DIRECTIONAL WIND-WAVE DEVELOPMENT

Using aircraft radar instruments designed for sea surface wave measure ments, we have obtained fetch-limited directional wind wave spectra un der steady off-shore wind conditions. The results from these observati ons in different areas at different times show that, up to a fetch of 150 km, the dominant waves propagate at an angle to the wind. The angl e is near to that suggested by the Phillips resonance wind wave genera tion condition, but with one important difference: The waves are not a lways symmetric to the left and right of the wind. Most of the cases s how the eventual dominance of one side lobe. The asymmetry of the wave direction relative to the wind suggests that the surface wind stress vector may not always be parallel to the mean wind direction.