Spectra of Internal Waves:In-SituMeasurements in a Multiple-Layered Structure

The persistence of layering between 200 and 400 m depth in the Arctic Ocean has enabled construction of accurate internal wave amplitude traces from a 30-hr series of successive temperature profiles taken at 4-min intervals. Spectral density estimates computed from this series diminish with frequency in proportion to f−2, over the frequency range 0.6 to 2.3 cycles hr−1 (cph). In the vicinity of the Vaisala frequency at 3.0 cph, the spectrum falls off as f−8. An equivalent wave amplitude signal, which would have been obtained from a sensor deployed at a fixed depth, is also constructed from the temperature profiles; the resulting spectral estimates decrease in proportion to f−2, over a frequency range from 0.7 to 7.5 cph, well beyond the Vaisala frequency. These results are consistent with recent analytical studies of internal wave spectra in the presence of fine-structure.