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), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 209-215). / Observations from a three-year field program on the inner shelf south of Martha's Vineyard, MA and a numerical model are used to describe the effect of stratification on inner shelf circulation, transport, and sediment resuspension height. Thermal stratification above the bottom mixed layer is shown to cap the height to which sediment is resuspended. Stratification increases the transport driven by cross-shelf wind stresses, and this effect is larger in the response to offshore winds than onshore winds. However, a one-dimensional view of the dynamics is not sufficient to explain the relationship between circulation and stratification. An idealized, cross-shelf transect in a numerical model (ROMS) is used to isolate the effects of stratification, wind stress magnitude, surface heat flux, cross-shelf density gradient, and wind direction on the inner shelf response to the cross-shelf component of the wind stress. In well mixed and weakly stratified conditions, the cross-shelf density gradient can be used to predict the transport efficiency of the cross-shelf wind stress. In stratified conditions, the presence of an along-shelf wind stress component makes the inner shelf response to cross-shelf wind stress strongly asymmetric. / by Rachel Mandy Horwitz. / Ph.D.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 69-74). / Interactions between physical and biological processes in the Southern Ocean have significant impacts on local ecosystems as well as on global climate. In this thesis, I present evidence that the Southern Ocean circulation affects the variability of zooplankton and sea surface temperature, both of which are involved in air-sea exchanges of carbon dioxide. First, I examine the formation of spatial patterns in the distribution of Antarctic krill (Euphausia superba) resulting from social behavior. Turbulence of the flow is found to provide favorable conditions for the evolution social behavior in an idealized biological-physical model. Second, I analyze observations of sea surface temperature variability in the region of the Antarctic circumpolar current. Results suggest that propagating anomalies can be explained as a linear response to local atmospheric forcing by the Southern Annular Mode and remote forcing by El-Nifio southern oscillation, in the presence of advection by a mean flow. / by Ariane Verdy. / S.M.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 81-86). / The impact of the Greenland tip jet on the wintertime mixed-layer of the southwest Irminger Sea is investigated using in-situ moored profiler data and a variety of atmospheric data sets. The mixed-layer was observed to reach 400 m in the spring of 2003, and 300 m in the spring of 2004. Both of these winters were mild and characterized by a low North Atlantic Oscillation (NAO) index. All of the storms that were advected through the region were tracked, and the tip jet events that occurred throughout the two winters were identified. Composite images of the tip jets elucidated the conditions during which tip jets were likely to take place, which led to an objective method of determining tip jet occurrences by taking into account the large-scale pressure gradients. Output from a trajectory model indicates that the air parcels entering a tip jet accelerate and descend as they are deflected around southern Greenland. A heat flux timeseries for the mooring site was constructed that includes the enhancing influence of the tip jet events. This was used to drive a one-dimensional mixed-layer model, which was able to reproduce the observed mixed-layer deepening in both winters. All of the highest heat flux events took place during tip jets, and removal of the tip jets from the heat flux timeseries demonstrated their importance in driving convection east of Greenland. / (cont.) The deeper mixed-layer of the first winter was in large part due to a higher number of robust tip jet events, which in turn was caused by a greater number of storms passing northeast of southern Greenland. This interannual change in storm tracks was attributable to a difference in upper level steering currents. Application of the mixed-layer model to the winter of 1994-1995, during a period characterized by a high NAO index, resulted in convection reaching 1600 m. This prediction is consistent with concurrent hydrographic data, supporting the notion that deep convection can occur in the Irminger Sea during strong winters. / by Kjetil Våge. / S.M.

Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008. / Includes bibliographical references (p. 64-67). / Coupled ocean/atmosphere simulations exhibit systematic warm biases over the South West African (SWA) coastal region. Recent investigations indicate that coastal ocean dynamics may play an important role in determining the SST patterns, but none of them provide a detailed analysis. In this study, I analyze simulations produced both by coupled models and by idealized models. Then results are interpreted on the basis of a theoretical framework. Finally the conclusion is reached that the insufficient resolution of the ocean component in the coupled model is responsible for the warm biases over the SWA coastal region. The coarse resolution used in the ocean model has an artificially stretched coastal side-wall boundary layer, which induces a smaller upwelling velocity in the boundary layer. The vertical heat transport decreases even when the volume transport is unchanged because of its nonlinear relationship with the magnitude of the upwelling velocity. Based on the scaling of the idealized model simulations, a simplified calculation shows that the vertical heat transport is inversely proportional to the zonal resolution over the coastal region. Therefore, increasing the horizontal resolution can considerably improve the coastal SST simulation, and better resolve the coastal dynamics. / by Jinbo Wang. / S.M.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1980. / Microfiche copy available in Archives and Science. / Bibliography: leaves 152-159. / by Long Sang Chiu. / Sc.D.

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2007. / Includes bibliographical references (p. 124-126). / This thesis introduces an algorithm for inverting for the geoacoustic properties of the seafloor in shallow water. The input data required by the algorithm are estimates of the amplitudes of the normal modes excited by a low-frequency pure-tone sound source, and estimates of the water column sound speed profiles at the source and receiver positions. The algorithm makes use of perturbation results, and computes the small correction to an estimated background profile that is necessary to reproduce the measured mode amplitudes. Range-dependent waveguide properties can be inverted for so long as they vary slowly enough in range that the adiabatic approximation is valid. The thesis also presents an estimator which can be used to obtain the input data for the inversion algorithm from pressure measurements made on a vertical line array (VLA). The estimator is an Extended Kalman Filter (EKF), which treats the mode amplitudes and eigenvalues as state variables. Numerous synthetic and real-data examples of both the inversion algorithm and the EKF estimator are provided. The inversion algorithm is similar to eigenvalue perturbation methods, and the thesis also presents a combination mode amplitude/eigenvalue inversion algorithm, which combines the advantages of the two techniques. / by Travis L. Poole. / 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), 2013. / Includes bibliographical references (pages 133-141). / Between 2002 and 2011 a single mooring was maintained in the core of the Pacific Water boundary current in the Alaskan Beaufort Sea near 152° W. Using velocity and hydrographic data from six year-long deployments during this time period, we examine the interannual variability of the current. It is found that the volume, heat, and freshwater transport have all decreased drastically over the decade, by more than 80%. The most striking changes have occurred during the summer months. Using a combination of weather station data, atmospheric reanalysis fields, and concurrent shipboard and mooring data from the Chukchi Sea, we investigate the physical drivers responsible for these changes. It is demonstrated that an increase in summertime easterly winds along the Beaufort slope is the primary reason for the drop in transport. The intensification of the local winds has in turn been driven by a strengthening of the summer Beaufort High in conjunction with a deepening of the summer Aleutian Low. Since the fluxes of mass, heat, and freshwater through Bering Strait have increased over the same time period, this raises the question as to the fate of the Pacific water during recent years and its impacts. We present evidence that more heat has been fluxed directly into the interior basin from Barrow Canyon rather than entering the Beaufort shelfbreak jet, and this is responsible for a significant portion of the increased ice melt in the Pacific sector of the Arctic Ocean. / by Eric T. Brugler. / S.M.

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), 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 79-81). / The ocean is a complex, constantly changing, highly dynamical system. Prediction capabilities are constantly being improved in order to better understand and forecast ocean properties for applications in science, industry, and maritime interests. Our overarching goal is to better predict the ocean environment in regions of complex topography with a continental shelf, shelfbreak, canyons and steep slopes using the MIT Multidisciplinary Simulation, Estimation and Assimilation Systems (MSEAS) primitive-equation ocean model. We did this by focusing on the complex region surrounding Taiwan, and the period of time immediately following the passage of Typhoon Morakot. This area and period were studied extensively as part of the intense observation period during August - September 2009 of the joint U.S. - Taiwan program Quantifying, Predicting, and Exploiting Uncertainty Department Research Initiative (QPE DRI). Typhoon Morakot brought an unprecedented amount of rainfall within a very short time period and in this research, we model and study the effects of this rainfall on Taiwan's coastal oceans as a result of river discharge. We do this through the use of a river discharge model and a bulk river-ocean mixing model. We complete a sensitivity study of the primitive-equation ocean model simulations to the different parameters of these models. By varying the shape, size, and depth of the bulk mixing model footprint, and examining the resulting impacts on ocean salinity forecasts, we are able to determine an optimal combination of salinity relaxation factors for highest accuracy. / by Jennifer Jacobs Landry. / S.M.

Southeastern South America (SESA), a region encompassing Paraguay, Southern Brazil, Uruguay, and northern Argentina, experienced a 23% increase in austral summer precipitation from 1902-2022, one of the largest precipitation trends observed globally. There is little consensus on the drivers of the precipitation trend, but Atlantic multidecadal variability, stratospheric ozone depletion, and greenhouse gas emissions stand out as key contributing factors. The work presented in this dissertation addresses two main questions. First, what are the historical drivers of the SESA precipitation increase? To address this, I investigate simulations from the Coupled Model Intercomparison Project (CMIP) Phases 3, 5, and 6 and find that not only do fully-coupled climate models simulate positive SESA precipitation trends that are much weaker over the historical interval, but some models persistently simulate negative precipitation trends. The same is true of two atmospheric models forced with observed historical sea surface temperatures. While future 21st-century projections yield positive ensemble mean precipitation trends that grow with increasing greenhouse-gas emissions, the mean forced response never exceeds the observed historical trend. Finally, some pre-industrial control runs occasionally simulate centennial-scale trends that fall within the observational range, but most do not. The second question I address is why climate models struggle to simulate the observed SESA precipitation trend. In an attempt to understand the model bias, I investigate one driver of SESA precipitation variability: the South American low-level jet. By developing a jet index from low-level moisture fluxes into SESA, I find that increased moisture flux through the jet accounts for 20-45% of the observed SESA precipitation trend from 1951-2020 in two reanalysis datasets. While results vary among reanalyses, both point to increased humidity as a fundamental driver of increased moisture flux and precipitation. Increased humidity within the jet is consistent with warming sea surface temperatures driven by anthropogenic forcing, although additional natural climate variations also may have played a role. The jet’s velocity also increased, further enhancing precipitation, but without a clear connection to anthropogenic forcing. These findings indicate that the SESA precipitation trend is partly attributable to jet intensification arising from both natural variability and anthropogenic forcing. In my final research chapter, I explore whether CMIP6 models simulate a realistic relationship between SESA precipitation and the jet, as well as whether inaccuracies in the characterization of the jet could explain muted trends in simulated SESA precipitation. I find that the interannual variability in the simulated jet-precipitation relationship aligns well with results from observations from 1951-2014. Interannual precipitation variability across the models is primarily dominated by the jet’s velocity. The models simulate a forced increase in humidity within the jet, consistent with observations and theory, that contributes a positive trend to SESA precipitation. Given that the models generally simulate realistic jet-precipitation relationships, I conclude that model misrepresentation of the jet is not a likely explanation for the discrepancy between simulated and observed SESA precipitation trends. Despite remaining uncertainties, my work sheds new light on our understanding of SESA precipitation variability and trends. Future work is needed to better understand the large-scale drivers of SESA precipitation outside of the jet and why climate models largely underestimate or fail to reproduce the observed precipitation trend. While Atlantic multidecadal variability is often cited as an important contributor to the SESA precipitation trend, I find austral summer forcing from the Atlantic to be ambiguous with regard to SESA precipitation and requires further analysis. Additionally, I highlight the Pacific South American mode as another contributing factor that warrants further exploration.

Radiative Transfer Models (RTM) have many applications in the satellite microwave remote sensing field, such as the retrieval of oceanic and atmospheric environmental parameters, including surface wind vectors and sea surface temperatures, integrated water vapor, cloud liquid, and precipitation. A key component of the ocean RTM is the emissivity model used to determine the brightness temperature (Tb) at the ocean’s surface. A new wideband ocean emissivity RTM developed by the Central Florida Remote Sensing Laboratory (CFRSL) calculates ocean emissivity over a wide range of frequencies, incidence angles, sea surface temperatures (SST), and wind speed. This thesis presents the validation of this CFRSL model using independent WindSat Tb measurements collocated with Global Data Assimilation System (GDAS) Numerical weather model environmental parameters for frequencies between 6.8 to 37 GHz and wind speeds between 0 – 20 m/s over the July 2005 – June 2006 year. In addition, the CFRSL emissivity model is validated using WindSat derived ocean wind speeds and SST that are contained in the Environmental Data Record (EDR) and combined with the GDAS environmental parameters. Finally, the validation includes comparisons to the well-established XCAL ocean emissivity RTM. The focus of this validation and comparison is to assess performance of the emissivity model results with respect to a wide range of frequency and wind speeds but limited to a narrow range of incidence angles between approximately 50° - 55°