[A-AS02] From weather predictability to controllability

[AAS02-P04] Laboratory measurements of the wind stress at high wind speed and long fetch condition

*Ryota Hayashi¹, Naohisa Takagaki¹, Naoya Suzuki², Kazuki Nishiumi¹, Naoki Kurihara¹, Kosuke Nishitani², Takumi Hamaguchi² (1.University of Hyogo, 2.Kindai University)

Keywords:typhoon, momentum flux, typhoon simulation tank

It is of great importance to predict the development and decay of typhoon accurately in order to minimize loss of life and damage. The development and decay of typhoon are determined by momentum transfer across the wind-driven breaking air-water interface. Therefore, reliable prediction about intensity of typhoon need accurate estimates of the momentum transfer across the sea surface. In this study, we aimed to investigate the momentum transfer across the breaking air-water interface under strong-wind and long-fetch conditions by momentum budget method. We used Typhoon Simulation Tank (TST), Research Institute for Applied Mechanics, Kyushu University. The TST has a test section 40.0 m long, 1.5 m wide and 2.0 m high. Wind waves were driven in TST by wind speeds of U₁₀ = 5 ~ 40 m/s. The momentum flux is measured at 20 m from the edge of the entrance slope plate. The momentum flux was measured by using moment budget method, which is the measurement system to measure momentum flux across breaking air-water at high wind speeds indirectly. In moment budget method, four water level meters are used to measure the pressure difference and water level difference between two points in TST. Then, momentum flux is estimated using the measured values of pressure difference and water level difference. We evaluate the momentum flux and compare it with the previous study conducted at a short fetch condition (Takagaki et al., 2012). At whole wind speed region, measured momentum fluxes take relatively similar values to that in Takagaki et al. (2012). Thus, we consider that the momentum flux that is estimated by moment budget method is measured accurately. Actually, the momentum flux is suppressed by increasing the wind speed in the high wind speed region.