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Depth-averaged eddy buoyancy diffusivities across continental shelves and slopes are investigated using a suite of eddy-resolving, process-oriented simulations of prograde frontal currents characterized by isopycnals tilted in the opposite direction to the seafloor, a flow regime commonly found along continental margins under downwelling-favorable winds or occupied by buoyant boundary currents. The diagnosed cross-slope eddy diffusivity varies by up to three orders of magnitude, decaying from (Formula presented.) in the relatively flat-bottomed region to (Formula presented.) over the steep continental slope, consistent with previously reported suppression effects of steep topography on baroclinic eddy fluxes. To theoretically constrain the simulated cross-slope eddy fluxes, we examine extant scalings for eddy buoyancy diffusivities across prograde shelf/slope fronts and in flat-bottomed oceans. Among all tested scalings, the GEOMETRIC framework developed by D. P. Marshall et al. (2012, https://doi.org/10.1175/JPO-D-11-048.1) and a parametrically similar Eady scale-based scaling proposed by Jansen et al. (2015, https://doi.org/10.1016/j.ocemod.2015.05.007) most accurately reproduce the diagnosed eddy diffusivities across the entire shelf-to-open-ocean analysis regions in our simulations. This result relies upon the incorporation of the topographic suppression effects on eddy fluxes, quantified via analytical functions of the slope Burger number, into the scaling prefactor coefficients. The predictive skills of the GEOMETRIC and Eady scale-based scalings are shown to be insensitive to the presence of along-slope topographic corrugations. This work lays a foundation for parameterizing eddy buoyancy fluxes across large-scale prograde shelf/slope fronts in coarse-resolution ocean models. © 2022 The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

Mesoscale eddy mixing profoundly modulates the ocean tracer budgets, and is typically parameterized via the isopycnal eddy diffusivity in ocean climate models. However, relatively little is known about the magnitude/structure of isopycnal eddy diffusivity across continental slopes, which hinders the understanding and prediction of shelf-open ocean exchanges. In this study, we quantify the isopycnal eddy diffusivity in a suite of eddy-resolving, process-oriented simulations of mesoscale turbulence over continental slopes under upwelling-favorable winds, a configuration that commonly arises around the margins of subtropical gyres. Cross-shore eddy diffusivity is found to be suppressed in the upper open ocean occupied by strong alongshore flows, but enhanced at depths where alongshore flows are weakened, a finding that is consistent with the enhancement of eddy mixing near the steering level. Over continental slopes, eddy diffusivity also strengthens at mid-depths, but almost vanishes near the seafloor. To theoretically constrain the simulated eddy fluxes, we examine the scaling of eddy diffusivity proposed by Ferrari and Nikurashin (2010, https://doi.org/10.1175/2010JPO4278.1), which accounts for the suppression of eddy mixing induced by the relative propagation of eddies to the mean flow. We show that, apart from the mean-flow suppression effect, the eddy anisotropy effect induced by steep topography shapes both the horizontal and vertical structures of cross-shore eddy diffusivity. Finally, we propose prospective closures of the eddy propagation speed and eddy anisotropy effect over continental slopes using the large-scale flow and bathymetric quantities. This work offers a basis upon which a “slope-aware” parameterization of mesoscale eddy mixing can be developed. © 2021. The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

Mesoscale eddy mixing profoundly modulates the ocean tracer budgets, and is typically parameterized via the isopycnal eddy diffusivity in ocean climate models. However, relatively little is known about the magnitude/structure of isopycnal eddy diffusivity across continental slopes, which hinders the understanding and prediction of shelf-open ocean exchanges. In this study, we quantify the isopycnal eddy diffusivity in a suite of eddy-resolving, process-oriented simulations of mesoscale turbulence over continental slopes under upwelling-favorable winds, a configuration that commonly arises around the margins of subtropical gyres. Cross-shore eddy diffusivity is found to be suppressed in the upper open ocean occupied by strong alongshore flows, but enhanced at depths where alongshore flows are weakened, a finding that is consistent with the enhancement of eddy mixing near the steering level. Over continental slopes, eddy diffusivity also strengthens at mid-depths, but almost vanishes near the seafloor. To theoretically constrain the simulated eddy fluxes, we examine the scaling of eddy diffusivity proposed by Ferrari and Nikurashin (2010, https://doi.org/10.1175/2010JPO4278.1), which accounts for the suppression of eddy mixing induced by the relative propagation of eddies to the mean flow. We show that, apart from the mean-flow suppression effect, the eddy anisotropy effect induced by steep topography shapes both the horizontal and vertical structures of cross-shore eddy diffusivity. Finally, we propose prospective closures of the eddy propagation speed and eddy anisotropy effect over continental slopes using the large-scale flow and bathymetric quantities. This work offers a basis upon which a “slope-aware” parameterization of mesoscale eddy mixing can be developed. © 2021. The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

Mesoscale eddy mixing profoundly modulates the ocean tracer budgets, and is typically parameterized via the isopycnal eddy diffusivity in ocean climate models. However, relatively little is known about the magnitude/structure of isopycnal eddy diffusivity across continental slopes, which hinders the understanding and prediction of shelf-open ocean exchanges. In this study, we quantify the isopycnal eddy diffusivity in a suite of eddy-resolving, process-oriented simulations of mesoscale turbulence over continental slopes under upwelling-favorable winds, a configuration that commonly arises around the margins of subtropical gyres. Cross-shore eddy diffusivity is found to be suppressed in the upper open ocean occupied by strong alongshore flows, but enhanced at depths where alongshore flows are weakened, a finding that is consistent with the enhancement of eddy mixing near the steering level. Over continental slopes, eddy diffusivity also strengthens at mid-depths, but almost vanishes near the seafloor. To theoretically constrain the simulated eddy fluxes, we examine the scaling of eddy diffusivity proposed by Ferrari and Nikurashin (2010, https://doi.org/10.1175/2010JPO4278.1), which accounts for the suppression of eddy mixing induced by the relative propagation of eddies to the mean flow. We show that, apart from the mean-flow suppression effect, the eddy anisotropy effect induced by steep topography shapes both the horizontal and vertical structures of cross-shore eddy diffusivity. Finally, we propose prospective closures of the eddy propagation speed and eddy anisotropy effect over continental slopes using the large-scale flow and bathymetric quantities. This work offers a basis upon which a “slope-aware” parameterization of mesoscale eddy mixing can be developed. © 2021. The Authors. Journal of Advances in Modeling Earth Systems published by Wiley Periodicals LLC on behalf of American Geophysical Union.

The dispersal of sand from submerged mounds in the nearshore is driven by the interplay of processes such as converging and recirculating flows, changing roughness, bed slope effects and wave focusing/refraction. This morphological diffusivity is key to understanding sand bars in shallow seas, tidal inlets, estuaries, and the nearshore response to human interventions such as nourishments and dredging. Most of the work on the evolution of submerged mounds has been based on fluvial studies, focusing on flow without waves. In these cases, circular mounds tend to deform to crescentic (barchan) shapes. In contrast, observations of sandbars and berms in the nearshore subjected to waves show much more complex translation and deformation behavior. This contribution introduces the laboratory MOrphological Diffusivity Experiment (MODEX) aimed at examining morphological diffusivity under different forcing conditions. The experiment particularly addresses the linkages between small scale (local) effects (e.g. bed slope, bedforms) on the adjustment of sandy mounds., Peer Reviewed, Postprint (published version)

Mesoscale eddies are ubiquitous in the ocean and play a key role in exchanges across continental slopes. In this study the properties of wind-driven baroclinic turbulence are investigated using eddy-resolving process simulations, focusing on the case of retrograde winds that arises around the margins of the subtropical gyres. In contrast to a flat-bottomed ocean, over steep slopes eddies develop from baroclinic instabilities are confined to the top few hundred meters. Deeper in the water column baroclinic instability and vertical momentum transfer are suppressed, so wind-input momentum is exported toward the open ocean by eddies before traversing down to the ocean bed. Close to the sloping topography, eddy energy sourced from the upper ocean is converted to potential energy, steepening isopycnals and driving bottom-trapped prograde flows. This process is associated with upgradient lateral buoyancy fluxes and downgradient isopycnal potential vorticity fluxes, and cannot be reproduced via linear stability calculations. These properties of wind-driven shelf/slope turbulence are contrasted against simulations with flat bathymetry. The key differences described above hinge on the flow close to the steep topographic slope, which may be sensitive to the model's vertical coordinate system. The simulations are therefore replicated using models that employ geopotential coordinates, terrain-following coordinates, and isopycnal coordinates. Quantitative inter-model discrepancies in the momentum and energy budgets are much more pronounced in the presence of a steep bottom slope. However, the key findings of this study are consistent across the models, suggesting that they are robust and warrant incorporation into parameterizations of eddy transfer across continental slopes. © 2017 Elsevier Ltd

Mesoscale eddies are ubiquitous in the ocean and play a key role in exchanges across continental slopes. In this study the properties of wind-driven baroclinic turbulence are investigated using eddy-resolving process simulations, focusing on the case of retrograde winds that arises around the margins of the subtropical gyres. In contrast to a flat-bottomed ocean, over steep slopes eddies develop from baroclinic instabilities are confined to the top few hundred meters. Deeper in the water column baroclinic instability and vertical momentum transfer are suppressed, so wind-input momentum is exported toward the open ocean by eddies before traversing down to the ocean bed. Close to the sloping topography, eddy energy sourced from the upper ocean is converted to potential energy, steepening isopycnals and driving bottom-trapped prograde flows. This process is associated with upgradient lateral buoyancy fluxes and downgradient isopycnal potential vorticity fluxes, and cannot be reproduced via linear stability calculations. These properties of wind-driven shelf/slope turbulence are contrasted against simulations with flat bathymetry. The key differences described above hinge on the flow close to the steep topographic slope, which may be sensitive to the model's vertical coordinate system. The simulations are therefore replicated using models that employ geopotential coordinates, terrain-following coordinates, and isopycnal coordinates. Quantitative inter-model discrepancies in the momentum and energy budgets are much more pronounced in the presence of a steep bottom slope. However, the key findings of this study are consistent across the models, suggesting that they are robust and warrant incorporation into parameterizations of eddy transfer across continental slopes. © 2017 Elsevier Ltd

The long-term goal of the research is to increase the physical understanding of acoustic propagation and scattering in continental shelf and slope environments in the 50-4000 Hz band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range- and azimuth-dependent littoral waveguides. For FY14, the first objective was to investigate the statistics of the mode intensity that result from scattering from a randomly rough seabed surface in a shallow water environment. The specific objective was to examine the feasibility of using a 2-way coupled mode methodology to analyze observed monostatic reverberation collected off Panama City, FL in 2013 in the 2-4 kHz band. The second objective was to extract information about the frequency dependence of seabed attenuation for a soft thick sediment. A third objective was to use ship radiated sound to extract marginal probability distributions for both alpha and gamma, in a shallow water environment with a sandy seabed.

The long term goal is to improve ocean physical state and acoustic state predictive capabilities. The goal fitting the scope of this project is the creation of physics-based, broadly applicable and portable acoustic prediction capabilities that include the effects of internal waves, surface waves, and larger scale features, with an emphasis on continental shelf and slope regions.

The Indian Ocean contains arguably the highest diversity of cetaceans in the world s oceans, yet research in this region is extremely limited. The strong environmental variability imposed on the northern Indian Ocean by the seasonal monsoons likely causes a wide variety of niches in both space and time that support the observed diversity of cetaceans. In addition to shelf, slope, and oceanic habitats, there are regions dominated by the input of fresh water (e.g., Bay of Bengal), by evaporation and low river runoff (e.g., Arabian Sea), as well as coastal currents, eddy activity, and large-scale oceanic currents. Moreover, the Arabian Sea and Bay of Bengal have well-developed oxygen minimum zones (mesopelagic regions with O2 concentrations 0.5 ml l-1) that likely have a significant influence on the behavior and distribution of cetacean prey. Our long-term goal is to understand the physical and biological oceanographic processes that influence the distribution and occurrence of tropical and subtropical cetaceans. We believe the northern Indian Ocean is particularly well suited for investigating these processes because of the large spatial and temporal variability in environmental conditions imposed by the monsoons. However, very little is known of the distribution, abundance, or behavior of cetaceans in the oceanic waters of the Bay of Bengal. What little research has been done in the region has focused on the river dolphins and nearshore porpoises (e.g., Smith et al. 2008). Indo-Pacific humpback dolphins and spinner dolphins are endemic to the coastal waters of the Bay of Bengal (de Boer et al. 2002), while a wide variety of oceanic dolphins, blackfish (pilot, melon-headed, and false killer whales), sperm whales, beaked whales, pygmy and dwarf sperm whales, and several baleen whale species occur over the continental slope and abyssal plain of the oceanic Bay (Leatherwood et al. 1984, Ballance and Pittman 1998, de Boer et al. 2002)., Prepared in collaboration with the Applied Physics Laboratory, University of Washington, Seattle.

An array of three bottom-mounted ADCP moorings was deployed on the prevailing propagation path of strong internal tides for nearly 1 year across the continental slope in the northern South China Sea. These velocity measurements are used to study the intra-annual variability of diurnal and semidiurnal internal tidal energy in the region. A numerical model, the Luzon Strait Ocean Nowcast/Forecast System developed at the U.S. Naval Research Laboratory that covers the northern South China Sea and the Kuroshio, is used to interpret the observed variation of internal tidal energy on the Dongsha slope. Internal tides are generated primarily at the two submarine ridges in the Luzon Strait. At the western ridge generation site, the westward energy flux of the diurnal internal tide is sensitive to the stratification and isopycnal slope associated with the Kuroshio. The horizontal shear at the Kuroshio front does not modify the propagation path of either diurnal or semidiurnal tides because the relative vorticity of the Kuroshio in Luzon Strait is not strong enough to increase the effective inertial frequency to the intrinsic frequency of the internal tides. The variation of internal tidal energy on the continental slope and Dongsha plateau can be attributed to the variation in tidal beam propagation in the northern South China Sea., Pub. in J Oceanogr., v69 p619-630, 2013.

The long-term goal of the research is to increase the physical understanding of acoustic propagation and scattering in continental shelf and slope environments in the 50-4000 Hz band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range- and azimuth-dependent littoral waveguides. For FY13, the first objective was to investigate the statistics of the mode intensity and cross-mode coherence that result from scattering from a randomly rough seabed surface in a shallow water environment. The second objective was to extract information about the frequency dependence of seabed attenuation for a soft thick sediment.

My long-term research goals are: (1) The characterization, understanding, and prediction of the statistics (mean, variance and coherence) of low-frequency acoustic signals and ambient noise in the littoral zone. The signal statistics are primarily influenced by the ocean variability and bottom properties. The noise statistics are influenced by atmospheric forcing and shipping in addition to the ocean and bottom variability. (2) The development and improvement of inverse techniques for measuring the dynamics and kinematics of meso and finer-scale sound speed structure and ocean currents in coastal regions. (3) The understanding of three-dimensional sound propagation physics including horizontal refraction and azimuthal coupling and the quantification of the importance of these complex physics in the prediction of sound signals transmitted over highly variable littoral regions.

The long-term goals of this research are to investigate the circulation, stratification, and the shelf-slope interactions within Lamon Bay on the eastern margin of the Philippines, marking the birth of the Kuroshio, before its encounter with the Luzon Strait. The specific objectives of the Lamon Bay program are to quantity the spatial and temporal characteristics of the ocean processes governing the stratification and circulation within Lamon Bay, including shelf/slope exchanges and their relationship to the regional marine ecosystem. We also investigate the linkage of Lamon Bay oceanography to the larger scale, such as the development of the Kuroshio. The objectives are attained using the observations obtained during the R/V Revelle May-June 2011 and April-May 2012 research cruises, time series data from moorings spanning the cruises, and satellite-derived data and other observations collected as part of the Origin of the Kuroshio and Mindanao Current (OKMC) program.

The long-term goal is to enhance our understanding of coastal oceanography by means of applying simple dynamical theories to high-quality observations obtained in the field. Objectives: * Conduct a field program in the South China Sea to determine the combined impact of large submarine sand dunes (hereafter dunes) and large amplitude nonlinear internal waves (hereafter waves) on sound transmission over the Chinese continental slope near Taiwan * Determine how the nonlinear internal waves (NLIW) and tides interact with the seafloor to form and maintain the dunes * Study how enhanced bottom roughness in the dune field affects energy dissipation in the NLIWs and tides as they shoal over the upper continental slope.

Our effort seeks to provide a more comprehensive description of the physical and optical roughness of the sea surface. This was achieved through the analysis of our suite of comprehensive sea surface roughness observational measurements within the RADYO field program. These measurements were designed to provide optimal coverage of fundamental optical distortion processes associated with the air-sea interface. In our data analysis, and complementary collaborative effort with RaDyO modelers, we investigated both spectral and phase-resolved perspectives. These will allow refining the representation of surface wave distortion in present air-sea interfacial optical transmission models., The original document contains color images.

Dense shelf waters are formed and spread in the Adriatic Sea during winter periods, which dynamics are usually investigated by means of sea truth campaigns and modeling efforts. The former are either based on observational approaches (moored instruments, CTD, current meters, etc.) or on more innovative techniques, e.g. employing Seismic Oceanography. Recent studies have shown that SO techniques can produce maps of vertical transects along the survey lines with horizontal and vertical resolution of, respectively, 10 and 100 m, suitable to explore the horizontal structures of BBL dynamics. Elaborating on these considerations, a novel approach combining the SO dataset collected during the ADRIASEISMIC cruise and high-resolution numerical model (ROMS) results was performed in two restricted areas of the Adriatic Sea: off the Gargano promontory and off the Bari shelf break. We present the first steps along the definition of a novel methodology. On one hand SO can help to image the existing dynamical structures and their spatial/temporal resolution; on the other, the numerical model can quantify these acoustic snapshots in terms of temperature, salinity and density, integrating the XBTs that are acquired during SO lines, and help identifying the nature of other processes (e.g. turbulence, internal waves, etc.)., The original document contains color images. Presented at the ICA 2013 Meeting on Acoustics, held in Montreal, Quebec, Canada on 2-7 Jun 2013. Published in the Proceedings of Meetings on Acoustics, v19, 2 Jun 2013.

Several acoustic Doppler current profilers and vertical strings of temperature, conductivity, and pressure sensors, deployed on and around the East Flower Garden Bank (EFGB), were used to examine surface wave effects on high-frequency flows over the bank and to quantify spatial and temporal characteristic of these high-frequency flows. The EFGB, about 5-km wide and 10-km long, is located about 180-km southeast of Galveston, Texas, and consists of steep slopes on southern and eastern sides that rise from water depths over 100 m to within 20 m of the surface. Three-dimensional flows with frequencies ranging from 0.2 to 2 cycles per hour (cph) were observed in the mixed layer when wind speed and Stokes drift at the surface were large. These motions were stronger over the bank than outside the perimeter. The squared vertical velocity w2 was strongest near the surface and decayed exponentially with depth, and the e-folding length of w2 was 2 times larger than that of Stokes drift. The 2-h-averaged w2 in the mixed layer, scaled by the squared friction velocity, was largest when the turbulent Langmuir number was less than unity and the mixed layer was shallow. It is suggested that Langmuir circulation is responsible for the generation of vertical flows in the mixed layer, and that the increase in kinetic energy is due to an enhancement of Stokes drift by wave focusing. The lack of agreement with open-ocean Langmuir scaling arguments is likely due to the enhanced kinetic energy by wave focusing., The original document contains color images. Published in the Journal of Physical Oceanography, v43 p1627-1647, Aug 2013. Prepared in cooperation with Coastal Carolina University, Conway, SC and Oregon State University, Corvallis.

Our long-term scientific goals are to understand the dynamics and identify mechanisms of small-scale processes in the ocean with the objective of developing improved parameterizations of mixing for ocean models. Internal tides, inertial waves, nonlinear internal waves (NLIWs), and turbulence mixing are all key components to understanding mixing within the stratified ocean. Each of these factors can lead to uncertainty within current ocean models due to their complex interplay. This study focuses primarily on small-scale processes, internal tides, and also key circulation features including cold dome events localized at the continental slope of the East China Sea (ECS) and intrusions generated as the Kuroshio and barotropic tides interact with the continental shelf of the ECS. These small-scale processes and circulation features modulate the temporal, horizontal, and vertical spatial structures of the water properties of the ocean. These processes may significantly modify acoustic properties and thus introduce uncertainty into sonar performance and acoustic propagation models. Our ultimate goal is to collaborate with acousticians to identify oceanic processes that alter acoustic properties. A detailed understanding of these properties, mechanism, and dynamics will aid in quantification and assessment of uncertainty in acoustic prediction., The original document contains color images.

The objective of this grant is to improve understanding of how the large-amplitude internal waves and tides in the northeastern South China Sea are generated via interaction of the barotropic tide with the ridges and islands in the Luzon Strait. In addition to the problem s inherent scientific interest, understanding the generation problem is essential for developing a forecast model to predict the wave characteristics in the deep basin and on the Chinese continental slope and shelf.

The long-term goal of the research is to increase the physical understanding of acoustic propagation in continental shelf and slope environments in the 50-4000 Hz band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range- and azimuth-dependent littoral waveguides. There were two main objectives of the current research. The first objective was to develop and test a new coupled-mode approach that can serve as the basis for an advanced seabed attenuation analysis of broadband propagation data. The second objective was to apply the coupled mode approach to investigate the physics of scattering from a rough seabed surface., The original document contains color images.

The long-term goal is to understand, parameterize and predict the impact of physical mechanisms on acoustic propagation in the ocean environment. The objective is to numerically investigate the spectral and angular characteristics of acoustic propagation in the vicinity of the shelfbreak due to the presence of the large subaqueous sand dunes on the upper continental slope in the South China Sea (SCS), and in the presence and absence of the episodic trans-basin internal solitary waves (ISW) approaching the shelfbreak.

The long term goals of our shallow water acoustics work are to: 1) understand the nature of low frequency (10-1500 Hz) acoustic propagation, scattering and noise in shallow water when strong oceanic variability is present in the form of fronts, eddies, boundary layers, and internal waves (using the SW06 and QPE data, primarily) and 2) begin planning a 2014-15 bottom acoustics experiment off Texas and a 2016-17 field experiment to look at the complicated boundary between deep and shallow water, i.e. the slope/canyon region. Our primary objectives this year were: 1) to finish publishing our SW06 results in a JASA Special Issue , as well as in other JASA manuscripts, 2) to finish manuscripts on the QPE shallow water acoustics/Uncertainty work, and submit them by the end of 2012 to IEEE JOE for a Special Issue, and 3) begin 2014 (bottom acoustics) and 2016 (shelfbreak, slope and canyon) experimental planning, both on an individual basis, and in conjunction with the whole ocean acoustics community., The original document contains color images.

The long-term goal is to improve accuracy, fidelity, and speed of reverberation models for modeling, simulation, training and sonar system performance predictions. The objective is to achieve more efficient transitions from the 6.1 basic research community to the applied modeling community.

LONG-TERM GOALS: *Improve our understanding of the ocean basins for scientific research and Naval operations. OBJECTIVES: *Improve global marine gravity maps by a factor of 2 in deep ocean areas and a factor of 4 in the Arctic areas and on shallow continental margins. *Use these improved gravity maps along with a global compilation of soundings to refine a 30-arcsecond bathymetry model (SRTM30_PLUS). *Prepare the next generation of scientists for ocean research., The original document contains color images.

Our long term goals are to understand (1) the biological-physical oceanographic characteristics and mechanisms on the shelf near Barrow, AK that together produce a favorable feeding environment for the bowhead whale there and (2) the potential impact of climate change, particularly the ongoing reduction in sea ice and variability in Pacific Water presence near Barrow, on this feeding environment. This region is a critical feeding area for migrating bowhead whales, particularly during the fall migration (e.g., Lowry et al., 2004). Results from biophysical sampling conducted during August-September 2005- 2008 demonstrated that the oceanography of the shelf is complex, dynamic, and highly variable and that advection is closely coupled to the direction and magnitude of the winds. In addition, oceanographic and atmospheric conditions impact the composition, distribution, and availability of plankton prey for the bowhead whale. Assessment and understanding of interannual and longer-term variability in the physical mechanisms influencing ocean conditions and the resulting distribution and abundance of plankton on the shelf are necessary to predict potential impacts of climate change., Prepared in collaboration with the Graduate School of Oceanography, University of Rhode Island, Narragansett, and the Applied Physical Laboratory, University of Washington, Seattle. The original document contains color images.

Our research seeks to determine processes which contribute to the transport of fresh water from the coast to the deep basin of the South China Sea, as well as determine the factors that determine the variability of this transport. We will participate in research cruises in 2013 and 2014 over the continental shelf and slope east of southern Vietnam to measure the distribution and offshore transport of fresh water across the continental shelf and continental slope.

The long term goal is to understand the coupling of bio-optical processes and properties with physical processes in ocean regions of strong physical forcing. Strong physical forcing can include wind forcing, tidal forcing, and significant freshwater buoyancy fluxes. The objectives are to study the dynamics of bio-optical properties in the South China Sea and their response to monsoonal winds, river inputs and topography; link in situ measurements with remote sensing to be able to constrain parameter values and processes using remote observations.

LONG-TERM GOALS: To develop improved predictive capabilities for the distribution of particulate and dissolved materials in the open and the coastal ocean. OBJECTIVES: To study the dynamics of absorbing and scattering materials in the South China Sea and its response to physical forcings, namely the monsoon, river inputs and topography. Link in-situ measurements with remote sensing to be able to constrain parameter values and processes using remote observations.

For this project, we jointly planned and executed a major field program in the East China Sea northeast of Taiwan. We along with our Taiwanese collaborators performed high-resolution hydrographic surveys over the outer continental shelf and upper continental slope during August/September 2009. The field work was in close collaboration with numerical modelers from MIT who were assimilating the high-resolution hydrographic data into their model and producing ocean circulation forecasts including uncertainty forecasts. During the field experiment, we measured a major fresh water pulse from the runoff from Typhoon Morakot, which caused the most typhoon-related rainfall over Taiwan in 50 years. Our results show strong alongshelf gradients of freshwater at the shelfbreak associated with this freshwater pulse. Our data has been used by the modelers to verify the uncertainty forecasts and the predicted error distribution compares very well with the actual error distribution.

Hurricanes are powerful, energetic storms that can be fueled by warm ocean waters, while simultaneously driving transport and mixing under their path. Wind-driven mixing is an important mechanism for generating internal waves, and hurricanes are capable of generating particularly high levels of mixing. The internal waves, in turn, allow diapycnal mixing in the ocean, accelerating heat transfer from the near surface to deeper waters. This plays a role in global thermohaline circulation, which affects heat transfer and density properties throughout the oceans. However, while the importance of internal waves is well established, direct measurements of hurricane-generated internal waves over the shelf and slope regions are scarce. As a result, the mechanisms for the generation of these waves by storms are poorly understood. In this paper, we examine the high frequency response and generation of internal waves by Hurricane Ivan as it travelled over the continental shelf edge and slope in the Gulf of Mexico. Velocity data were collected as part of the Naval Research Laboratory's Shelf Energetics and Exchange Dynamics (SEED) experiment. Moorings consisted of Trawl Resistant Bottom Mounts (TRBMs) in the form of a dome-shaped pod known as a Barny due to its barnacle-like shape. The Barnies housed ADCPs and wave/tide gauges, and during the hurricane were subject to extreme current conditions. In particular, over the shelf where water depths are 60 - 90 meters and surface waves reached significant wave heights of at least 20 meters, bottom currents generated by these waves were over 2 meters s(exp -1). Despite these extreme conditions, which set the nearby National Data Buoy Center buoy 42040 adrift, the Barnies proved themselves to be robust and continued to measure water velocity and pressure both during and after the hurricane's presence in the region., Presented at the Oceans 2011 MTS/IEEE Conference held at the Hilton Waikoloa Village, Kona, Hawaii, on 19-22 September, 2011.

This thesis describes the physics of fully three-dimensional low frequency acoustic interaction with internal waves, bottom sediment waves and surface swell waves that are often observed in shallow waters and on continental slopes. A simple idealized model of the ocean waveguide is used to analytically study the properties of acoustic normal modes and their perturbations due to waves of each type. The combined approach of a semi-quantitative study based on the geometrical acoustics approximation and on fully three-dimensional coupled mode numerical modeling is used to examine the azimuthal dependence of sound wave horizontal reflection from, transmission through and ducting between straight parallel waves of each type. The impact of the natural crossings of nonlinear internal waves on horizontally ducted sound energy is studied theoretically and modeled numerically using a three-dimensional parabolic equation acoustic propagation code. A realistic sea surface elevation is synthesized from the directional spectrum of long swells and used for three-dimensional numerical modeling of acoustic propagation. As a result, considerable normal mode amplitude scintillations were observed and shown to be strongly dependent on horizontal azimuth, range and mode number. Full field numerical modeling of low frequency sound propagation through large sand waves located on a sloped bottom was performed using the high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic ducting is shown to steer acoustic energy beams along the sand wave s curved crests., The original document contains color images.

The objective of this grant is to improve understanding of how the large-amplitude internal waves and tides in the northeastern South China Sea are generated via interaction of the barotropic tide with the ridges and islands in the Luzon Strait. In addition to the problem's inherent scientific interest, understanding the generation problem is essential for developing a forecast model to predict the wave characteristics in the deep basin and on the Chinese continental slope and shelf., The original document contains color images.

The long term goal of our QPE work is to: 1) quantitatively understand what the uncertainties are in low frequency (10-1000 Hz) acoustic propagation and noise that are caused by variable and complex oceanography and seabed structure, 2) determine the limits to predicting the fluctuating and variable propagation and noise in this frequency regime and others, and 3) ascertain what naval advantage may be gained (if any) by understanding the nature of the uncertainty., Code 1 only. The original document contains color images.

The long-term goal is to improve understanding of the generation of nonlinear internal waves by stratified flow over sills (e.g. straits) and shelves. The primary objective will be on connecting the generation process with the dynamics of the disintegration of the radiated internal tide into shorter, nonlinear internal solitary-like waves and to predict the space and time scales for the emergence of waves and their properties (e.g. wave amplitudes, numbers, etc.). A central aspect of this work is to explore the role of rotation in the process. Rotation permits the presence of periodic, nonlinear inertia-gravity waves (i.e., the tide) that can act as attractors and arrest the steepening of the internal tide, and hence affect the production of the shorter solitary-like waves (Gerkema, 1996; Helfrich and Grimshaw, 2008). A second objective is to study the conditions that promote production of modal nonlinear internal waves on continental shelves from internal tidal beams generated at locations of critical slopes on the continental slopes. Again, the role of rotation will be explored.

Our long-term scientific goal is to better understand the mechanisms by which mixing occurs in the ocean so that we can develop improved parameterizations of mixing for ocean models. Mixing within the stratified ocean is our particular focus, as the complex interplay of internal waves from a variety of sources and turbulence makes this a current locus of uncertainty. In this project, our broad focus is on the energy sources of nonlinear internal waves (NLIWs) in a complex environment of strong internal tides and abrupt topography (continental shelf and slope). We expect a rapid evolution of internal tides and NLIWs, and aim to understand their dynamics, energy cascade, and role in mixing. The primary objectives of the project are as follows: (1) to identify the generation sites and understand the generation mechanism of NLIWs, (2) to understand the evolution of NLIW interactions with abrupt topography, (3) to quantify the energy budget and energy cascade from internal tides to NLIWs, and (4) to quantify the seasonal variation of the energy of NLIWs near Dongsha Plateau in the northern South China Sea (SCS). Our particular interest is to understand the energy cascade from barotropic tides, internal tides, and NLIWs to turbulence mixing in the northern SCS, and to understand the evolution of NLIWs interacting with the shoaling continental slope. Our approach is to take direct observations of NLIWs near Dongsha Island, where NLIWs are often captured in satellite images. Primary platforms include an ADV Lagrangian Float; an array of bottom-mounted ADCP moorings; and shipboard EK500, marine radar, ADCP, and CTD. Our main goals are to quantify the energy budget and evolution of NLIWs across the rapidly shoaling continental slope and the gentle plateau near Dongsha Island, and to quantify the seasonal variation of NLIW characteristics.

LONG-TERM GOALS: The goal of this work is to better understand the generation, propagation, modal transformations and interaction of multiple Nonlinear Internal Waves (NLIWs) on the continental slope and shelf using nonhydrostatic models embedded in nested hydrostatic models with realistic forcing and bathymetry. Accuracy will be assessed by hindcasting and forecasting the temperature, salinity and velocity fields for the SCS (South China Sea) north and east of Dongsha island and comparing the results with data from the experiments of this DRI and from the ASIAEX experiment. This work will provide the understanding needed to build an operational system to predict the timing, location and intensity of NLIWs as required for tactical planning. OBJECTIVES: * To identify the mechanisms responsible for the generation, propagation, fission, interaction and modal transformations of NLIWs on the slope and the plateau north and east of Dongsha Island in the SCS. * To hindcast these NLIWs using high resolution nonhydrostatic and hydrostatic numerical models with realistic ocean topography and surface forcing and using open boundary conditions provided by the large scale ocean model. * To determine the space and time scales involved in these processes that influence NLIWs on the continental shelf and slope of the SCS and their relationship to local and remote forcing.

The objective of this grant is to improve understanding of how the large-amplitude internal waves and tides in the northeastern South China Sea are generated via interaction of the barotropic tide with the ridges and islands in the Luzon Strait. In addition to the problem's inherent scientific interest, understanding the generation problem is essential for developing a forecast model to predict the wave characteristics in the deep basin and on the Chinese continental slope and shelf. The approach is to analyze two data sets obtained in the South China Sea in the context of large amplitude, nonlinear internal wave theory. The data sets were obtained during the Windy Islands Soliton Experiment / Variability Around the Northern South China Sea (WISE/VANS) experiment from April 2005 to June 2006 and the Nonlinear Internal Wave Investigation (NLIWI) from April to July 2007. Maximal effort during this work period focused on writing up the WISE/VANS data for publication, with emphasis on the seasonal climatology of wave occurances. We also collaborated frequently with Oliver Fringer and PhD student Zhonghua Zhang at Stanford to understand the SUNTANS numerical model runs.

Deep (~1000 m) currents were observed off California from August 1994 to September 2009 using current meters and RAFOS floats. Current meter data were collected at nine locations for time periods ranging from two months to 76 months. A total of 144 months of float data were collected. Analysis of current meter data included histograms, progressive vector diagrams, stick plots, kinetic energy and rotary spectra, stick plots, means and standard deviations. Float data were analyzed using trajectories and calculating means, standard deviations, and diffusivities. For current meter data, semidiurnal tidal energy dominated the kinetic energy spectrum, anticyclonic rotary motion exceeded cyclonic motion, kinetic energy was typically an order of magnitude greater than for diurnal frequencies, and kinetic energy decreased about an order of magnitude as depth increased by 1000 m. Mean speed for current meter (float) data was 6.1 (4.0) cm/s and alongshore variability exceeded across shore variability. Two floats were entrained in mesoscale eddies, one cyclonic and the other anticyclonic; the eddies moved westward at a speed of about one cm/s. Seasonal variability along the continental slope was marked by late summer or early fall warming; eddy kinetic energy was minimum in February, 3 cubic centimeters per second squared., The original document contains color images.

Recent observations over the Sigsbee Escarpment in the Gulf of Mexico have revealed extremely energetic deep currents (near 1 m/sec), which are trapped along the escarpment. Both scientific interest and engineering needs demand dynamical understanding of these extreme events, and can benefit from a numerical model designed to complement observational and theoretical investigations in this region of complicated topography. The primary objective of this study is to develop a modeling methodology capable of simulating these physical processes and apply the model to the Sigsbee Escarpment region. The very steep slope of the Sigsbee Escarpment (0.05-0.1) limits the application of ocean models with traditional terrain-following (sigma) vertical coordinates. These models may represent the very complicated topography in the region adequately, but they can result in large truncation errors during calculation of the horizontal pressure gradient. A new vertical coordinate system, termed a vanishing quasi-sigma coordinate, is implemented in the Navy Coastal Ocean Model for application to the Sigsbee Escarpment region. Vertical coordinate surfaces for this grid have noticeably gentler slopes than a traditional sigma grid, while still following the terrain near the ocean bottom. The new vertical grid is tested with a suite of numerical experiments and compared to a classical sigma-layer model. The numerical error is substantially reduced in the model with the new vertical grid. A one-year, realistic, numerical simulation is performed to simulate strong, deep currents over the Escarpment using a very-high-resolution nested modeling approach. The model results are analyzed to demonstrate that the deep-ocean currents in the simulation replicate the prominent dynamical features of the observed intense currents in the region., Published in Ocean Modelling, v28, p250-265, 2009. Prepared in collaboration with the Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL and Chevron Energy Technology Co., San Ramon, CA. The original document contains color images. All DTIC reproductions will be in black and white.

We performed a custom climatology of the northern South China Sea, Taiwan Strait, and the Kuroshio east of Taiwan using the historical hydrographic archives of Taiwan. This work was performed jointly with scientists at National Taiwan University. The climatology focuses on the thermohaline and soundspeed fields over the outer shelf and continental slope and are seasonal. Important features which were resolved were the shelfbreak current system in the northern South China Sea, the coastal current passing southward on the western side of Taiwan Strait, and the northward flow of Kuroshio water in Taiwan Strait on the eastern side of the strait. In addition to the climatology, several research cruises were performed examining the stratification over the outer shelf and upper slope and processes occurring where the seasonal pycnocline intersects the bottom over the shelf, and the Kuroshio in Luzon Strait. In collaboration with National Taiwanese University colleagues, a stability analysis of the Kuroshio in Taiwan Strait indicates frontal instability can account for variability observed in a mooring array., The original document contains color images. All DTIC reproductions will be in black and white.

This project, in collaboration with Eric Kunze at the University of Victoria, aimed to increase our understanding of (primarily tidal) internal wave processes and how they affect diapycnal mixing in the coastal ocean, with an eventual goal of improved representation of baroclinic tides and mixing parameterizations in numerical models. Our work is expected to add significantly to the knowledge of the internal wave field, its interactions with topography, and implications for mixing of tracers and momentum. Both the wave field and the topographic interactions are generally not well-represented in numerical models, resulting in a great degree of uncertainty over appropriate mixing coefficients or parameterizations. Our measurements will permit validation of existing parameterizations in a small highly-resolved region, as well as aid in the development of new parameterizations. Our work will continue on our new grant N00014-08-1-0983, "Analysis of Internal Tide Observations from the August 2006 AESOP Experiment.", Prepared in cooperation with the University of Victoria. The original document contains color images. All DTIC reproductions will be in black and white.

Interaction between the Antarctic Circumpolar Current and the continental slope/shelf in the Marguerite Bay and west Antarctic Peninsula is examined as interaction between a wind-driven channel flow and a zonally uniform slope with a bay-shaped shelf to the south. Two control mechanisms, eddy advection and propagation of topographic waves, are found important for eddy topography interactions. The topographic waves become more nonlinear near the western (eastern if in the Northern Hemisphere) boundary of the bay, inducing strong cross-escarpment motions. A two-layer wind-driven channel flow spontaneously generates eddies through baroclinic instability. A PV front forms in the first layer shoreward of the base of the topography due to the lower-layer eddy-slope interactions. Both the cross-slope-edge transport and the out-of-bay transport are comparable with the model Ekman transport, suggesting the significance of the examined mechanism. The wave-boundary interaction is essential for the out-of-bay transport. Much more water is transported out of the bay from the west, and the southeastern area is the most isolated region. These results suggest that the southeastern region of the Marguerite Bay is a retention area for Antarctic krill., Prepared in cooperation with Massachusetts Institute of Technology, Cambridge, MA. The original document contains color images.

Current velocity from moored arrays of acoustic Doppler current profilers (ADCPs) deployed on the outer shelf and slope, south of Mobile Bay in the northeastern Gulf of Mexico, shows evidence of alongslope, generally westward-propagating subinertial baroclinic Kelvin waves with periods of about 16 and 21 days, amplitudes of 5-10 cm/sec, and wavelengths of about 500 km. The observed waves were highly coherent over the slope between about 200 and 500 meters and accounted for a significant amount of the current variability below 200 meters. The source of the waves could be attributed to effects of the Loop Current on the west Florida slope, but is more likely due to direct forcing by Loop Current-generated eddies impacting the experimental area., Published in the Journal of Physical Oceanography, v39, p1475-1485, Jun 2009. Prepared in collaboration with Planning Systems Inc., Slidell, LA. The original document contains color images. All DTIC reproductions will be in black and white.

This project seeks to quantify and better define the dynamics of those processes, including mixing, tides, current-topography interactions and nonlinear equation of state phenomena, that impact vertical transports of heat and mass in the Southern Ocean. These transports are crucial to the formation of Antarctic Bottom Water (AABW) and are integral to the Southern Ocean branch of the meridional overturning circulation (MOC). Improved understanding of the related processes will enhance our ability to predict climate-related changes in the MOC., The original document contains color images.

Our goal is to understand mixing in shallow water, i.e., the upper 500 to 1000 m, by observing it in relation to the larger-scale processes producing it. Regimes of interest include open-ocean fronts, continental slopes and shelves, ridges and canyons.

Eddy-topography (ET) interactions are important in determining the path and evolution of oceanic eddies, including Loop Current Eddies (LCE) in the Gulf of Mexico (GOM). We use the Hybrid Coordinate Ocean Model and satellite altimetry data to investigate the ET interactions and the impact on LCE pathway evolution in the GOM. Satellite altimetry reveals that LCEs translate dominantly westward in the central GOM and strongly collide and reflect against topography near the continental slope in the northern and western GOM. The result is the frequent generation of an anticyclone-cyclone (AC) pair in conjunction with the LCEs. In the absence of lateral or surface boundary forcing but including realistic topography, simulations initialized with idealized eddies at various locations in the GOM reveal the following results. Southward eddy reflection from the northern slope occurs when a cyclone drastically strengthens east of the anticyclone because of the ET collision. The prevailing westward propagation in the central GOM occurs because the cyclone is very dispersive toward nearby topographic features, causing a reduced southward component of drift and/or moves to the south, forming a meridional AC pair, causing an enhanced westward component. ET collision is strongest over the northwestern slope (north of 24N) because of the eddy colliding relatively normal to the steep slope, and the eddy typically tracks anticyclonic pathways during the collision/reflection process. Along the western slope, a strong ET collision produces a southeastward reflection, and the accompanying cyclone to the northeast strongly enhances the reflection. Near the southern GOM slope, eddy pathways tend to propagate alongslope with an onshore-offshore oscillatory trajectory because of the competition between topographic and planetary Beta effects., Published in Journal of Geophysical Research, v113, article C12026, 2008.

The aim of this project was to generate data to identify the forces and motions on a ship model while positioned in breaking surf. The two types of breaking waves analyzed were plunging and spilling waves. A 140 feet long model test basin at the Naval Surface Warfare Center Carderock Division (NSWCCD) was used to create the waves with a flap wave maker and the heave motions, pitch motions, and surge forces found acting on the model were measured. To create a breaking wave, a beach was built to represent an actual beach slope and continental shelf slope. The ship model tested is similar to landing craft that operate in the surf zone: broad beam and shallow draft. All data will be utilized in a Master's thesis where it will be thoroughly analyzed and used to create a transfer function that will help predict ship motions and forces in actual seaways.

The evolution of anticyclonic vortices in the presence of topographic effects associated with continental slope steepness and orientation is investigated using the Hybrid Coordinate Ocean Model. The trajectories of the vortices are analyzed using various configurations of slope steepness and orientation, including a flat bottom. As the steepness of the slope is increased, the development and evolution of a counter-rotating subsurface vortex (`deep cyclone') is strongly dispersive resulting in strong zonal translation over the slope, although the translation is southwest with a coherent deep cyclone, in the flat bottom case. In particular, the zonal translation is faster with a gentle slope (relative to the flat bottom case) due to an upslope tilt of the deep cyclone. As the surface vortex collides with the steep topography, the deflection angle increases as the slope increases (i.e. it deflects along slope) at the same time the bottom vorticity peaks. generating a `collision' cyclone and a slope jet south of the vortex-slope impact. In the realistic steep slope case, along slope translation is dominant when the vortex departs over/near the slope, although the vortex strongly collides with (and rapidly crosses) the slope if it has strong westward inertia. During the cross-slope translation, vorticity restoration by vortex compression occurs with relatively small poleward translation. At the point of maximum bottom vorticity, rapid vortex erosion occurs horizontally and vertically and southwestward translation is restored. Comparison of vortex translation over four different slope orientations suggests that the vortex is strongly affected by the location of adjacent cyclones which tend to propagate onshore and poleward simultaneously, and that the combined planetary and topographic Beta-effect slows the vortex translation on the northern slope., The original document contains color images. All DTIC reproductions will be in black and white. Published in Jnl. of Continental Shelf Research, v28 p1246-1260, 2008. Sponsored in part by the Office of Naval Research (ONR).

The Polar Ice Prediction System (PIPS) Version 3.0 is a dynamic sea-ice model that forecasts conditions in all sea-ice covered areas in the northern hemisphere (down to 30 degrees north in latitude). It has a horizontal resolution of approximately 9 km. The vertical resolution in the model has been set at 45 levels so that Arctic shelves, continental slopes, and submarine ridges are accurately represented. Currently, the domain includes the Irminger, Labrador, North, and Baltic Seas on the Atlantic side and the Bering Sea, Sea of Japan, and the Sea of Okhotsk on the Pacific. The PIPS 3.0 system is based on the Los Alamos ice model and coupled (via file transfer) to the operational, global Navy Coastal Ocean Model (gNCOM). The system forecasts daily ice thickness, concentration, and drift in the Artic Ocean. This report documents the matematical formulations, flow charts, and descriptions of the programs and subroutines., Prepared in collaboration with Planning Systems, Inc., Stennis Space Center, MS.