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- Title
- Global Observations Of Horizontal Mixing From Argo Float And Surface Drifter Trajectories.
- Creator
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Roach, Christopher J., Balwada, Dhruv, Speer, Kevin
- Abstract/Description
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Mixing by mesoscale eddies in the ocean plays a major role in setting the distribution of oceanic tracers, with important implications for physical and biochemical systems at local to global scales. Roach et al. (2016; https://doi.org/10.1002/2015JC011440) demonstrated that a two-particle analysis of Argo trajectories produces robust estimates of horizontal mixing in the Southern Ocean. Here we extend this analysis to produce global 1 degrees x1 degrees maps of eddy diffusivity at the nominal...
Show moreMixing by mesoscale eddies in the ocean plays a major role in setting the distribution of oceanic tracers, with important implications for physical and biochemical systems at local to global scales. Roach et al. (2016; https://doi.org/10.1002/2015JC011440) demonstrated that a two-particle analysis of Argo trajectories produces robust estimates of horizontal mixing in the Southern Ocean. Here we extend this analysis to produce global 1 degrees x1 degrees maps of eddy diffusivity at the nominal Argo parking depth of 1,000 m. We also applied this methodology to estimate surface eddy diffusivities from Global Drifter Program (GDP) surface drifters. The global mean eddy diffusivity was 543 +/- 155 m(2)/s at 1,000m and 2637 +/- 311 m(2)/s at the surface, with elevated diffusivities in regions of enhanced eddy kinetic energy, such as western boundary currents and along the Antarctic Circumpolar Current. The eddy kinetic energy at the equator is high at both the surface and depth, but the eddy diffusivity is only enhanced near the surface. At depth the eddy diffusivity is strongly suppressed due to the presence of mean flow. We used our observational estimates to test the validity of an eddy diffusivity parameterization that accounts for mixing suppression in the presence of zonal mean flows. Our results indicated that this parameterization generally agrees with the directly observed eddy diffusivities in the midlatitude and high-latitude oceans.
Show less - Date Issued
- 2018-07-01
- Identifier
- FSU_libsubv1_wos_000441888200008, 10.1029/2018JC013750
- Format
- Citation
- Title
- The Relationship Of Near-surface Flow, Stokes Drift And The Wind Stress.
- Creator
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Clarke, Allan J., Van Gorder, Stephen
- Abstract/Description
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Many years of simultaneous hourly buoy wind and directional wave spectra data in the Gulf of Mexico and the Pacific were used to estimate Stokes drift and u* e(w) where u* = (magnitude of the local windstress/water density)(1/2) and e(w) is a unit vector in the direction of the local wind. Stokes drift and u* e(w) were strongly vectorally correlated, the two vectors on average being within a few degrees of one another. This result remained valid even when there was evidence of remotely forced...
Show moreMany years of simultaneous hourly buoy wind and directional wave spectra data in the Gulf of Mexico and the Pacific were used to estimate Stokes drift and u* e(w) where u* = (magnitude of the local windstress/water density)(1/2) and e(w) is a unit vector in the direction of the local wind. Stokes drift and u* e(w) were strongly vectorally correlated, the two vectors on average being within a few degrees of one another. This result remained valid even when there was evidence of remotely forced swell. Extension of the observed wave spectra above 0.35 Hz to the u(*)-dependent wave breaking frequency shows that typically the e-folding scale of the Stokes drift with depth is less than 1.8 m, much smaller than the Ekman layer e-folding scale. Therefore, there is negligible induced Eulerian cancellation of the Stokes drift, and the surface particle movement is governed by the Eulerian velocity + vertical bar u(Stokes)vertical bar e(w). Taking into account wave spreading, vertical bar u(Stokes)vertical bar typically ranges from about 3 to 13 cm/s. Thus, the Stokes drift, which can be estimated directly from the wind stress, is an order one contributor to the surface transport of particles. Plain Language Summary Although crucial for the movement of oil spills, red tide, fish eggs and larvae, and floating garbage, much still has to be learned about net particle movement in the top 1 or 2 m of the ocean. George Gabriel Stokes showed mathematically in 1847 that ocean surface waves may affect the net movement of particles at the ocean surface, but later it was shown that because we live on a rotating Earth, the net particle movement in the direction of the waves (the "Stokes drift") might be canceled by another opposite flow. In this paper we demonstrate that because of the ocean turbulence generated by the wind, the main part of the Stokes drift in the top 2 m of the ocean is not canceled by an opposing flow. Furthermore, analysis of simultaneous hourly wind and wave measurements for many years at Christmas Island in the equatorial Pacific, ocean station Papa in the north Pacific, and 10 stations in the Gulf of Mexico shows that Stokes drift is strongly related to the local wind and is in the direction of the wind. Stokes drift is therefore not primarily due to remotely driven swell; rather, it is mainly due to the much shorter waves that the local wind generates. By taking into account when the short waves break, it is shown how Stokes drift can be approximately estimated directly from the local wind.
Show less - Date Issued
- 2018-07-01
- Identifier
- FSU_libsubv1_wos_000441888200015, 10.1029/2018JC014102
- Format
- Citation
- Title
- Metrics For The Evaluation Of The Southern Ocean In Coupled Climate Models And Earth System Models.
- Creator
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Russell, Joellen L., Kamenkovich, Igor, Bitz, Cecilia, Ferrari, Raffaele, Gille, Sarah T., Goodman, Paul J., Hallberg, Robert, Johnson, Kenneth, Khazmutdinova, Karina, Marinov,...
Show moreRussell, Joellen L., Kamenkovich, Igor, Bitz, Cecilia, Ferrari, Raffaele, Gille, Sarah T., Goodman, Paul J., Hallberg, Robert, Johnson, Kenneth, Khazmutdinova, Karina, Marinov, Irina, Mazloff, Matthew, Riser, Stephen, Sarmiento, Jorge L., Speer, Kevin, Talley, Lynne D., Wanninkhof, Rik
Show less - Abstract/Description
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The Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water-mass structure and dynamics, Southern Ocean carbon...
Show moreThe Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water-mass structure and dynamics, Southern Ocean carbon and heat uptake depend on a combination of winds, eddies, mixing, buoyancy fluxes, and topography. Observationally based metrics are critical for discerning processes and mechanisms, and for validating and comparing climate and earth system models. New observations and understanding have allowed for progress in the creation of observationally based data/model metrics for the Southern Ocean. Metrics presented here provide a means to assess multiple simulations relative to the best available observations and observational products. Climate models that perform better according to these metrics also better simulate the uptake of heat and carbon by the Southern Ocean. This report is not strictly an intercomparison, but rather a distillation of key metrics that can reliably quantify the "accuracy" of a simulation against observed, or at least observable, quantities. One overall goal is to recommend standardization of observationally based benchmarks that the modeling community should aspire to meet in order to reduce uncertainties in climate projections, and especially uncertainties related to oceanic heat and carbon uptake. Plain Language Summary Observationally based metrics are essential for the standardized evaluation of climate and earth system models, and for reducing the uncertainty associated with future projections by those models.
Show less - Date Issued
- 2018-05-01
- Identifier
- FSU_libsubv1_wos_000436111400001, 10.1002/2017JC013461
- Format
- Thesis
- Title
- Semidiurnal Internal Tide Incoherence In The Equatorial Pacific.
- Creator
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Buijsman, Maarten C., Arbic, Brian K., Richman, James G., Shriver, Jay F., Wallcraft, Alan J., Zamudio, Luis
- Abstract/Description
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The jets in the equatorial Pacific Ocean of a realistically forced global circulation model with a horizontal resolution of 1/12.5 degrees cause a strong loss of phase coherence in semidiurnal internal tides that propagate equatorward from the French Polynesian Islands and Hawaii. This loss of coherence is quantified with a baroclinic energy analysis, in which the semidiurnal-band terms are separated into coherent, incoherent, and cross terms. For time scales longer than a year, the coherent...
Show moreThe jets in the equatorial Pacific Ocean of a realistically forced global circulation model with a horizontal resolution of 1/12.5 degrees cause a strong loss of phase coherence in semidiurnal internal tides that propagate equatorward from the French Polynesian Islands and Hawaii. This loss of coherence is quantified with a baroclinic energy analysis, in which the semidiurnal-band terms are separated into coherent, incoherent, and cross terms. For time scales longer than a year, the coherent energy flux approaches zero values at the equator, while the total flux is similar to 500 W/m. The time variability of the incoherent energy flux is compared with the internal-tide travel-time variability, which is based on along-beam integrated phase speeds computed with the Taylor-Goldstein equation. The variability of monthly mean Taylor-Goldstein phase speeds agrees well with the phase speed variability inferred from steric sea surface height phases extracted with a plane-wave fit technique. On monthly time scales, the loss of phase coherence in the equatorward beams from the French Polynesian Islands is attributed to the time variability in the vertically sheared background flow associated with the jets and tropical instability waves. On an annual time scale, the effect of stratification variability is of equal or greater importance than the shear variability is to the loss of coherence. In the model simulations, low-frequency equatorial jets do not noticeably enhance the dissipation of the internal tide, but merely decohere and scatter it.
Show less - Date Issued
- 2017-07
- Identifier
- FSU_libsubv1_wos_000409893600005, 10.1002/2016JC012590
- Format
- Citation
- Title
- Frequency Content Of Sea Surface Height Variability From Internal Gravity Waves To Mesoscale Eddies.
- Creator
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Savage, Anna C., Arbic, Brian K., Richman, James G., Shriver, Jay F., Alford, Matthew H., Buijsman, Maarten C., Farrar, J. Thomas, Sharma, Hari, Voet, Gunnar, Wallcraft, Alan J....
Show moreSavage, Anna C., Arbic, Brian K., Richman, James G., Shriver, Jay F., Alford, Matthew H., Buijsman, Maarten C., Farrar, J. Thomas, Sharma, Hari, Voet, Gunnar, Wallcraft, Alan J., Zamudio, Luis
Show less - Abstract/Description
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High horizontal-resolution (1/12: 5 degrees and 1/25 degrees) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical...
Show moreHigh horizontal-resolution (1/12: 5 degrees and 1/25 degrees) 41-layer global simulations of the HYbrid Coordinate Ocean Model (HYCOM), forced by both atmospheric fields and the astronomical tidal potential, are used to construct global maps of sea surface height (SSH) variability. The HYCOM output is separated into steric and nonsteric and into subtidal, diurnal, semidiurnal, and supertidal frequency bands. The model SSH output is compared to two data sets that offer some geographical coverage and that also cover a wide range of frequencies-a set of 351 tide gauges that measure full SSH and a set of 14 in situ vertical profilers from which steric SSH can be calculated. Three of the global maps are of interest in planning for the upcoming Surface Water and Ocean Topography (SWOT) two-dimensional swath altimeter mission: (1) maps of the total and (2) nonstationary internal tidal signal (the latter calculated after removing the stationary internal tidal signal via harmonic analysis), with an average variance of 1: 05 and 0: 43 cm(2), respectively, for the semidiurnal band, and (3) a map of the steric supertidal contributions, which are dominated by the internal gravity wave continuum, with an average variance of 0: 15 cm2. Stationary internal tides (which are predictable), nonstationary internal tides (which will be harder to predict), and nontidal internal gravity waves (which will be very difficult to predict) may all be important sources of high-frequency "noise" that could mask lower frequency phenomena in SSH measurements made by the SWOT mission.
Show less - Date Issued
- 2017-03
- Identifier
- FSU_libsubv1_wos_000400678900047, 10.1002/2016JC012331
- Format
- Citation
- Title
- Comparison Of The Ocean Surface Vector Winds From Atmospheric Reanalysis And Scatterometer-based Wind Products Over The Nordic Seas And The Northern North Atlantic And Their Application For Ocean Modeling.
- Creator
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Dukhovskoy, Dmitry S., Bourassa, Mark A., Petersen, Guorun Nina, Steffen, John
- Abstract/Description
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Ocean surface vector wind fields from reanalysis data sets and scatterometer-derived gridded products are analyzed over the Nordic Seas and the northern North Atlantic for the time period from 2000 to 2009. The data sets include the National Center for Environmental Prediction Reanalysis 2 (NCEPR2), Climate Forecast System Reanalysis (CFSR), Arctic System Reanalysis (ASR), Cross-Calibrated Multiplatform (CCMP) wind product version 1.1 and recently released version 2.0, and QuikSCAT. The goal...
Show moreOcean surface vector wind fields from reanalysis data sets and scatterometer-derived gridded products are analyzed over the Nordic Seas and the northern North Atlantic for the time period from 2000 to 2009. The data sets include the National Center for Environmental Prediction Reanalysis 2 (NCEPR2), Climate Forecast System Reanalysis (CFSR), Arctic System Reanalysis (ASR), Cross-Calibrated Multiplatform (CCMP) wind product version 1.1 and recently released version 2.0, and QuikSCAT. The goal of the study is to assess discrepancies across the wind vector fields in the data sets and demonstrate possible implications of these differences for ocean modeling. Large-scale and mesoscale characteristics of winds are compared at interannual, seasonal, and synoptic timescales. A cyclone tracking methodology is developed and applied to the wind fields to compare cyclone characteristics in the data sets. Additionally, the winds are evaluated against observations collected from meteorological buoys deployed in the Iceland and Irminger Seas. The agreement among the wind fields is better for longer time and larger spatial scales. The discrepancies are clearly apparent for synoptic timescales and mesoscales. CCMP, ASR, and CFSR show the closest overall agreement with each other. Substantial biases are found in the NCEPR2 winds. Numerical sensitivity experiments are conducted with a coupled ice-ocean model forced by different wind fields. The experiments demonstrate differences in the net surface heat fluxes during storms. In the experiment forced by NCEPR2 winds, there are discrepancies in the large-scale wind-driven ocean dynamics compared to the other experiments.
Show less - Date Issued
- 2017-03
- Identifier
- FSU_libsubv1_wos_000400678900018, 10.1002/2016JC012453
- Format
- Citation
- Title
- Semidiurnal Internal Tide Energy Fluxes And Their Variability In A Global Ocean Model And Moored Observations.
- Creator
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Ansong, Joseph K., Arbic, Brian K., Alford, Matthew H., Buijsman, Maarten C., Shriver, Jay F., Zhao, Zhongxiang, Richman, James G., Simmons, Harper L., Timko, Patrick G.,...
Show moreAnsong, Joseph K., Arbic, Brian K., Alford, Matthew H., Buijsman, Maarten C., Shriver, Jay F., Zhao, Zhongxiang, Richman, James G., Simmons, Harper L., Timko, Patrick G., Wallcraft, Alan J., Zamudio, Luis
Show less - Abstract/Description
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We examine the temporal means and variability of the semidiurnal internal tide energy fluxes in 1/25 degrees global simulations of the Hybrid Coordinate Ocean Model (HYCOM) and in a global archive of 79 historical moorings. Low-frequency flows, a major cause of internal tide variability, have comparable kinetic energies at the mooring sites in model and observations. The computed root-mean-square (RMS) variability of the energy flux is large in both model and observations and correlates...
Show moreWe examine the temporal means and variability of the semidiurnal internal tide energy fluxes in 1/25 degrees global simulations of the Hybrid Coordinate Ocean Model (HYCOM) and in a global archive of 79 historical moorings. Low-frequency flows, a major cause of internal tide variability, have comparable kinetic energies at the mooring sites in model and observations. The computed root-mean-square (RMS) variability of the energy flux is large in both model and observations and correlates positively with the time-averaged flux magnitude. Outside of strong generation regions, the normalized RMS variability (the RMS variability divided by the mean) is nearly independent of the flux magnitudes in the model, and of order 23% or more in both the model and observations. The spatially averaged flux magnitudes in observations and the simulation agree to within a factor of about 1.4 and 2.4 for vertical mode-1 and mode-2, respectively. The difference in energy flux computed from the full-depth model output versus model output subsampled at mooring instrument depths is small. The global historical archive is supplemented with six high-vertical resolution moorings from the Internal Waves Across the Pacific (IWAP) experiment. The model fluxes agree more closely with the high-resolution IWAP fluxes than with the historical mooring fluxes. The high variability in internal tide energy fluxes implies that internal tide fluxes computed from short observational records should be regarded as realizations of a highly variable field, not as "means" that are indicative of conditions at the measurement sites over all time.
Show less - Date Issued
- 2017-03
- Identifier
- FSU_libsubv1_wos_000400678900015, 10.1002/2016JC012184
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- Citation
- Title
- Atmospheric forcing during active convection in the Labrador Sea and its impact on mixed-layer depth.
- Creator
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Schulze, Lena M., Pickart, Robert S., Moore, G. W. K.
- Abstract/Description
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Hydrographic data from the Labrador Sea collected in February-March 1997, together with atmospheric reanalysis fields, are used to explore relationships between the air-sea fluxes and the observed mixed-layer depths. The strongest winds and highest heat fluxes occurred in February, due to the nature and tracks of the storms. While greater numbers of storms occurred earlier and later in the winter, the storms in February followed a more organized track extending from the Gulf Stream region to...
Show moreHydrographic data from the Labrador Sea collected in February-March 1997, together with atmospheric reanalysis fields, are used to explore relationships between the air-sea fluxes and the observed mixed-layer depths. The strongest winds and highest heat fluxes occurred in February, due to the nature and tracks of the storms. While greater numbers of storms occurred earlier and later in the winter, the storms in February followed a more organized track extending from the Gulf Stream region to the Irminger Sea where they slowed and deepened. The canonical low-pressure system that drives convection is located east of the southern tip of Greenland, with strong westerly winds advecting cold air off the ice edge over the warm ocean. The deepest mixed layers were observed in the western interior basin, although the variability in mixed-layer depth was greater in the eastern interior basin. The overall trend in mixed-layer depth through the winter in both regions of the basin was consistent with that predicted by a 1-D mixed-layer model. We argue that the deeper mixed layers in the west were due to the enhanced heat fluxes on that side of the basin as opposed to oceanic preconditioning.
Show less - Date Issued
- 2016-09
- Identifier
- FSU_libsubv1_wos_000386913200024, 10.1002/2015JC011607
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- Citation
- Title
- Horizontal mixing in the Southern Ocean from Argo float trajectories.
- Creator
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Roach, Christopher J., Balwada, Dhruv, Speer, Kevin
- Abstract/Description
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We provide the first observational estimate of the circumpolar distribution of cross-stream eddy diffusivity at 1000 m in the Southern Ocean using Argo float trajectories. We show that Argo float trajectories, from the float surfacing positions, can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from RAFOS floats, where they overlap. Using the Southern Ocean State Estimate (SOSE) velocity fields to advect synthetic...
Show moreWe provide the first observational estimate of the circumpolar distribution of cross-stream eddy diffusivity at 1000 m in the Southern Ocean using Argo float trajectories. We show that Argo float trajectories, from the float surfacing positions, can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from RAFOS floats, where they overlap. Using the Southern Ocean State Estimate (SOSE) velocity fields to advect synthetic particles with imposed behavior that is "Argo-like'' and "RAFOS-like'' diffusivity estimates from both sets of synthetic particles agreed closely at the three dynamically very different test sites, the Kerguelen Island region, the Southeast Pacific Ocean, and the Scotia Sea, and support our approach. Observed cross-stream diffusivities at 1000 m, calculated from Argo float trajectories, ranged between 300 and 2500 m(2) s(-1), with peaks corresponding to topographic features associated with the Scotia Sea, the Kerguelen Plateau, the Campbell Plateau, and the Southeast Pacific Ridge. These observational estimates agree with previous regional estimates from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) near the Drake Passage, and other estimates from natural tracers (helium), inverse modeling studies, and current meter measurements. These estimates are also compared to the suppressed eddy diffusivity in the presence of mean flows. The comparison suggests that away from regions of strong topographic steering suppression explains both the structure and magnitude of eddy diffusivity but that eddy diffusivities in the regions of topographic steering are greater than what would be theoretically expected and the ACC experiences localized enhanced cross-stream mixing in these regions.
Show less - Date Issued
- 2016-08
- Identifier
- FSU_libsubv1_wos_000386912700011, 10.1002/2015JC011440
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- Citation
- Title
- Effects Of Rotation On Turbulent Buoyant Plumes In Stratified Environments.
- Creator
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Tomas, Alexandre Fabregat, Poje, Andrew C., Ozgokmen, Tamay M., Dewar, William K.
- Abstract/Description
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We numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large Rossby numbers characteristic of deep oceanic releases. When compared to nonrotating environments, rotating plumes are distinguished by a significant decrease in vertical buoyancy and momentum fluxes leading to lower and thicker neutrally buoyant intrusion layers. The primary dynamic effect of background rotation is the concentration of...
Show moreWe numerically investigate the effects of rotation on the turbulent dynamics of thermally driven buoyant plumes in stratified environments at the large Rossby numbers characteristic of deep oceanic releases. When compared to nonrotating environments, rotating plumes are distinguished by a significant decrease in vertical buoyancy and momentum fluxes leading to lower and thicker neutrally buoyant intrusion layers. The primary dynamic effect of background rotation is the concentration of entraining fluid into a strong cyclonic flow at the base of the plume resulting in cyclogeostrophic balance in the radial momentum equation. The structure of this cyclogeostrophic balance moving upward from the well head is associated with a net adverse vertical pressure gradient producing an inverted hydrostatic balance in the mean vertical momentum budgets. The present simulations reveal that the primary response to the adverse pressure gradient is an off-axis deflection of the plume that evolves into a robust, organized anticyclonic radial precession about the buoyancy source. The off-axis evolution is responsible for the weaker inertial overshoots, the increased thickness of lateral intrusion layers, and the overall decrease in the vertical extent of rotating plumes at intermediate Rossby numbers compared to the nonrotating case. For inlet buoyancy forcings and environmental Rossby numbers consistent with those expected in deepwater blowout plumes, the speed of the organized precession is found to be as large as typical oceanic cross-flow speeds.
Show less - Date Issued
- 2016-08
- Identifier
- FSU_libsubv1_wos_000386912700001, 10.1002/2016JC011737
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- Citation
- Title
- Dissipation processes in the Tongue of the Ocean.
- Creator
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Hooper, James A., Baringer, Molly O., St Laurent, Louis C., Dewar, William K., Nowacek, Doug
- Abstract/Description
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The Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively understudied region in terms of both its biological and physical oceanographic characteristics. A prey-field mapping cruise took place in the fall between 15 September 2008 and 1 October 2008, consisting of a series of transects and "clovers" to study the spatial and temporal variability. The region is characterized by a deep scattering layer (DSL), which is preyed on by nekton that serves as the food...
Show moreThe Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively understudied region in terms of both its biological and physical oceanographic characteristics. A prey-field mapping cruise took place in the fall between 15 September 2008 and 1 October 2008, consisting of a series of transects and "clovers" to study the spatial and temporal variability. The region is characterized by a deep scattering layer (DSL), which is preyed on by nekton that serves as the food for beaked whale and other whale species. This study marks the first of its kind where concurrent measurements of acoustic backscatter and turbulence have been conducted for a nekton scattering layer well below the euphotic zone. Turbulence data collected from a Deep Microstructure Profiler are compared to biological and shear data collected by a 38 kHz Simrad EK 60 echo sounder and a hydrographic Doppler sonar system, respectively. From these measurements, the primary processes responsible for the turbulent production in the TOTO region are assessed. The DSL around 500 m and a surface scattering layer (SSL) are investigated for raised epsilon values. Strong correlation between turbulence levels and scattering intensity of prey is generally found in the SSL with dissipation levels as large as similar to 10(-7) W kg(-1), 3 orders of magnitude above background levels. In the DSL and during the diel vertical migration, dissipation levels similar to 10(-8) W kg(-1) were observed.
Show less - Date Issued
- 2016-05
- Identifier
- FSU_libsubv1_wos_000383466500019, 10.1002/2015JC011165
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- Citation
- Title
- A framework to quantify uncertainty in simulations of oil transport in the ocean.
- Creator
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Goncalves, Rafael C., Iskandarani, Mohamed, Srinivasan, Ashwanth, Thacker, W. Carlisle, Chassignet, Eric, Knio, Omar M.
- Abstract/Description
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An uncertainty quantification framework is developed for the DeepC Oil Model based on a nonintrusive polynomial chaos method. This allows the model's output to be presented in a probabilistic framework so that the model's predictions reflect the uncertainty in the model's input data. The new capability is illustrated by simulating the far-field dispersal of oil in a Deepwater Horizon blowout scenario. The uncertain input consisted of ocean current and oil droplet size data and the main model...
Show moreAn uncertainty quantification framework is developed for the DeepC Oil Model based on a nonintrusive polynomial chaos method. This allows the model's output to be presented in a probabilistic framework so that the model's predictions reflect the uncertainty in the model's input data. The new capability is illustrated by simulating the far-field dispersal of oil in a Deepwater Horizon blowout scenario. The uncertain input consisted of ocean current and oil droplet size data and the main model output analyzed is the ensuing oil concentration in the Gulf of Mexico. A 1331 member ensemble was used to construct a surrogate for the model which was then mined for statistical information. The mean and standard deviations in the oil concentration were calculated for up to 30 days, and the total contribution of each input parameter to the model's uncertainty was quantified at different depths. Also, probability density functions of oil concentration were constructed by sampling the surrogate and used to elaborate probabilistic hazard maps of oil impact. The performance of the surrogate was constantly monitored in order to demarcate the spacetime zones where its estimates are reliable.
Show less - Date Issued
- 2016-04
- Identifier
- FSU_libsubv1_wos_000383462300002, 10.1002/2015JC011311
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- Citation
- Title
- The Antarctic Slope Current near 30 degrees E.
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Dong, Jun, Speer, Kevin, Jullion, Loic
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The Antarctic Slope Current flows westward above the continental slope of Antarctica, entering the Weddell Sea near 30 degrees E and supplying dense water to the deep overturning cell there, and contributing to global Antarctic Bottom Water formation. Observations from the 2008 I6S hydrographic section are used to investigate the strength of the Slope Current near 30 degrees E. A prominent topographic feature, the Gunnerus Bank, diverts the Slope Current upstream of this longitude, and has a...
Show moreThe Antarctic Slope Current flows westward above the continental slope of Antarctica, entering the Weddell Sea near 30 degrees E and supplying dense water to the deep overturning cell there, and contributing to global Antarctic Bottom Water formation. Observations from the 2008 I6S hydrographic section are used to investigate the strength of the Slope Current near 30 degrees E. A prominent topographic feature, the Gunnerus Bank, diverts the Slope Current upstream of this longitude, and has a large effect on the current's structure, splitting it into a coastal and offshore component. The bank also enhances water mass mixing and lateral exchange across the slope. As part of the 2008 occupation, an additional line was made along the crest of the bank, forming a closed volume over the western side. By combining hydrographic and Lowered Acoustic Doppler Current Profiler measurements in this box using an inverse method, the Slope Current transport is estimated to be 9.62.3 Sv; the transport associated with the Antarctic Slope Front is 4.00.3 Sv, of which 1.80.3 Sv enters the Weddell Gyre as recently formed dense water.
Show less - Date Issued
- 2016-02
- Identifier
- FSU_libsubv1_wos_000373134600002, 10.1002/2015JC011099
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- Citation
- Title
- Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers.
- Creator
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Dukhovskoy, Dmitry S., Myers, Paul G., Platov, Gennady, Timmermans, Mary-Louise, Curry, Beth, Proshutinsky, Andrey, Bamber, Jonathan L., Chassignet, Eric, Hu, Xianmin, Lee,...
Show moreDukhovskoy, Dmitry S., Myers, Paul G., Platov, Gennady, Timmermans, Mary-Louise, Curry, Beth, Proshutinsky, Andrey, Bamber, Jonathan L., Chassignet, Eric, Hu, Xianmin, Lee, Craig M., Somavilla, Raquel
Show less - Abstract/Description
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Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland...
Show moreAccelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06-0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15-0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.
Show less - Date Issued
- 2016-01
- Identifier
- FSU_libsubv1_wos_000371432200050, 10.1002/2015JC011290
- Format
- Citation
