ALBERT

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1987

Description: Several problems connected by the theme of thermal forcing are addressed herein. The main topic is the stratification and flow field resulting from imposing a specified heat flux on a fluid that is otherwise confined to a rigid insulating basin. In addition to the traditional eddy viscosity and diffusivity, turbulent processes are also included by a convective overturning adjustment at locations where the local density field is unstable. Two classes of problems are treated. The first is the large scale meridional pattern of a fluid in an annulus. The detailed treatment is carried out in two steps. In the beginning (chapter 2) it is assumed that the fluid is very diffusive, hence, to first approximation no flow field is present. It is found that the convective overturning adjustment changes the character of the stratification in all the regions that are cooled from the top, resulting in a temperature field that is nearly depth independent in the northernmost latitudes. The response to a seasonal cycle in the forcing, and the differences between averaging the results from the end of each season compared to driving the fluid by a mean forcing are analyzed. In particular, the resulting sea surface temperature is warmer in the former procedure. This observation is important in models where the heat flux is sensitive to the gradient of air to sea surface temperatures. The analysis of the problem continues in chapter 5 where the contribution of the flow field is included in the same configuration. The dimensionless parameter controlling the circulation is now the Rayleigh number, which is a measure of the relative importance of gravitational and viscous forces. The effects of the convective overturning adjustment is investigated at different Rayleigh numbers. It is shown that not only is the stratification now always stable, but also that the vigorous vertical mixing reduces the effective Rayleigh number; thereby the flow field is more moderate, the thermocline deepens, and the horizontal surface temperature gradients are weaker. The interior of the fluid is colder compared to cases without convective overturning, and, because the amount of heat in the system is assumed to be fixed, the surface temperature is warmer. The fluid is not only forced by a mean heat flux, or a seasonally varying one, but its behavior under permanent winter and summer conditions is also investigated. A steady state for the experiments where the net heat flux does not vanish is defined as that state where the flow field and temperature structure are not changing with time except for an almost uniform temperature decrease or increase everywhere. It is found that when winter conditions prevail the circulation is very strong, while it is rather weak for continuous summer forcing. In contrast to those results, if a yearly cycle is imposed, the circulation tends to reach a minimum in the winter time and a maximum in the summer. This suggests that, depending on the Rayleigh number, there is a phase leg of several months between the response of the ocean and the imposed forcing. Differences between the two averaging procedures mentioned before are also observed when the flow field is present, especially for large Rayleigh numbers. The circulation is found to be weaker and the sea surface temperature colder in the mean of the seasonal realizations compared to the steady state derived by the mean forcing. As an extension to the numerical results, an analytic model is presented in chapter 4 for a similar annular configuration. The assumed dynamics is a bit different, with a mixed layer on top of a potential vorticity conserving interior. It is demonstrated that the addition of the thermal wind balance to the conservation of potential vorticity in the axially symmetric problem leads to the result that typical fluid trajectories in the interior are straight lines pointing downward going north to south. The passage of information in the system is surprisingly in the opposite sense to the clockwise direction of the flow. A model for water mass formation by buoyancy loss in the absence of a flow field is introduced in chapter 3. The idea behind it is to use the turbulent mixing parameterization to generate chimney-like structures in open water, followed by along-isopycnal advection and diffusion. This model can be applied to many observations of mode water. In particular, in this work it is related to the chimneys observed by the MEDOC Group (1970), and the Levantine Intermediate Water in the Eastern Mediterranean Basin. An analytic prediction of the depth of the water mass is derived and depends on the forcing and initial stratification. It suggests that the depth of shallow mode water like the 18°C water or the Levantine Intermediate Water would not be very sensitive to reasonable changes in atmospheric forcing. Similar conclusions were also reached by Warren (1972) by assuming that the temperature in the thermocline decreases linearly with depth, and by approximating the energy balance in a water column by a Newtonian cooling law.

Description: 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 2010

Description: Observational and modeling techniques are employed to investigate the thermal and inertial upper ocean response to wind and buoyancy forcing in the North Atlantic Ocean. First, the seasonal kinetic energy variability of near-inertial motions observed with a moored profiler is described. Observed wintertime enhancement and surface intensification of near-inertial kinetic energy support previous work suggesting that near-inertial motions are predominantly driven by surface forcing. The wind energy input into surface ocean near-inertial motions is estimated using the Price-Weller- Pinkel (PWP) one-dimensional mixed layer model. A localized depth-integrated model consisting of a wind forcing term and a dissipation parameterization is developed and shown to have skill capturing the seasonal cycle and order of magnitude of the near-inertial kinetic energy. Focusing in on wintertime storm passage, velocity and density records from drifting profiling floats (EM-APEX) and a meteorological spar buoy/tethered profiler system (ASIS/FILIS) deployed in the Gulf Stream in February 2007 as part of the CLIvar MOde water Dynamics Experiment (CLIMODE) were analyzed. Despite large surface heat loss during cold air outbreaks and the drifting nature of the instruments, changes in the upper ocean heat content were found in a mixed layer heat balance to be controlled primarily by the relative advection of temperature associated with the strong vertical shear of the Gulf Stream. Velocity records from the Gulf Stream exhibited energetic near-inertial oscillations with frequency that was shifted below the local resting inertial frequency. This depression of frequency was linked to the presence of the negative vorticity of the background horizontal current shear, implying the potential for near-inertial wave trapping in the Gulf Stream region through the mechanism described by Kunze and Sanford (1984). Three-dimensional PWP model simulations show evidence of near-inertial wave trapping in the Gulf Stream jet, and are used to quantify the resulting mixing and the effect on the stratification in the Eighteen Degree Water formation region.

Description: This work was supported by National Science Foundation grants OCE-0241354 and OCE-0424865, as well as the Woods Hole Oceanographic Institution's Ocean and Cli- mate Change Institute. Funding to initiate the McLane Moored Pro ler observations at Line W were provided by grants from the G. Unger Vetlesen Foundation and the Comer Charitable Fund to the Woods Hole Oceanographic Institutions Ocean and Climate Change Institute.

Description: 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 1997

Description: In order to constrain the processes controlling the cycles of biogeochemically important gases such as 02 and C02, and thereby infer rates of biological activity in the upper ocean or the uptake of radiatively important "greenhouse" gases, the noble gases are used to characterize and quantify the physical processes affecting the dissolved gases in aquatic environments. The processes of vertical mixing, gas exchange, air injection, and radiative heating are investigated using a 2 year time-series of the noble gases, temperature, and meteorological data from Station S near Bermuda, coupled with a 1- dimensional upper ocean mixing model to simulate the physical processes in the upper ocean. The rate of vertical mixing that best simulates the thermal cycle is 1.1±0.1 x104 m The gas exchange rate required to simulate the data is consistent with the formulation of Wanninkhof (1992) to ± 40%, while the formulation of Liss and Merlivat 1986 must be increased by a factor of 1.7± 0.6. The air injection rate is consistent with the formulation of Monahan and Torgersen (1991) using an air entrainment velocity of 3±1 cm s1. Gas flux from bubbles is dominated on yearly time-scales by larger bubbles that do not dissolve completely, while the bubble flux is dominated by complete dissolution of bubbles in the winter at Bermuda. In order to obtain a high-frequency time-series of the noble gases to better parameterize the gas flux from bubbles, a moorable, sequential noble gas sampler was developed. Preliminary results indicate that the sampler is capable of obtaining the necessary data. Dissolved gas concentrations can be significantly modified by ice formation and melting, and due to the solubility of He and Ne in ice, the noble gases are shown to be unique tracers of these interactions. A three-phase equilibrium partitioning model was constructed to quantify these interactions in perennially ice-covered Lake Fryxell, and this work was extended to oceanic environments. Preliminary surveys indicate that the noble gases may provide useful and unique information about interactions between water and ice.

Description: This work has been supported by the National Science Foundation - OCE 9302812 and DPP 9118363, the Ocean Ventures Fund Ditty Bag Fund and Westcott Fund and the WHOI Education Office.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011

Description: Remote sensing and in situ observations are used to investigate the ocean response to the Tokar Wind Jet in the Red Sea. The wind jet blows down the pressure gradient through the Tokar Gap on the Sudanese coast, at about 18°N, during the summer monsoon season. It disturbs the prevailing along-sea (southeastward) winds with strong cross-sea (northeastward) winds that can last from days to weeks and reach amplitudes of 20-25 m/s. By comparing scatterometer winds with along-track and gridded sea level anomaly observations, it is shown that an intense dipolar eddy spins up in less than seven days in response to the wind jet. The eddy pair has a horizontal scale of 140 km. Maximum ocean surface velocities can reach 1 m/s and eddy currents extend at least 200 m into the water column. The eddy currents appear to cover the width of the sea, providing a pathway for rapid transport of marine organisms and other drifting material from one coast to the other. Interannual variability in the strength of the dipole is closely matched with variability in the strength of the wind jet. The dipole is observed to be quasi-stationary, although there is some evidence for slow eastward propagation—simulation of the dipole in an idealized high-resolution numerical model suggests that this is the result of self-advection. These and other recent in situ observations in the Red Sea show that the upper ocean currents are dominated by mesoscale eddies rather than by a slow overturning circulation.

Description: This work is supported by Award Nos. USA 00002, KSA 00011 and KSA 00011/02 made by King Abdullah University of Science and Technology (KAUST).

Description: 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 2012

Description: 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.

Description: This work was supported through National Science Foundation grant no. OCE-0548961, the WHOI Academic Programs Office, and the WHOI Coastal Ocean Institute.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1990

Description: An acoustic tomography experiment consisting of a source near Hawaii and seven receivers along the west coast of North America was conducted from November 1987 to May 1988 and from February 1989 to July 1989. In this thesis, the acoustic ray travel times are analyzed in order to investigate inter-annual basin-scale thermal variability. These thermal fluctuations may help detect any greenhouse warming and greater understanding of them will increase knowledge of ocean-atmosphere interactions which affect weather and climate. A discussion of the program for finding the travel times is included along with a comparison of two methods of measuring travel times.

Description: 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 1990

Description: A recently developed technique for determining past sea surface temperatures (SST), based on an analysis of the unsaturation ratio of long chain C37 methyl alkenones (Uk37) produced by Prymnesiophyceae phytoplankton, has been applied to late Quaternary sediment cores. Previous studies have shown that the Uk37 ratio of these alkenones is linearly proportional to the sea-water temperature in which the plankton grow, both in culture and water column samples. Furthermore, a reasonable correlation has been found between open ocean paleo-SST estimates based on Uk37 values and those derived from δ180, for the period spanning approximately the last 100,000 years (Brassell, 1986b). These results indicate this technique has potential for determining paleo-SST from analysis of alkenones extracted from marine sediments. In order to apply the Uk37 method quantitatively, it is necessary to calibrate the method for sediment samples, and to assess how well the alkenones maintain their temperature signal under some common conditions of sediment deposition and sample handling. It is also necessary to determine the method's usefulness downcore, that is, back in time, by comparing it to established methods. This study examined the effect on Uk37 of conditions that cause dissolution of carbonates in the sediment, and methods of storage and 'sample handling. These are two problems that must be resolved before the method can be applied rigorously and quantitatively to sediments for paleotemperature estimations. A comparison of duplicate samples collected and stored frozen versus those stored at room temperature for up to four years showed no resolvable differences in Uk37. Laboratory experiments of carbonate dissolution indicated there is no effect on Uk37 values under the acidic conditions that dissolve carbonates. Initial field results support this, but indicate more studies are necessary. The Uk37 "thermometer" was calibrated by analyzing Uk37 in coretops from widely varying open ocean sites. Sediment values of Uk37 reflected overlying SST for the appropriate season of the phytoplankton bloom, which for this study was assumed to be summer in high latitudes. These results fall on the same regression line for culture and water column samples derived by Prahl and Wakeham (1987), indicating that their equation (Uk37 = 0.033 T + 0.043) is suitable for use in converting Uk37 values in sediments to overlying SST for the season of coccolith bloom. Using this calibration for sediments, the Uk37 paleotemperature method can be quantitatively applied down core to open ocean sediments. In the Equatorial Atlantic, Uk37 temperature estimates were compared to those obtained from δ18O of the planktonic foraminifer Globigerinoides sacculifer, and planktonic foraminiferal assemblages for the last glacial cycle. The alkenone method showed ~1.56°C cooling at the last glacial maximum. This is about half the decrease shown by both the isotopic method ( ~3.40°C) and foraminiferal assemblages (~3.75°C), implying that, if Uk37 estimates are correct, SST in the equatorial Atlantic was only reduced slightly in the last glaciation. In the Northeast Atlantic, Uk37 temperature estimates show a profile downcore which is similar to the estimates from foram assemblages but with a constant offset toward warmer values throughout the core. Uk37 SST estimates are substantially warmer than foraminiferal estimates at all times, which may indicate inaccuracy in Uk37 temperatures at this site. Uk37 indicates a SST of 12°C for the late glacial and 18°C for the Recent, whereas assemblages give estimates of 9°C and 13°C, respectively. At 12,700 yrs BP, the Uk37 and foram assemblage methods indicate a 2°C warming. A temperature change of 2°C can account for only 0.44°/oo of the observed 1.2°/oo δ18O signal, indicating that the additional 0.8°/oo change in δ18O must result from changes in surface salinity most likely due to a meltwater lid. Uk37 estimates show the major temperature shift from glacial to interglacial temperatures occured at about 9,000 yrs BP disagreeing with assemblage data which shows the shift to Holocene values at about 12,700 yrs BP. If Uk37 temperature estimates are accurate, this disagreement may reflect differing habitats of flora and fauna under the unusual sea surface conditions in this area during the deglaciation.

Description: Primary financial support for this research came from the Ocean Ventures Fund (grant 25/ 85.08), without which this project would not have been possible. Funding supporting the labs of John Farrington (OCE 88-11409) and Lloyd Keigwin (OCE 83-08893 and ATM 84-14335) in which I worked also provided funding for part for this research.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2013

Description: 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.

Description: The majority of the data for this project was funded by grant # ARC-0856244 from the O ce of Polar Programs of the National Science Foundation. My time at WHOI was funded by the United States Navy, the National Science Foundation Graduate Research Fellowship Program and the WHOI Academic Programs O ffice.

Description: 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 2000

Description: Estimation of the upper ocean heat budget from one year of observations at a moored array in the north central Arabian Sea shows a rough balance between the horizontal advection and time change in heat when the one-dimensional balance between the surface heat flux and oceanic heat content breaks down. The two major episodes of horizontal advection, during the early northeast (NE) and late southwest (SW) monsoon seasons, are both associated with the propagation of mesoscale eddies. During the NE monsoon, the heat fluxes within the mixed layer are not significantly different from zero, and the large heat flux comes from advected changes in the thermocline depth. During the SW monsoon a coastal filament exports recently upwelled water from the Omani coast to the site of the array, 600 km offshore. Altimetry shows mildly elevated levels of surface eddy kinetic energy along the Arabian coast during the SW monsoon, suggesting that such offshore transport may be an important component of the Arabian Sea heat budget. The sea surface temperature (SST) and mixed layer depth are observed to respond to high frequency (HF, diurnal to atmospheric synoptic time scales) variability in the surface heat flux and wind stress. The rectified effect of this HF forcing is investigated in a three-dimensional reduced gravity thermodynamic model of the Arabian Sea and Indian Ocean. Both the HF heat and wind forcing act locally to increase vertical mixing in the model, reducing the SST. Interactions between the local response to the surface forcing, Ekman divergences, and remotely propagated signals in the model can reverse this, generating greater SSTs under HF forcing, particularly at low latitudes. The annual mean SST, however, is lowered under HF forcing, changing the balance between the net surface heat flux (which is dependent on the SST) and the meridional heat flux in the model. A suite of experiments with one-dimensional upper ocean models with different representations of vertical mixing processes suggests that the rectified effect of the diurnal heating cycle is dependent on the model, and overstated in the formulation used in the three-dimensional model.

Description: Funded by the Office of Naval Research (ONR), grant NOOO14-94-1-0161 and National Defense Science and Engineering Graduate Fellowship and by ONR grant NOOO14-99-1-0090.

Description: 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 January 1988

Description: Analysis of vertical profiles of absolute horizontal velocity collected in January 1981, February 1982 and April 1982 in the central equatorial Pacific as part of the Pacific Equatorial Ocean Dynamics (PEQUOD) program, revealed two significant narrow band spectral peaks in the zonal velocity records, centered at vertical wavelengths of 560 and 350 stretched meters (sm). Both signals were present in all three cruises, but the 350 sm peak showed a more steady character in amplitude and a higher signal-to-noise ratio. In addition, its vertical scales corresponded to the scales of the conspicuous alternating flows generically called the equatorial deep jets in the past (the same terminology will be used here). Meridional velocity and vertical displacement spectra did not show any such energetic features. Energy in the 560 sm band roughly doubled between January 1981 and April 1982. Time lagged coherence results suggested upward phase propagation at time scales of about 4 years. East-west phase lines computed from zonally lagged coherences, tilted downward towards the west, implying westward phase propagation. Estimates of zonal wavelength (on the order of 10000 km) and period based on these coherence calculations, and the observed energy meridional structure at this vertical wavenumber band, seem consistent, within experimental errors, with the presence of a first meridional mode long Rossby wave packet, weakly modulated in the zonal direction. The equatorial deep jets, identified with the peak centered at 350 sm, are best defined as a finite narrow band process in vertical wavenumber (311-400 sm), accounting for only 20% of the total variance present in the broad band energetic background. At the jets wavenumber band, latitudinal energy scaling compared well with Kelvin wave theoretical values and a general tilt of phase lines downward towards the east yielded estimates of 10000-16000 km for the zonal wavelengths. Time-lagged coherence calculations revealed evidence for vertical shifting of the jets on interannual time scales. Interpretation of results in terms of single frequency linear wave processes led to inconsistencies, but finite bandwidth (in frequency and wavenumber) Kelvin wave processes of periods on the order of three to five years could account for the observations. Thus, the records do not preclude equatorial waves as a reasonable kinematic description of the jets.

Description: This research was supported by grant OCE-8600052 from the National Science Foundation, through the Woods Hole Oceanographic Institution.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 1996

Description: TOPEX/POSEIDON altimetry data are employed in the analysis of the global ocean response to atmospheric forcing. We use two different approaches to test the hypothesis that the global sea surface height variability can be adequately described by linear barotropic ocean models: the multichannel regression and the optimal smoothing techniques. We start with the simplest linear vorticity balance and continue by building a hierarchy of more complicated models by including effects of topography and time dependence. We use auto-regressive external (ARX) time-series models to test the hypothesis in all of the Pacific Ocean. We also test whether any significant residual regression on the atmospheric loading is left after the inverted barometer effect is corrected for. We find that no linear barotropic model is consistent with the data. We provide a check on the results of the multichannel regression by using a Kalman filter and optimal smoother. We use sequential estimation in the form of filteringsmoothing algorithm. We run the estimate for an area of 4000 km by 2000 km in the Northeast Pacific. We analyze model and data error structures by simulating the model without data assimilation. The results show that the model forecast on average explains 33% of the data variability. The Kalman filter updates the model very efficiently and produces an estimate which explains 76% of the data variance. The optimal smoother estimate is very similar to the Kalman filter estimate. Running the model in other regions of the Pacific produced worse fits of the model to the data. This supports the conclusion that the linear barotropic dynamics fails to describe the SSH variability.

Description: This research was partially funded by a NASA Global Change Fellowship.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2010

Description: Wind waves in the ocean are a product of complex interaction of turbulent air flow with gravity driven water surface. The coupling is strong and the waves are non-stationary, irregular and highly nonlinear, which restricts the ability of traditional phase averaged models to simulate their complex dynamics. We develop a novel phase resolving model for direct simulation of nonlinear broadband wind waves based on the High Order Spectral (HOS) method (Dommermuth and Yue 1987). The original HOS method, which is a nonlinear pseudo-spectral numerical technique for phase resolving simulation of free regular waves, is extended to simulation of wind forced irregular broadband wave fields. Wind forcing is modeled phenomenologically in a linearized framework of weakly interacting spectral components of the wave field. The mechanism of wind forcing is assumed to be primarily form drag acting on the surface through wave-induced distribution of normal stress. The mechanism is parameterized in terms of wave age and its magnitude is adjusted by the observed growth rates. Linear formulation of the forcing is adopted and applied directly to the nonlinear evolution equations. Development of realistic nonlinear wind wave simulation with HOS method required its extension to broadband irregular wave fields. Another challenge was application of the conservative HOS technique to the intermittent non-conservative dynamics of wind waves. These challenges encountered the fundamental limitations of the original method. Apparent deterioration of wind forced simulations and their inevitable crash raised concerns regarding the validity of the proposed modeling approach. The major question involved application of the original HOS low-pass filtering technique to account for the effect of wave breaking. It was found that growing wind waves break more frequently and violently than free waves. Stronger filtering was required for stabilization of wind wave simulations for duration on the time scale of observed ocean evolution. Successful simulations were produced only after significant sacrifice of resolution bandwidth. Despite the difficulties our modeling approach appears to suffice for reproduction of the essential physics of nonlinear wind waves. Phase resolving simulations are shown to capture both - the characteristic irregularity and the observed similarity that emerges from the chaotic motions. Energy growth and frequency downshift satisfy duration limited evolution parameterizations and asymptote Toba similarity law. Our simulations resolve the detailed kinematics and the nonlinear energetics of swell, windsea and their fast transition under wind forcing. We explain the difference between measurements of initial growth driven by a linear instability mechanism and the balanced nonlinear growth. The simulations validate Toba hypothesis of wind-wave nonlinear quasi-equilibrium and confirm its function as a universal bound on combined windsea and swell evolution under steady wind.

Description: 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 2000

Description: The plausibility of local baroclinic instability as a generation mechanism for midocean mesoscale eddies is examined with a two-layer, quasi-geostrophic (QG) model forced by an imposed, horizontally homogeneous, vertically sheared mean flow and dissipated through bottom Ekman friction, Explanations are sought for two observed features of mid-ocean eddies: 1) substantial energy is retained in the baroclinic mode and in the associated deformation radius (Rd) scale, and 2) the ratio of eddy to mean kinetic energy is much larger than one, The tendency of QG to cascade energy into the barotropic mode and into scales larger than Rd can be counteracted when stratification is surface-trapped, for then the baroclinic mode is weakly damped, and hence enhanced, Numerical experiments are performed with both surface-trapped and uniform stratification to quantify this, Experiments with equal Ekman frictions in the two layers are also performed for purposes of contrast, Interpretation is aided with an inequality derived from the energy and enstrophy equations, The inequality forbids the simultaneous retention of substantial energy in the baroclinic mode and in scales near Rd when Ekman friction is symmetric, but points towards surface-trapped stratification and bottomtrapped friction as an environment in which both of these can be achieved, The dissertation also contains a systematic study of geostrophic turbulence forced by nonzonal flows, Narrow zonal jets emerge when shear-induced mean potential vorticity (PV) gradients are small compared to the planetary gradient (β), and energy is a strong function of the angle shear presents to the east-west direction, When shear-induced PV gradients are comparable to β, and the mean shear has a westward component, fields of monopolar vortices form and persist, Energy is asymmetric between fields of cyclones and anticyclones, Such asymmetry was commonly thought not to occur in QG, but is shown here to be introduced by the nonzonal basic state, In both jet and vortex regimes, eddy energy can be much larger than mean kinetic energy, contrary to the expectation that β stabilizes weak shear flows,

Description: My first three years here were funded by an Office of Naval Research/National Defense Science and Engineering Graduate Fellowship administered by Jeff Jarocz at the American Society for Engineering Education. During the last three years, most of my support has come the National Science Foundation via grant OCE-9617848, with some additional support coming from the Office of Naval Research via grant N00014-95-1-0824.

Description: 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 1998

Description: Planktonic protozoan grazers have the potential to significantly affect the chemistry of particle-associated trace metals. This is due both to the importance of protists as consumers of bacterial-sized particles, and to the unique low-pH, enzyme-rich microenvironment of the grazer food vacuole. This thesis examines the role of protozoan grazers in the marine geochemistry of strongly hydrolyzed, particle-reactive trace metals, in particular Th and Fe. A series of tracer experiments was carried out in model systems in order to determine the effect of grazer-mediated transformations on the chemical speciation and partitioning of radioisotopes C9Fe, 234Th, 51Cr) associated with prey cells. Results indicate that protozoan grazers are equally able to mobilize intracellular and extracellular trace metals. In some cases, protozoan regeneration of trace metals appears to lead to the formation of metal-organic complexes. Protozoan grazing may generate colloidal material that can scavenge trace metals and, via aggregation, lead to an increase in the metal/organic carbon ratio of aggregated particles. Model system experiments were also conducted in order to determine the effect of grazers on mineral phases, specifically colloidal iron oxide (ferrihydrite). Several independent techniques were employed, including size fractionation ors9Fe-labeled colloids, competitive ligand exchange, and iron-limited diatoms as "probes" for bioavailable Fe. Experimental evidence strongly suggests that protozoan grazing can affect the surface chemistry and increase the dissolution rate of iron oxide phases through phagotrophic ingestion. In further work on protozoan-mediated dissolution of colloidal Fe oxides, a novel tracer technique was developed based on the synthesis of colloidal ferrihydrite impregnated with 133Ba as an inert tracer. This technique was shown to be a sensitive, quantitative indicator for the extent of ferrihydrite dissolution/alteration by a variety of mechanisms, including photochemical reduction and ligand-mediated dissolution. In field experiments using this technique, grazing by naturally occuring protistan assemblages was shown to significantly enhance the dissolution rate of colloidal ferrihydrite over that in non-grazing controls. Laboratory and field results indicate that, when integrated temporally over the entire euphotic zone, protozoan grazing may equal or exceed photoreduction as a pathway for the dissolution of iron oxides.

Description: This work was financially supported by a Department of Defense ONR-NDSEG Graduate Fellowship, Office ofNaval Research AASERT Award (N00014-94-1-0711), and the National Science Foundation EGB Program (OCE-9523910).

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012

Description: The purpose of this study is to understand the interactions of tropical cyclones with ocean eddies. In particular we examine the influence of a cold-core eddy on the cold wake formed during the passage of Typhoon Fanapi (2010). The three-dimensional version of the numerical Price–Weller–Pinkel (PWP) vertical mixing model has previously been used to simulate and study the cold wakes of Atlantic hurricanes. The model has not been used in comparison with observations of typhoons in the Western Pacific Ocean. In 2010 several typhoons were studied during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign and Fanapi was particularly well observed. We use these observations and the 3DPWP to understand the ocean cold wake generated by Fanapi. The cold wake of Fanapi was advected by a cyclonic eddy that was south of the typhoon track. The 3DPWP model outputs with and without an eddy are compared with observations made during the field campaign. These observations are compared to model outputs with eddies in a series of positions right and left of the storm track in order to study effects of mesoscale eddies on ocean vertical mixing in the cold wake of typhoons.

Description: 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 2012

Description: This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO2 concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of δ18O and δ13C compiled byMarchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein successfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic δ18O and δ13C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded.

Description: Primary support was provided by a National Defense Science and Engineering Graduate Fellowship and two National Science Foundation awards: Award #OCE-0645936: “Beyond the Instrumental Record: the Case of Circulation at the Last Glacial Maximum” and Award #OCE-1060735: “Collaborative Research: Beyond the Instrumental Record - the Ocean Circulation at the Last Glacial Maximum and the de-Glacial Sequence”. Important secondary support came from the National Ocean Partnership Program and the National Aeronautics and Space Administration via the ECCO effort at MIT.

Description: 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 2014

Description: Recent work has documented dramatic changes in the West Antarctic Ice Sheet (WAIS) over the past 30 years (e.g., mass loss, glacier acceleration, surface warming) due largely to the influence of the marine environment. WAIS is particularly vulnerable to largescale atmospheric dynamics that remotely influence the transport of marine aerosols to the ice sheet. Understanding seasonal- to decadal-scale changes in the marine influence on WAIS (particularly sea-ice concentration) is vital to our ability to predict future change. In this thesis, I develop tools that enable us to reconstruct the source and transport variability of marine aerosols to West Antarctica in the past. I validate new firn-core sea-ice proxies over the satellite era; results indicate that firn-core glaciochemical records from this dynamic region may provide a proxy for reconstructing Amundsen Sea and Pine Island Bay polynya variability prior to the satellite era. I next investigate the remote influence of tropical Pacific variability on marine aerosol transport to West Antarctica. Results illustrate that both source and transport of marine aerosols to West Antarctica are controlled by remote atmospheric forcing, linking local dynamics (e.g., katabatic winds) with large-scale teleconnections to the tropics (e.g., Rossby waves). Oxygen isotope records allow me to further investigate the relationship between West Antarctic firn-core records and temperature, precipitation origin, sea-ice variability, and large-scale atmospheric circulation. I show that the tropical Pacific remotely influences the source and transport of the isotopic signal to the coastal ice sheet. The regional firn-core array reveals a spatially varying response to remote tropical Pacific forcing. Finally, I investigate longer-term (~200 year) ocean and ice-sheet changes using the methods and results gleaned from the previous work. I utilize sea-ice proxies to reconstruct long-term changes in sea-ice and polynya variability in the Amundsen Sea, and show that the tropics remotely influence West Antarctica over decadal timescales. This thesis utilizes some of the highest-resolution, most coastal records in the region to date, and provides some of the first analyses of the seasonal- to decadal-scale controls on source and transport of marine aerosols to West Antarctica.

Description: This research was supported by an award from the Department of Energy Office of Science Graduate Fellowship Program (DOE SCGF) to ASC, a James E. and Barbara V. Moltz Research Fellowship, and by grants from the National Science Foundation Office of Polar Programs (NSF-OPP; #ANT-0632031 & #ANT-0631973), the National Science Foundation Major Research Instrumentation Program (NSF-MRI; #EAR-1126217), the NASA Cryosphere Program (#NNX10AP09G), and a WHOI Andrew W. Mellon Foundation Award for Innovative Research.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2011

Description: Throughout this thesis we will discuss the theoretical background and empirical observation of a swell band shore normal flux divergence reversal. Specifically, we will demonstrate the existence and persistence of the energy flux divergence reversal in the nearshore region of Atchafalaya Bay, Gulf of Mexico, across storms during the March through April 2010 deployment. We will show that the swell band offshore component of energy flux is rather insignificant during the periods of interest, and as such we will neglect it during the ensuing analysis. The data presented will verify that the greatest flux divergence reversal is seen with winds from the East to Southeast, which is consistent with theories which suggest shoreward energy flux as well as estuarine sediment transport and resuspension prior to passage of a cold front. Employing the results of theoretical calculations and numerical modeling we will confirm that a plausible explanation for this phenomena can be found in situations where temporally varying wind input may locally balance or overpower bottom induced dissipation, which may also contravene the hypothesis that dissipation need increase shoreward due to nonlinear wave-wave interactions and maturation of the spectrum. Lastly, we will verify that the data presented is consistent with other measures collected during the same deployment in the Atchafalaya Bay during March - April 2010.

Description: 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 1998

Description: Efforts to understand the Arctic system have recently focused on the role in local and global circulation of waters from the Arctic shelf seas. In this study, steady-state exchanges between the Arctic shelves and the central basins are estimated using an inverse box model. The model accounts for data uncertainty in the estimates, and quantifies the solution uncertainty. Other features include resolution of the two-basin Arctic hydrographic structure two-way shelf-basin exchange in the surface mixed layer, the capacity for shelfbreak upwelling, and recognition that most inflows enter the Arctic via the shelves. Aggregate estimates of all fluxes across the Arctic boundary, with their uncertainties, are generated from flux estimates published between 1975 and 1997. From the aggregate estimates, mass-, heat-, and salt-conserving boundary flux estimates are derived, which imply a net flux of water from the shelves to the basins of 1.2±0.4 Sv. Due primarily to boundary flux data uncertainty, constraints of mass, heat, and salt conservation alone cannot determine how much shelf-basin exchange occurs via dense overflows, and how much via the surface mixed layer. Adding δ180 constraints, however, greatly reduces the uncertainty. Dense water flux from the shelves to the basins is necessary for maintaining steady state, but shelfbreak upwelling is not required. Proper representation of external sources feeding the shelves, rather than the basins, is important to obtain the full range of plausible steady solutions. Implications of the results for the study of Arctic change are discussed.

Description: This work was supported by National Science Foundation grant OPP-9422292 as part of the Arctic System Science ARCSS program, administered by the Office of Polar Programs.

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1999

Description: 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.

Description: Funding for this research came from the Department of Defense under a National Defense Science and Engineering Graduate Fellowship. Financial support was also contributed by the National Science Foundation through grants #OCE-9617570 and #OCE-9730071, and the Tokyo Electric Power Company through the TEPCO/MIT Environmental Research Program. The author received partial support from an MIT Climate Modeling Fellowship, made possible by a gift from the American Automobile Manufacturers Association.

Description: 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 1993

Description: The dynamical aspects involved in the assimilation of altimeter data in a numerical ocean model have been investigated. The model used for this study is a quasi-geostrophic model of the Gulf Stream region. The data that have been assimilated are maps of sea surface height which have been obtained as the superposition of sea surface height variability deduced from the Geosat altimeter measurements and a mean field constructed from historical hydrographic data. The method used for assimilating the data is the nudging technique. Nudging has been implemented in such a way as to achieve a high degree of convergence of the surface model fields toward the observations. We have analyzed the mechanisms of the model adjustment, and the final statistical equilibrium characteristics of the model simulation when the surface data are assimilated. Since the surface data are the superposition of a mean component and an eddy component, in order to understand the relative role of these two components in determining the characteristics of the final st atistical steady state, we have considered two different experiments: in the first experiment only the climatological mean field is assimilated, while in the second experiment the total surface streamfunction field (mean + eddies) has been used. We have found that the mean component of the surface data determines, to a large extent, the structure of the flow field in the subsurface layers, while the eddy field, as well as the inflow/outflow conditions at the open boundaries, affect its intensity. In particular, if surface eddies are not assimilated only a weak flow develops in the two deeper model layers where no inflow/ outflow is prescribed at the boundaries. Comparisons of the assimilation results with available in situ observations show a considerable improvement in the degree of realism of the climatological model behavior, with respect to the model in which no data are assimilated. In particular, the possibility of building into the model more realistic eddy characteristics, through the assimilation of the surface eddy field, proves very successful in driving components of the mean model circulation that are in good agreement with the available observations.

Description: This research was carried out with the support of the National Aeronaut ics Space Administration, through a contract to MIT from the Jet Propulsion Laboratory, # 958208, as a part of the TOPEX-Poseidon investigation.

Description: 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 November 1992

Description: Cosmogeruc P-32 (14.28 days) and P-33 (25.3 days) are powerful tracers of upper ocean P cycling, when coupled with time-series of the atmospheric sources. A method was developed to determine the low-level beta activities in rainwater and plankton. The wet deposition rates of P-32 and P-33 were determined during 12 months at a marine site, at Bermuda, coinciding with measurements of the activities and activity ratio P-33/P-32 in suspended particles and plankton tows at BATS station. The in situ production rates of radiophosphorus in the upper ocean were estimated by measuring the activities induced in Cl, K and S targets by cosmic rays. Knowledge of all the sources of radiophosphorus to the Sargasso Sea allowed the cycling of P-32 and P-33 in suspended particles and macrozooplankton to be studied. The study was based on the determination of the activity ratio P-33/P-32 in different particulate pools. The activity ratio was higher in particle collections dominated by higher levels in the food web. The increase in the ratio in plankton relative to rain allowed the determination of the turnover times of P in plankton and in situ grazing rates.

Description: Funding for this research was provided by NSF (grants OCE-8800957. OCE- 8817836 and OCE-902284), DOE (grant DE-FG02-88ER60681), Woods Hole Oceanographic Institution, Ocean Venture Funding of Woods Hole Oceanographic Institution and Scurlock Funds of Mr Arch Scurlock to MIT/WHOI Joint Program.

Description: 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 2013

Description: Efforts to monitor the ocean for signs of climate change are hampered by ever-present noise, in the form of stochastic ocean variability, and detailed knowledge of the character of this noise is necessary for estimating the significance of apparent trends. Typically, uncertainty estimates are made by a variety of ad hoc methods, often based on numerical model results or the variability of the data set being analyzed. We provide a systematic approach based on the four-dimensional frequency-wavenumber spectrum of low-frequency ocean variability. This thesis presents an empirical model of the spectrum of ocean variability for periods between about 20 days and 15 years and wavelengths of about 200{10,000 km, and describes applications to ocean circulation trend detection, observing system design, and satellite data processing. The horizontal wavenumber-frequency part of the model spectrum is based on satellite altimetry, current meter data, moored temperature records, and shipboard ADCP data. The spectrum is dominated by motions along a "nondispersive line". The observations considered are consistent with a universal ω-2 power law at the high end of the frequency range, but inconsistent with a universal wavenumber power law. The model spectrum is globally varying and accounts for changes in dominant phase speed, period, and wavelength with location. The vertical structure of the model spectrum is based on numerical model results, current meter data, and theoretical considerations. We find that the vertical structure of kinetic energy is surface intensified relative to the simplest theoretical predictions. We present a theory for the interaction of linear Rossby waves with rough topography; rough topography can explain both the observed phase speeds and vertical structure of variability. The improved description of low-frequency ocean variability presented here will serve as a useful tool for future oceanographic studies.

Description: This research was supported by NASA under grants NNG06GC28G and NNX08AR33G.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1997

Description: The unusual twice-yearly cycle of mixed layer deepening and cooling driven by the monsoon is analyzed using a recently collected (1994-95) dataset of concurrent local air-sea fluxes and upper ocean dynamics from the Arabian Sea. The winter northeast monsoon has moderate wind forcing and a strongly destabilizing surface buoyancy flux, driven by large radiative and latent heat losses at the sea surface. Convective entrainment is the primary local mechanism driving the observed mixed layer cooling and deepening, although horizontal advection of thermocline depth variations affect the depth which the mixed layer attains. Modifications of a one-dimensional mixed layer model and heat balance show that the primary nonlocal forcing of the upper ocean is the horizontal advection of temperature gradients below the mixed layer base. The summer southwest monsoon has strong wind stresses and a neutral to stabilizing surface buoyancy flux, limited by the extreme humidity of the atmosphere, which suppresses both the radiative and latent heat losses at the surface. Wind-driven shear instabilities at the base of the mixed layer, which entrain cooler and fresher water primarily produces the observed mixed layer cooling and deepening. Horizontal advection of cooler water within the mixed layer influences the local heat balance at the mooring site. Ekman pumping velocities play only a small role in the upper ocean evolution during both monsoon seasons.

Description: This research was funded by ONR grant N00014-94- 1-0161, and I was supported during this time by a generous NDSEG fellowship.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1992

Description: A basin-scale acoustic tomography experiment was conducted in the northeast Pacific from May 1987 to September 1987. In this thesis, the stability of the forward model is analyzed. There are large non-linearities in the changes in travel time between ray paths for the four seasons . I constructed a model in which the change in warming in the upper 100 m of the ocean was due only to changes in surface solar irradiance. The value of the surface solar irradiance anomalies necessary to cause the tomography results for warming (Spiesberger and Metzger, 1991) was computed. This value was larger than the actual value of surface solar irradiance anomaly which was computed using inputs measured by satellite (Chertock, 1989).

Description: 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 1995

Description: Data from fifteen globally distributed, modern, high resolution, hydrographic oceanic transects are combined in an inverse calculation using large scale box models. The models provide estimates of the global meridional heat and freshwater budgets and are used to examine the sensitivity of the global circulation, both inter and intra-basin exchange rates, to a variety of external constraints provided by estimates of Ekman, boundary current and throughflow transports. A solution is found which is consistent with both the model physics and the global data set, despite a twenty five year time span and a lack of seasonal consistency among the data. The overall pattern of the global circulation suggested by the models is similar to that proposed in previously published local studies and regional reviews. However, significant qualitative and quantitative differences exist. These differences are due both to the model definition and to the global nature of the data set. The picture of the global circulation which emerges from the models IS a complex, turbulent flow. When integrated across ocean basins not one, but two major cells emerge. The first connects an Atlantic overturning cell (estimated at 18± 4x 109 kg s- 1) to the Southern Ocean where the Antarctic Circumpolar Current carries lower deep waters to the Indian and Pacific basins where they are converted to upper deep and intermediate waters before returning to the Atlantic. The second cell connects the Pacific and Indian Basins to the north and south of Australia. In t his cell deep waters pass into the Pacific and return within the Indian Basin as intermediate waters after passing through the Indonesian Passages. The two cells are found to be independent of one another, i.e. within the models, the Indonesian Passages do not represent a significant element in a net global circulation. While there is ample evidence of westward flow around the southern tip of South Africa which would support a "warm" water path scenario, the variability of flow in this region, rich with eddies makes hydrography a poor estimator of the relative strengths of the controversial "warm" and "cold" water paths. All existing estimates of Indonesian Passage throughflow, including the smallest (O x 106 m3 s-1) and the largest (20 x 106 m3 s-1), are consistent with the model constraints. When the Pacific- Indian throughflow is not constrained, the model produces an estimate of 11 ± 14x 109 kg s-1. The model heat flux estimates are both significantly different from zero and quite robust to changes in initial assumptions, with the exception of the choice of wind field. Although in this work it was not possible to compute freshwater fluxes which were significantly different from zero, future inclusion of salinity anomaly constraints along with terms describing vertical diffusion may yet make it possible to compute significant freshwater :flux estimates from hydrography.

Description: This research was partially funded by a NASA Global Change Fellowship and was also supported by NASA under contract NAGW-1048 and NSF under contract OCE-9205942.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1991

Description: This thesis reviews observational and theoretical work on the equatorial deep jets and work related to the study of the role of the horizontal Coriolis parameter. Most existing analytical models interpret the equatorial deep jets as either low frequency, long Rossby waves or stationary,long Kelvin waves generated at or near the ocean surface. These models are unable to answer the question of how wind generated energy propagates down through the equatorial undercurrent and thermocline into the deep ocean. Existing numerical models do not display deep jet features due mainly to their in low vertical resolution and the high eddy viscosity associated with these models. These numerical models also suggest that very tittle energy is able to get into the deep ocean. A natural question is raised: can the equatorial deep jets possibly be interpreted as free, steady inertial motion below the thermocline? We develop a simple model for the deep jets as a free, stationary inertial motion. After scaling the fluid dynamical equations in the appropriate regime, it is found that neither the advective nonlinearity nor the horizontal Coriolis parameter can be neglected. An important conservation equation, the so called potential zonal vorticity conservation equation which governs the equatorial steady and zonal independent equatorial flow is derived. From this conservation principle, an inertial equatorial deep jets model is developed which captures some important features of the deep jets. The horizontal Coriolis parameter is important in this inertial model. The role of the horizontal Coriolis parameter has long been controversial in the literature. We discuss this role for several equatorial flow systems. It is found that the horizontal Coriolis parameter is not significant for inviscid linear equatorial waves due to the presence of stratification in the real ocean. However, when the ratio of momentum eddy viscosity to the density dissipation coefficient becomes small enough, the effect of the horizontal Coriolis parameter becomes more important in a simple viscous model. Some general aspects of this parameter have also been discussed in terms of angular momentum conservation and energy conservation principles. It is suggested that for the ocean circulation of large vertical excursion of the fluid particle, the horizontal Coriolis parameter effect may not be small and should be included in future numerical models.

Description: 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 1991

Description: In this thesis, I study the time-varying behavior of a ventila ted thermocline with basin scales at annual and decadal time scales. The variability is forced by three external forcings: the wind stress (chapter 3), the surface heat flux (chapter 4) and the upwelling along the eastern boundary (chapter 5). It is found that the thermocline variability is forced mainly by wind in a shadow zone while m~inly by surface buoyancy flux in a ventilated zone. A two-layer planetary geostrophic model is developed (chapter 2) to simulate a thermocline. The model includes some novel physical mechanisms. Most importantly, it captures the essential feature of subduction; it also is able to account for a time-varying surface temperature. The equation for the interface is a quasi-linear equation, which can be solved analytically by the method of characteristics. The effect of a varying Ekman pumping is investigated. In a shadow zone, it is found that the driving due to the Ekman pumping is mainly balanced by the propagation of planetary waves. However, in a ventilated zone, the cold advection of subducted water plays the essential role in opposing the Ekman pumping. The different dynamics also results in different thermocline variability between the two zones. After a change of Ekman pumping, in the shadow zone, since the baroclinic Ross by wave responds to a changing Ekman pumping slowly (in years to decades), an imbalance arises between the Rossby wave and the Ekman pumping, which then excites thermocline variability. However, in the ventilated zone, both the advection and the Ekman pumping vary rapidly after a barotropic process (about one week) to reach a new steady balance, leaving little thermocline variability. In addition, the evolution of the thermocline and circulation are also discussed. Furthermore, with a periodic Ekman pumping, it is found that linear solutions are approximate the fully nonlinear solution well, particularly for annual forcings. However, the linear disturbance is strongly affected by the basic thermocline structure and circulation. The divergent group velocity field, which is mainly caused by the divergent Sverdrup flow field, produces a decay effect on disturbances. The mean thermocline structure also strongly affects the relative importance of the local Ekman pumping and remote Rossby waves. As a result, in a shadow zone, local response dominates for a shallow interface while the remote Rossby wave dominates for a deep interface. With a strong decadal forcing, the nonlinearity becomes important in the shadow zone, particularly in the western part. The time-mean thermocline which results, becomes shallower than the steady thermocline under the mean Ekman pumping. Then, we investigate the effect on the permanent thermocline by a moving outcrop line, which simulates the effect of a varying surface heat flux. The two layer model is modified by adding an (essentially passive) mixed layer atop. The outcrop line and the mixed layer depth are specified. It is found that, opposite to a surface wind stress, a surface buoyancy flux causes strong variability in the ventilated zone through subducted water while it affects the shadow zone very little. Furthermore, two regimes of buoyancy-forced solution are found. When the outcrop line moves slowly, the solutions are non-entrainment solutions. For these solutions, the surface heat flux is mainly balanced by the horizontal advection. The mixed layer is never entrained. The time-mean thermocline is close to the steady thermocline with the time-mean outcrop line. When the outcrop line moves southward rapidly during the cooling season, the solutions become entrainment solutions. Now, deep vertical convection must occur, because the horizontal advection in the permanent thermocline is no longer strong enough to balance the surface cooling. The mixed layer penetrates rapidly such that water mass is entrained into the mixed layer through the bottom. The time-mean thermocline resembles the steady thermocline with the early spring mixed layer, as suggested by Stommel (1979). The local variability in the permanent thermocline is most efficiently produced by decadal forcings. Finally, two issues about the waves radiating from the eastern boundary are discussed. The first is the penetration of planetary waves across the southern boundary of a subtropical gyre. We find that the wave penetration across the southern boundary is substantially changed by the zonal variation of the thermocline structure. The zonal variation alters both the effective β and the wave front orientation. As a result, the wave penetration differs for interfaces at different depths. For an interface near the surface, part of the waves penetrate into the equatorial region. For middle depths, most waves will be trapped within the subtropical gyre. In contrast, for deep depths, all waves penetrate southward. The second issue of the eastern boundary waves mainly concerns with the breaking of planetary waves in the presence of an Ekman pumping and the associated two-dimensional mean flow. It is found that the breaking is affected significantly by an Ekman pumping and the associated mean flow. With an Ekman pumping, downwelling breaking is suppressed and the breaking time is delayed; upwelling breaking is enhanced and their times are shortened. The breaking times and positions are mainly determined by the maximum vertical perturbation speed while the intensity of the breaking front mainly depends on the amplitude of the perturbation. The intensity of a breaking front increases with the amplitude of the forcing, but decreases with the distance from the eastern boundary. The orientation of a breaking front is overall in northeast-southwest (x ~ -1/f2).

Description: This thesis is supported by National Science Foundation, Division of Atmospheric Sciences.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1998

Description: This thesis presents an investigation of the influence of surface waves on momentum exchange. A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved flux estimates, modifications to the traditional flux parameterizations are explored. Modification to the bulk aerodynamic method involves incorporating sea state dependence into the roughness length calculation. For the inertial dissipation method, a new parameterization for the dimensionless dissipation rate is proposed. The modifications lead to improved momentum flux estimates for both methods.

Description: This project was funded by the Oceanographer of the Navy.

Description: 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 1999

Description: Climate simulation with numerical oceanic models requires a proper parameterization scheme in order to represent the effects of unresolved mesoscale eddies. Even though a munber of schemes have been proposed and some have led to improvements in the simulation of the bulk climatological properties, the success of the parameterizations in representing the mesoscale eddies has not been investigated in detail. This thesis examines the role of eddies in a 105-years long basin scale eddy resolving simulation with the MIT General Circulation Model (GCM) forced by idealized wind stress and relaxation to prescribed meridional temperature; this thesis also evaluates the Fickian diffusive, the diabatic Green-Stone (GS) and the quasi-adiabatic Gent-McWilliams (GM) parameterizations in a diagnostic study and a series of coarse resolution experiments with the same model in the same configuration. The mesoscale eddies in the reference experiment provide a significant contribution to the thermal balance in limited areas of the domain associated with the upper 1000M of the boundary regions. Specifically designed diagnostic tests of the schemes show that the horizontal and vertical components of the parameterized flux are not simultaneously downgradient to the eddy heat flux. The transfer vectors are more closely aligned with the isopycnal surfaces for deeper layers, thus demonstrating the adiabatic nature of the eddy heat flux for deeper layers. The magnitude of the coefficients is estimated to be consistent with traditionally used values. However, the transfer of heat associated with timedependent motions is identified as a complicated process that cannot be fully explained with any of the local parameterization schemes considered. The eddy parameterization schemes are implemented in the coarse resolution configuration with the same model. A series of experiments exploring the schemes' parameter space demonstrate that Fickian diffusion has the least skill in the climatological simulations because it overestimates the temperature of the deep ocean and underestimates the total heat transport. The GS and GM schemes perform better in the simulation of the bulk climatological properties of the reference solution, although the GM scheme in particular produces an ocean that is consistently colder than the reference state. Comparison of the eddy heat flux divergence with the parameterized divergences for typical parameter values demonstrates that the success of the schemes in the climatological simulation is not related to the representation of the eddy heat flux but to the representation of the overall internal mixing processes.

Description: The financial support for this research was provided by ONR grant number NOOOl4- 98-1-0881, Alliance for Global Sustainability and American Automobile Manufactures Association.

Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2014

Description: 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.

Description: Office of Naval Research for research support under grants N00014-08-1-0586 (QPE) to the Massachusetts Institute of Technology