Developing coupled wind-wave-current interaction framework with sea spray effects for hurricanes models

One of the main goals of the Hurricane Forecast Improvement Project (HFIP) recently launched by NOAA is to improve hurricane intensity prediction. The HFIP research and development program focuses on novel theoretical concepts and the next generation of very high resolution coupled atmosphere-wave-ocean numerical models with improved boundary layer and surface flux parameterizations, tested against high-quality observations. As part of this effort we are developing a new air-sea interaction framework that includes the wind-wave-current and air-sea energy and momentum budget models developed at URI coupled with the sea spray model developed at NOAA/ESRL. One of the features implemented in the new air-sea framework is the method of coupling between breaking waves and the sea spray generation model. In the NOAA/ESRL sea-spray model, the source function is parameterized in terms of energy lost to the wave breaking process, which is related to the wind speed. The effective droplet source height is related to the significant wave height. Within the new framework, the total energy lost to breaking is accurately estimated by explicitly accounting for the sea state dependence and the air-sea flux budget. The source height is determined not from the significant wave height but from the input wave age (wave age of the wind-forced part of the spectrum) and the wind stress. This modification is important under tropical cyclones because the dominant scale of breaking waves is related to the scale of the actively wind-forced waves – not related to the scale of swell generated elsewhere.

The air-sea interaction framework is being implemented and tested into the GFDL hurricane-wave-ocean experimental model and will be soon transitioned to the coupled Hurricane WRF system.