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  • Mixing  (16)
  • Electronic structure and strongly correlated systems
  • Magnetism
  • American Geophysical Union  (13)
  • John Wiley & Sons  (4)
  • 2020-2024  (1)
  • 2010-2014  (16)
  • 1
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    Volcano monitoring with magnetic measurements: a simulation of eruptions at axial seamount, Kilauea, Baroarbunga, and Mount Saint Helens (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biasi, J., Tivey, M., & Fluegel, B. Volcano monitoring with magnetic measurements: a simulation of eruptions at axial seamount, Kilauea, Baroarbunga, and Mount Saint Helens. Geophysical Research Letters, 49(17), (2022): e2022GL100006, https://doi.org/10.1029/2022GL100006.
    Description: Monitoring of active volcanic systems is a challenging task due in part to the trade-offs between collection of high-quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically “transparent,” but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk.
    Description: This work was supported by the NSF Grant No 2052963 to J. Biasi and an internal Woods Hole Oceanographic Institution grant to M. Tivey.
    Keywords: Magnetism ; Volcanic hazards ; Hawaii ; Iceland ; Volcanology ; Monitoring
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Large-scale alignment of oceanic nitrate and density (2014)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 5322–5332, doi:10.1002/jgrc.20379.
    Description: By analyzing global data, we find that over large scales, surfaces of constant nitrate are often better aligned with isopycnals than with isobars, particularly below the euphotic zone. This is unexplained by the movement of isopycnal surfaces in response to eddies and internal waves, and is perhaps surprising given that the biological processes that alter nitrate distributions are largely depth dependent. We provide a theoretical framework for understanding the orientation of isonitrate surfaces in relation to isopycnals. In our model, the nitrate distribution results from the balance between depth-dependent biological processes (nitrate uptake and remineralization), and the along-isopycnal homogenization of properties by eddy fluxes (parameterized by eddy diffusivity). Where the along-isopycnal eddy diffusivity is relatively large, nitrate surfaces are better aligned with isopycnals than isobars. We test our theory by estimating the strength of the eddy diffusivity and biological export production from global satellite data sets and comparing their contributions. Indeed, we find that below the euphotic zone, the mean isonitrate surfaces are oriented along isopycnals where the isopycnal eddy diffusivity is large, and deviate where the biological export of organic matter is relatively strong. Comparison of nitrate data from profiling floats in different regions corroborates the hypothesis by showing variations in the nitrate-density relationship from one part of the ocean to another.
    Description: We acknowledge the support of the National Science Foundation (Grant OCE-0928617) and NASA (Grant NNX- 08AL80G).
    Description: 2014-04-15
    Keywords: Nitrate ; Export ; Mixing ; Isopycnal ; Alignment ; Large-scale
    Repository Name: Woods Hole Open Access Server
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  • 3
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    Diffusive vertical heat flux in the Canada Basin of the Arctic Ocean inferred from moored instruments (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 496-508, doi:10.1002/2013JC009346.
    Description: Observational studies have shown that an unprecedented warm anomaly has recently affected the temperature of the Atlantic Water (AW) layer lying at intermediate depth in the Arctic Ocean. Using observations from four profiling moorings, deployed in the interior of the Canada Basin between 2003 and 2011, the upward diffusive vertical heat flux from this layer is quantified. Vertical diffusivity is first estimated from a fine-scale parameterization method based on CTD and velocity profiles. Resulting diffusive vertical heat fluxes from the AW are in the range 0.1–0.2 W m−2 on average. Although large over the period considered, the variations of the AW temperature maximum yields small variations for the temperature gradient and thus the vertical diffusive heat flux. In most areas, variations in upward diffusive vertical heat flux from the AW have only a limited effect on temperature variations of the overlying layer. However, the presence of eddies might be an effective mechanism to enhance vertical heat transfer, although the small number of eddies sampled by the moorings suggest that this mechanism remains limited and intermittent in space and time. Finally, our results suggest that computing diffusive vertical heat flux with a constant vertical diffusivity of ∼2 × 10−6 m2 s−1 provides a reasonable estimate of the upward diffusive heat transfer from the AW layer, although this approximation breaks down in the presence of eddies.
    Description: C. Lique acknowledge support from JISAO and the Program on Climate Change of the University of Washington. J. Guthrie and J. Morison are supported by National Science Foundation grants ARC-0909408 and ARC-0856330. M. Steele is supported by the Office of Naval Researches Arctic and Global Prediction Program, by NSFs Division of Polar Programs, and by NASAs Cryosphere and Physical Oceanography programs. Support for the BGOS program and R. Krishfield was provided by the National Science Foundation (under grants ARC-0806115, ARC-0631951, ARC-0806306, and ARC-0856531) and Woods Hole Oceanographic Institution internal funding. For A. Proshutinsky, this research is supported by the National Science Foundation Office of Polar Programs, awards ARC-1203720 and ARC-0856531.
    Description: 2014-07-22
    Keywords: Arctic Ocean ; Atlantic water ; Mixing
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Physical controls on hypoxia in Chesapeake Bay : a numerical modeling study (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 1239–1256, doi:10.1002/jgrc.20138.
    Description: A three-dimensional circulation model with a relatively simple dissolved oxygen model is used to examine the role that physical forcing has on controlling hypoxia and anoxia in Chesapeake Bay. The model assumes that the biological utilization of dissolved oxygen is constant in both time and space, isolating the role that physical forces play in modulating oxygen dynamics. Despite the simplicity of the model, it demonstrates skill in reproducing the observed variability of dissolved oxygen in the bay, highlighting the important role that variations in physical forcing have on the seasonal cycle of hypoxia. Model runs demonstrate significant changes in the annual integrated hypoxic volume as a function of river discharge, water temperature, and wind speed and direction. Variations in wind speed and direction had the greatest impact on the observed seasonal cycle of hypoxia and large impacts on the annually integrated hypoxic volume. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in river discharge, but integrated hypoxic volumes were sensitive to the overall magnitude of river discharge at annual time scales. Increases in river discharge were shown to increase hypoxic volumes, independent from the associated biological response to higher nutrient delivery. However, increases in hypoxic volume were limited at very high river discharge because increased advective fluxes limited the overall length of the hypoxic region. Changes in water temperature and its control on dissolved oxygen saturation were important to both the seasonal cycle of hypoxia and the overall magnitude of hypoxia in a given year.
    Description: The funding for this research was obtained from NSF Grant OCE-0954690 and supported by NOAA via the U.S. IOOS Office (Award Numbers NA10NOS0120063 and NA11NOS0120141) and managed by the Southeastern Universities Research Association.
    Description: 2013-09-14
    Keywords: Hypoxia ; Stratification ; Mixing ; Wind
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean : results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 2774–2792, doi:10.1002/jgrc.20217.
    Description: The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from inline image in the Southeast Pacific to inline image in the Scotia Sea, typically reaching inline image within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wavefield is found to have enhanced energy, a less-inertial frequency content and a dominance of upward propagating energy. These results strongly suggest that bottom-generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mW m−2 in the Southeast Pacific and 14 mW m−2 in the Scotia Sea. Typically, 10%–30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure-derived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.
    Description: The DIMES experiment is supported by the Natural Environment Research Council (NERC) of the U.K. and U.S. National Science Foundation. K.L.S. and J.A.B. are supported by NERC.
    Description: 2013-12-04
    Keywords: Turbulent dissipation ; Internal wave ; Antarctic Circumpolar Current ; Mixing
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Vorticity generation by short-crested wave breaking (2013)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L24604, doi:10.1029/2012GL054034.
    Description: Eddies and vortices associated with breaking waves rapidly disperse pollution, nutrients, and terrestrial material along the coast. Although theory and numerical models suggest that vorticity is generated near the ends of a breaking wave crest, this hypothesis has not been tested in the field. Here we report the first observations of wave-generated vertical vorticity (e.g., horizontal eddies), and find that individual short-crested breaking waves generate significant vorticity [O(0.01 s−1)] in the surfzone. Left- and right-handed wave ends generate vorticity of opposite sign, consistent with theory. In contrast to theory, the observed vorticity also increases inside the breaking crest, possibly owing to onshore advection of vorticity generated at previous stages of breaking or from the shape of the breaking region. Short-crested breaking transferred energy from incident waves to lower frequency rotational motions that are a primary mechanism for dispersion near the shoreline.
    Description: Funding was provided by a National Security Science and Engineering Faculty Fellowship, the Office of Naval Research, and a Woods Hole Oceanographic Institution Postdoctoral Fellowship.
    Description: 2013-06-21
    Keywords: Mixing ; Nearshore ; Turbulence ; Vorticity ; Waves
    Repository Name: Woods Hole Open Access Server
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  • 7
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    The spatial distribution and annual cycle of upper ocean thermohaline structure (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02027, doi:10.1029/2011JC007033.
    Description: Observations of the spatial distribution and persistence of thermohaline structure are presented, and show how advection and diffusion affect a passive tracer. More than two years of underwater glider observations in the central subtropical North Pacific showed thermohaline variability over horizontal scales from 5 to 1300 km. Thermohaline fluctuations along isopycnals (spice fluctuations) were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions. Fluctuations were uncorrelated between the layers but stirred by the same velocity field. Spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses. Spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated. Horizontal wave number spectra of spice had slopes of −2 everywhere in the upper 1000 m. Submesoscale spice fluctuations had slopes in physical space near the ratio of the Coriolis parameter to the buoyancy frequency (f/N), consistent with predictions of quasi-geostrophic theory. In the mixed layer, thermohaline structure had a significant annual cycle with smaller interannual differences. Thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals. Horizontal diffusivity estimates in the remnant mixed layer were 0.4 m2 s−1 at 15–28 km wavelengths and 0.9 m2 s−1 at 35–45 km wavelengths.
    Description: We gratefully acknowledge the National Science Foundation for funding this work under grant number OCE0452574.
    Description: 2012-08-18
    Keywords: Diffusion ; Mixing ; Spice ; Stirring ; Thermohaline structure
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Modeling surf zone tracer plumes : 2. Transport and dispersion (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C11028, doi:10.1029/2011JC007211.
    Description: Five surf zone dye tracer releases from the HB06 experiment are simulated with a tracer advection diffusion model coupled to a Boussinesq surf zone model (funwaveC). Model tracer is transported and stirred by currents and eddies and diffused with a breaking wave eddy diffusivity, set equal to the breaking wave eddy viscosity, and a small (0.01 m2 s−1) background diffusivity. Observed and modeled alongshore parallel tracer plumes, transported by the wave driven alongshore current, have qualitatively similar cross-shore structures. Although the model skill for mean tracer concentration is variable (from negative to 0.73) depending upon release, cross-shore integrated tracer moments (normalized by the cross-shore tracer integral) have consistently high skills (≈0.9). Modeled and observed bulk surf zone cross-shore diffusivity estimates are also similar, with 0.72 squared correlation and skill of 0.4. Similar to the observations, the model bulk (absolute) cross-shore diffusivity is consistent with a mixing length parameterization based on low-frequency (0.001–0.03 Hz) eddies. The model absolute cross-shore dispersion is dominated by stirring from surf zone eddies and does not depend upon the presence of the breaking wave eddy diffusivity. Given only the bathymetry and incident wave field, the coupled Boussinesq-tracer model qualitatively reproduces the observed cross-shore absolute tracer dispersion, suggesting that the model can be used to study surf zone tracer dispersion mechanisms.
    Description: This research was supported by SCCOOS, CA Coastal Conservancy, NOAA, NSF, ONR, and CA Sea Grant.
    Description: 2012-05-18
    Keywords: Dispersion ; Mixing ; Surf zone ; Tracer
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Modeling surf zone tracer plumes : 1. Waves, mean currents, and low-frequency eddies (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C11027, doi:10.1029/2011JC007210.
    Description: A model that accurately simulates surf zone waves, mean currents, and low-frequency eddies is required to diagnose the mechanisms of surf zone tracer transport and dispersion. In this paper, a wave-resolving time-dependent Boussinesq model is compared with waves and currents observed during five surf zone dye release experiments. In a companion paper, Clark et al. (2011) compare a coupled tracer model to the dye plume observations. The Boussinesq model uses observed bathymetry and incident random, directionally spread waves. For all five releases, the model generally reproduces the observed cross-shore evolution of significant wave height, mean wave angle, bulk directional spread, mean alongshore current, and the frequency-dependent sea surface elevation spectra and directional moments. The largest errors are near the shoreline where the bathymetry is most uncertain. The model also reproduces the observed cross-shore structure of rotational velocities in the infragravity (0.004 〈 f 〈 0.03 Hz) and very low frequency (VLF) (0.001 〈 f 〈 0.004 Hz) bands, although the modeled VLF energy is 2–3 times too large. Similar to the observations, the dominant contributions to the modeled eddy-induced momentum flux are in the VLF band. These eddies are elliptical near the shoreline and circular in the mid surf zone. The model-data agreement for sea swell waves, low-frequency eddies, and mean currents suggests that the model is appropriate for simulating surf zone tracer transport and dispersion.
    Description: This research was supported by SCCOOS, CA Coastal Conservancy, NOAA, NSF, ONR, and CA Sea Grant.
    Description: 2012-05-18
    Keywords: Mixing ; Surf zone ; Tracer dispersion
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Eddy stirring in the Southern Ocean (2011)
    American Geophysical Union
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C09019, doi:10.1029/2010JC006818.
    Description: There is an ongoing debate concerning the distribution of eddy stirring across the Antarctic Circumpolar Current (ACC) and the nature of its controlling processes. The problem is addressed here by estimating the isentropic eddy diffusivity κ from a collection of hydrographic and altimetric observations, analyzed in a mixing length theoretical framework. It is shown that, typically, κ is suppressed by an order of magnitude in the upper kilometer of the ACC frontal jets relative to their surroundings, primarily as a result of a local reduction of the mixing length. This observation is reproduced by a quasi-geostrophic theory of eddy stirring across a broad barotropic jet based on the scaling law derived by Ferrari and Nikurashin (2010). The theory interprets the observed widespread suppression of the mixing length and κ in the upper layers of frontal jets as the kinematic consequence of eddy propagation relative to the mean flow within jet cores. Deviations from the prevalent regime of mixing suppression in the core of upper-ocean jets are encountered in a few special sites. Such ‘leaky jet’ segments appear to be associated with sharp stationary meanders of the mean flow that are generated by the interaction of the ACC with major topographic features. It is contended that the characteristic thermohaline structure of the Southern Ocean, consisting of multiple upper-ocean thermohaline fronts separated and underlaid by regions of homogenized properties, is largely a result of the widespread suppression of eddy stirring by parallel jets.
    Description: This study was conducted during A.C.N. G.’s stay at MIT, which was supported jointly by MIT and the U.K. Natural Environment Research Council (NERC) through a NERC Advanced Research Fellowship (NE/C517633/1). R.F. acknowledges the support of NSFaward OCE‐0825376. K.P.’s participation in this work was supported by WHOI bridge support funds.
    Keywords: Antarctic Circumpolar Current ; Eddy stirring ; Mixing
    Repository Name: Woods Hole Open Access Server
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