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- Author or Editor: G. Ph van Vledder x
- Journal of Physical Oceanography x
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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.
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.
Abstract
A simple, computationally efficient method is proposed as a standard procedure for the routine analysis of pitch-and-roll buoy wave data. The method yields four directional model-free parameters per frequency: the mean direction, the directional width, the skewness, and the kurtosis of the directional energy distribution. For most applications these parameters provide sufficient directional information. The estimation procedure and error characteristics of the parameter estimates are discussed and illustrated with computer simulated data. An optional interpretation of the combination of skewness and kurtosis as an indicator of uni-modality of the directional energy distribution is suggested and illustrated with field observations.
Abstract
A simple, computationally efficient method is proposed as a standard procedure for the routine analysis of pitch-and-roll buoy wave data. The method yields four directional model-free parameters per frequency: the mean direction, the directional width, the skewness, and the kurtosis of the directional energy distribution. For most applications these parameters provide sufficient directional information. The estimation procedure and error characteristics of the parameter estimates are discussed and illustrated with computer simulated data. An optional interpretation of the combination of skewness and kurtosis as an indicator of uni-modality of the directional energy distribution is suggested and illustrated with field observations.
