Directional response of wind waves to a large wind shift

The directional response of a fully arisen sea to a similar to 90 degrees w ind shift is studied using a combination of airborne radar and in situ dire ctional wave observations. The observations were made in February 1991 as a part of the Surface Wave Dynamics Experiment. Radar and buoy mean wave dir ections in several frequency bands are polynomial-smoothed in fetch and dur ation coordinates and analyzed for the directional relaxation parameter b b y using finite differences of the gridded, smoothed data in a one-dimension al advection equation for the mean wave direction. The analysis is carried out using several different sets of buoy wind and wave data in an event win dow of 40 h in duration by 200 km in fetch (100-300 km offshore). For the m ost well-populated and reliable inverse wave age class in the study, 1.2 le ss than or equal to U/c < 1.6, the authors find b = 3.3(+/- 0.1) x 10(-5). The data do not support any inference as to possible wave age dependence ot her than, perhaps, the null hypothesis, b = const (U/c). Frequencies near t he spectral peak do not respond according to the relaxation model, and misl eading values of b may result from st standard analysis of the data. Wave-c urrent interactions are a potential source of bias. Reflected waves in the study area may be biasing the present result low by as much as 20%.