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  • American Meteorological Society  (16)
  • 1
    Online Resource
    Online Resource
    Microstructure Measurements from an Underwater Glider in the Turbulent Faroe Bank Channel Overflow
    American Meteorological Society ; 2014
    In:  Journal of Atmospheric and Oceanic Technology Vol. 31, No. 5 ( 2014-05), p. 1128-1150
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 31, No. 5 ( 2014-05), p. 1128-1150
    Abstract: Measurements of ocean microstructure are made in the turbulent Faroe Bank Channel overflow using a turbulence instrument attached to an underwater glider. Dissipation rate of turbulent kinetic energy ε is measured using airfoil shear probes. A comparison is made between 152 profiles from dive and climb cycles of the glider during a 1-week mission in June 2012 and 90 profiles collected from the ship using a vertical microstructure profiler (VMP). Approximately one-half of the profiles are collocated. For 96% of the dataset, measurements are of high quality with no systematic differences between dives and climbs. The noise level is less than 5 × 10 −11 W kg −1 , comparable to the best microstructure profilers. The shear probe data are contaminated and unreliable at the turning depth of the glider and for U / u t 〈 20, where U is the flow past the sensor, u t = ( ε / N ) 1/2 is an estimate of the turbulent velocity scale, and N is the buoyancy frequency. Averaged profiles of ε from the VMP and the glider agree to better than a factor of 2 in the turbulent bottom layer of the overflow plume, and beneath the stratified and sheared plume–ambient interface. The glider average values are approximately a factor of 3 and 9 times larger than the VMP values in the layers defined by the isotherms 3°–6° and 6°–9°C, respectively, corresponding to the upper part of the interface and above. The discrepancy is attributed to a different sampling scheme and the intermittency of turbulence. The glider offers a noise-free platform suitable for ocean microstructure measurements.
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    DOI: 10.1175/JTECH-D-13-00221.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2021720-1
    detail.hit.zdb_id: 48441-6
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  • 2
    Online Resource
    Online Resource
    Global Patterns of Diapycnal Mixing from Measurements of the Turbulent Dissipation Rate
    American Meteorological Society ; 2014
    In:  Journal of Physical Oceanography Vol. 44, No. 7 ( 2014-07-01), p. 1854-1872
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 44, No. 7 ( 2014-07-01), p. 1854-1872
    Abstract: The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10−4) m2 s−1 and above 1000-m depth is O(10−5) m2 s−1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-13-0104.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 3
    Online Resource
    Online Resource
    Near-Inertial Mixing in the Central Arctic Ocean
    American Meteorological Society ; 2014
    In:  Journal of Physical Oceanography Vol. 44, No. 8 ( 2014-08-01), p. 2031-2049
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 44, No. 8 ( 2014-08-01), p. 2031-2049
    Abstract: Observations were made in April 2007 of horizontal currents, hydrography, and shear microstructure in the upper 500 m from a drifting ice camp in the central Arctic Ocean. An approximately 4-day-long time series, collected about 10 days after a storm event, shows enhanced near-inertial oscillations in the first half of the measurement period with comparable upward- and downward-propagating energy. Rough estimates of wind work and near-inertial flux imply that the waves were likely generated by the previous storm. The near-inertial frequency band is associated with dominant clockwise rotation in time of the horizontal currents and enhanced dissipation rates of turbulent kinetic energy. The vertical profile of dissipation rate shows elevated values in the pycnocline between the relatively turbulent underice boundary layer and the deeper quiescent water column. Dissipation averaged in the pycnocline is near-inertially modulated, and its magnitude decays approximately at a rate implied by the reduction of energy over time. Observations suggest that near-inertial energy and internal wave–induced mixing play a significant role in vertical mixing in the Arctic Ocean.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-13-0133.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 4
    Online Resource
    Online Resource
    Internal Waves and Mixing in the Marginal Ice Zone near the Yermak Plateau*
    American Meteorological Society ; 2010
    In:  Journal of Physical Oceanography Vol. 40, No. 7 ( 2010-07-01), p. 1613-1630
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 40, No. 7 ( 2010-07-01), p. 1613-1630
    Abstract: Observations were made of oceanic currents, hydrography, and microstructure in the southern Yermak Plateau in summer 2007. The location is in the marginal ice zone at the Arctic Front northwest of Svalbard, where the West Spitsbergen Current (WSC) carries the warm Atlantic Water into the Arctic Ocean. Time series of approximately 1-day duration from five stations (upper 520 m) and of an 8-day duration from a mooring are analyzed to describe the characteristics of internal waves and turbulent mixing. The spectral composition of the internal-wave field over the southern Yermak Plateau is 0.1–0.3 times the midlatitude levels and compares with the most energetic levels in the central Arctic. Dissipation rate and eddy diffusivity below the pycnocline increase from the noise level on the cold side of the front by one order of magnitude on the warm side, where 100-m-thick layers with average diffusivities of 5 × 10−5 m2 s−1 lead to heat loss from the Atlantic Water of 2–4 W m−2. Dissipation in the upper 150 m is well above the noise level at all stations, but strong stratification at the cold side of the front prohibits mixing across the pycnocline. Close to the shelf, at the core of the Svalbard branch of the WSC, diffusivity increases by another factor of 3–6. Here, near-bottom mixing removes 15 W m−2 of heat from the Atlantic layer. Internal-wave activity and mixing show variability related to topography and hydrography; thus, the path of the WSC will affect the cooling and freshening of the Atlantic inflow. When generalized to the Arctic Ocean, diapycnal mixing away from abyssal plains can be significant for the heat budget. Around the Yermak Plateau, it is of sufficient magnitude to influence heat anomaly pulses entering the Arctic Ocean; however, diapycnal mixing alone is unlikely to be significant for regional cooling of the WSC.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2010JPO4371.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 5
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    Online Resource
    Turbulent Upper-Ocean Mixing Affected by Meltwater Layers during Arctic Summer
    American Meteorological Society ; 2017
    In:  Journal of Physical Oceanography Vol. 47, No. 4 ( 2017-04), p. 835-853
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 47, No. 4 ( 2017-04), p. 835-853
    Abstract: Every summer, intense sea ice melt around the margins of the Arctic pack ice leads to a stratified surface layer, potentially without a traditional surface mixed layer. The associated strengthening of near-surface stratification has important consequences for the redistribution of near-inertial energy, ice–ocean heat fluxes, and vertical replenishment of nutrients required for biological growth. The authors describe the vertical structure of meltwater layers and quantify their seasonal evolution and their effect on turbulent mixing in the oceanic boundary layer by analyzing more than 450 vertical profiles of velocity microstructure in the seasonal ice zone north of Svalbard. The vertical structure of the density profiles can be summarized by an equivalent mixed layer depth h BD , which scales with the depth of the seasonal stratification. As the season progresses and melt rates increase, h BD shoals following a robust pattern, implying stronger vertical stratification, weaker vertical eddy diffusivity, and reduced vertical extent of the mixing layer, which is bounded by h BD . Through most of the seasonal pycnocline, the vertical eddy diffusivity scales inversely with buoyancy frequency ( K ρ ∝ N −1 ). The presence of mobile sea ice alters the magnitude and vertical structure of turbulent mixing primarily through stronger and shallower stratification, and thus vertical eddy diffusivity is greatly reduced under sea ice. This study uses these results to develop a quantitative model of surface layer turbulent mixing during Arctic summer and discuss the impacts of a changing sea ice cover.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-16-0200.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 6
    Online Resource
    Online Resource
    Dissipation of Turbulent Kinetic Energy Inferred from Seagliders: An Application to the Eastern Nordic Seas Overflows
    American Meteorological Society ; 2012
    In:  Journal of Physical Oceanography Vol. 42, No. 12 ( 2012-12-01), p. 2268-2282
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 42, No. 12 ( 2012-12-01), p. 2268-2282
    Abstract: Turbulent mixing is an important process controlling the descent rate, water mass modification, and volume transport augmentation due to entrainment in the dense overflows across the Greenland–Scotland Ridge. These overflows, along with entrained Atlantic waters, form a major portion of the North Atlantic Deep Water, which pervades the abyssal ocean. Three years of Seaglider observations of the overflows across the eastern Greenland–Scotland Ridge are leveraged to map the distribution of dissipation of turbulent kinetic energy on the Iceland–Faroe Ridge. A method has been applied using the finescale vertical velocity and density measurements from the glider to infer dissipation. The method, termed the large-eddy method (LEM), is compared with a microstructure survey of the Faroe Bank Channel (FBC). The LEM reproduces the patterns of dissipation observed in the microstructure survey, which vary over several orders of magnitude. Agreement between the inferred LEM and more direct microstructure measurements is within a factor of 2. Application to the 9432 dives that encountered overflow waters on the Iceland–Faroe Ridge reveals three regions of enhanced dissipation: one downstream of the primary FBC sill, another downstream of the secondary FBC sill, and a final region in a narrow jet of overflow along the Iceland shelf break.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-12-094.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 7
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    Online Resource
    Baroclinic Instability of the Faroe Bank Channel Overflow*
    American Meteorological Society ; 2014
    In:  Journal of Physical Oceanography Vol. 44, No. 10 ( 2014-10-01), p. 2698-2717
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 44, No. 10 ( 2014-10-01), p. 2698-2717
    Abstract: The generation mechanism of mesoscale eddies in the Faroe Bank Channel (FBC) overflow region and their spatiotemporal characteristics are examined using the high-resolution regional Massachusetts Institute of Technology general circulation model (MITgcm). From the modeled overflow, it is found that the volume transport downstream of the FBC sill exhibits strong variability with a distinct period of ~4 days. Energetic, alternating cyclonic and anticyclonic eddies appear at ~40 km downstream of the sill. They grow side by side in the nascent stage, but later the cyclones migrate along the 800-m isobath to the south of Iceland, whereas the anticyclones descend downslope across the isobath and gradually dissipate. Analysis of the eddy characteristics shows that the cyclones are associated with a larger plume thickness and width, larger volume transport, colder and denser water, and a plume core located farther downslope, whereas the opposite is true for the anticyclones. The oscillatory structure developed at the lower boundary of the mean plume and the following generation of alternating cyclones and anticyclones are typical features of baroclinic instability. A linear instability analysis of a two-layer analytical baroclinic model yields a most unstable mode that agrees favorably with the simulations. The calculation of the divergent eddy heat flux shows a substantial rightward (upslope)-directed component downstream of the FBC sill. This region is also associated with a strong baroclinic conversion rate. The above arguments constitute evidence for the generation of unstable plume and mesoscale eddies in the FBC region by baroclinic instability.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    URL: Article
    DOI: 10.1175/JPO-D-14-0080.1
    DOI: 10.1175/JPO-D-14-0080.s1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 8
    Online Resource
    Online Resource
    Observations of Thermohaline Convection adjacent to Brunt Ice Shelf
    American Meteorological Society ; 2012
    In:  Journal of Physical Oceanography Vol. 42, No. 3 ( 2012-03-01), p. 502-508
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 42, No. 3 ( 2012-03-01), p. 502-508
    Abstract: Observations were made of ocean microstructure and horizontal currents adjacent to Brunt Ice Shelf in the southeastern Weddell Sea. Periods of in situ supercooled water extending as deep as 65 m were associated with ice nucleation and frazil formation at depth. Ascending ice crystals due to convection lead to increased dissipation rates. The main outflow of potentially supercooled water from deep beneath ice shelf is suggested to be in the deep channel northeast of the measurement site. Because this water is advected southward along the front, it becomes in situ supercooled, leading to suspended ice formation, thermohaline convection, and enhanced dissipation.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-11-0211.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 9
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    Online Resource
    Data Availability Principles and Practice
    American Meteorological Society ; 2020
    In:  Journal of Physical Oceanography Vol. 50, No. 12 ( 2020-12), p. 3377-3378
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 50, No. 12 ( 2020-12), p. 3377-3378
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-20-0266.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 10
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    Online Resource
    The Generation of Linear and Nonlinear Internal Waves Forced by Subinertial Tides over the Yermak Plateau, Arctic Ocean
    American Meteorological Society ; 2022
    In:  Journal of Physical Oceanography Vol. 52, No. 9 ( 2022-09), p. 2183-2203
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 52, No. 9 ( 2022-09), p. 2183-2203
    Abstract: The propagation of internal waves (IWs) of tidal frequency is inhibited poleward of the critical latitude, where the tidal frequency is equal to the Coriolis frequency ( f ). These subinertial IWs may propagate in the presence of background vorticity, which can reduce rotational effects. Additionally, for strong tidal currents, the isopycnal displacements may evolve into internal solitary waves (ISWs). In this study, wave generation by the subinertial K 1 and M 2 tides over the Yermak Plateau (YP) is modeled to understand the linear response and the conditions necessary for the generation of ISWs. The YP stretches out into Fram Strait, a gateway into the Arctic Ocean for warm Atlantic-origin waters. We consider the K 1 tide for a wide range of tidal amplitudes to understand the IW generation for different forcing. For weak tidal currents, the baroclinic response is predominantly at the second harmonic due to critical slopes. For sufficiently strong diurnal currents, ISWs are generated and their generation is not sensitive to the range of f and stratifications considered. The M 2 tide is subinertial yet the response shows propagating IW beams with frequency just over f . We discuss the propagation of these waves and the influence of variations of f , as a proxy for variations in the background vorticity, on the energy conversion to IWs. An improved understanding of tidal dynamics and IW generation at high latitudes is needed to quantify the magnitude and distribution of turbulent mixing, and its consequences for the changes in ocean circulation, heat content, and sea ice cover in the Arctic Ocean.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-21-0264.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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