Abstract
Profiles of temperature versus depth in the top 440 m of the sea were taken repeatedly at three horizontal locations surrounding the research platform Flip. The time fluctuation of the temperature profiles was used to determine isotherm displacement and slope variation in the region 60-400 m. Measurements were taken during three Flip operations. Two were off the California coast in November 1972 and June 1973. The third was north-northwest of Hawaii in November 1973. Horizontal and vertical coherence measurements indicate that the internal wave field can be divided into two frequency regions. Above 2 cph the bandwidth of energetic horizontal and vertical wave numbers is comparatively narrow. The isotherm displacement spectrum and slope spectrum have irregular slopes. A comparison of the two spectra indicates that first mode is strongly dominant. Below 2 cph the bandwidth of energetic wave numbers is broader, corresponding to multiple energetic modes. The displacement spectrum has an f-2 frequency dependence down to about 2 cpd. The slope spectrum has an approximate f- /2 spectral form in this region. This indicates that the bandwidth or energetic horizontal wave numbers decreases with decreasing frequency, corresponding to a bandwidth of vertical wave number approximately constant with frequency. A vertical spectral analysis of the data substantiates this general picture, while it reveals the presence of a low-frequency high-mode region of surprising spectral intensity. This region might be the spectral signature of horizontally advecting features in the temperature field which are not necessarily associated with vertical density perturbations. However, estimates of horizontal wave number indicate that these features, as well as those of longer wavelength, tend to satisfy the linear internal wave dispersion relation.
Published Version
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