ALBERT

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009

Beschreibung: Observations and inverse models suggest that small-scale turbulent mixing is enhanced in the Southern Ocean in regions above rough topography. The enhancement extends 1 km above the topography suggesting that mixing is supported by breaking of gravity waves radiated from the ocean bottom. In other regions, gravity wave radiation by bottom topography has been primarily associated with the barotropic tide. In this study, we explore the alternative hypothesis that the enhanced mixing in the Southern Ocean is sustained by internal waves generated by geostrophic motions flowing over bottom topography. Weakly-nonlinear theory is used to describe the internal wave generation and the feedback of the waves on the zonally averaged flow. A major finding is that the waves generated at the ocean bottom at finite inverse Froude numbers drive vigorous inertial oscillations. The wave radiation and dissipation at equilibrium is therefore the result of both geostrophic flow and inertial oscillations and differs substantially from the classical lee wave problem. The theoretical predictions are tested versus two-dimensional and three-dimensional high resolution numerical simulations with parameters representative of the Drake Passage region. Theory and fully nonlinear numerical simulations are used to estimate internal wave radiation from LADCP, CTD and topography data from two regions in the Southern Ocean: Drake Passage and the Southeast Pacific. The results show that radiation and dissipation of internal waves generated by geostrophic motions reproduce the magnitude and distribution of dissipation measured in the region.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1982

Beschreibung: The development of nonlinear surface and internal wave groups is investigated. Surface wave evolution was observed in an unusually long wave channel as a function of steepness and group length. Dissipation and frequency downshifting were important characteristics of the long-time evolution. The amplitude and phase modulations were obtained using the Hilbert transform and specified as an initial condition to the cubic nonlinear Schrodinger equation, which was solved numerically. This equation is known to govern the slowly varying complex modulation envelope of gravity waves on deep water. When dissipation was included, the model compared quite well with the observations. Phase modulation was used to interpret the long-time behavior, using the phase evolution of exact asymptotic solutions as a guide. The wave groups exhibited a long-time coherence but not the recurrence predicted by the inviscid theory. An oceanic field study of the generation of groups of large amplitude internal waves by stratified tidal flow over a submarine ridge indicates that the large amplitude and asymmetry of the topography are critical in determining the type of flow response. The calculated Froude numbers response length scale and duration differ markedly between the two phases of the tide due to the asymmetry.

Beschreibung: Research assistantship provided by the Office of Naval Research contract no. N00014-80-C-0273

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1982

Beschreibung: Velocity and temperature time series from Hudson Submarine Canyon and hydrographic surveys of seven canyons of the Middle Atlantic Bight indicate that the effects of storms, tides, and incoming internal waves are intensified in submarine canyons. Storms with strong eastward and westward wind stress were found to cause strong upwelling and downwelling through the upper layers of Hudson Canyon. Storm-forced upwelling also caused strong down-canyon flows at the canyon floor. Internal waves were found to be concentrated in the canyon head and near the floor, in agreement with theoretical predictions. Slope water apparently circulates slowly through the outer part of the canyon and is mixed in near-floor layers which could be caused by breaking internal waves. Internal tides are generated at the floor in the central part of the canyon. Oscillations at tidal frequencies dominate the near-floor velocity field below the thermocline, and are accompanied by high-frequency spikes that may be nonlinear interface waves propagating on the top of the bottom mixed layer. A numerical model was used to calculate mixing in the canyon's bottom boundary layer caused by an unstable density gradient during flood tide. Energetic internal wave activity is apparently responsible for sediment sorting in the canyon head; the internal waves become more energetic as the sediment grain size increases. Below the thermocline, the tidal oscillations vary in amplitude with the phases of the moon; the observed deposition of mud can easily occur during weeks of low velocity.

Beschreibung: Foundation graduate fellowship and by the Office of Naval Research under Contracts N00014-75-C-029l and N00014-80-C-0273.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2007

Beschreibung: Oceanic spreading centers are sites of magmatic, tectonic, and hydrothermal processes. In this thesis I present experimental and seismological constraints on the evolution of these complex regions of focused crustal accretion and extension. Experimental results from drained, triaxial deformation experiments on partially molten olivine reveal that melt extraction rates are linearly dependent on effective mean stress when the effective mean stress is low and non-linearly dependent on effective mean stress when it is high. Microearthquakes recorded above an inferred magma reservoir along the TAG segment of the Mid-Atlantic Ridge delineate for the first time the arcuate, subsurface structure of a long-lived, active detachment fault. This fault penetrates the entire oceanic crust and forms the high-permeability pathway necessary to sustain long-lived, high-temperature hydrothermal venting in this region. Long-lived detachment faulting exhumes lower crustal and mantle rocks. Residual stresses generated by thermal expansion anisotropy and mismatch in the uplifting, cooling rock trigger grain boundary microfractures if stress intensities at the tips of naturally occurring flaws exceed a critical stress intensity factor. Experimental results coupled with geomechanical models indicate that pervasive grain boundary cracking occurs in mantle peridotite when it is uplifted to within 4 km of the seafloor. Whereas faults provide the high-permeability pathways necessary to sustain high-temperature fluid circulation, grain boundary cracks form the interconnected network required for pervasive alteration of the oceanic lithosphere. This thesis provides fundamental constraints on the rheology, evolution, and alteration of the lithosphere at oceanic spreading centers.

Beschreibung: Research was funded by a MIT Presidential Fellowship and NSF grants OCE-0095936, OCE-9907224, OCE-0137329, OCE-6892222, and OCE-6897400.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February, 1980

Beschreibung: The structure of the inertial peak in deep ocean kinetic energy spectra is studied here. Records were obtained from Polymode arrays deployed in the Western North Atlantic Ocean (40°W to 70°W, 15°N to 42°N). The results are interpreted both in terms of local sources and of turning point effects on internal waves generated at lower latitudes. In most of the data, there is a prominent inertial peak slightly above f; however, the peak height above the background continuum varies with depth and geographical environment. Three classes of environment and their corresponding spectra emerge from peak height variations: class 1 is the 1500 m level near the Mid-Atlantic Ridge, with the greatest peak height of 18 db; class 2 includes (a) the upper ocean (depth less than 2000 m), (b) the deep ocean (depth greater than 2000 m) over rough topography, and (c) the deep ocean underneath the Gulf Stream, with intermediate peak height of 11.5 db; class 3 is the deep ocean over smooth topography, with the lowest peak height of 7.5 db. Near f, the horizontal coherence scale is 0(60 km) at depths from 200 m to 600 m, and the vertical coherence scale is O(200 m) just below the main thermocline. A one turning point model is developed to describe inertial waves at mid-latitudes, based on the assumption that inertial waves are randomly generated at lower latitudes (global generation) where their frequency-wavenumber spectrum is given by the model of Garrett and Munk (1972 a, 1975). Using the globally valid wave functions obtained by Munk and Phillips (1968), various frequency spectra near f are calculated numerically. The model yields a prominent inertial peak of 7 db in the horizontal velocity spectrum but no peaks in the temperature spectrum. The model is latitudinally dependent: the frequency shift and bandwidth of the inertial peak decrease with latitude; energy level near f is minimum at about 30° and higher at low and high latitudes. The observations of class 3 can be well-described by the model; a low zonal wavenumber cutoff is required to produce the observed frequency shift of the inertial peak. The differences between the global generation model and the observations of class 1 and class 2 are interpreted as the effects of local sources. A locally forced model is developed based on the latitudinal modal decomposition of a localized source function. Asymptotic eigensolutions of the Laplace's tidal equation are therefore derived and used as a set of expansion functions. The forcing is through a vertical velocity field specified at the top or bottom boundaries of the ocean. For white noise forcing, the horizontal velocity spectrum of the response has an inertial peak which diminishes in the far-field. With the forcing located at either the surface or the bottom, several properties of the class 2 observations can be described qualitatively by a combination of the global and local models. The reflection of inertial waves from a turbulent benthic boundary layer is studied by a slab model of given depth. Frictional effects are confined to the boundary layer and modelled by a quadratic drag law. For given incident waves, reflection coefficients are found to be greater than 0.9 for the long waves which contain most of the energy. This result suggests that energy-containing inertial waves can propagate over great distance as is required by the validity of the model of global generation.

Beschreibung: This work was supported by the National Science Foundation through grant OCE 76-80210 and its continuation OEE 78-19833.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution December 1997

Beschreibung: A new tomographic technique is employed to investigate the structure and dynamics of the Pacific upper mantle. We invert band-center travel times of ScS reverberations and frequency-dependent travel times of direct S phases, upper-mantle guided waves such as SS and SSS, and the R1 and G1 surface waves for the 2D composite structure in the plane of two Pacific corridors. The frequency-dependent travel times of the turning and surface waves are measured from all three components of ground motion as phase delays relative to a radially-anisotropic, spherically-symmetric oceanic mantle model, and their 2D Fréchet kernels are constructed by a coupled-mode algorithm. The travel times of the primary ScSn and sScSn phases and their first-order reverberations from the 410 and 660 discontinuities are measured as individual phases and the 2D Fréchet kernels for these band-limited signals are calculated using the paraxial ray approximation. The model parameters include shear-speed variations throughout the mantle, perturbations to radial shear-wave anisotropy in the uppermost mantle, and the topography of the 410 and 660 discontinuities. We construct vertical tomograms through two mantle corridors: one between the Tonga subduction zone and Oahu, Hawaii, which traverses the central Pacific Ocean; and the other between the Ryukyu subduction zone and Oahu, which samples the northern Philippine Sea, the western Pacific, and the entire Hawaiian swell. Tests demonstrate that the data sets for the two corridors resolve the lateral structure in the upper mantle with a scale length of a few hundreds kilometers and greater but that the resolving power decreases rapidly in the lower mantle. The model for the Tonga-Hawaii corridor reveals several interesting features, the most significant being a regular pattern of high and low shear velocities in the upper mantle between Tonga and Hawaii. These variations, which are well resolved by the data set, have a horizontal wavelength of 1500 km, a vertical dimension of 700 km, and an amplitude of about 3%, and they show a strong positive correlation with seafloor topography and geoid-height variations along this corridor. The geoid highs correspond to a series of northwest-trending swells associated with the major hotspots of the Society, Marquesas, and Hawaiian Islands. Where these swells cross the corridor, they are underlain by high shear velocities throughout the uppermost mantle, so it is unlikely that their topography is supported by thermal buoyancy. This result is substantiated by the model from the Ryukyu-Hawaii corridor, which exhibits a prominent, fast region that extends beneath the entire Hawaiian swell. This anomaly, which resides in the uppermost 200-300 km of the mantle, is also positively correlated with the undulations of the Hawaiian-swell height. The other dominant features in the Ryukyu-Hawaii model include the high-velocity subducting slabs beneath the Ryukyu and Izu-Bonin seismic zones, which extend throughout the entire upper mantle; a very low-velocity in the uppermost 160 km of the mantle beneath the northern Philippine Sea, which is ascribed to the presence of extra water in this region; and a pronounced minimum in the amount of radial anisotropy near Hawaii, which is also seen along the Tonga-Hawaii corridor. A joint inversion of the data from the two corridors reveals the same anomaly pattern and clearly demonstrates that the swells in the Central Pacific are underlain by fast velocities. It is therefore implied that the topography of the swells in the central Pacific is supported by a chemical buoyancy mechanism which is generated by basaltic volcanism and the formation of its low-density peridotitic residuum. While the basaltic depletion mechanism can produce high shear velocities in the uppermost 200 km, it cannot explain the depth extent of the fast anomalies beneath the swells which, along Tonga-Hawaii corridor, extend well into the transition zone. It is therefore hypothesized that the central Pacific is underlain by a system of convective rolls that are confined above the 660-km discontinuity. It is likely that these rolls are predominantly oriented in the direction of plate motion (like "Richter rolls ") but the limited depth of the fast anomaly beneath the Hawaiian swell (200-300 km) suggests that their pattern is probably more complicated. Nevertheless, this convection pattern appears to be strongly correlated with the locations of the Tahitian, Marquesan, and Hawaiian hotspots, which raises interesting questions for Morgan's hypothesis that these hotspots are the surface manifestations of deep-mantle plumes.

Beschreibung: This research was supported by the National Science Foundation under grant EAR- 9628351 and by the Defense Special Weapons Agency under grant DSW A-F49620-95-1- 0051.

Beschreibung: Submitted in partial fulfillment of the requirements of the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2004

Beschreibung: Laterally extensive, well-developed clinoforms have been mapped in Early Cretaceous deposits located in the northeastern 27,000 km2 of the Colvile Basin, North Slope of Alaska. Using public domain 2-D seismic data, well logs, core photographs, and grain size data, depositional geometries within the Nanushuk and Torok formations were interpreted in order to constrain the transport conditions associated with progradation of the shoreline and construction of the continental margin out of detritus shed from the ancestral Brooks Range. Using STRATA, a synthetic stratigraphic modeling package, constructional clinoform geometries similar to those preserved in the North Slope clinoform volume (32,400 km3) were simulated. Sediment flux, marine and nonmarine diffusivities, and basin subsidence were systematically varied until a match was found for the foreset and topset slopes, as well as progradation rates over a 6 milion year period. The ability of STRATA to match the seismically interpreted geometries allows us to constrain measures of possible water and sediment discharges consistent with the observed development of the Early Cretaceous c1inoform suite. Simulations indicate that, in order to reproduce observed geometries and trends using constant input parameters, the subsidence rate must be very small, only a fraction of the most likely rate calculated from the seismic data. Constant sediment transport parameters can successfully describe the evolution of the prograding margin only in the absence of tectonic subsidence. However, further work is needed to constrain the absolute magnitude of these values and determine a unique solution for the NPR-A clinoforms.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April, 1977

Beschreibung: A total of four moorings from POLYMODE Array I and II were analyzed in an investigation of internal wavefield-mean flow interactions. In particular, evidence for wave-mean flow interaction was sought by searching for time correlations between the wavefield vertically-acting Reynolds stress (estimated using the temperature and velocity records), and the mean shear. No significant stress-shear correlations were found at the less energetic moorings, indicating that the magnitude of the eddy viscosity was under 200 cm2/sec, with the sign of the energy transfer uncertain. This is considerably below the 0(4500 cm2/sec) predicted by Müller (1976). An extensive error analysis indicates that the large wave stress predicted by the theory should have been clearly observable under the conditions of measurement. Theoretical computations indicate that the wavefield "basic state" may not be independent of the mean flow as assumed by Müller, but can actually be modified by large-scale vertical shear and still remain in equilibrium. In that case, the wavefield does not exchange momentum with a large-scale vertical shear flow, and, excepting critical layer effects, a small vertical eddy viscosity is to be expected. Using the Garrett-Munk (1975) model internal wave spectrum, estimates were made of the maximum momentum flux (stress) expected to be lost to critical layer absorption. Stress was found to increase almost linearly with the velocity difference across the shear zone, corresponding to a vertical eddy viscosity of -100 cm2 s -1. Stresses indicative of this effect were not observed in the data. The only significantly non-zero stress correlations were found at the more energetic moorings. Associated with the 600 m mean velocity and the shear at the thermocline were a positively correlated stress at 600 m, and a negatively correlated stress at 1000 m. These stress correlations were most clearly observable in the frequency range corresponding to 1 to 8 hour wave periods. The internal wavefield kinetic and potential energy were modulated by the mean flow at both levels, increasing by a factor of two with a factor of ten in the mean flow. The observed stress correlations and energy level changes were found to be inconsistent with ideas of a strictly local eddy viscosity, in which the spectrum of waves is only slightly modified by the shear. When Doppler effects in the temperature equation used to estimate vertical velocity were considered, the observations of stress and energy changes were found to be consistent with generation of short (0.4 to 3 km) internal waves at the level of maximum shear, about 800 m. The intensity of the generated waves increases with the shear, resulting in an effective vertical eddy viscosity (based on the main thermocline shear) of about +100 cm2 s-1 The stresses were not observable at the 1500 m level, indicating that the waves were absorbed within 500 m of vertical travel. The tendency for internal wave currents to be horizontally anisotropic in the presence of a mean current was investigated. Using the Garrett- Munk (1975) model internal wave spectrum, it was found that critical layer absorption cannot induce anisotropies as large as observed. A mechanical noise problem was found to be the cause of large anisotropies measured with Geodyne 850 current meters. It could not be decided, however, whether or not the A.M.F. Vector Averaging Current Meter is able to satisfactorily remove the noise with its averaging scheme.

Beschreibung: The research reported here was provided by Office of Naval Research Contract Numer N00014-76-C-0197 NR 083-400.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 1976

Beschreibung: Measurements of horizontal and vertical current by propeller cluster current meters and temperature by thermistors mounted on a rigid array 8 m high and 20 m long moored in the oceanic main thermocline near Bermuda are interpreted in terms of thermocline-trapped internal wave modes in the presence of temperature and density fine-structure. Two turning-point uniformly valid asymptotic solutions to the internal wave equation are developed to describe the wave functions. Mode decay beyond the turning point in depth or frequency produces a sharp cutoff in vertical current spectra above the local buoyancy frequency N(z). An internal wave wavenumber-frequency spectral model Ε(α,ω) = E(ω/No)-2 (α./α0)-2 describes vertical current spectra and potential energy to horizontal kinetic energy ratios. The red wavenumer shape suppresses peaks in both these quantities at frequencies near N(z). The data are consistent with time-averaged horizontal isotropy of the wave field. A dip in the vertical current spectra at 0.5 cph not predicted by the model appears related to the bottom slope. Temperature fine-structure is modeled as a passive vertical field advected by internal waves. Quasi-permanent fine-scale features of the stratification and vertically small-scale internal waves are indistinguishable in this study. The model of McKean (1974) is generalized to include fine-structure fields specified by their vertical wavenumber spectra as well as different Poisson-distributed layer models. Together with the trapped internal wave model, moored temperature spectra, temperature vertical difference spectra, and coherence over vertical separations are described using a fine-structure vertical wavenumber spectrum PT(k) =ATk-5/2 which agrees with other spectra made using vertical profiling instruments in the range 0.1 to 1.0 cpm. Horizontal current fine-structure is also modeled as a passive field advected vertically by long internal waves. The model describes moored horizontal current spectra (least successfully at frequencies near N(z)) and finite-difference vertical shear spectra. Contours of temperature in depth versus time indicate possible mixing events. These events appear concurrently with high shear and Richardson numbers O. 25≤ R ≤ 1.0. Over 7 m a cutoff in Ri at 0.25 is observed, indicating saturation of the internal wave spectrum. Spectra of finite-difference approximations to shear and buoyancy frequency are dominated by fine-structure contributions over nearly the whole internal wave range, suggesting that breaking is enhanced by fine-structure. Breaking appears equally likely at all frequencies in the internal wave range.

Beschreibung: This research was supported by Office of Naval Research contract N00014-67-0204-0047 and continuation contract NOOOl4-75-C-0291.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution April, 1975

Beschreibung: This thesis reports on an investigation into the structure, energetics and propagation of tidal frequency internal waves. Data from Site D, near the New England continental slope, Muir Seamount northeast of Bermuda, and the Mid-Ocean Dynamics Experiment in the deep Sargasso Sea were used. Site D, in the near-field of a near-critical semidiurnal generation region, shows variable tidal currents and a marked surface intensification of M2 energy at the southern Site, related to the beam-like nature of the internal tide. The M2 tide dominates the semidiurnal band, with about 3 times more energy than at adjacent frequencies at 1/15 cpd separation. There is a significant phase locking between the M2 baroclinic currents and the equilibrium tide, and evidence for southward propagation of internal wave energy, suggesting generation at the slope to the north. The M2 baroclinic energy density is about 40% as great as the total barotropic energy density, but the internal tides have more horizontal kinetic energy. A seaward energy flux of .6 x 106 erg/s cm in the first three baroclinic M2 modes is much less than the .2 x 1010 erg/s cm shoreward energy flux in the surface tide. Difficul ties in interpreting the measurements are ascribed to the near-singular generation case. The MODE-l semidiurnal internal tides are also dominated by the M2 frequency, with a 3-fold energy increase over adjacent frequencies at 1/15 cpd separation. MODE-l is far from any major source of internal tides, but the measurements are much less variable than those from Site D. The extensive temperature measurements defining the MODE-l M2 internal tide are significantly coherent (phase locked) with the equilibrium tide, with about 80% of the coherent energy deriving from the first baroclinic mode, typical thermocline displacements being 3 m. A horizontal wavenumber spectrum estimate for the first mode M2 displacement fluctuations gives a peak at 160 km wavelength, in excellent agreement with the theoretical dispersion relation. The coherent first mode propagates on a bearing of 125°T, with a horizontal energy flux of .3 x 108 erg/s cm. Use of the weaker S2 internal tide and the dispersive nature of oceanic internal waves yields an estimate of 700 km to a common semidiurnal source region. The inferred range and bearing are consistent with generation at the Blake Escarpment and the continental slope to the northwest of the experiment. In one special case current and temperature measurements are combined in a local demonstration of the first mode M2 propagation, and the less extensive current data gives estimates of the barotropic tidal currents. Mooring motion, measured by pressure recorders on the mooring lines, accounts for about 15% of the semidiurnal temperature variance, but it is incoherent with the equilibrium tide. Diurnal tides were examined at all three locations. At the MODE-1 site - near the critical latitude for diurnal period internal waves - the current and temperture fields are dominated by high mode, incoherent, inertial-character morions which mask the tidal currents. About 25% of the diurnal band temperature variance is related to mooring motion. Muir Seamount provides a clear example of diurnal period internal tides trapped to their source region north of the critical latitude. A simple analytical model is developed for the diurnal period flow adjustment in a seamount geometry. Site D shows some evidence for diurnal period internal tides, but most of the energy in the diurnal currents is not simply related to the tidal forcing. Diurnal barotropic currents measured at Site D are combined with currents on the New England shelf, showing that the diurnal tidal wave behaves as a Kelvin-Stokes mode trapped to the slope, propagating along the depth contours to the west. Some aspects of simple generation models are considered. The slope north of Site D is not at all well described as an abrupt step for the M2 generations problem, but a more realistic model of Baines (1974) predicts the coherent fields observed. But the relatively small energy conversion from the surface tide to internal modes suggests that the globally near-critical slope north of Site D is a poor generator of internal tides in the deep sea, although the local energy density is high. The step shelf generation model is well suited for the steep Blake Escarpment, and predicts a seaward energy flux of .4 x 108 erg/s cm in the first mode, comparable to the measurements at MODE-1. This confirms theoretical expectations that the first baroclinic mode is not significantly damped by turbulent diffusion after propagating through the 700 km of ocean between the generation region and the MODE-1 deep ocean site.

Beschreibung: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 1975

Beschreibung: A set of vertical profiles of horizontal ocean currents, obtained by electro-magnetic profilers in the Atlantic Ocean southwest of Bermuda in the spring of 1973, has been analyzed in order to study the vertical structure and temporal behavior of internal waves, particularly those with periods near the local inertial period. An important feature of the observed structure is the polarization of horizontal velocity components in the vertical. This polarization, along with temporal changes of the vertical wave structure seen in a time series of profiles made at one location, has been related to the direction of vertical energy flux due to the observed waves. Whereas the observed vertical phase propagation can be affected by horizontal advection of waves past the point of observation, the use of wave polarization to infer the direction of vertical energy propagation has the advantage that it is not influenced by horizontal advection. The result shows that at a location where profiles were obtained over smooth topography, the net energy flux was downward, indicating that the energy sources for these waves were located at or near the sea surface. An estimate of the net, downward energy flux (~ .2 - .3 erg/cm2/sec) has been obtained. Calculations have been made which show that a frictional bottom boundary layer can be an important energy sink for near-inertial waves. A rough estimate suggests that the observed, net, downward energy flux coul d be accounted for by energy losses in this frictional boundary layer. A reflection coefficient for the observed waves as they reflect off the bottom has been estimated. In contrast, some profiles made over a region of rough topography indicate that the rough bottom may also be acting to generate near-inertial waves which propagate energy upward. Ca1culations of vertical flux of horizontal kinetic energy, using an empirical form for the energy spectrum of internal waves, show that this vertical flux reaches a maximum for frequencies 10% - 20% greater than the local inertial frequency. Comparison with profiler velocity data and frequency spectra supports the conclusion that the dominant waves had frequencies 10% - 20% greater than the inertial frequency. The fact that the waves were propagating energy in the vertical is proposed as the reason for the observed frequency shift. Finally, energy spectra in vertical wave number have been calculated from the profiles in order to compare the data with an empirical model of the energy density spectrum for internal waves proposed by C. Garrett and W. Munk (1975). The result shows that although the general shape and magnitude of the observed spectrum compares well with the empirica1 model, the two-sided spectrum is not symmetric in vertical wave number. This asymmetry has been used to infer that more energy was propagating downward than upward. These calculations have also been used to obtain the coherence between profiles made at the same location, but separated in time (the so-called dropped, lagged, rotary coherence). This coherence is compared with the aforementioned empirical model. The coherence results show that the contribution of the semidiurnal tide to the energy of the profiles is restricted to long vertical wave lengths.

Beschreibung: Support for the experiment which is described in this report was provided by the Office of Naval Research under contracts N00014-66-C-0241, NR 083-004 and N00014-74-C-0262, NR 083-004.