The Directional Response of Ocean Waves to Turning Winds

Abstract

The directional response of ocean waves in turning wind situations has been studied with detailed wind and wave observations in open sea and with numerical simulations of the physical processes involved. The observations were acquired with pitch-and-roll buoys in the central and southern North Sea. They are selected and corrected to represent locally generated homogeneous wave fields in deep water. The response time scales thus obtained agree well with one published dataset. The disagreement with other published datasets is shown to be due to differences in analysis techniques, at least partially. The numerical simulations are carried out for homogeneous situations in which a constant wind suddenly shifts direction or rotates. These simulations show that the atmospheric input to the waves tends to rapidly turn the mean wave direction to the new wind direction. This, however, is opposed by whitecapping dissipation and nonlinear wave-wave interactions. The effect of whitecapping on the turning rate of the waves is of the same order of magnitude as that of the atmospheric input (but of opposite sign), but that of the nonlinear interactions is one order of magnitude smaller. Both observed and simulated time scales depend on the stage of development of the wave field, but the simulated time scales are considerably larger than the observed time scales.