Collaborative Research: Surface wave impacts on upper ocean response to tropical cyclones

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The current development of global weather/climate numerical models is moving in the direction of higher spatial resolutions, such that they are now capable to resolve extreme weather events, including tropical cyclones (TCs). In fact, TC prediction models and global weather prediction models are expected to merge in a near future. Turbulent mixing in the ocean surface layer under TCs effectively couples the ocean and atmosphere through air-sea exchanges of heat and momentum. This air-sea coupling is modulated by ocean surface waves (sea states) that are particularly complex and varied under TC conditions. Surface waves affect both one-dimensional (vertical mixing/diffusion), and three-dimensional (upwelling and horizontal advection) processes in the upper ocean. The focus of this study is to advance ocean turbulent mixing schemes that explicitly include the impact of surface waves. Although similar efforts are underway in modeling centers worldwide, few of such efforts include extreme (TC) conditions. Results from this study will inform on the leading order impacts from surface waves on upper ocean processes in high wind conditions, on the benefits of coupling wave and ocean models, and on optimal approaches to implementing wave-dependent parameterizations. The proposed effort is timely and will immediately benefit both the regional and global weather and climate modeling communities. The results of the research will be integrated into the Hurricanes: Science and Society website that is currently used by tens of thousands of educators and students as well as the general public. In addition to their technical training, the graduate students will receive training from education and outreach professionals on how to translate complex scientific concepts into non-expert language.This collaborative study will be carried out by combining state-of-the-art modeling and observational data obtained in previous field programs. Specifically, upper ocean responses to several historical Tropical Cyclones will be simulated using a coupled ocean-wave model that includes sea-state dependent Langmuir turbulence parameterizations and other significant surface wave impacts (the Stokes advection, the Coriolis Stokes force, the Stokes shear force, and the air-sea momentum flux budget). First, the model results will be used to constrain the wind stress and the drag coefficient. Next, the model results, with and without the wave effects, will be compared with observational data, including mixed layer temperature, current, and turbulence data. This investigation will clarify whether the Langmuir turbulence and other surface wave effects make leading order impacts on upper ocean responses to Tropical Cyclones, and whether their accurate prediction requires a fully coupled ocean-wave model with sea-state dependent parameterizations. This study will be conducted in close collaboration with NOAA/Geophysical Fluid Dynamics Laboratory scientists and will contribute to the NOAA research and coupled atmosphere-ocean model development involving the role of upper ocean mixing on climate and weather prediction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.