Trowbridge John H.

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Trowbridge

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John H.

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The influence of stratification and nonlocal turbulent production on estuarine turbulence : an assessment of turbulence closure with field observations

(American Meteorological Society, 2011-01) Scully, Malcolm E. ; Geyer, W. Rockwell ; Trowbridge, John H.

Field observations of turbulent kinetic energy (TKE), dissipation rate ε, and turbulent length scale demonstrate the impact of both density stratification and nonlocal turbulent production on turbulent momentum flux. The data were collected in a highly stratified salt wedge estuary using the Mobile Array for Sensing Turbulence (MAST). Estimates of the dominant length scale of turbulent motions obtained from the vertical velocity spectra provide field confirmation of the theoretical limitation imposed by either the distance to the boundary or the Ozmidov scale, whichever is smaller. Under boundary-limited conditions, anisotropy generally increases with increasing shear and decreased distance to the boundary. Under Ozmidov-limited conditions, anisotropy increases rapidly when the gradient Richardson number exceeds 0.25. Both boundary-limited and Ozmidov-limited conditions demonstrate significant deviations from a local production–dissipation balance that are largely consistent with simple scaling relationships for the vertical divergence in TKE flux. Both the impact of stratification and deviation from equilibrium turbulence observed in the data are largely consistent with commonly used turbulence closure models that employ “nonequilibrium” stability functions. The data compare most favorably with the nonequilibrium version of the L. H. Kantha and C. A. Clayson stability functions. Not only is this approach more consistent with the observed critical gradient Richardson number of 0.25, but it also accounts for the large deviations from equilibrium turbulence in a manner consistent with the observations.
The 17-meter flume at the Coastal Research Laboratory. Part II, Flow characteristics : technical report

(Woods Hole Oceanographic Institution, 1989-05) Trowbridge, John H. ; Geyer, W. Rockwell ; Butman, Cheryl Ann ; Chapman, Robert J.

This report summarizes the characteristics of the idealized one-dimensional turbulent channel flow for which the 17-Meter Flume was designed, and describes a measurement program designed to determine whether the flume can in fact produce such a flow. The measured quantities include mean velocities, Reynolds stresses, turbulence intensities and velocity spectra. Measured profiles of mean velocity, Reynolds stress and turbulence intensity are consistent with previous theoretical and empirical results. Measured spectra, although consistent with expectations over a wide range of frequencies, indicate a few unexpected features, including a constant spectral density at high frequencies (possibly due to aliasing or high-frequency noise) , motion at a few well-defined high frequencies of order 10 hz (possibly due to structual vibrations), oscillations with time scales of order 30 s (possibly due to low-mode standing surface waves) and irregular motions with time scales of several minutes (possibly due to fluctuations in pump performance) . The unexpected features indicated by the spectra at high and low frequencies do not have a significant effect on mean velocities and low-order statistics, but they may be important in some applications.
Measurements of momentum and heat transfer across the air–sea interface

(American Meteorological Society, 2008-05) Gerbi, Gregory P. ; Trowbridge, John H. ; Edson, James B. ; Plueddemann, Albert J. ; Terray, Eugene A. ; Fredericks, Janet J.

This study makes direct measurements of turbulent fluxes in the mixed layer in order to close heat and momentum budgets across the air–sea interface and to assess the ability of rigid-boundary turbulence models to predict mean vertical gradients beneath the ocean’s wavy surface. Observations were made at 20 Hz at nominal depths of 2.2 and 1.7 m in 16 m of water. A new method is developed to estimate the fluxes and the length scales of dominant flux-carrying eddies from cospectra at frequencies below the wave band. The results are compared to independent estimates of those quantities, with good agreement between the two sets of estimates. The observed temperature gradients were smaller than predicted by standard rigid-boundary closure models, consistent with the suggestion that wave breaking and Langmuir circulation increase turbulent diffusivity in the upper ocean. Similarly, the Monin–Obukhov stability function ϕh was smaller in the authors’ measurements than the stability functions used in rigid-boundary applications of the Monin–Obukhov similarity theory. The dominant horizontal length scales of flux-carrying turbulent eddies were found to be consistent with observations in the bottom boundary layer of the atmosphere and from laboratory experiments in three ways: 1) in statically unstable conditions, the eddy sizes scaled linearly with distance to the boundary; 2) in statically stable conditions, length scales decreased with increasing downward buoyancy flux; and 3) downwind length scales were larger than crosswind length scales.
Martha's Vineyard Coastal Observatory 2021

(Woods Hole Oceanographic Institution, 2022-06-24) Cinquino, Eve ; Batchelder, Sidney ; Fredericks, Janet J. ; Sisson, John D. ; Faluotico, Stephen M. ; Popenoe, Hugh ; Sandwith, Zoe O. ; Crockford, E. Taylor ; Peacock, Emily E. ; Shalapyonok, Alexi ; Sosik, Heidi M. ; Kirincich, Anthony R. ; Edson, James B. ; Trowbridge, John H.

Martha's Vineyard Coastal Observatory (MVCO) is a leading research and engineering facility operated by Woods Hole Oceanographic Institution. MVCO has been collecting ocean and atmospheric data at 3 sites on and near Martha's Vineyard since 2001. A meteorological mast (met mast) on South Beach in Edgartown, MA has collected atmospheric data since May 31 2001. An Air Sea Interaction Tower (ASIT) has been collecting atmospheric and subsurface oceanic data since August 5, 2004. A seafloor node (12m node) has been collecting oceanic data from the seafloor since June 14, 2001. This dataset encompasses the core data (wind speed and direction, air pressure, temperature and relative humidity, water temperature and salinity, and wave data) that has been collected during this period. To learn more about the facility and see additional data collected during short term deployments, visit the MVCO Website (https://mvco.whoi.edu/).
Rapid mixed layer depening by the combination of Langmuir and shear instabilities : a case study

(American Meteorological Society, 2010-11) Kukulka, Tobias ; Plueddemann, Albert J. ; Trowbridge, John H. ; Sullivan, Peter P.

Langmuir circulation (LC) is a turbulent upper-ocean process driven by wind and surface waves that contributes significantly to the transport of momentum, heat, and mass in the oceanic surface layer. The authors have previously performed a direct comparison of large-eddy simulations and observations of the upper-ocean response to a wind event with rapid mixed layer deepening. The evolution of simulated crosswind velocity variance and spatial scales, as well as mixed layer deepening, was only consistent with observations if LC effects are included in the model. Based on an analysis of these validated simulations, in this study the fundamental differences in mixing between purely shear-driven turbulence and turbulence with LC are identified. In the former case, turbulent kinetic energy (TKE) production due to shear instabilities is largest near the surface, gradually decreasing to zero near the base of the mixed layer. This stands in contrast to the LC case in which at middepth range TKE production can be dominated by Stokes drift shear. Furthermore, the Eulerian mean vertical shear peaks near the base of the mixed layer so that TKE production by mean shear flow is elevated there. LC transports horizontal momentum efficiently downward leading to an along-wind velocity jet below LC downwelling regions at the base of the mixed layer. Locally enhanced vertical shear instabilities as a result of this jet efficiently erode the thermocline. In turn, enhanced breaking internal waves inject cold deep water into the mixed layer, where LC currents transport temperature perturbation advectively. Thus, LC and locally generated shear instabilities work intimately together to facilitate strongly the mixed layer deepening process.
Significance of Langmuir circulation in upper ocean mixing : comparison of observations and simulations

(American Geophysical Union, 2009-05-28) Kukulka, Tobias ; Plueddemann, Albert J. ; Trowbridge, John H. ; Sullivan, Peter P.

Representing upper ocean turbulence accurately in models remains a great challenge for improving weather and climate projections. Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. We present a direct comparison between observations and large eddy simulations, based on the wave-averaged Navier-Stokes equation, of an LC growth event. The evolution of cross-wind velocity variance and spatial scales, as well as mixed layer deepening are only consistent with simulations if LC effects are included in the model. Our results offer a validation of the large eddy simulation approach to understanding LC dynamics, and demonstrate the importance of LC in ocean surface layer mixing.
Turbulence-plankton interactions : a new cartoon

( 2009-02-11) Jumars, Peter A. ; Trowbridge, John H. ; Boss, Emmanuel S. ; Karp-Boss, Lee

Climate change will alter turbulence intensity, motivating greater attention to mechanisms of turbulence effects on organisms. Many analytic and analog models used to simulate and assess effects of turbulence on plankton rely on a one-dimensional simplification of the dissipative scales of turbulence, i.e., simple, steady, uniaxial shears, as produced in Couette vessels. There shear rates are constant and spatially uniform, and hence so is vorticity. Studies in such Couette flows have greatly informed, spotlighting stable orientations of nonspherical particles and predictable, periodic, rotational motions of steadily sheared particles in Jeffery orbits that steepen concentration gradients around nutrient-absorbing phytoplankton and other chemically (re)active particles. Over the last decade, however, turbulence research within fluid dynamics has focused on the structure of dissipative vortices in space and time and on spatially and temporally varying 2 vorticity fields in particular. Because steadily and spatially uniformly sheared flows are exceptional, so therefore are stable orientations for particles in turbulent flows. Vorticity gradients, finite net diffusion of vorticity and small radii of curvature of streamlines are ubiquitous features of turbulent vortices at dissipation scales that are explicitly excluded from simple, steady Couette flows. All of these flow components contribute instabilities that cause rotational motions of particles and so are important to simulate in future laboratory devices designed to assess effects of turbulence on nutrient uptake, particle coagulation and predatorprey encounter in the plankton. The Burgers vortex retains these signature features of turbulence and provides a simplified “cartoon” of vortex structure and dynamics that nevertheless obeys the Navier-Stokes equations. Moreover, this idealization closely resembles many dissipative vortices observed in both the laboratory and the field as well as in direct numerical simulations of turbulence. It is simple enough to allow both simulation in numerical models and fabrication of analog devices that selectively reproduce its features. Exercise of such numerical and analog models promises additional insights into mechanisms of turbulence effects on passive trajectories and local accumulations of both living and nonliving particles, into solute exchange with living and nonliving particles and into more subtle influences on sensory processes and swimming trajectories of plankton, including demersal organisms and settling larvae in turbulent bottom boundary layers. The literature on biological consequences of vortical turbulence has focused primarily on the smallest, Kolmogorov-scale vortices of length scale η. Theoretical dissipation spectra and direct numerical simulation, however, indicate that typical dissipative vortices with radii of 7η to 8η, peak azimuthal speeds of order 1 cm s-1 and lifetimes of order 10 s as a minimum (and much longer for moderate pelagic turbulence intensities) deserve new attention in studies of biological effects of turbulence.
Martha’s Vineyard Coastal Observatory

(Woods Hole Oceanographic Institution, 2021-10-15) Cinquino, Eve ; Batchelder, Sidney ; Fredericks, Janet J. ; Sisson, John D. ; Faluotico, Stephen M. ; Popenoe, Hugh ; Sandwith, Zoe O. ; Crockford, E. Taylor ; Peacock, Emily E. ; Shalapyonok, Alexi ; Sosik, Heidi M. ; Kirincich, Anthony R. ; Edson, James B. ; Trowbridge, John H.

Martha's Vineyard Coastal Observatory (MVCO) is a leading research and engineering facility operated by Woods Hole Oceanographic Institution. MVCO has been collecting ocean and atmospheric data at 3 sites on and near Martha's Vineyard since 2001. A meteorological mast (met mast) on South Beach in Edgartown, MA has collected atmospheric data since May 31 2001. An Air Sea Interaction Tower (ASIT) has been collecting atmospheric and subsurface oceanic data since August 5, 2004. A seafloor node (12m node) has been collecting oceanic data from the seafloor since June 14, 2001. This dataset encompasses the core data (wind speed and direction, air pressure, temperature and relative humidity, water temperature and salinity, and wave data) that has been collected during this period. To learn more about the facility and see additional data collected during short term deployments, visit the MVCO Website (https://mvco.whoi.edu/).
The Ocean Observatories Initiative

(Frontiers Media, 2019-03-04) Trowbridge, John H. ; Weller, Robert A. ; Kelley, Deborah S. ; Dever, Edward P. ; Plueddemann, Albert J. ; Barth, John A. ; Kawka, Orest

The Ocean Observatories Initiative (OOI) is an integrated network that enables scientific investigation of interlinked physical, chemical, biological and geological processes throughout the global ocean. With near real-time data delivery via a common Cyberinfrastructure, the OOI instruments two contrasting ocean systems at three scales. The Regional Cabled Array instruments a tectonic plate and overlying ocean in the northeast Pacific, providing a permanent electro-optical cable connecting multiple seafloor nodes that provide high power and bandwidth to seafloor sensors and moorings with instrumented wire crawlers, all with speed-of-light interactive capabilities. Coastal arrays include the Pioneer Array, a relocatable system currently quantifying the New England shelf-break front, and the Endurance Array, a fixed system off Washington and Oregon with connections to the Regional Cabled Array. The Global Arrays host deep-ocean moorings and gliders to provide interdisciplinary measurements of the water column, mesoscale variability, and air-sea fluxes at critical high latitude locations. The OOI has unique aspects relevant to the international ocean observing community. The OOI uses common sensor types, verification protocols, and data formats across multiple platform types in diverse oceanographic regimes. OOI observing is sustained, with initial deployment in 2013 and 25 years of operation planned. The OOI is distributed among sites selected for scientific relevance based on community input and linked by important oceanographic processes. Scientific highlights include real-time observations of a submarine volcanic eruption, time-series observations of methane bubble plumes from Southern Hydrate Ridge off Oregon, observations of anomalous low-salinity pulses off Oregon, discovery of new mechanisms for intrusions of the Gulf Stream onto the shelf in the Middle Atlantic Bight, documentation of deep winter convection in the Irminger Sea, and observations of extreme surface forcing at the most southerly surface mooring in the world ocean.
Fluid mechanical measurements within the boundary layer over the northern California Continental Shelf during STRESS

(Woods Hole Oceanographic Institution, 1993-09) Fredericks, Janet J. ; Trowbridge, John H. ; Williams, Albert J. ; Lentz, Steven J. ; Butman, Bradford ; Gross, Thomas F.

In studying the processes controlling particle distrbution of fine sediments over the continental shelf, the height, structure and dynamics of the bottom boundary layer must be better understood. The Sediment Transport Events on Shelves and Slopes (STRESS) program provides a comprehensive set of data over the bottom half of the water column at the 90m and the 130m isobaths along the northern California continental shelf during the winters of 1988-89 and 1990-91. This report presents the STRESS salinity, temperature, velocity, wave characteristics and attenuation data. The report describes the processing, provides plots and tables of the data and corresponding statistics for evaluation of the data, and documents the data fies. The combined set of moored and tripod mounted instrument measurements provides integrated, hourly-averaged profiles of the lower half of the water column at the four sites which can be used for analysis and modeling purposes.
Dynamic response of electromagnetic current meters

(Woods Hole Oceanographic Institution, 1984-05) Aubrey, David G. ; Spencer, Wayne D. ; Trowbridge, John H.

The dynamic response of electromagnetic current meters (manufactured by Marsh-McBirney, Inc.) has been clarified through a comprehensive laboratory measurement program combined with a thorough literature review. Elucidation of the behavior of these flowmeters under a variety of dynamic conditions has been neglected in the past. Since flow past a spherical body has considerable hydrodynamic complexity for different dynamic conditions, a careful laboratory study was carried out for pure steady, pure oscillatory (horizontal plane), and combined steady/oscillatory conditions at two test facilities. Test results indicate that flowmeter behavior under pure steady flow is excellent in the absence of high levels of free-stream turbulence, with an r.m.s. error of 1-5 cm/sec. These errors could· be reduced with a higher-order polynomial regression fit. Pure oscillatory response was also excellent, with r.m.s. errors of 1-2 cm/sec, and sensitivity which is correlated with the oscillatory Reynolds number, (Re)o, and the Keulegan-Carpenter number, (A/d). Combined steady/oscillatory flows degraded current meter performance with larger residual errors (1-6 em/sec) and significant differences in sensitivity (up to 20°/o). Horizontal cosine response showed systematic deviations from pure cosine behavior, with a notable inter-cardinal undersensitivity and cosine "shoulder" at lower Reynolds numbers. Error analysis shows these current sensors are adequate for many kinematic measurements, but may lead to excessive errors when using velocity to calculate dynamical quantities (such as bottom friction, Reynolds Stress, or log-layer friction velocities). A careful error analysis must precede any use of these meters for estimating dynamical quantities. These studies pointed out a potential difficulty in using these meters in areas of large ambient turbulence levels (20°/o turbulent intensities), which are characteristic of many near-bottom shallow water environments. Further study is needed to clarify this behavior.
Observations of the transfer of energy and momentum to the oceanic surface boundary layer beneath breaking waves

(American Meteorological Society, 2016-06-02) Scully, Malcolm E. ; Trowbridge, John H. ; Fisher, Alexander W.

Measurements just beneath the ocean surface demonstrate that the primary mechanism by which energy from breaking waves is transmitted into the water column is through the work done by the covariance of turbulent pressure and velocity fluctuations. The convergence in the vertical transport of turbulent kinetic energy (TKE) balances the dissipation rate of TKE at first order and is nearly an order of magnitude greater than the sum of the integrated Eulerian and Stokes shear production. The measured TKE transport is consistent with a simple conceptual model that assumes roughly half of the surface flux of TKE by wave breaking is transmitted to depths greater than the significant wave height. During conditions when breaking waves are inferred, the direction of momentum flux is more aligned with the direction of wave propagation than with the wind direction. Both the energy and momentum fluxes occur at frequencies much lower than the wave band, consistent with the time scales associated with wave breaking. The largest instantaneous values of momentum flux are associated with strong downward vertical velocity perturbations, in contrast to the pressure work, which is associated with strong drops in pressure and upward vertical velocity perturbations.
Vorticity measurements within the bottom boundary layer in the Strait of Juan De Fuca

(Woods Hole Oceanographic Institution, 1998-07) Fredericks, Janet J. ; Trowbridge, John H. ; Williams, Albert J.

Electromagnetic fluctuations and turbulent vorticity fluctuations were measured over a nine month period in the strong tidal flows of the Strait of Juan De Fuca off the coast of the Olympic Peninsula of Washington. A collaborative experiment was designed to test the hypothesis that electromagnetic fluctuations at the sea floor are forced by turbulent vorticity fluctuations in the bottom boundary layer. This report describes the measurement of turbulent vorticity fluctuations and the associated analysis which focuses on testing existing theoretical predictions for the inertial subrange and on characterizing spectra at frequencies below the inertial subrange.
The cospectrum of stress-carrying turbulence in the presence of surface gravity waves

(American Meteorological Society, 2017-12-28) Trowbridge, John H. ; Scully, Malcolm E. ; Sherwood, Christopher R.

The cospectrum of the horizontal and vertical turbulent velocity fluctuations, an essential tool for understanding measurements of the turbulent Reynolds shear stress, often departs in the ocean from the shape that has been established in the atmospheric surface layer. Here, we test the hypothesis that this departure is caused by advection of standard boundary layer turbulence by the random oscillatory velocities produced by surface gravity waves. The test is based on a model with two elements. The first is a representation of the spatial structure of the turbulence, guided by rapid distortion theory, and consistent with the one-dimensional cospectra that have been measured in the atmosphere. The second model element is a map of the spatial structure of the turbulence to the temporal fluctuations measured at fixed sensors, assuming advection of frozen turbulence by the velocities associated with surface waves. The model is adapted to removal of the wave velocities from the turbulent fluctuations using spatial filtering. The model is tested against previously published laboratory measurements under wave-free conditions and two new sets of measurements near the seafloor in the coastal ocean in the presence of waves. Although quantitative discrepancies exist, the model captures the dominant features of the laboratory and field measurements, suggesting that the underlying model physics are sound.
The effect of wave breaking on surf-zone turbulence and alongshore currents : a modeling study

(American Meteorological Society, 2005-11) Feddersen, Falk ; Trowbridge, John H.

The effect of breaking-wave-generated turbulence on the mean circulation, turbulence, and bottom stress in the surf zone is poorly understood. A one-dimensional vertical coupled turbulence (k–ε) and mean-flow model is developed that incorporates the effect of wave breaking with a time-dependent surface turbulence flux and uses existing (published) model closures. No model parameters are tuned to optimize model–data agreement. The model qualitatively reproduces the mean dissipation and production during the most energetic breaking-wave conditions in 4.5-m water depth off of a sandy beach and slightly underpredicts the mean alongshore current. By modeling a cross-shore transect case example from the Duck94 field experiment, the observed surf-zone dissipation depth scaling and the observed mean alongshore current (although slightly underpredicted) are generally reproduced. Wave breaking significantly reduces the modeled vertical shear, suggesting that surf-zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations. Model-inferred drag coefficients follow parameterizations (Manning–Strickler) that depend on the bed roughness and inversely on the water depth, although the inverse depth dependence is likely a proxy for some other effect such as wave breaking. Variations in the bed roughness and the percentage of breaking-wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient. However, covarying the wave height, forcing, and dissipation and bed roughness separately results in an alongshore current (drag coefficient) only weakly (strongly) dependent on the bed roughness because of the competing effects of increased turbulence, wave forcing, and orbital wave velocities.
Asymmetric tidal mixing due to the horizontal density gradient

(American Meteorological Society, 2008-02) Li, Ming ; Trowbridge, John H. ; Geyer, W. Rockwell

Stratification and turbulent mixing exhibit a flood–ebb tidal asymmetry in estuaries and continental shelf regions affected by horizontal density gradients. The authors use a large-eddy simulation (LES) model to investigate the penetration of a tidally driven bottom boundary layer into stratified water in the presence of a horizontal density gradient. Turbulence in the bottom boundary layer is driven by bottom stress during flood tides, with low-gradient (Ri) and flux (Rf) Richardson numbers, but by localized shear during ebb tides, with Ri = ¼ and Rf = 0.2 in the upper half of the boundary layer. If the water column is unstratified initially, the LES model reproduces periodic stratification associated with tidal straining. The model results show that the energetics criterion based on the competition between tidal straining and tidal stirring provides a good prediction for the onset of periodic stratification, but the tidally averaged horizontal Richardson number Rix has a threshold value of about 0.2, which is lower than the 3 suggested in a recent study. Although the tidal straining leads to negative buoyancy flux on flood tides, the authors find that for typical values of the horizontal density gradient and tidal currents in estuaries and shelf regions, buoyancy production is much smaller than shear production in generating turbulent kinetic energy.
Turbulence in the shallow nearshore environment during SANDYDUCK '97

(Woods Hole Oceanographic Institution, 2001-02) Fredericks, Janet J. ; Trowbridge, John H. ; Voulgaris, George

An array of five acoustic Doppler velocimeters (ADV), which produce high quality measurements of the three-dimensional velocity vector in a sample volume with a scale of one centimeter, was deployed from late August through late November of 1997 at a water depth of approximately 4.5 m off Duck, North Carolina. The sensors were deployed near the sea floor but above the centimeters-thick wave boundary layer, and the sampling scheme was designed to resolve turbulence statistics averaged over tens of minutes, much longer than typical wave periods but shorter than time scales associated with variablity of energetic wind-driven and wave-driven alongshore flows.
Turbulence in the coastal environment during HYCODE

(Woods Hole Oceanographic Institution, 2004-03) Fredericks, Janet J. ; Trowbridge, John H.

A tall tripod equipped with two acoustic Doppler velocimeters (ADVs) was deployed at a water depth of 15 m off the coast of New Jersey near the LEO-15 site. Sensors were co-located near the bottom to provide good estimates of Reynolds stress. Thermistors were located within several centimeters of the velocity sample volume to provide simultaneously sampled estimates of turbulent temperature variance and vertical temperature flux. One of the ADVs was equipped with a pressure and a temperature sensor. A wave/tide gauge was placed at 4 meters above bottom. The instruments were deployed late July through early December of 2000 and late June through early August of 2001. For the 2001 deployment, a single beam acoustic Doppler velocity sensor (DopBeam) was added to measure high frequency vertical velocity variance and echo intensity within the bottom boundary layer. A second tripod was deployed nearby and was equipped with an array of LISST sensors and an MSCAT. The purpose of this report is to document the instrumentation and deployment of the tripods and to document the tall tripod data by providing a description of the processing and data formats, time-series summaries of the burst averaged data along with preliminary analyses.
At Sea Test 2 recovery cruise : Cruise 206 on board R/V Knorr April 10 - 15, 2012 Woods Hole - Woods Hole, MA

(Woods Hole Oceanographic Institution, 2012-06) Weller, Robert A. ; Lund, John M. ; O’Brien, Jeff ; Kemp, John N. ; Kostel, Ken ; Waldorf, Walt ; Holm, Chris ; Risien, Craig ; Matthewson, Michael ; Trowbridge, John H.

The R/V Knorr, on Cruise 206, carried out the recovery of three moorings for the Coastal and Global Scale Nodes (CGSN) Implementing Organization of the NSF Ocean Observatories Initiative. These three moorings are prototypes of the moorings to be used by CGSN at the Pioneer, Endurance, and Global Arrays. Knorr departed from Woods Hole, Massachusetts on April 10, 2012 and steamed south to the location of the mooring deployments on the shelf break. Over five days, April 10-15, Knorr surveyed the bottom at the planned mooring sites, recovered the moorings, and carried out preliminary investigations of mechanical and electrical functionality on the recovered moorings and mooring hardware, including observations of biofouling and corrosion. Knorr returned to Woods Hole on April 15, 2012.
The influence of crosswind tidal currents on Langmuir circulation in a shallow ocean

(American Geophysical Union, 2011-08-04) Kukulka, Tobias ; Plueddemann, Albert J. ; Trowbridge, John H. ; Sullivan, Peter P.

Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. On the coastal shelves the largest-scale LC span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing. Observations and large eddy simulations (LES) of a shallow coastal ocean demonstrate that these relatively large scale Langmuir cells are strongly influenced by crosswind tidal currents. Two mechanisms by which crosswind tidal shear may distort and disrupt Langmuir cells are proposed. The first mechanism involves cell shearing due to differential advection across the whole cell. For the second mechanism, middepth vertical LC currents advect sheared mean crosswind current, leading to the attraction of upwelling and downwelling regions, so that LC cells are unsustainable when both regions overlap. Scaling arguments indicate that LC cells are more susceptible to crosswind shear distortion for smaller LC surface velocity convergence and greater cell aspect ratio (vertical to horizontal LC scale), which is consistent with the results obtained from the observations and LES. These results imply that scaling of LC characteristics in a coastal ocean differs from that in the open ocean, which has important practical implications for parameterizing enhanced mixing due to LC.

Trowbridge John H.

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