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Also published as Journal of Geophysical Research, Vol. 80, No. 9, March 20, 1975, Towed sensor data from the main thermocline in the Sargasso Sea south of Bermuda during the Mid‐Ocean Dynamics Experiment are reported and compared with the Garrett and Munk internal wave model. The tows consisted of two sensor suites vertically spaced 11 or 21 m apart; the depth of tow was varied so as to continuously bracket an isothermal surface. Spectral analysis in the wave number band from 0.015 to 5 cycles km−1 results in a vertical displacement spectrum of the isopycnal surface that is statistically indistinguishable from earlier estimates in the same area. In this wave number band, agreement with both the 1972 and the 1975 versions of the Garrett and Munk internal wave model is good, though the model predicts a spectral level about one third too high. The vertical coherence spectra obtained from the temperature fluctuations at the two separations describe the horizontal wave number bands over which vertical coherency is lost. The 1975 model underestimates coherency but can be brought into better agreement by reducing the ‘mode number scale.’, Prepared for the Office of Naval Research under Contract N00014-70-C-0205; NR 263-103 and NSF/IDOE Grant GX-34906.

Also published as Journal of Geophysical Research, 83(C6), 1978, pp. 2921–2938, As part of a field study of the relation between fine scale and large‐scale variations of water properties in the western North Atlantic, the waters in the vicinity of Bermuda were investigated in detail. Previous work in the area had revealed regions of intense temperature fine structure confined to the sides of the island. Generally quieter levels of activity elsewhere in the midocean have suggested that significant mixing might only occur at the solid and fluid boundaries of the ocean. During the course of our investigation, two Gulf Stream rings were found in the vicinity of the island. The exchange of water between them caused three regions of strong alongshore flow. In these three areas we find elevated levels of temperature fine structure in the upper 800 m as measured by the variance in the temperature gradient normalized by the square of the mean temperature gradient over the interval. The normalized temperature variances on small scales (0.2–1 m) are most energetic in patches tightly bound to the island sides, whereas the fine structure on larger scales (5–25 m) is also energetic away from the island in a region of outflow. Velocity profiles show that vertical scales shorten as one approaches the island, and the energy increases in the counterclockwise component. There is no correlation evident between the shear measurements of the internal wave field and the intensity of the fine structure. Possible mechanisms for the production of fine structure are explored within the context of these observations., This research was carried out with funding from the Office of Naval Research under contracts NOOOI4-74-C- 0262 NR083-004 (N .G.H. and T.B.S.) and the National Science Foundation under grant OCE74-19608 (E.J.K.).

Also published as: Journal of Physical Oceanography 9 (1979): 518-530, Constant depth and isopycnal‐following tows are used to estimate the, towed vertical coherence of the internal wave field, at vertical separations of 8.5, 18, 28 and 70 m. The depths of the tows are ∼750 m at the maximum of the buoyancy frequency in the main thermocline of the Sargasso Sea, and near 350 m in the buoyancy frequency minimum between the main and seasonal thermoclines. The towed spectra and towed vertical coherence are compared with three model spectra (GM75, GM76 and IWEX): at 750 m the agreement between data and models is very good, with IWEX being slightly better. At 350 m several of the measured towed vertical coherence spectra are more complex than the spectra from the deeper tows, there are anomalously high coherences in a band from 0.7 to 2 cycles per kilometer that are not predictable by the models. We suggest this coherence bump may be evidence of Eckart resonance, i.e., modes tunneling between the two thermoclines into the region of low buoyancy frequency., Prepared for the Office of Naval Research under Contract N00014-74-C-0262; NR 083-004 and for the National Science Foundation under Grant OCE 74-19608.

Two examples of high wave number (one cycle per 5 m to one cycle per kilometer) temperature spectra from constant depth tow segments are presented. The first is from observations in the center of the main thermocline of the northwest Atlantic at a depth of about 700 m. Four independent estimates of the spectrum are statistically similar to one another. The result is continuous with previous results at lower wave numbers and compares favorably with the 1975 Garrett and Munk internal wave model prediction. The second example is from a tow through a surface mixed layer, at a depth of 26 m, in a nearby area. In contrast to the above, it describes the lack of stationarity of the near-surface spectrum; a result reminiscent of the frequency spectra observed by Sabinin.