HF Radar Measurements of Wave Spectral Development

Abstract

Measurements are reported of ocean spectral wave growth rates parametric in wave frequency and azimuth using measurements of first-order Bragg lines of HF radar Doppler spectra. Preliminary analysis indicates that: (1) growth rates versus angle show the same narrow shape that the directional spectra did, between cosine 16th to 32nd about the wave direction; (2) magnitudes were slightly larger than those by Stewart and Teague (1980) and were in the range predicted by the wave-wave interaction contribution as reported in the JONSWAP results (Hasselmann et al, 1973); (3) the wave growth rate did not approach zero as the ratio of wind speed to phase velocity, U/c, approached 1, as did the atmospheric contribution measured by Snyder et al. (1981), implying a wave-wave interaction contribution; (4) a pronounced overshoot in time was observed for values of U/c greater than 1, with weak overshoot for this ratio less than 1. For wave frequencies in the region of UJc nearly equal to 1, the exponential growth period had finished and a steady- state level was reached before the data collection had begun.