea water temperature directly below the typhoon center position. Maximum winds and radius of strong winds, and moving speed of typhoons were used to estimate Co. For 865 typhoons that occurred in the Northwest Pacific from 1982 to 2015, Co was calculated at a total of 30,300 points every 6 hours. The ”TC-Co” was calculated by averaging Co over time during the development period of each typhoon, from the genesis time to the time of maximum intensity.
A single OTEC peaks at a depth of about 30 m and decreases the temperature by about 0.25°C. Assuming that the water temperature can drop further if the number of OTEC is increased to several tens, an OTEC sensitivity experiment was conducted to estimate Co from a temperature profile that peaks at a depth of about 30m and decease to 0.1-1.0°C. As a result, from the median value of TC-Co in 0.0°C experiment (CTL), the increase rate of the mixed layer after the passage of typhoons was theoretically about 4.4 times, but in the 0.25°C decrease experiment, it was about 4.5 times. In the 1.0°C drop experiment, it is 4.8 times. The amount of SST decrees after the mixing that effectively affects the typhoon’s intensity will be investigated. This research was supported by JST Moonshot R&D Grant Number JPMJMS2282.