Note on the directional properties of meter-scale gravity waves

The directional distribution of the energy of young waves is bimodal for frequencies above twice the peak frequency, and that distribution can be obscured by the presence of bound waves. Here we analyze in detail a typical case measured with a peak frequency fp = 0.18 Hz and a wind speed of 10.7 m s−1. The directional distribution for a given wavenumber is nearly symmetric, with the separation of two peaks of the directional distribution growing with frequency, reaching a separation of 150° at 35 times the peak wave number kp, with a separation that increases for wavenumbers up to 45 kp. When considering only free waves, the lobe ratio of peak energy density to the minimum energy level, in the wind direction, increases linearly with the non-dimensional wavenumber k / kp, up to a value of 6 at k / kp ≃ 22, possibly more for shorter components. These observations extend to shorter components previous measurements, and have important consequences for wave properties sensitive to the directional distribution, such as surface slopes, Stokes drift or microseism sources