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  • Artikel  (3)
  • Abyssal circulation  (2)
  • Autonomous vehicle  (1)
  • 1
    Publikationsdatum: 2022-10-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Szuts, Z. B., Bower, A. S., Donohue, K. A., Girton, J. B., Hummon, J. M., Katsumata, K., Lumpkin, R., Ortner, P. B., Phillips, H. E., Rossby, H. T., Shay, L. K., Sun, C., & Todd, R. E. The scientific and societal uses of global measurements of subsurface velocity. Frontiers in Marine Science, 6, (2019): 358, doi:10.3389/fmars.2019.00358.
    Beschreibung: Ocean velocity defines ocean circulation, yet the available observations of subsurface velocity are under-utilized by society. The first step to address these concerns is to improve visibility of and access to existing measurements, which include acoustic sampling from ships, subsurface float drifts, and measurements from autonomous vehicles. While multiple programs provide data publicly, the present difficulty in finding, understanding, and using these data hinder broader use by managers, the public, and other scientists. Creating links from centralized national archives to project specific websites is an easy but important way to improve data discoverability and access. A further step is to archive data in centralized databases, which increases usage by providing a common framework for disparate measurements. This requires consistent data standards and processing protocols for all types of velocity measurements. Central dissemination will also simplify the creation of derived products tailored to end user goals. Eventually, this common framework will aid managers and scientists in identifying regions that need more sampling and in identifying methods to fulfill those demands. Existing technologies are capable of improving spatial and temporal sampling, such as using ships of opportunity or from autonomous platforms like gliders, profiling floats, or Lagrangian floats. Future technological advances are needed to fill sampling gaps and increase data coverage.
    Beschreibung: This work was supported by the National Science Foundation, United States, Grant Numbers 1356383 to ZBS, OCE 1756361 to ASB at the Woods Hole Oceanographic Institution, and 1536851 to KAD and HTR; the National Oceanographic and Atmospheric Administration, United States, Ocean Observations and Monitoring Division and Atlantic Oceanographic and Meteorological Laboratory to RL; Royal Caribbean Cruise Ltd., to PBO; the Australian Government Department of the Environment and Energy National Environmental Science Programme and Australian Research Council Centre of Excellence for Climate Extremes to HEP; and the Gulf of Mexico Research Initiative Grant V-487 to LS.
    Schlagwort(e): Velocity ; Ocean measurements ; Subsurface ; Database ; Sampling network ; ADCP ; Autonomous vehicle ; Floats
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2022-05-26
    Beschreibung: 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(6), (2019): 1577-1592, doi:10.1175/JPO-D-18-0124.1.
    Beschreibung: The main source feeding the abyssal circulation of the North Pacific is the deep, northward flow of 5–6 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) through the Samoan Passage. A recent field campaign has shown that this flow is hydraulically controlled and that it experiences hydraulic jumps accompanied by strong mixing and dissipation concentrated near several deep sills. By our estimates, the diapycnal density flux associated with this mixing is considerably larger than the diapycnal flux across a typical isopycnal surface extending over the abyssal North Pacific. According to historical hydrographic observations, a second source of abyssal water for the North Pacific is 2.3–2.8 Sv of the dense flow that is diverted around the Manihiki Plateau to the east, bypassing the Samoan Passage. This bypass flow is not confined to a channel and is therefore less likely to experience the strong mixing that is associated with hydraulic transitions. The partitioning of flux between the two branches of the deep flow could therefore be relevant to the distribution of Pacific abyssal mixing. To gain insight into the factors that control the partitioning between these two branches, we develop an abyssal and equator-proximal extension of the “island rule.” Novel features include provisions for the presence of hydraulic jumps as well as identification of an appropriate integration circuit for an abyssal layer to the east of the island. Evaluation of the corresponding circulation integral leads to a prediction of 0.4–2.4 Sv of bypass flow. The circulation integral clearly identifies dissipation and frictional drag effects within the Samoan Passage as crucial elements in partitioning the flow.
    Beschreibung: This work was supported by the National Science Foundation under Grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657870, OCE-1658027, and OCE-1657795. We thank the captain, crew, and engineers at APL/UW for their hard work and skill.
    Beschreibung: 2020-06-11
    Schlagwort(e): Abyssal circulation ; Bottom currents ; Boundary currents ; Channel flows ; Mixing ; Transport
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cusack, J. M., Voet, G., Alford, M. H., Girton, J. B., Carter, G. S., Pratt, L. J., Pearson-Potts, K. A., & Tan, S. Persistent turbulence in the Samoan Passage. Journal of Physical Oceanography, 49(12), (2019): 3179-3197, doi: 10.1175/JPO-D-19-0116.1.
    Beschreibung: Abyssal waters forming the lower limb of the global overturning circulation flow through the Samoan Passage and are modified by intense mixing. Thorpe-scale-based estimates of dissipation from moored profilers deployed on top of two sills for 17 months reveal that turbulence is continuously generated in the passage. Overturns were observed in a density band in which the Richardson number was often smaller than ¼, consistent with shear instability occurring at the upper interface of the fast-flowing bottom water layer. The magnitude of dissipation was found to be stable on long time scales from weeks to months. A second array of 12 moored profilers deployed for a shorter duration but profiling at higher frequency was able to resolve variability in dissipation on time scales from days to hours. At some mooring locations, near-inertial and tidal modulation of the dissipation rate was observed. However, the modulation was not spatially coherent across the passage. The magnitude and vertical structure of dissipation from observations at one of the major sills is compared with an idealized 2D numerical simulation that includes a barotropic tidal forcing. Depth-integrated dissipation rates agree between model and observations to within a factor of 3. The tide has a negligible effect on the mean dissipation. These observations reinforce the notion that the Samoan Passage is an important mixing hot spot in the global ocean where waters are being transformed continuously.
    Beschreibung: The authors thank Zhongxiang Xao and Jody Klymak, who provided earlier setups of the numerical model, and also Arjun Jagannathan for insightful discussions on the subject of flow over topography. We also thank John Mickett and Eric Boget for their assistance in designing, deploying, and recovering the moorings. In addition, we also thank the crew and scientists aboard the R/V Revelle and R/V Thompson, without whom the data presented in this paper could not have been gathered. Ilker Fer and two anonymous reviewers provided thoughtful feedback that improved the paper. This work was supported by the National Science Foundation under Grants OCE-1029268, OCE-1029483, OCE-1657264, OCE-1657795, OCE-1657870, and OCE-1658027.
    Schlagwort(e): Gravity waves ; Turbulence ; Abyssal circulation ; Mixing ; Tides
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Standort Signatur Erwartet Verfügbarkeit
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