Observation-based source functions for wave forecast models

Forecast of wind-generated waves is of primary importance across a broad range of applications such as naval exercises, marine transport, navigation, ship traffic control, ship design, coastal and offshore industries, maritime safety issues, coastal storm warnings, pollution control and mitigation, fishing, recreational activities at sea, among many others. The forecast is routinely conducted by meteorological centres of every country adjacent to significant water bodies, based on spectral wave models. The models operate by estimating evolution of wave spectra caused by energy sources/sinks. Physics of two primary source/sink terms employed by the operational models, namely wavebreaking energy dissipation and wind-to-wave energy input have not been updated for decades. In the meantime, the new physics is available. For the first time under field conditions, in the course of ONR Lake George (Australia) project, estimates of the spectral distribution of the wave-breaking dissipation were obtained, and measurements of the wind input spectral function were conducted, including conditions of strong-to-extreme wind forcing. Corresponding outcomes were parameterised as source functions suitable for spectral wave models, and both exhibit a number of physical features presently not accounted for. The source terms were tested, calibrated and validated on the basis of a research thirdgeneration wave model. Physical constraints were imposed on the source functions in terms of the known experimental dependences for the total wind-wave momentum flux and for the ratio between the total input and total dissipation. Enforcing the constraints in the course of wavespectrum evolution allowed calibration of the free experimental parameters of the new input and dissipation functions. The approach allows separate calibration of the source functions, before they are employed in the evolution tests. The evolution simulations were then conducted. The resulting time-limited development of integral, spectral and directional wave properties, based on implementation of the new physically-justified source/sink terms and constraints, is then analysed. Good agreement of the simulated evolution with known experimental dependences is demonstrated.