Justin Shaw (4967152), Marek Stastna (314798) · Figshare · 2019
<p>An internal wave train propagates from left to right and encounters a sharp change in the background density profile. The bottom panel is the error map with time increasing left to right, and vertical axis of increasing <i>D</i>, with pairs of vertical green lines indicating the times of the upper panels as time increases from left to right. See text for details.</p>
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Sérazin, Guillaume, Tréguier, Anne Marie, De Boyer Montégut, Clement · SEANOE · 2022
The upper ocean pycnocline (UOP) monthly climatology is based on the ISAS20 ARGO dataset containing Argo and Deep-Argo temperature and salinity profiles on the period 2002-2020. Regardless of the season, the UOP is defined as the shallowest significant stratification peak captured by the method described in Sérazin et al. (2022), whose detection threshold is proportional to the standard deviation of the stratification profile. The three main characteristics of the UOP are provided -- intensity, depth and thickness -- along with hydrographic variables at the upper and lower edges of the pycnocline, the Turner angle and density ratio at the depth of the UOP. A stratification index (SI) that evaluates the amount of buoyancy required to destratify the upper ocean down to a certain depth, is also included. When evaluated at the bottom of the UOP, this gives the upper ocean stratification index (UOSI) as discussed in Sérazin et al. (2022). Three mixed layer depth variables are also included in this dataset, including the one using the classic density threshold of 0.03 kg.m-3, along with the minimum of these MLD variables. Several statistics of the UOP characteristics and the associated quantities are available in 2°×2° bins for each month of the year, whose results were smoothed using a diffusive gaussian filter with a 500 km scale. UOP characteristics are also available for each profile, with all the profiles sorted in one file per month.
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Lilian A. Dove, Mara Freilich, Lia Siegelman et al. · 2024
Pycnocline stratification is increasing across multiple ocean basins due to a warming surface ocean and increasing sea ice melt. Pycnocline stratification plays a leading order role in tracer transport, shaping capacity for heat and carbon uptake, making it a key parameter of interest on timescales ranging from paleoclimate to plankton blooms. Part of the challenge in assessing the role of pycnocline stratification in global models is the two-way connection between physical processes at the (sub)mesoscale and stratification with important implications for tracer subduction. Using a suite of numerical simulations of an idealized front, we find that the strength of pycnocline stratification influences the formation and evolution of submesoscale structure and the resulting tracer transport. The impact of changing stratification on tracer flux strongly depends on whether frontal strength is also changed correspondingly by holding the isopycnal slope fixed. When a constant isopycnal slope is initialized, tracers get efficiently transferred across the base of the mixed layer and get trapped in anticyclonic submesoscale vortices below the mixed layer. This leads to tracer concentrations below the mixed layer and fluxes through it to be stronger under decreased stratification conditions. In contrast, when frontal lateral buoyancy gradient is held fixed while stratification changes, the vertical flux of tracers and the concentrations at depth stay constant across all examined stratification conditions. Understanding the relationship between pycnocline stratification and fine-scale physical motions is necessary to diagnose and predict trends in carbon uptake and storage, particularly in the Southern Ocean.
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David W. Pierce, Peter B. Rhines · Journal of Physical Oceanography · 1996
The convective building of a pycnocline is examined using a laboratory model forced by surface fluxes of saline water at one end and fresh water at the other. A deep recirculation evolves in the tank, which homogenizes the interior fluid by repeated passes through the dense, descending plume. A thin, fresh surface layer develops and modifies the effective buoyancy flux into the dense plume, causing the interior velocities to fall to an intermediate-time minimum. Adding bottom topography under the dense source greatly reduces the amount of entrainment that the descending plume undergoes. In this case, the tank fills with a deep, heavy layer, which causes the plume to “lift off” the bottom of the tank and detrain at successively higher depths in the water column. A simple numerical “plume” model shows that this cannot be a steady state, as it is not in diffusive balance; the plume must eventually return to the bottom of the tank and ventilate the interior waters. Adding rotation increases the surface mixing, thickens the halocline, and increases the observed variability in the salinity field.
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Cheryl Greengrove · Medical Entomology and Zoology · 1986
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Patrick Denny · AquaDocs (United Nations Educational, Scientific and Cultural Organization) · 1972
The vertical temperature profile is a poor indicator of sratification in most tropical lake. Data from Lake Bunyonyi, Uganda, showed, however, that the density profile highlighted discontinuity layers whieh were not obvious from the temperature profile, It is suggested that the verticaldensity profile and the region of maximum discontinuity, the pycnocline, could be adopted as a useful index of stratification especially in tropical lakes.
Cited by 7Open access
Jeffrey R. Carpenter (2938020), Lucas Merckelbach (2938032), Ulrich Callies (2938017) et al. · Figshare · 2016
<p>The results of both low- and high-turbulence simulations are identical but span different time periods, since the solutions collapse if the dimensionless time <i>t</i><sub>*</sub> is used. The evolution of the dimensionless density profile 2(<i>ρ</i> − <i>ρ</i><sub>0</sub>)/Δ<i>ρ</i> is shown in (a), along with the decrease in the stratification over time in (b). Also shown in (b) are the constant pycnocline thickness model mixing rates given by <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0160830#pone.0160830.e035" target="_blank">Eq (13)</a> with <i>b</i> = 6 m and <i>b</i> = <i>H</i> = 40 m for comparison (slopes of red lines). In the low- and high-turbulence cases of (a), density profiles are identical, and plotted every 18 and 4 days, respectively.</p>
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Guillaume Sérazin, Anne‐Marie Tréguier, Clément de Boyer Montégut · 2022
&lt;p&gt;Climatologies of the mixed layer depth have been provided using several definitions based on temperature/density thresholds or hybrid approaches. The upper ocean pycnocline (UOP) that sits below the mixed layer base, sometimes referred to as the transition layer or as the seasonal pycnocline, remains poorly characterised though it is an ubiquitous feature of the ocean surface layer. The UOP often consists in a rapid change in density with depth and enhanced vertical shear that connects the well-mixed surface layer to the stratified ocean interior. The UOP is important for the ventilation of the ocean as it represents a barrier to mixing between the upper ocean and the ocean interior.&lt;br&gt;&lt;br&gt;Available hydrographic profiles (e.g., Argo, CTD on marine mammals) provide near-global coverage of the world's oceans and allow the characterisation of spatial and seasonal variations of the upper ocean vertical stratification, including the UOP. Based on these profiles, we estimate the depth, thickness and intensity of the UOP, and assess when and where the UOP can be considered as a layer with constant thickness. We provide monthly maps of the UOP complementing the available MLD climatologies and we compare the UOP characteristics with the depth and stratification of the mixed layer. We&amp;#160; aim at assessing the UOP intensity in winter and spring when the stratification is usually weak and submesoscale vertical motions can penetrate below the mixed layer base. During these seasons, the UOP intermittency must be taken into account because restratification may occur with intermittent events.&lt;/p&gt;
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Guillaume Maze, Virginie Thierry, Herlé Mercier · Institutional Archive of Ifremer (French Research Institute for Exploitation of the Sea) · 2013
At mid-latitudes, the oceanic vertical structure of density is characterized by a permanent highly stratified layer: the pycnocline. The pycnocline is the transition layer between surface water masses ventilated every winter when penetrated locally by the mixed layer and deeper water masses which have been ventilated at high latitudes and circulate equatorward. \n\nThe pycnocline thus reflects a large scale balance between the penetration of local air-sea interactions and the re-emergence of remote ones.\n\nThe overall question we want to address is whether and to which extent the variability of the pycnocline properties (depth, thickness and thermohaline characteristics) are influenced by those of air-sea interactions. \n\nTo this end, we first developed a new method to characterize the permanent pycnocline properties from Argo data. We then applied this method to study the pycnocline in the subtropical North Atlantic Ocean.\n\nWe will present the first results of this analysis: the climatological (over the Argo observational period) and seasonal variability of the pycnocline properties.
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Tiselius, P., Nielsen, G., Nielsen, T. G. · 1994
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Guillaume Sérazin, Anne‐Marie Tréguier, Clément de Boyer Montégut · Frontiers in Marine Science · 2023
Climatologies of the mixed layer depth (MLD) have been provided using several definitions based on temperature/density thresholds or hybrid approaches. The upper ocean pycnocline (UOP) that sits below the mixed layer base remains poorly characterized, though this transition layer is an ubiquitous feature of the ocean surface layer. Available hydrographic profiles provide near-global coverage of the world’s ocean and are used to build a seasonal climatology of UOP properties – intensity, depth, thickness – to characterize the spatial and seasonal variations of upper ocean stratification. The largest stratification values O (10 −3 s −2 ) are found in the intertropical band, where seasonal variations of the UOP are also very small. The deepest (&gt; 200 m) and least stratified O (10 −6 s −2 ) UOPs are found in winter along the Antarctic Circumpolar Current (ACC) and at high latitudes of the North Atlantic. The UOP thickness has a median value of 23 m with limited seasonal and spatial variations; only a few regions have UOP thicknesses exceeding 35 m. The UOP properties allow the characterization of the upper ocean restratification that generally occurs in early spring and is generally associated with large variability. Depending on the region, this restratification may happen gradually as around the Rockall plateau or abruptly as in the Kuroshio Extension. The UOP is also likely to merge intermittently with the permanent pycnocline in winter. The upper edge of the UOP is eventually close to MLD estimates, except in a few notable regions such as in the Pacific Warm Pool where barrier layers are important, and during wintertime at high latitudes of the North Pacific.
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Kaylie Cohanim · Zenodo (CERN European Organization for Nuclear Research) · 2026
Modeling Ice Shelf Submesoscale Instabilities (MISSI). Model configuration in MITgcm of idealized sub-ice shelf cavity.
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Cynthia Cudaback, David A. Jay · Journal of Geophysical Research Atmospheres · 2001
Flood currents in shallow estuaries are driven by an along‐channel barotropic and baroclinic pressure gradient that increases monotonically toward the bottom, while friction retards near‐bottom currents. Therefore, in many estuaries there is a middepth maximum in flood currents. We explore this phenomenon using a simple three‐layer model in which each layer has vertically uniform currents and constant density. In this model the middle layer is of intermediate density and grows by shear‐induced entrainment from the other two layers. This very simple model produces a middepth maximum in flood currents and simulates observed currents in the Columbia River entrance channel within about 10%. There is good qualitative agreement between model salinity transport and observed transport. The model pycnocline rises and falls tidally, in phase with the observed pycnocline, although pycnocline depth and thickness are better simulated using results from a two‐layer model [ Cudaback and Jay , 2000].
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S. A. Thorpe · Cambridge University Press eBooks · 2005
Preceding chapters have described the mechanisms or processes that lead to turbulence in the ocean, and the means that are available for its measurement. Described in this chapter are observations of the processes, and of the consequent turbulence and mixing within the body of the ocean, here referred to as the pycnocline or as ‘mid-water’ to distinguish it from the parts of the ocean that are in close contact and affected by the immediate presence of boundaries. Later chapters are devoted to describing turbulence within the boundary layers themselves, those at the seabed or the air–sea interface.
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Zhou JF, Yang Sh · 中国科学院力学研究所 · 2010
Internal solitons have drawn much attention from ocean engineering and oceanography, due to the significant impacts on ocean structures, submarines and sonar communication. In order to investigate the evolution law of internal solitary waves, we have formulated a mathematical model for sharply stratified oceans. The model involves the effects of topography, dissipation, bottom friction and shoaling, with the related coefficients calibrated by field data over the Continental Slope in South China Sea. Then, we have explored shoreward propagation process of internal solitons generated in deep ocean by using the formulated model, particularly aiming at the variation of internal soliton’s amplitude. Detailed discussions focus on the effects of physical parameters of pycnocline, i.e. its location or depth and the density difference between water layers below and above pycnocline, on the variation of internal soliton’s amplitude. Results show that internal soliton’s amplitude decreases when it propagates from deep sea to shallow continental shelf. The shallower the pycnocline and the smaller the density difference between water layers below and above pycnocline, the faster the internal soliton’s amplitude decreases.
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Anand Gnanadesikan, Agatha M. de Boer, Bryan K. Mignone · Geophysical monograph · 2007
This chapter contains sections titled: Introduction Theory and Models The G99 Theory in an Ocean-Only Model Changes in Flow Pathways The Role of Density The Single Length-Scale Approximation Conclusions
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Yu. V. Gur’ev, I. V. Tkachenko · Fluid Dynamics · 2010
A flow past an ellipsoid immersed in a flow of a viscous stratified fluid is studied using a Large Eddy Simulation (LES) method for different locations of the body relative to a density discontinuity. It is shown that, even when the internal Froude number is large, for small angles of attack of the body the stratification affects its drag force. When the body is located above the pycnocline, the presence of the discontinuity results in the ascending of a vortex filament. A spectral analysis showed that the internal waves in the body wake have a multimode structure.
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Nicolas Grisouard, Chantal Staquet, Louis Gostiaux et al. · HAL (Le Centre pour la Communication Scientifique Directe) · 2012
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Rooth, Claes., Düing, Walter., Rosenstiel School of Marine and Atmospheric Science. et al. · The Journal of the Abraham Lincoln Association
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Monika Nitsche, P. D. Weidman, Roger Grimshaw et al. · Journal of Fluid Mechanics · 2009
Over two decades ago, some numerical studies and laboratory experiments identified the phenomenon of leapfrogging internal solitary waves located on separated pycnoclines. We revisit this problem to explore the behaviour of the near resonance phenomenon. We have developed a numerical code to follow the long-time inviscid evolution of isolated mode-two disturbances on two separated pycnoclines in a three-layer stratified fluid bounded by rigid horizontal top and bottom walls. We study the dependence of the solution on input system parameters, namely the three fluid densities and the two interface thicknesses, for fixed initial conditions describing isolated mode-two disturbances on each pycnocline. For most parameter values, the initial disturbances separate immediately and evolve into solitary waves, each with a distinct speed. However, in a narrow region of parameter space, the waves pair up and oscillate for some time in leapfrog fashion with a nearly equal average speed. The motion is only quasi-periodic, as each wave loses energy into its respective dispersive tail, which causes the spatial oscillation magnitude and period to increase until the waves eventually separate. We record the separation time, oscillation period and magnitude, and the final amplitudes and celerity of the separated waves as a function of the input parameters, and give evidence that no perfect periodic solutions occur. A simple asymptotic model is developed to aid in interpretation of the numerical results.
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