17:15 〜 19:15
[ACG36-P03] Analysis of Ocean Cooling and Wave Development due to Differences in Typhoon Characteristics
キーワード：台風‐波浪‐海洋相互作用、大気海洋波浪結合モデル、海洋応答、波浪効果
Typhoons are generated over the ocean, and ocean conditions critically affect their intensification and weakening. In particular, Ocean responses and wave development significantly affect typhoon intensity and structure through feedback mechanisms. Understanding these processes is critical for improving typhoon forecasts and mitigating their impacts.
This study investigated the typhoon-induced ocean cooling and wave development using the coupled numerical model COAWST (Warner et al., 2010), which integrates WRF (Weather Research and Forecasting model), ROMS (Regional Ocean Modeling System), and WW3 (WaveWatch III). We targeted Cimaron and Jebi (2018) and Faxai and Hagibis (2019). These typhoons with varying characteristics were analyzed through simulations conducted with an atmosphere-ocean coupled model and a fully coupled atmosphere-ocean-wave coupled model. The wave effects were analyzed using three surface roughness parameterizations (Taylor and Yelland, 2001; Drennan et al., 2003; Oost et al., 2002), considering wave height, wave steepness, wavelength, and age.
Sea surface temperature (SST) cooling along the typhoon tracks was observed in all cases. While the distribution of cooled regions varied depending on typhoon characteristics, the SST decreased by less than 2°C for Cimaron and Faxai, and by more than 3°C for Jebi and Hagibis. These results were consistent with observations from Himawari-8, confirming that the coupled simulations successfully reproduced SST cooling. The effect of wave coupling on SST cooling was less than 1°C, regardless of the parameterization. Vertical cross-sectional analyses of ocean temperature at arbitrary latitudes revealed that vertical mixing caused by typhoon passage led to ocean surface cooling and mixed layer deepening in all cases. Strong upwelling occurred 12 hours after the typhoon passage, except for Faxai, preventing SST recovery and maintaining the cooled state. Ocean cooling changes latent heat flux patterns, with Hagibis showing a 1000 W/m² flux difference between the front and rear. These findings demonstrate that the degree and distribution of SST cooling depend on typhoon characteristics, influencing the latent heat flux and providing feedback to typhoons while also impacting the marine environment. Understanding these ocean responses to typhoon passage is, therefore, crucial.
Regarding wave development, the maximum significant wave heights were above 15 m for Cimaron and Hagibis, 14 m for Jebi, and 12 m for Faxai. Differences in typhoon characteristics resulted in variations in the quadrants and distributions of maximum wave heights. This not only contributes to wave-related disasters but also impacts sea surface roughness, which is associated with the loss of momentum energy from typhoons. Spatial analysis of sea surface roughness for each parameterization showed significant differences in the distribution of high roughness values. In cases without wave coupling, roughness primarily depended on wind speed, whereas roughness became independent of wind speed distribution in wave-coupled cases. This indicates that wave-based roughness significantly influences wind speed distribution and provides feedback to typhoons.
Recent advances in wave observation technology in open oceans suggest that further improvements in wave-based parameterizations are feasible. The findings of this study lay a critical foundation for advancing typhoon forecasting accuracy and reducing wave-induced disasters by promoting the development of improved wave-based parameterizations and more accurate coupled modeling systems.
This study investigated the typhoon-induced ocean cooling and wave development using the coupled numerical model COAWST (Warner et al., 2010), which integrates WRF (Weather Research and Forecasting model), ROMS (Regional Ocean Modeling System), and WW3 (WaveWatch III). We targeted Cimaron and Jebi (2018) and Faxai and Hagibis (2019). These typhoons with varying characteristics were analyzed through simulations conducted with an atmosphere-ocean coupled model and a fully coupled atmosphere-ocean-wave coupled model. The wave effects were analyzed using three surface roughness parameterizations (Taylor and Yelland, 2001; Drennan et al., 2003; Oost et al., 2002), considering wave height, wave steepness, wavelength, and age.
Sea surface temperature (SST) cooling along the typhoon tracks was observed in all cases. While the distribution of cooled regions varied depending on typhoon characteristics, the SST decreased by less than 2°C for Cimaron and Faxai, and by more than 3°C for Jebi and Hagibis. These results were consistent with observations from Himawari-8, confirming that the coupled simulations successfully reproduced SST cooling. The effect of wave coupling on SST cooling was less than 1°C, regardless of the parameterization. Vertical cross-sectional analyses of ocean temperature at arbitrary latitudes revealed that vertical mixing caused by typhoon passage led to ocean surface cooling and mixed layer deepening in all cases. Strong upwelling occurred 12 hours after the typhoon passage, except for Faxai, preventing SST recovery and maintaining the cooled state. Ocean cooling changes latent heat flux patterns, with Hagibis showing a 1000 W/m² flux difference between the front and rear. These findings demonstrate that the degree and distribution of SST cooling depend on typhoon characteristics, influencing the latent heat flux and providing feedback to typhoons while also impacting the marine environment. Understanding these ocean responses to typhoon passage is, therefore, crucial.
Regarding wave development, the maximum significant wave heights were above 15 m for Cimaron and Hagibis, 14 m for Jebi, and 12 m for Faxai. Differences in typhoon characteristics resulted in variations in the quadrants and distributions of maximum wave heights. This not only contributes to wave-related disasters but also impacts sea surface roughness, which is associated with the loss of momentum energy from typhoons. Spatial analysis of sea surface roughness for each parameterization showed significant differences in the distribution of high roughness values. In cases without wave coupling, roughness primarily depended on wind speed, whereas roughness became independent of wind speed distribution in wave-coupled cases. This indicates that wave-based roughness significantly influences wind speed distribution and provides feedback to typhoons.
Recent advances in wave observation technology in open oceans suggest that further improvements in wave-based parameterizations are feasible. The findings of this study lay a critical foundation for advancing typhoon forecasting accuracy and reducing wave-induced disasters by promoting the development of improved wave-based parameterizations and more accurate coupled modeling systems.