Hogg Nelson G.

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Hogg
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Nelson G.
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  • Technical Report
    A compilation of moored current meter data from SYNOP arrays: one and two (September 1987 to July 1991), volume XLVI
    (Woods Hole Oceanographic Institution, 1992-11) Tarbell, Susan A. ; Worrilow, Scott E. ; Hogg, Nelson G.
    The Synoptic Ocean Prediction Experiment (SYNOP) was an ambitious, multi-faceted program focused on the dynamics and predictailty of the Gulf Stream and its recirculations. The moored array component contained the arrays; one just downstream of Cape Hatteras (the "Inlet Array"), one near 68°W (the SYNOP "Central Array") and one near 55°W ("SYNOP East") to which this report is addessed. There were two settings of the SYNOP East array, the first, from fall 1987 to summer 1989, contained 42 current meters on 13 moorings straddling the mean axis of the Stream and extending north and south into the two recirculations. The second extended the southernmost six moorings for an additional two years until summer 1991. Performance was excellent and all instruments but one were recovered.
  • Technical Report
    Space and time scales of mesoscale motion in the western North Atlantic
    (Woods Hole Oceanographic Institution, 2018-08) Richman, James G. ; Wunsch, Carl ; Hogg, Nelson G.
    From moored data, primarily temperature, of the Mid-Ocean Dynamics Experiment (ModeI) and its successor experiments we find a statistical description of the mesoscale variability. In the ModeI area itself the spectral characteristics of the thermocline and the deep water are different. The thermocline is conveniently described as being made up of three spectral bands: a ' low-frequency' band dominated by zonal velocity fluctuations, an 'eddy-containing' band in which the velocity field is nearly isotropic, and a 'high-frequency' band consistent with models of geostrophic turbulence. In the deep water the zonal dominance at low frequencies is not apparent, and there is enhanced energy at periods of 20-50 days. Vertical structure scales with WK BJ approximation in the high-frequency band but not in the lower frequencies, where low vertical modes dominate the motion. Linear models do not adequately describe the data in the ModeI region. Differences between rough and smooth topography regions are clearly seen only at 1500 m, where there is a loss of energy consistent with a reduced barotropic motion. Other differences, while apparently real, are small. It is found, consistent with the results of Schmitz (1976a), that the ModeI region is atypical of the midocean in that large changes of energy level are found elsewhere. A region due east of ModeI has slightly reduced kinetic energy levels in the main thermocline, but deep energy levels are much lower. Potential energy is less variable than kinetic; in the eastern region the frequency spectra change structure slightly. Linear models may be more adequate there. With more than 2 years of data, no statistically significant heat flux was found in the ModeI area, except for a weak zonal flux in the deep water. There is no direct evidence for baroclinic instability as a significant mechanism of eddy generation; the Gulf Stream is a possible, if unconfirmed, source.