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  • Diapycnal mixing  (3)
  • Remote sensing  (3)
  • American Meteorological Society  (5)
  • American Geophysical Union  (1)
  • American Chemical Society
  • National Academy of Sciences
  • University of Chicago Press
  • 2020-2023  (6)
  • 1980-1984
  • 1935-1939
  • 1925-1929
  • 1920-1924
  • 2020  (6)
  • 1984
  • 1925
  • 1924
  • 1920
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  • 2020-2023  (6)
  • 1980-1984
  • 1935-1939
  • 1925-1929
  • 1920-1924
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  • 1
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(2), (2020): 415-437, doi:10.1175/JPO-D-19-0019.1.
    Description: Results are presented from two dye release experiments conducted in the seasonal thermocline of the Sargasso Sea, one in a region of low horizontal strain rate (~10−6 s−1), the second in a region of intermediate horizontal strain rate (~10−5 s−1). Both experiments lasted ~6 days, covering spatial scales of 1–10 and 1–50 km for the low and intermediate strain rate regimes, respectively. Diapycnal diffusivities estimated from the two experiments were κz = (2–5) × 10−6 m2 s−1, while isopycnal diffusivities were κH = (0.2–3) m2 s−1, with the range in κH being less a reflection of site-to-site variability, and more due to uncertainties in the background strain rate acting on the patch combined with uncertain time dependence. The Site I (low strain) experiment exhibited minimal stretching, elongating to approximately 10 km over 6 days while maintaining a width of ~5 km, and with a notable vertical tilt in the meridional direction. By contrast, the Site II (intermediate strain) experiment exhibited significant stretching, elongating to more than 50 km in length and advecting more than 150 km while still maintaining a width of order 3–5 km. Early surveys from both experiments showed patchy distributions indicative of small-scale stirring at scales of order a few hundred meters. Later surveys show relatively smooth, coherent distributions with only occasional patchiness, suggestive of a diffusive rather than stirring process at the scales of the now larger patches. Together the two experiments provide important clues as to the rates and underlying processes driving diapycnal and isopycnal mixing at these scales.
    Description: Results are presented from two dye release experiments conducted in the seasonal thermocline of the Sargasso Sea, one in a region of low horizontal strain rate (~10−6 s−1), the second in a region of intermediate horizontal strain rate (~10−5 s−1). Both experiments lasted ~6 days, covering spatial scales of 1–10 and 1–50 km for the low and intermediate strain rate regimes, respectively. Diapycnal diffusivities estimated from the two experiments were κz = (2–5) × 10−6 m2 s−1, while isopycnal diffusivities were κH = (0.2–3) m2 s−1, with the range in κH being less a reflection of site-to-site variability, and more due to uncertainties in the background strain rate acting on the patch combined with uncertain time dependence. The Site I (low strain) experiment exhibited minimal stretching, elongating to approximately 10 km over 6 days while maintaining a width of ~5 km, and with a notable vertical tilt in the meridional direction. By contrast, the Site II (intermediate strain) experiment exhibited significant stretching, elongating to more than 50 km in length and advecting more than 150 km while still maintaining a width of order 3–5 km. Early surveys from both experiments showed patchy distributions indicative of small-scale stirring at scales of order a few hundred meters. Later surveys show relatively smooth, coherent distributions with only occasional patchiness, suggestive of a diffusive rather than stirring process at the scales of the now larger patches. Together the two experiments provide important clues as to the rates and underlying processes driving diapycnal and isopycnal mixing at these scales.
    Description: 2020-08-06
    Keywords: Ocean ; Atlantic Ocean ; Diapycnal mixing ; Diffusion ; Dispersion ; Mixing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Reviews of Geophysics 58(3), (2020): e2019RG000672, doi:10.1029/2019RG000672.
    Description: Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea‐level observing system, the knowledge of regional sea‐level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea‐level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea‐level change. Here we review the individual processes which lead to sea‐level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea‐level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea‐level observation network—particularly as related to satellite observations—in the improved scientific understanding of the contributors to regional sea‐level change.
    Description: The research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The authors acknowledge support from the National Aeronautics and Space Administration under Grants 80NSSC17K0565, 80NSSC170567, 80NSSC17K0566, 80NSSC17K0564, and NNX17AB27G. A. A. acknowledges support under GRACE/GRACEFO Science Team Grant (NNH15ZDA001N‐GRACE). T. W. acknowledges support by the National Aeronautics and Space Administration (NASA) under the New (Early Career) Investigator Program in Earth Science (Grant: 80NSSC18K0743). C. G. P was supported by the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists at the Woods Hole Oceanographic Institution.
    Keywords: Sea level ; Satellite observations ; Remote sensing
    Repository Name: Woods Hole Open Access Server
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  • 3
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Schlundt, M., Farrar, J. T., Bigorre, S. P., Plueddemann, A. J., & Weller, R. A. (2020). Accuracy of wind observations from open-ocean buoys: correction for flow distortion. Journal of Atmospheric and Oceanic Technology, 37(4), 687-703, doi:10.1175/JTECH-D-19-0132.1.
    Description: The comparison of equivalent neutral winds obtained from (i) four WHOI buoys in the subtropics and (ii) scatterometer estimates at those locations reveals a root-mean-square (RMS) difference of 0.56–0.76 m s−1. To investigate this RMS difference, different buoy wind error sources were examined. These buoys are particularly well suited to examine two important sources of buoy wind errors because 1) redundant anemometers and a comparison with numerical flow simulations allow us to quantitatively assess flow distortion errors, and 2) 1-min sampling at the buoys allows us to examine the sensitivity of buoy temporal sampling/averaging in the buoy–scatterometer comparisons. The interanemometer difference varies as a function of wind direction relative to the buoy wind vane and is consistent with the effects of flow distortion expected based on numerical flow simulations. Comparison between the anemometers and scatterometer winds supports the interpretation that the interanemometer disagreement, which can be up to 5% of the wind speed, is due to flow distortion. These insights motivate an empirical correction to the individual anemometer records and subsequent comparison with scatterometer estimates show good agreement.
    Description: We gratefully acknowledge the help of three anonymous reviewers, whose input greatly improved the paper. In particular, one reviewer pointed out a mistake in our initial interpretation of scatterometer stability, which was corrected in the final manuscript. JTF and MS were supported by NASA Grant NNX14AM71G (International Ocean Vector Winds Science Team). The SPURS observations were supported by NASA (Grants NNX11AE84G, NNX15AG20G, and 80NSSC18K1494). The Stratus, NTAS, and WHOTS ocean reference stations (ORS) are long-term surface moorings deployed as part of the OceanSITES (http://www.oceansites.org) component of the Global Ocean Observing System, and are supported by NOAA’s Climate Program Office’s Ocean Observing and Monitoring Division, as are RAW, AJP, and SPB through the Cooperative Institute for the North Atlantic Region (CINAR) under Cooperative Agreement NA14OAR4320158 with NOAA Climate Program Office (CPO) (FundRef No. 100007298). The technical staff of the UOP Group at WHOI and the crews of NOAA and UNOLS vessels have been essential to the successful long-term maintenance of the ORS.
    Keywords: Ocean ; Wind ; Buoy observations ; Remote sensing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    American Meteorological Society
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(12), (2019): 3061-3068, doi: 10.1175/JPO-D-18-0172.1.
    Description: The calculation of energy flux in coastal trapped wave modes is reviewed in the context of tidal energy pathways near the coast. The significant barotropic pressures and currents associated with coastal trapped wave modes mean that large errors in estimating the wave flux are incurred if only the baroclinic component is considered. A specific example is given showing that baroclinic flux constitutes only 10% of the flux in a mode-1 wave for a reasonable choice of stratification and bathymetry. The interpretation of baroclinic energy flux and barotropic-to-baroclinic conversion at the coast is discussed: in contrast to the open ocean, estimates of baroclinic energy flux do not represent a wave energy flux; neither does conversion represent the scattering of energy from the tidal Kelvin wave to higher modes.
    Description: This work was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship, and by NSF under Grant OCE-1756781. I am grateful to K. Brink for the many useful conversations that contributed to this work and to J. Toole for providing detailed comments on an early version of this paper. The comments of three anonymous reviewers were very helpful in improving this paper.
    Description: 2020-06-03
    Keywords: Diapycnal mixing ; Internal waves ; Kelvin waves ; Topographic effects ; Waves, oceanic ; Tides
    Repository Name: Woods Hole Open Access Server
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  • 5
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 37(5), (2020): 807-824, doi:10.1175/JTECH-D-19-0054.1.
    Description: Marine mammals are under growing pressure as anthropogenic use of the ocean increases. Ship strikes of large whales and loud underwater sound sources including air guns for marine geophysical prospecting and naval midfrequency sonar are criticized for their possible negative effects on marine mammals. Competent authorities regularly require the implementation of mitigation measures, including vessel speed reductions or shutdown of acoustic sources if marine mammals are sighted in sensitive areas or in predefined exclusion zones around a vessel. To ensure successful mitigation, reliable at-sea detection of animals is crucial. To date, ship-based marine mammal observers are the most commonly implemented detection method; however, thermal (IR) imaging–based automatic detection systems have been used in recent years. This study evaluates thermal imaging–based automatic whale detection technology for its use across different oceans. The performance of this technology is characterized with respect to environmental conditions, and an automatic detection algorithm for whale blows is presented. The technology can detect whales in polar, temperate, and subtropical ocean regimes over distances of up to several kilometers and outperforms marine mammal observers in the number of whales detected. These results show that thermal imaging technology can be used to assist in providing protection for marine mammals against ship strike and acoustic impact across the world’s oceans.
    Description: This work was funded by the Office of Naval Research (ONR) under Award N000141310856, by the Environmental Studies Research Fund (ESRF; esrfunds.org) under Award 2014-03S and by the Alfred-Wegener-Institute Helmholtz Zentrum für Polar- und Meeresforschung. DPZ and OB declare competing financial interests: 1) Patent US8941728B2, DE102011114084B4: A method for automatic real-time marine mammal detection. The patent describes the ideas basic to the automatic whale detection software as used to acquire and process the data presented in this paper. 2) Licensing of the Tashtego automatic whale detection software to the manufacturer of IR sensor. The authors confirm that these competing financial interests did not alter their adherence good scientific practice. We thank P. Abgrall, J. Coffey, K. Keats, B. Mactavish, V. Moulton, and S. Penney-Belbin for data collection or IR image review. We thank S. Besaw, J. Christian, A. Coombs, P. Coombs, W. Costello, T. Elliott, E. Evans, I. Goudie, C. Jones, K. Knowles, R. Martin, A. Murphy, D. and J. Shepherd; and the staffs at the Irish Loop Express, the Myrick Wireless Interpretive Centre, the Mistaken Point Ecological Reserve, and the lighthouse keepers for logistical assistance at our remote field site. We thank D. Boutilier and B. McDonald (DFO) for assisting us in obtaining license to occupy permits for Cape Race. We thank D. Taylor (ESRF Research Manager) for his support.
    Keywords: Ocean ; Instrumentation/sensors ; Remote sensing ; Animal studies ; Field experiments
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(3), (2020): 715-726, doi:10.1175/JPO-D-19-0021.1.
    Description: Closing the overturning circulation of bottom water requires abyssal transformation to lighter densities and upwelling. Where and how buoyancy is gained and water is transported upward remain topics of debate, not least because the available observations generally show downward-increasing turbulence levels in the abyss, apparently implying mean vertical turbulent buoyancy-flux divergence (densification). Here, we synthesize available observations indicating that bottom water is made less dense and upwelled in fracture zone valleys on the flanks of slow-spreading midocean ridges, which cover more than one-half of the seafloor area in some regions. The fracture zones are filled almost completely with water flowing up-valley and gaining buoyancy. Locally, valley water is transformed to lighter densities both in thin boundary layers that are in contact with the seafloor, where the buoyancy flux must vanish to match the no-flux boundary condition, and in thicker layers associated with downward-decreasing turbulence levels below interior maxima associated with hydraulic overflows and critical-layer interactions. Integrated across the valley, the turbulent buoyancy fluxes show maxima near the sidewall crests, consistent with net convergence below, with little sensitivity of this pattern to the vertical structure of the turbulence profiles, which implies that buoyancy flux convergence in the layers with downward-decreasing turbulence levels dominates over the divergence elsewhere, accounting for the net transformation to lighter densities in fracture zone valleys. We conclude that fracture zone topography likely exerts a controlling influence on the transformation and upwelling of bottom water in many areas of the global ocean.
    Description: The data used in this study were collected in the context of several projects funded by the U.S. National Science Foundation (NSF), in particular BBTRE (OCE-9415589 and OCE-9415598) and DoMORE (OCE-1235094). Funding for the analysis was provided as part of the NSF DoMORE and DECIMAL (OCE-1735618) projects. Author Ijichi is a Japan Society for the Promotion of Science (JSPS) Overseas Research Fellow. Comments on an early draft of this paper by Jim Ledwell and Bryan Kaiser, as well as topical discussions with Jörn Callies and Trevor McDougall, are gratefully acknowledged. The paper was greatly improved during the review process, in particular because of the critical comments from one of the two anonymous reviewers.
    Keywords: Diapycnal mixing ; Topographic effects ; Turbulence ; Upwelling/downwelling ; Bottom currents/bottom water
    Repository Name: Woods Hole Open Access Server
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