Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1987. / Includes bibliographies. / by Paola Cessi. / Ph.D.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references (p. 206-211). / Data assimilation methods, such as the Kalman filter, are routinely used in oceanography. The statistics of the model and measurement errors need to be specified a priori. In this study we address the problem of estimating model and measurement error statistics from observations. We start by testing the Myers and Tapley (1976, MT) method of adaptive error estimation with low-dimensional models. We then apply the MT method in the North Pacific (5°-60° N, 132°-252° E) to TOPEX/POSEIDON sea level anomaly data, acoustic tomography data from the ATOC project, and the MIT General Circulation Model (GCM). A reduced state linear model that describes large scale internal (baroclinic) error dynamics is used. The MT method, closely related to the maximum likelihood methods of Belanger (1974) and Dee (1995), is shown to be sensitive to the initial guess for the error statistics and the type of observations. It does not provide information about the uncertainty of the estimates nor does it provide information about which structures of the error statistics can be estimated and which cannot. A new off-line approach is developed, the covariance matching approach (CMA), where covariance matrices of model-data residuals are "matched" to their theoretical expectations using familiar least squares methods. This method uses observations directly instead of the innovations sequence and is shown to be related to the MT method and the method of Fu et al. (1993). The CMA is both a powerful diagnostic tool for addressing theoretical questions and an efficient estimator for real data assimilation studies. It can be extended to estimate other statistics of the errors, trends, annual cycles, etc. Twin experiments using the same linearized MIT GCM suggest that altimetric data are ill-suited to the estimation of internal GCM errors, but that such estimates can in theory be obtained using acoustic data. After removal of trends and annual cycles, the low frequency /wavenumber (periods> 2 months, wavelengths> 16°) TOPEX/POSEIDON sea level anomaly is of the order 6 cm2. The GCM explains about 40% of that variance. By covariance matching, it is estimated that 60% of the GCM-TOPEX/POSEIDON residual variance is consistent with the reduced state linear model. The CMA is then applied to TOPEX/POSEIDON sea level anomaly data and a linearization of a global GFDL GCM. The linearization, done in Fukumori et al.(1999), uses two vertical mode, the barotropic and the first baroclinic modes. We show that the CMA method can be used with a global model and a global data set, and that the estimates of the error statistics are robust. We show that the fraction of the GCMTOPEX/ POSEIDON residual variance explained by the model error is larger than that derived in Fukumori et al.(1999) with the method of Fu et al.(1993). Most of the model error is explained by the barotropic mode. However, we find that impact of the change in the error statistics on the data assimilation estimates is very small. This is explained by the large representation error, i.e. the dominance of the mesoscale eddies in the TIP signal, which are not part of the 20 by 10 GCM. Therefore, the impact of the observations on the assimilation is very small even after the adjustment of the error statistics. This work demonstrates that simultaneous estimation of the model and measurement error statistics for data assimilation with global ocean data sets and linearized GCMs is possible. However, the error covariance estimation problem is in general highly underdetermined, much more so than the state estimation problem. In other words there exist a very large number of statistical models that can be made consistent with the available data. Therefore, methods for obtaining quantitative error estimates, powerful though they may be, cannot replace physical insight. Used in the right context, as a tool for guiding the choice of a small number of model error parameters, covariance matching can be a useful addition to the repertory of tools available to oceanographers. / by Michael Y. Chechelnitsky. / Ph.D.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1999. / Includes bibliographical references (leaves 235-243). / A detailed examination of the development of a deep convection event observed in the Greenland Sea in 1988-89 is carried out through a combination of modeling, scale estimates, and data analysis. We develop a prognostic one-dimensional mixed layer model which is coupled to a thermodynamic ice model. Our model contains a representation of the lowest order boundary layer dynamics and adjustable coupling strengths between the mixed layer, ice, and atmosphere. We find that the model evolution is not very sensitive to the strength of the coupling between the ice and the mixed layer sufficiently far away from the limits of zero and infinite coupling; we interpret this result in physical terms. Further, we derive an analytical expression which provides a scale estimate of the rate of salinification of the mixed layer during the ice-covered preconditioning period as a function of the rate of ice advection. / by Jay Alan Austin. / Ph.D.

Thesis (Sc. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and Woods Hole Oceanographic Institution), 1999. / Includes bibliographical references (p. 161-169). / A state-of-the-art, high-resolution ocean general circulation model is used to estimate the time-dependent global ocean heat transport and investigate its dynamics. The north-south heat transport is the prime manifestation of the ocean's role in global climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing mechanism. These issues are addressed in this thesis. Technical problems associated with the forcing and sampling of the model, and the impact of high-frequency motions are discussed. Numerical schemes are suggested to remove the inertial energy to prevent aliasing when the model fields are stored for later analysis. Globally, the cross-equatorial, seasonal heat transport fluctuations are close to +4.5 x 1015 watts, the same amplitude as the seasonal, cross-equatorial atmospheric energy transport. The variability is concentrated within 200 of the equator and dominated by the annual cycle. The majority of it is due to wind-induced current fluctuations in which the time-varying wind drives Ekman layer mass transports that are compensated by depth-independent return flows. The temperature difference between the mass transports gives rise to the time-dependent heat transport. The rectified eddy heat transport is calculated from the model. It is weak in the central gyres, and strong in the western boundary currents, the Antarctic Circumpolar Current, and the equatorial region. It is largely confined to the upper 1000 meters of the ocean. The rotational component of the eddy heat transport is strong in the oceanic jets, while the divergent component is strongest in the equatorial region and Antarctic Circumpolar Current. The method of estimating the eddy heat transport from an eddy diffusivity derived from mixing length arguments and altimetry data, and the climatological temperature field, is tested and shown not to reproduce the model's directly evaluated eddy heat transport. Possible reasons for the discrepancy are explored. / by Steven Robert Jayne. / Sc.D.

Thesis: S.M., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2020 / Cataloged from student-submitted PDF of thesis. / Includes bibliographical references (pages 129-130). / Airborne eXpendable BathyThermographs (AXBTs) are air-launched, single use temperature-depth probes that telemeter temperature observations as a VHF-modulated frequency. This study describes the AXBT Realtime Editing System (ARES), which was developed to receive and quality control temperature-depth profiles with no external hardware other than a VHF radio receiver. The ARES Data Acquisition System performs fast Fourier transforms on windowed segments of demodulated signal transmitted from the AXBT and uses the resulting spectra to identify valid temperature-depth observations. When evaluated using 389 profiles, the ARES data acquisition system produced temperature-depth profiles nearly identical to those generated using a Sippican MK-21 processor, while reducing the amount of noise from VHF interference included in those profiles. The ARES Profile Editor applies a series of automated checks to identify and correct common profile discrepancies, before displaying the profile on an editing interface that provides simple user controls to make additional corrections. When evaluated against 1,177 tropical Atlantic and Pacific AXBT profiles, the ARES automated quality control system successfully corrected 87% of the profiles without any manual intervention necessary. The ARES Data Acquisition and Profile Editing Systems performed exceptionally well when operationally tested with 44 AXBTs during Hurricane Dorian (2019), enabling high resolution observations across key oceanic features including Dorian's cold wake and the Gulf Stream. Necessary future work includes improvements on the automated quality control algorithm and evaluation against a more diverse dataset of temperature-depth profiles. / by Casey R. Densmore. / S.M. / S.M. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 219-222). / Interaction between the Antarctic Circumpolar Current and the continental slope/shelf in the Marguerite Bay and west Antarctic Peninsula is examined as interaction between a wind-driven channel flow and a zonally uniform slope with a bay-shaped shelf to the south. Two control mechanisms, eddy advection and propagation of topographic waves, are identified in barotropic vortex-escarpment interactions. The two mechanisms advect the potential vorticity (PV) perturbations in opposite directions in anticyclone-induced interactions but in the same direction in cyclone-induced interactions, resulting in dramatic differences in the two kinds of interactions. The topographic waves become more nonlinear near the western(eastern if in the Northern Hemisphere) boundary of the bay, where strong cross-escarpment motion occurs. In the interaction between a surface anticyclone and a slope penetrating into the upper layer in a two-layer isopycnal model, the eddy advection decays on length scales on the order of the internal deformation radius, so shoreward over a slope that is wider than the deformation radius, the wave mechanism becomes noticeably significant. It acts to spread the cross-isobath transport in a much wider range while the transport directly driven by the anticyclone is concentrated in space. A two-layer wind-driven channel flow is constructed to the north of the slope in the Southern Hemisphere, spontaneously generating eddies through baroclinic instability. A PV front forms in the first layer shoreward of the base of the topography due to the lower-layer eddy-slope interactions. / (cont.) Perturbed by the jet in the center of the channel, the front interacts with the slope/shelf persistently yet episodically, driving a clockwise mean circulation within the bay as well as crossisobath transport. Both the transports across the slope edge and out of the bay are comparable with the maximum Ekman transport in the channel, indicative of the significance of the examined mechanism. The wave-boundary interaction identified in the barotropic model is found essential for the out-of-bay transport and responsible for the heterogeneity of the transport within the bay. Much more water is transported out of the bay from the west than from the east, and the southeastern area is the most isolated region. These results suggest that strong out-of-bay transport may be found near the western boundary of the Marguerite Bay while the southeastern region is a retention area where high population of Antarctic krill may be found. / by Yu Zhang. / Ph.D.

Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Bibliography: leaves 70-72. / M.S.

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), 2002. / Includes bibliographical references (leaves 140-148). / This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically efficient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animal. / (cont.) Imaging technologies used to exactly measure the morphology of the scattering features of fish include very high-resolution Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which are used for morphological evaluation and incorporation into the scattering model. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean. / by D. Benjamin Reeder. / Ph.D.

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references (leaves 184-189). / In the ocean, low frequency acoustic waves propagate with low attenuation and cylindrical spreading loss over long-ranges, making them an effective tool for underwater source localization, tomography, and communications. Underwater mountains, or seamounts, are ubiquitous throughout the world's oceans and can absorb and scatter acoustic energy, offering many interesting acoustic modeling challenges. The goal of the research performed in support of this thesis is to measure the acoustic scattered field of a large, conical seamount at long-range, and reconcile observations with 2-D range-dependent acoustic models, for the purpose of understanding the effects of highly range-dependent bathymetry. The Basin Acoustic Seamount Scattering Experiment (BASSEX) was conducted to measure the scattered fields of the two seamounts which form the Kermit-Roosevelt Seamount Complex in the Northeast Pacific Ocean during September and October of 2004. The experiment used fixed and ship-deployed acoustic sources transmitting m-sequence signals at 68.2 and 250 Hz carrier frequencies, with 35 and 83 Hz bandwidth, respectively. The receiver was a towed hydrophone array with 3 m sensor spacing, cut for 250 Hz. BASSEX is the first experiment to measure acoustic arrival patterns in the scattered field of a seamount at many locations at sound path ranges of order 500 km, utilizing a rich bathymetry and sound velocity database. Convergence zones in the forward-scattered field of seamounts at long-range are observed, created by higher order mode coupling and blockage. Acoustic ray arrival angles, travel times, and amplitudes show good agreement with parabolic equation (PE) acoustic modeling results inside the forward-scattered fields; in particular, simulated results are fairly accurate for weak surface-reflected-bottom-reflected acoustic rays. The width of the forward-scattered field is shown to span the projected width of a seamount. / (cont.) Temporal coherence of ray amplitude inside a seamount scattered field could not be determined due to array movement issues, and should be the focus of future research to determine the stability of scattered acoustic rays for applications such as acoustic tomography. Robust adaptive beamforming methods are used to process hydrophone array data gathered in the BASSEX experiment. Non-stationarity in the observed noise field caused by array fluctuations and data acquisition system malfunctions motivate the use of a time varying Capon adaptive beam former, and strong acoustic harmonics from ship operations motivate the use of a frequency and steering angle dependent white noise gain constraint. In an effort to process snap-shot deficient data sets, the novel physically constrained maximum likelihood (PCML) beamformer was further developed and applied. By using orthonormal trigonometric eigenvector bases to determine the maximum likelihood spectral covariance matrix, the PCML beamformer computational efficiency is significantly increased. / by Joseph J. Sikora, III. / Ph.D.

Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 75-81). / The copepod Calanus glacialis is one of the most important zooplankton taxa in the Arctic shelf seas where it serves as a key grazer, predator, and food source. Its summer distribution and abundance has direct effects on much of the food web, from blooming phytoplankton to migrating bowhead whales. The Chukchi Sea represents a highly advective regime dominated by a barotropicly driven northward flow modulated by wind driven currents that reach the bottom boundary layer of this shallow environment. In addition, a general northward gradient of decreasing temperature and food concentration leads to geographically divergent copepod growth and development rates. The physics of this system establish the connection potential between specific regions. Unless biological factors are uniform and ideal the true connections will be an uneven subset of this physically derived connection potential. In August 2012 and 2013, C. glacialis distributions were observed over Hanna Shoal in the northeast Chukchi Sea. Here we used the Finite Volume Community Ocean Model i-State Configuration Model to advect these distributions forward and back in time to determine the source and sink regions of the transient Hanna Shoal C. glacialis population. We found that Hanna Shoal supplies diapause competent C. glacialis to both the Beaufort Slope and the Chukchi Cap, mainly receives juveniles from the broad slope between Hanna Shoal and Herald Canyon and receives second year adults from as far as the Anadyr Gulf and as close as the broad slope between Hanna Shoal and Herald Canyon. These connection potentials were not sensitive to precise times and locations of release, but were quite sensitive to depth of release. Deeper particles often traveled further than shallow particles due to strong vertical shear in the shallow Chukchi. The 2013 sink region was shifted west relative to the 2012 region and the 2013 adult source region was shifted north relative to the 2012 region. / by Stephen M. Elliott. / S.M.