Numerical wave models have been developed to reproduce the evolution of waves generated in all directions and over a wide range of wavelengths. The amount of wave energy in the different directions and wavelength is the result of a number of physical processes that are not well understood and that may not be represented in parameterizations. Models have generally been tuned to reproduce dominant wave properties: significant wave height, mean direction, dominant wavelengths. A recent update in wave dissipation parameterizations has shown that it can produce realistic energy levels and directional distribution for shorter waves too. Here we show that this new formulation of the wave energy sink can reproduce the variability of measured infrasound power below a frequency of 2 Hz, associated with a large energy level of waves propagating perpendicular to the wind, for waves with frequencies up to 1 Hz. The details are sensitive to the balance between the non-linear transfer of energy away from the wind direction, and the influence of dominant and relatively long waves on the dissipation of shorter waves in other directions.

Key Points

A spectral wave model is adjusted to produce accurate properties for both dominant and short waves

A balance between 4-wave non-linear interactions and dissipation can explain directional bimodality

Dissipation must be very weak for waves travelling at 90 degrees and more from the wind direction

Plain Language Summary

As the wind blows over the ocean, waves are generated in all directions and over a wide range of wavelengths. The amount of wave energy in the different directions and wavelength is the result of a number of physical processes that are not well understood. Practical models used for marine weather and engineering use a decomposition of the wave field across all these different directions and wavelengths. The sources and sinks of energy of the different components have usually been adjusted to properly represent the total energy, the dominant wavelengths and mean directions, with generally bad results for the shorter wave energy and its directional distribution. Here we show that a recently proposed formulation for the energy sink can be adapted to produce realistic levels of short wave energy in all directions, revealing the importance of different evolution time scales for different wave components. Our wave model is validated using a wide range of measurements, including underwater infrasound power that is related to the presence of waves in opposing directions.