227 results on '"Alford, Matthew H."'
Search Results
2. Near-slope turbulence in a Rockall canyon
- Author
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van Haren, Hans, Voet, Gunnar, Alford, Matthew H., Fernández-Castro, Bieito, Naveira Garabato, Alberto C., Wynne-Cattanach, Bethan L., Mercier, Herlé, and Messias, Marie-José
- Published
- 2024
- Full Text
- View/download PDF
3. Internal wave breaking near the foot of a steep East-Pacific continental slope
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van Haren, Hans, Voet, Gunnar, Alford, Matthew H., and Torres, Daniel J.
- Published
- 2022
- Full Text
- View/download PDF
4. A novel cross-shore transport mechanism revealed by subsurface, robotic larval mimics : Internal wave deformation of the background velocity field
- Author
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Garwood, Jessica C., Lucas, Andrew J., Naughton, Perry, Alford, Matthew H., Roberts, Paul L. D., Jaffe, Jules S., deGelleke, Laura, and Franks, Peter J. S.
- Published
- 2020
5. Effect of crossflow on trapping depths of particle plumes: laboratory experiments and application to the PLUMEX field experiment
- Author
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Wang, Dayang, Adams, E. Eric, Munoz-Royo, Carlos, Peacock, Thomas, and Alford, Matthew H.
- Published
- 2021
- Full Text
- View/download PDF
6. UNDERSTANDING VORTICITY : CAUSED BY FLOW PASSING AN ISLAND
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Rudnick, Daniel L., Zeiden, Kristin L., Ou, Celia Y., Johnston, T.M. Shaun, MacKinnon, Jennifer A., Alford, Matthew H., and Voet, Gunnar
- Published
- 2019
7. EDDIES, TOPOGRAPHY, AND THE ABYSSAL FLOW : BY THE KYUSHU-PALAU RIDGE NEAR VELASCO REEF
- Author
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Andres, Magdalena, Siegelman, Mika, Hormann, Verena, Musgrave, Ruth C., Merrifield, Sophia T., Rudnick, Daniel L., Merrifield, Mark A., Alford, Matthew H., Voet, Gunnar, Wijesekera, Hemantha W., MacKinnon, Jennifer A., Centurioni, Luca, Nash, Jonathan D., and Terrill, Eric J.
- Published
- 2019
8. A SPATIAL GEOGRAPHY OF ABYSSAL TURBULENT MIXING IN THE SAMOAN PASSAGE
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Carter, Glenn S., Voet, Gunnar, Alford, Matthew H., Girton, James B., Mickett, John B., Klymak, Jody M., Pratt, Larry J., Pearson-Potts, Kelly A., Cusack, Jesse M., and Tan, Shuwen
- Published
- 2019
9. FLOW ENCOUNTERING ABRUPT TOPOGRAPHY (FLEAT) : A MULTISCALE OBSERVATIONAL AND MODELING PROGRAM TO UNDERSTAND HOW TOPOGRAPHY AFFECTS FLOWS IN THE WESTERN NORTH PACIFIC
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Johnston, T.M. Shaun, Schönau, Martha C., Paluszkiewicz, Terri, MacKinnon, Jennifer A., Arbic, Brian K., Colin, Patrick L., Alford, Matthew H., Andres, Magdalena, Centurioni, Luca, Graber, Hans C., Helfrich, Karl R., Hormann, Verena, Lermusiaux, Pierre F.J., Musgrave, Ruth C., Powell, Brian S., Qiu, Bo, Rudnick, Daniel L., Simmons, Harper L., St. Laurent, Louis, Terrill, Eric J., Trossman, David S., Voet, Gunnar, Wijesekera, Hemantha W., and Zeiden, Kristin L.
- Published
- 2019
10. OBSERVATIONS OF NEAR-INERTIAL SURFACE CURRENTS AT PALAU
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Siegelman, Mika, Merrifield, Mark A., Firing, Eric, MacKinnon, Jennifer A., Alford, Matthew H., Voet, Gunnar, Wijesekera, Hemantha W., Schramek, Travis A., Zeiden, Kristin L., and Terrill, Eric J.
- Published
- 2019
11. FLOW-TOPOGRAPHY INTERACTIONS IN THE SAMOAN PASSAGE
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Girton, James B., Mickett, John B., Zhao, ZhongXiang, Alford, Matthew H., Voet, Gunnar, Cusack, Jesse M., Carter, Glenn S., Pearson-Potts, Kelly A., Pratt, Larry J., Tan, Shuwen, and Klymak, Jody M.
- Published
- 2019
12. Breaking Internal Waves and Ocean Diapycnal Diffusivity in a High‐Resolution Regional Ocean Model: Evidence of a Wave‐Turbulence Cascade.
- Author
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Momeni, Kayhan, Ma, Yuchen, Peltier, William R., Menemenlis, Dimitris, Thakur, Ritabrata, Pan, Yulin, Arbic, Brian K., Skitka, Joseph, and Alford, Matthew H.
- Subjects
WATER waves ,INTERNAL waves ,OCEAN waves ,GENERAL circulation model ,OCEAN ,STRATIFIED flow ,OCEAN circulation ,ROTATION of the earth ,SEISMIC waves - Abstract
It is generally understood that the origin of ocean diapycnal diffusivity is primarily associated with the stratified turbulence produced by breaking internal (gravity) waves (IW). However, it requires significant effort to verify diffusivity values in ocean general circulation models in any particular geographical region of the ocean due to the scarcity of microstructure measurements. Recent analyses of downscaled IW fields from an internal‐wave‐admitting global ocean simulation into higher‐resolution regional configurations northwest of Hawaii have demonstrated a much‐improved fit of the simulated IW spectra to the in‐situ profiler measurements such as the Garrett‐Munk (GM) spectrum. Here, we employ this dynamically downscaled ocean simulation to directly analyze the nature of the IW‐breaking and the wave‐turbulence cascade in this region. We employ a modified version of the Kappa Profile Parameterization (KPP) to infer what the horizontally averaged vertical profile of diapycnal diffusivity should be, and compare this to the background profile that would be employed in the ocean component of a low‐resolution coupled climate model such as the Community Earth System Model (CESM) of the US National Center for Atmospheric Research (NCAR). In pursuing this goal, we also demonstrate that the wavefield in the high‐resolution regional domain is dominated by a well‐resolved spectrum of low‐mode IWs that are predictable by solving an appropriate eigenvalue problem for stratified flow. We finally suggest a new tentative approach to improve the KPP parameterization. Plain Language Summary: A much‐improved spectrum of the simulated internal wave (IW) field has recently been obtained by downscaling a global ocean model into a higher‐resolution regional configuration. The global simulation is based on the Massachusetts Institute of Technology general circulation model (MITgcm) forced by both astronomical tidal potential and surface atmospheric processes. By employing a mathematical framework to predict the structure of IWs, we first demonstrate that the interior wavefield of the high‐resolution regional domain is well dominated by a series of low‐order IW modes. Then, we address the issue as to whether the component of the K‐Profile Parameterization (KPP) associated with IW shear might be able to explain the physical origins of the background depth dependence of diapycnal diffusivity that would normally be employed in the ocean component of a modern coupled climate model. Finally, we suggest a tentative approach to further improve KPP. Key Points: A representation of internal wave modes that includes dissipation is derived that explains spectra in a tidally forced numerical simulationEliminating the background component of KPP leads to a representation of the physics of internal wave breakingRealistic diapycnal diffusivity profiles can be obtained by minor adjustments to the shear component of KPP [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
13. Surface and Sub‐Surface Kinetic Energy Wavenumber‐Frequency Spectra in Global Ocean Models and Observations.
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Ansong, Joseph K., Arbic, Brian K., Nelson, Arin D., Alford, Matthew H., Kunze, Eric, Menemenlis, Dimitris, Savage, Anna C., Shriver, Jay F., Wallcraft, Alan J., and Buijsman, Maarten C.
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KINETIC energy ,OCEAN surface topography ,INTERNAL waves ,GRAVITY waves ,GENERAL circulation model ,OCEANOGRAPHY - Abstract
This paper examines spectra of horizontal kinetic energy (HKE) in the surface and sub‐surface ocean, with an emphasis on internal gravity wave (IGW) motions, in global high‐resolution ocean simulations. Horizontal wavenumber‐frequency spectra of surface HKE are computed over seven oceanic regions from two global simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three global simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). In regions with high IGW activity, high surface HKE variance in the horizontal wavenumber‐frequency spectra is aligned along IGW linear dispersion curves. For both HYCOM and MITgcm, and in almost all regions, finer horizontal resolution yields more energetic supertidal IGW continuum spectra. The ratio of high‐horizontal‐wavenumber variance in semi‐diurnal and supertidal motions relative to lower‐frequency motions, a quantity of great interest for swath altimetry, depends on the model employed and the horizontal resolution within the model, implying that quantitative predictions of the partition between low‐ and high‐frequency motions taken from particular simulations should be treated with care. The frequency‐vertical wavenumber spectra, frequency spectra, and vertical wavenumber spectra from the models are compared to spectra computed from McLane profilers at nine locations. In general, MITgcm spectra match the McLane profiler spectra more closely at high frequencies (|ω| > 4.5 cpd). In both models, vertical wavenumber spectra roll off more steeply than observations at high vertical wavenumbers (m > 10−2 cpm). The vertical wavenumber spectra in such models is an important target for improvement, due to turbulence production and dissipation that takes place at high vertical wavenumbers. Plain Language Summary: Recently, a small but growing number of global ocean models have begun to employ simultaneous tidal and atmospheric forcing. At the same time, increasing supercomputer power has allowed for simulations of oceanic motions with increasing accuracy, increasing feature (spatial) resolution, and more frequent time slices. Global ocean models with fine grid spacing, and simultaneous tidal and atmospheric forcing, host a vigorous spectrum of high‐frequency waves that control mixing over most of the ocean water column, and are important for many operational oceanography challenges. As an example of the latter, high‐resolution global internal wave models have been used to study the relative partition of high‐frequency versus low‐frequency motions at the small horizontal scales that will be measured by the new Surface Water Ocean Topography mission. The partition described above depends on the model employed and the grid spacing employed within that model, meaning that conclusions about the partition are dependent on the model used to estimate it. Comparisons between the models and vertically profiling instruments indicate that resolving fine scale motions in the vertical direction, where ocean mixing takes place, is not yet handled well by the models. Modeling of fine‐vertical scale motions is therefore an important future research direction. Key Points: Vertical wavenumber spectra of internal gravity wave kinetic energy in two high‐resolution global models are compared to observed spectraModels under‐estimate motions at high vertical wavenumbers (small vertical scales), flagging this as a target for model improvementThe ratio of high‐ versus low‐frequency surface kinetic energy at small horizontal scales is dependent on the model and grid spacings employed [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
14. Turbulent diapycnal fluxes as a pilot Essential Ocean Variable.
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Le Boyer, Arnaud, Couto, Nicole, Alford, Matthew H., Drake, Henri F., Bluteau, Cynthia E., Hughes, Kenneth G., Naveira Garabato, Alberto C., Moulin, Aurélie J., Peacock, Thomas, Fine, Elizabeth C., Mashayek, Ali, Cimoli, Laura, Meredith, Michael P., Melet, Angelique, Fer, Ilker, Dengler, Marcus, and Stevens, Craig L.
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EDDY flux ,GLOBAL Ocean Observing System ,OCEAN ,FOREIGN exchange rates ,KINETIC energy - Abstract
We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (e) and of thermal/salinity/tracer variance (c), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
15. A warm jet in a cold ocean
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MacKinnon, Jennifer A., Simmons, Harper L., Hargrove, John, Thomson, Jim, Peacock, Thomas, Alford, Matthew H., Barton, Benjamin I., Boury, Samuel, Brenner, Samuel D., Couto, Nicole, Danielson, Seth L., Fine, Elizabeth C., Graber, Hans C., Guthrie, John, Hopkins, Joanne E., Jayne, Steven R., Jeon, Chanhyung, Klenz, Thilo, Lee, Craig M., Lenn, Yueng-Djern, Lucas, Andrew J., Lund, Björn, Mahaffey, Claire, Norman, Louisa, Rainville, Luc, Smith, Madison M., Thomas, Leif N., Torres-Valdés, Sinhué, and Wood, Kevin R.
- Published
- 2021
- Full Text
- View/download PDF
16. Extent of impact of deep-sea nodule mining midwater plumes is influenced by sediment loading, turbulence and thresholds
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Muñoz-Royo, Carlos, Peacock, Thomas, Alford, Matthew H., Smith, Jerome A., Le Boyer, Arnaud, Kulkarni, Chinmay S., Lermusiaux, Pierre F. J., Haley, Jr., Patrick J., Mirabito, Chris, Wang, Dayang, Adams, E. Eric, Ouillon, Raphael, Breugem, Alexander, Decrop, Boudewijn, Lanckriet, Thijs, Supekar, Rohit B., Rzeznik, Andrew J., Gartman, Amy, and Ju, Se-Jong
- Published
- 2021
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- View/download PDF
17. Observations of Tidally Driven Turbulence over Steep, Small-Scale Topography Embedded in the Tasman Slope.
- Author
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Marques, Olavo B., Alford, Matthew H., Pinkel, Robert, MacKinnon, Jennifer A., Voet, Gunnar, Klymak, Jody M., and Nash, Jonathan D.
- Subjects
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INTERNAL waves , *TURBULENCE , *MERIDIONAL overturning circulation , *TURBULENT mixing , *MOUNTAIN wave , *CONTINENTAL slopes - Abstract
Enhanced diapycnal mixing induced by the near-bottom breaking of internal waves is an essential component of the lower meridional overturning circulation. Despite its crucial role in the ocean circulation, tidally driven internal wave breaking is challenging to observe due to its inherently short spatial and temporal scales. We present detailed moored and shipboard observations that resolve the spatiotemporal variability of the tidal response over a small-scale bump embedded in the continental slope of Tasmania. Cross-shore tidal currents drive a nonlinear trapped response over the steep bottom around the bump. The observations are roughly consistent with two-dimensional high-mode tidal lee-wave theory. However, the alongshore tidal velocities are large, suggesting that the alongshore bathymetric variability modulates the tidal response driven by the cross-shore tidal flow. The semidiurnal tide and energy dissipation rate are correlated at subtidal time scales, but with complex temporal variability. Energy dissipation from a simple scattering model shows that the elevated near-bottom turbulence can be sustained by the impinging mode-1 internal tide, where the dissipation over the bump is O(1%) of the incident depth-integrated energy flux. Despite this small fraction, tidal dissipation is enhanced over the bump due to steep topography at a horizontal scale of O(1) km and may locally drive significant diapycnal mixing. Significance Statement: Near-bottom turbulent mixing is a key element of the global abyssal circulation. We present observations of the spatiotemporal variability of tidally driven turbulent processes over a small-scale topographic bump off Tasmania. The semidiurnal tide generates large-amplitude transient lee waves and hydraulic jumps that are unstable and dissipate the tidal energy. These processes are consistent with the scattering of the incident low-mode internal tide on the continental slope of Tasmania. Despite elevated turbulence over the bump, near-bottom energy dissipation is small relative to the incident wave energy flux. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
18. CLIMATE PROCESS TEAM ON INTERNAL WAVE–DRIVEN OCEAN MIXING
- Author
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MacKinnon, Jennifer A., Zhao, Zhongxiang, Whalen, Caitlin B., Waterhouse, Amy F., Trossmaman, David S., Sun, Oliver M., St. Laurent, Louis C., Simmmmons, Harper L., Polzin, Kurt, Pinkel, Robert, Pickering, Andrew, Norton, Nancy J., Nash, Jonathan D., Musgrave, Ruth, Merchant, Lynne M., Melet, Angelique V., Mater, Benjamin, Legg, Sonya, Large, Williamam G., Kunze, Eric, Klymak, Jody M., Jochum, Markus, Jayne, Steven R., Hallberg, Robert W., Griffies, Stephen M., Diggs, Steve, Danabasoglu, Gokhan, Chassignet, Eric P., Buijsman, Maarten C., Bryan, Frank O., Briegleb, Bruce P., Barna, Andrew, Arbic, Brian K., Ansong, Joseph K., and Alford, Matthew H.
- Published
- 2017
19. Turbulent diapycnal fluxes as a pilot Essential Ocean Variable.
- Author
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Le Boyer, Arnaud, Couto, Nicole, Alford, Matthew H., Drake, Henri F., Bluteau, Cynthia E., Hughes, Kenneth G., Naveira Garabato, Alberto C., Moulin, Aurélie J., Peacock, Thomas, Fine, Elizabeth C., Mashayek, Ali, Cimoli, Laura, Meredith, Michael P., Melet, Angelique, Fer, Ilker, Dengler, Marcus, and Stevens, Craig L.
- Subjects
EDDY flux ,GLOBAL Ocean Observing System ,BUOYANCY ,OCEAN ,FOREIGN exchange rates ,KINETIC energy ,THERMAL stresses - Abstract
We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (J
b ), heat (Jq ), salinity (JS ) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (ϵ) and of thermal/salinity/tracer variance (χ), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
20. Numerical Simulations of Internal Tide Dynamics in a Steep Submarine Canyon.
- Author
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Masunaga, Eiji, Alford, Matthew H., Lucas, Andrew J., and Freudmann, Andrea Rodriguez-Marin
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SUBMARINE valleys , *INTERNAL waves , *COMPUTER simulation , *OCEAN circulation , *STANDING waves , *ENERGY budget (Geophysics) , *COASTS - Abstract
This study investigates three-dimensional semidiurnal internal tide (IT) energetics in the vicinity of La Jolla Canyon, a steep shelf submarine canyon off the Southern California coast, with the Stanford Unstructured Nonhydrostatic Terrain-Following Adaptive Navier–Stokes Simulator (SUNTANS) numerical simulator. Numerical simulations show vertical structure and temporal phasing consistent with detailed field observations. ITs induce large (approximately 34 m from peak to peak) isotherm displacements and net onshore IT energy flux up to 200 W m−1. Although the net IT energy flux is onshore, the steep supercritical slope around the canyon results in strong reflection. The model provides the full life span of internal tides around the canyon, including internal tide generation, propagation, and dissipation. ITs propagate into the canyon from the south and are reflected back toward offshore from the canyon's north side. In the inner part of the canyon, elevated mixing occurs in the middle layer due to an interaction between incident mode-1 ITs and reflected higher-mode ITs. The magnitude of IT flux, generation, and dissipation on the south side of the canyon are higher than those on the north side. An interference pattern in horizontal kinetic energy and available potential energy with a scale of approximately 20–50 km arises due to low-mode wave reflections. Our results provide new insight into IT dynamics associated with a small-scale canyon topography. Significance Statement: Internal waves play an important role in ocean circulations and ecosystems. In particular, internal waves with frequencies of tides, known as internal tides, strongly enhance energy, heat, and mass transport in coastal oceans. This study presents internal tide dynamics in La Jolla Canyon, California, using a high-resolution numerical model. Model results show energy convergence in the canyon leading to internal tide energy dissipation and mixing. Some parts of internal tide energy reflect back offshore resulting in standing internal waves off California. This study provides new insights into internal tide dynamics and energy budgets in submarine canyons. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
21. A Tale of Two Spicy Seas
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MacKinnon, Jennifer A., Nash, Jonathan D., Alford, Matthew H., Lucas, Andrew J., Mickett, John B., Shroyer, Emily L., Waterhouse, Amy F., Tandon, Amit, Sengupta, Debasis, Mahadevan, Amala, Ravichandran, M., Pinkel, Robert, Rudnick, Daniel L., Whalen, Caitlin B., Alberty, Marion S., Lekha, J. Sree, Fine, Elizabeth C., Chaudhuri, Dipanjan, and Wagner, Gregory L.
- Published
- 2016
22. Internal tsunami waves transport sediment released by underwater landslides
- Author
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Brizuela, Noel, Filonov, Anatoliy, and Alford, Matthew H.
- Published
- 2019
- Full Text
- View/download PDF
23. Observations and simulations of caustic formation due to oceanographic fine structure.
- Author
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DeFilippis, Jacob P., Cornuelle, Bruce D., Lucas, Andrew J., Hodgkiss, William S., Lenain, Luc, Kuperman, W. A., and Alford, Matthew H.
- Subjects
OCEANOGRAPHIC instruments ,MEASURING instruments ,OCEAN ,SPEED of sound ,ACOUSTIC emission testing - Abstract
An at-sea experiment in deep water was conducted to explore the impact of small-scale sound-speed variability on mid-frequency (1 – 10 kHz) acoustic propagation. Short-range (1 – 5 km) acoustic transmissions were sent through the upper ocean (0 – 200 m) while oceanographic instruments simultaneously measured the ocean environment within 2 km of the single upper turning points of the acoustic transmissions. During these transmissions, acoustic receptions over a 7.875 m vertical line array show closely spaced, sometimes interfering arrivals. Ray and full-wave simulations of the transmissions using nearby sound-speed profiles are compared deterministically to the received acoustic signals. The sensitivity of the acoustic arrivals to the vertical scales of ocean sound speed is tested by comparing the observed and simulated arrival intensity where the sound-speed profile used by the simulation is smoothed to varying scales. Observations and modeling both suggest that vertical fine-scale structures (1 – 10 m) embedded in the sound-speed profile have strong second derivatives which allow for the formation of acoustic caustics as well as potentially interfering acoustic propagation multipaths. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
24. Prolonged thermocline warming by near-inertial internal waves in the wakes of tropical cyclones.
- Author
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Gutiérrez Brizuela, Noel, Alford, Matthew H., Shang-Ping Xie, Sprintall, Janet, Voet, Gunnar, Warner, Sally J., Hughes, Kenneth, and Moum, James N.
- Subjects
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INTERNAL waves , *TROPICAL cyclones , *OCEANIC mixing , *WATER masses , *EDDY flux , *PERMEATION tubes - Abstract
Turbulence-enhanced mixing of upper ocean heat allows interaction between the tropical atmosphere and cold water masses that impact climate at higher latitudes thereby regulating air-sea coupling and poleward heat transport. Tropical cyclones (TCs) can drastically enhance upper ocean mixing and generate powerful near-inertial internal waves (NIWs) that propagate down into the deep ocean. Globally, downward mixing of heat during TC passage causes warming in the seasonal thermocline and pumps 0.15 to 0.6 PW of heat into the unventilated ocean. The final distribution of excess heat contributed by TCs is needed to understand subsequent consequences for climate; however, it is not well constrained by current observations. Notably, whether or not excess heat supplied by TCs penetrates deep enough to be kept in the ocean beyond the winter season is a matter of debate. Here, we show that NIWs generated by TCs drive thermocline mixing weeks after TC passage and thus greatly deepen the extent of downward heat transfer induced by TCs. Microstructure measurements of the turbulent diffusivity (κ) and turbulent heat flux (Jq) in the Western Pacific before and after the passage of three TCs indicate that mean thermocline values of κ and Jq increased by factors of 2 to 7 and 2 to 4 (95% confidence level), respectively, after TC passage. Excess mixing is shown to be associated with the vertical shear of NIWs, demonstrating that studies of TC-climate interactions ought to represent NIWs and their mixing to accurately capture TC effects on background ocean stratification and climate. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
25. Energy and Momentum of a Density-Driven Overflow in the Samoan Passage.
- Author
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Voet, Gunnar, Alford, Matthew H., Cusack, Jesse M., Pratt, Larry J., Girton, James B., Carter, Glenn S., Klymak, Jody M., Tan, Shuwen, and Thurnherr, Andreas M.
- Subjects
- *
INTERNAL waves , *TURBULENT mixing , *MOUNTAIN wave , *PRESSURE drop (Fluid dynamics) , *KINETIC energy - Abstract
The energy and momentum balance of an abyssal overflow across a major sill in the Samoan Passage is estimated from two highly resolved towed sections, set 16 months apart, and results from a two-dimensional numerical simulation. Driven by the density anomaly across the sill, the flow is relatively steady. The system gains energy from divergence of horizontal pressure work O (5) kW m − 1 and flux of available potential energy O (2) kW m − 1 . Approximately half of these gains are transferred into kinetic energy while the other half is lost to turbulent dissipation, bottom drag, and divergence in vertical pressure work. Small-scale internal waves emanating downstream of the sill within the overflow layer radiate O (1) kW m − 1 upward but dissipate most of their energy within the dense overflow layer and at its upper interface. The strongly sheared and highly stratified upper interface acts as a critical layer inhibiting any appreciable upward radiation of energy via topographically generated lee waves. Form drag of O (2) N m − 2 , estimated from the pressure drop across the sill, is consistent with energy lost to dissipation and internal wave fluxes. The topographic drag removes momentum from the mean flow, slowing it down and feeding a countercurrent aloft. The processes discussed in this study combine to convert about one-third of the energy released from the cross-sill density difference into turbulent mixing within the overflow and at its upper interface. The observed and modeled vertical momentum flux divergence sustains gradients in shear and stratification, thereby maintaining an efficient route for abyssal water mass transformation downstream of this Samoan Passage sill. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
26. A Vorticity‐Divergence View of Internal Wave Generation by a Fast‐Moving Tropical Cyclone: Insights From Super Typhoon Mangkhut.
- Author
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Brizuela, Noel G., Johnston, T. M. Shaun, Alford, Matthew H., Asselin, Olivier, Rudnick, Daniel L., Moum, James N., Thompson, Elizabeth J., Wang, Shuguang, and Lee, Chia‐Ying
- Subjects
TROPICAL cyclones ,INTERNAL waves ,TURBULENT mixing ,TYPHOONS ,OCEAN circulation ,OCEAN temperature ,OCEAN waves ,STORMS - Abstract
Tropical cyclones (TCs) are powered by heat fluxes across the air‐sea interface, which are in turn influenced by subsurface physical processes that can modulate storm intensity. Here, we use data from 6 profiling floats to recreate 3D fields of temperature (T), salinity (S), and velocity around the fast‐moving Super Typhoon Mangkhut (western North Pacific, September 2018). Observational estimates of vorticity (ζ) and divergence (Γ) agree with output from a 3D coupled model, while their relation to vertical velocities is explained by a linear theoretical statement of inertial pumping. Under this framework, inertial pumping is described as a linear coupling between ζ and Γ, whose oscillations in quadrature cause periodic displacements in the ocean thermocline and generate near‐inertial waves (NIWs). Vertical profiles of T and S show gradual mixing of the upper ocean with diffusivities as high as κ ∼ 10−1 m2 s−1, which caused an asymmetric cold wake of sea surface temperature (SST). We estimate that ∼10% of the energy used by mixing was used to mix rainfall, therefore inhibiting SST cooling. Lastly, watermass transformation analyses suggest that κ > 3 × 10−3 m2 s−1 above ∼110 m depth and up to 600 km behind the TC. These analyses provide an observational summary of the ocean response to fast‐moving TCs, demonstrate some advantages of ζ and Γ for the study of internal wave fields, and provide conceptual clarity on the mechanisms that lead to NIW generation by winds. Plain Language Summary: Near‐inertial internal waves (NIWs) are generated by winds and lead to oscillations in the internal structure of ocean currents and stratification. Turbulence induced by the vertical current shear in these waves helps sustain the upper ocean stratification and circulation. In this study, we use data from six autonomous floats deployed ahead of Super Typhoon Mangkhut to reconstruct the ocean's 3D response and compare it to output from a coupled air‐sea model. Patterns in NIW are explained using simple linear equations based on vorticity and divergence rather than current velocities, providing an alternative view of how TC winds help generate waves in the stratified ocean interior. Measurements of temperature and salinity detail how turbulence mixed rainfall and thermocline waters into the upper ocean. Our analyses indicate that turbulent mixing rates are greatest within 100 km of the typhoon eye but remain elevated hundreds of kilometers in the TC wake. Theory and observations presented here provide a comprehensive view of the ocean response to fast‐moving tropical cyclones. Key Points: Float data, linear theory, and a 3D model reveal vorticity and divergence control on inertial pumping beneath a fast‐moving tropical cycloneRightward‐enhanced sea surface cooling of 1.2°C was dominated by mixing and modulated by rainfall, which suppressed cold water entrainmentEstimates of turbulent diffusivity explain sea surface cooling rates 0.1°C hr−1 under the tropical cyclone eye and thermocline mixing in its wake [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
27. Significance of Diapycnal Mixing Within the Atlantic Meridional Overturning Circulation.
- Author
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Cimoli, Laura, Mashayek, Ali, Johnson, Helen L., Marshall, David P., Naveira Garabato, Alberto C., Whalen, Caitlin B., Vic, Clément, de Lavergne, Casimir, Alford, Matthew H., MacKinnon, Jennifer A., and Talley, Lynne D.
- Published
- 2023
- Full Text
- View/download PDF
28. The Impact of Oceanic Near-Inertial Waves on Climate
- Author
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Jochum, Markus, Briegleb, Bruce P., Danabasoglu, Gokhan, Large, William G., Norton, Nancy J., Jayne, Steven R., Alford, Matthew H., and Bryan, Frank O.
- Published
- 2013
29. Tidally Forced Turbulent Dissipation on a Three-Dimensional Fan in Luzon Strait.
- Author
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Alford, Matthew H., Nash, Jonathan D., and Buijsman, Maarten
- Subjects
- *
MOUNTAIN wave , *ACOUSTIC Doppler current profiler , *INTERNAL waves , *SPEED , *OCEAN turbulence , *WATER waves , *DOPPLER effect , *STRAITS - Abstract
Moored observations and a realistic, tidally forced 3D model are presented of flow and internal-tide-driven turbulence over a supercritical 3D fan in southeastern Luzon Strait. Two stacked moored profilers, an acoustic Doppler current profiler, and a thermistor string measured horizontal velocity, density, and salinity over nearly the entire water column every 1.5 h for 50 days. Observed dissipation rate computed from Thorpe scales decays away from the bottom and shows a strong spring–neap cycle; observed depth-integrated dissipation rate scales as U BT 2.5 ± 0.6 where UBT is the barotropic velocity. Vertical velocities are strong enough to be comparable at times to the vertical profiling speed of the moored profilers, requiring careful treatment to quantify bias in dissipation rate estimates. Observations and the model are in reasonable agreement for velocity, internal wave displacement and depth-integrated dissipation rate, allowing the model to be used to understand the 3D flow. Turbulence is maximum following the transition from up-fan to down-fan flow, consistent with breaking lee waves advected past the mooring as seen previously at the Hawaiian Ridge, but asymmetric flow arises because of the 3D topography. Observed turbulence varies by a factor of 2 over the four observed spring tides as low-frequency near-bottom flow changes, but the exact means for inclusion of such low-frequency effects is not clear. Our results suggest that for the extremely energetic turbulence associated with breaking lee waves, dissipation rates may be quantitatively predicted to within a factor of 2 or so using numerical models and simple scalings. Significance Statement: This paper describes deep ocean turbulence caused by strong tidal and low-frequency meandering flows over and around a three-dimensional bump, using moored observations and a computer simulation. Such information is important for accurately including these effects in climate simulations. The observations and model agree well enough to be able to use both to synthesize a coherent picture. The observed and modeled turbulence scale as the cube of the tidal speed as expected from theory, but low-frequency flows complicate the picture. We also demonstrate the underestimation of the turbulence that can result when vertical profiling rates are comparable to the internal wave velocities. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
30. Simulating the Long-Range Swell of Internal Waves Generated by Ocean Storms
- Author
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SIMMONS, HARPER L. and ALFORD, MATTHEW H.
- Published
- 2012
31. The Direct Breaking of Internal Waves at Steep Topography
- Author
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KLYMAK, JODY M., LEGG, SONYA, ALFORD, MATTHEW H., BUIJSMAN, MAARTEN, PINKEL, ROBERT, and NASH, JONATHAN D.
- Published
- 2012
32. AN INTROUDUCTION TO THE SPECIAL ISSUE ON INTERNAL WAVES
- Author
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ST. LAURENT, LOUIS, ALFORD, MATTHEW H., and PALUSZKIEWICZ, TERRI
- Published
- 2012
33. Internal Waves on the Washington Continental Shelf
- Author
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ALFORD, MATTHEW H., MICKETT, JOHN B., ZHANG, SHUANG, MACCREADY, PARKER, ZHAO, ZHONGXIANG, and NEWTON, JAN
- Published
- 2012
34. Mapping Low-Mode Internal Tides from Multisatellite Altimetry
- Author
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ZHAO, ZHONGXIANG, ALFORD, MATTHEW H., and GIRTON, JAMES B.
- Published
- 2012
35. From Luzon Strait to Dongsha Plateau : Stages in the Life of an Internal Wave
- Author
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FARMER, DAVID M., ALFORD, MATTHEW H., LIEN, REN-CHIEH, YANG, YIING JIANG, CHANG, MING-HUEI, and LI, QIANG
- Published
- 2011
36. Atmospheric and Oceanic Processes in the Vicinity of an Island Strait
- Author
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PULLEN, JULIE D., GORDON, ARNOLD L., SPRINTALL, JANET, LEE, CRAIG M., ALFORD, MATTHEW H., DOYEL, JAMES D., and MAY, PAUL W.
- Published
- 2011
37. Internal Wave Climates of the Philippine Seas
- Author
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GIRTON, JAMES B., CHINN, BRIAN S., and ALFORD, MATTHEW H.
- Published
- 2011
38. Corrigendum: Turbulent diapycnal fluxes as a pilot Essential Ocean Variable.
- Author
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Le Boyer, Arnaud, Couto, Nicole, Alford, Matthew H., Drake, Henri F., Bluteau, Cynthia E., Hughes, Kenneth G., Naveira Garabato, Alberto C., Moulin, Aurélie J., Peacock, Thomas, Fine, Elizabeth C., Mashayek, Ali, Cimoli, Laura, Meredith, Michael P., Melet, Angelique, Fer, Ilker, Dengler, Marcus, and Stevens, Craig L.
- Subjects
EDDY flux ,OCEAN ,EARTH system science ,EARTH sciences ,OCEANOGRAPHY - Abstract
This document is a corrigendum for an article titled "Turbulent diapycnal fluxes as a pilot Essential Ocean Variable." The corrigendum addresses an error in Table 1 of the published article, where the equations for eddy diffusion coefficients KT, KS, and Kr were incorrect. The corrected table and its caption are provided in the corrigendum. The authors apologize for the error and state that it does not affect the scientific conclusions of the article. [Extracted from the article]
- Published
- 2024
- Full Text
- View/download PDF
39. Global Observations of Rotary-with-Depth Shear Spectra.
- Author
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Waterhouse, Amy F., Hennon, Tyler, Kunze, Eric, MacKinnon, Jennifer A., Alford, Matthew H., Pinkel, Robert, Simmons, Harper, Whalen, Caitlin B., Fine, Elizabeth C., Klymak, Jody, and Hummon, Julia M.
- Subjects
ACOUSTIC Doppler current profiler ,INTERNAL waves ,FRICTION velocity ,HYDROGRAPHIC surveying ,WAVENUMBER - Abstract
Internal waves are predominantly generated by winds, tide–topography interactions, and balanced flow–topography interactions. Observations of vertical shear of horizontal velocity (uz, υz) from lowered acoustic Doppler current profilers (LADCP) profiles conducted during GO-SHIP hydrographic surveys, as well as vessel-mounted sonars, are used to interpret these signals. Vertical directionality of intermediate-wavenumber [ λ z ∼ O (100 ) m ] internal waves is inferred in this study from rotary-with-depth shears. Total shear variance and vertical asymmetry ratio (Ω), i.e., the normalized difference between downward- and upward-propagating intermediate wavenumber shear variance, where Ω > 0 (<0) indicates excess downgoing (upgoing) shear variance, are calculated for three depth ranges: 200–600 m, 600 m–1000 mab (meters above bottom), and below 1000 mab. Globally, downgoing (clockwise-with-depth in the Northern Hemisphere) exceeds upgoing (counterclockwise-with-depth in the Northern Hemisphere) shear variance by 30% in the upper 600 m of the water column (corresponding to the globally averaged asymmetry ratio of Ω ¯ = 0.13), with a near-equal distribution below 600-m depth ( Ω ¯ ∼ 0). Downgoing shear variance in the upper water column dominates at all latitudes. There is no statistically significant correlation between the global distribution of Ω and internal wave generation, pointing to an important role for processes that redistribute energy within the internal wave continuum on wavelengths of O (100) m. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
40. Near‐Surface Oceanic Kinetic Energy Distributions From Drifter Observations and Numerical Models.
- Author
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Arbic, Brian K., Elipot, Shane, Brasch, Jonathan M., Menemenlis, Dimitris, Ponte, Aurélien L., Shriver, Jay F., Yu, Xiaolong, Zaron, Edward D., Alford, Matthew H., Buijsman, Maarten C., Abernathey, Ryan, Garcia, Daniel, Guan, Lingxiao, Martin, Paige E., and Nelson, Arin D.
- Subjects
KINETIC energy ,GENERAL circulation model ,INTERNAL waves ,OCEAN-atmosphere interaction ,TIDAL forces (Mechanics) ,OCEAN currents - Abstract
The geographical variability, frequency content, and vertical structure of near‐surface oceanic kinetic energy (KE) are important for air‐sea interaction, marine ecosystems, operational oceanography, pollutant tracking, and interpreting remotely sensed velocity measurements. Here, KE in high‐resolution global simulations (HYbrid Coordinate Ocean Model; HYCOM, and Massachusetts Institute of Technology general circulation model; MITgcm), at the sea surface (0 m) and at 15 m, are compared with KE from undrogued and drogued surface drifters, respectively. Global maps and zonal averages are computed for low‐frequency (<0.5 cpd), near‐inertial, diurnal, and semidiurnal bands. Both models exhibit low‐frequency equatorial KE that is low relative to drifter values. HYCOM near‐inertial KE is higher than in MITgcm, and closer to drifter values, probably due to more frequently updated atmospheric forcing. HYCOM semidiurnal KE is lower than in MITgcm, and closer to drifter values, likely due to inclusion of a parameterized topographic internal wave drag. A concurrent tidal harmonic analysis in the diurnal band demonstrates that much of the diurnal flow is nontidal. We compute simple proxies of near‐surface vertical structure—the ratio 0 m KE/(0 m KE + 15 m KE) in model outputs, and the ratio undrogued KE/(undrogued KE + drogued KE) in drifter observations. Over most latitudes and frequency bands, model ratios track the drifter ratios to within error bars. Values of this ratio demonstrate significant vertical structure in all frequency bands except the semidiurnal band. Latitudinal dependence in the ratio is greatest in diurnal and low‐frequency bands. Plain Language Summary: It is important to map and understand ocean surface currents because they affect climate and marine ecosystems. Recent advances in global ocean models include the addition of astronomical tidal forcing alongside atmospheric forcing and the usage of more powerful computers that can resolve finer features. Here, we evaluate ocean surface currents in high‐resolution simulations of two different ocean models through comparison with observations from surface drifting buoys. We examine near‐inertial motions, forced by fast‐changing winds; semidiurnal tides, forced by the astronomical tidal potential; diurnal motions, arising from tidal and other sources; and low‐frequency currents and eddies, forced by atmospheric fields. Global patterns in the models and drifters are broadly consistent. The two models differ in their degree of proximity to drifter measurements in the near‐inertial band, most likely due to different update intervals for atmospheric forcing and in the semidiurnal band, most likely due to different damping schemes. A simple proxy for vertical structure of the currents, measured by differences in drifter flows at the surface versus 15 m depth, is tracked reasonably well by the models. Discrepancies between models and observations motivate future improvements in the models. Key Points: We examine frequency content of ocean kinetic energy (KE) at the sea surface (0 m) and 15 m depth with global drifter data and two modelsNear‐surface near‐inertial and tidal KE in numerical models are sensitive to atmospheric forcing frequency and dampingThe ratio 0 m KE/(0 m KE + 15 m KE) in models lies within error bars of the observational ratios over some latitudes and frequency bands [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
41. The formation and fate of internal waves in the South China Sea
- Author
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Alford, Matthew H., Peacock, Thomas, MacKinnon, Jennifer A., Nash, Jonathan D., Buijsman, Maarten C., Centuroni, Luca R., Chao, Shenn-Yu, Chang, Ming-Huei, Farmer, David M., Fringer, Oliver B., Fu, Ke-Hsien, Gallacher, Patrick C., Graber, Hans C., Helfrich, Karl R., Jachec, Steven M., Jackson, Christopher R., Klymak, Jody M., Ko, Dong S., Jan, Sen, Johnston, T. M. Shaun, Legg, Sonya, Lee, I-Huan, Lien, Ren-Chieh, Mercier, Matthieu J., Moum, James N., Musgrave, Ruth, Park, Jae-Hun, Pickering, Andrew I., Pinkel, Robert, Rainville, Luc, Ramp, Steven R., Rudnick, Daniel L., Sarkar, Sutanu, Scotti, Alberto, Simmons, Harper L., St Laurent, Louis C., Venayagamoorthy, Subhas K., Wang, Yu-Huai, Wang, Joe, Yang, Yiing J., Paluszkiewicz, Theresa, and (David) Tang, Tswen-Yung
- Published
- 2015
- Full Text
- View/download PDF
42. Impact of Vertical Mixing Parameterizations on Internal Gravity Wave Spectra in Regional Ocean Models.
- Author
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Thakur, Ritabrata, Arbic, Brian K., Menemenlis, Dimitris, Momeni, Kayhan, Pan, Yulin, Peltier, W. R., Skitka, Joseph, Alford, Matthew H., and Ma, Yuchen
- Subjects
GRAVITY waves ,INTERNAL waves ,OCEAN surface topography ,OCEAN ,OCEANIC mixing ,PARAMETERIZATION ,GEOGRAPHIC boundaries - Abstract
We present improvements in the modeling of the vertical wavenumber spectrum of the internal gravity wave continuum in high‐resolution regional ocean simulations. We focus on model sensitivities to mixing parameters and comparisons to McLane moored profiler observations in a Pacific region near the Hawaiian Ridge, which features strong semidiurnal tidal beams. In these simulations, the modeled continuum exhibits high sensitivity to the background mixing components of the K‐Profile Parameterization (KPP) vertical mixing scheme. Without the KPP background mixing, stronger vertical gradients in velocity are sustained in the simulations and the modeled kinetic energy and shear spectral slopes are significantly closer to the observations. The improved representation of internal wave dynamics in these simulations makes them suitable for improving ocean mixing estimates and for the interpretation of satellite missions such as the Surface Water and Ocean Topography mission. Plain Language Summary: Internal waves (IWs) exist in the ocean interior due to differences in fluid densities. Breaking IWs cause mixing, which has important effects on ocean temperatures and nutrients. Interactions between internal tides generated by tidal flow over bathymetric features and near‐inertial waves generated by wind yield a spectrum of IWs at many frequencies. Here, we compare the IW spectrum in high‐resolution numerical simulations of a region in the North Pacific with observations from moored instruments. We study the effects of the "background" mixing components of the widely used K‐Profile Parameterization (KPP) vertical mixing scheme on the vertical structure of the IW field. The KPP background parameterizes the mixing action of IWs, which is not resolved in coarser‐resolution global ocean models. In our high‐resolution simulations, the IW field is highly active, and the KPP background components turn out to be mostly redundant in this setting. The modeled IW field lies closer to observations when we turn off the KPP background. Improved IW representation in ocean models can play an important role in the accurate representation of IW‐driven mixing in ocean simulations and interpretation of IW signatures from the upcoming Surface Water and Ocean Topography mission. Key Points: Regional ocean simulations are ideal for examining sensitivity of internal gravity wave (IGW) spectra to model mixing parametersTurning off the background components of K‐Profile Parameterization yields more realistic IGW vertical structure in high‐resolution regional modelsIGW spectra are most correctly estimated in models away from tidal generation sites and lateral boundaries [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
43. Measurements of Turbulence Generated by Wake Eddies Near a Steep Headland.
- Author
-
Wynne‐Cattanach, Bethan L., Alford, Matthew H., MacKinnon, Jennifer A., and Voet, Gunnar
- Subjects
TURBULENCE ,EDDIES ,MOMENTUM transfer ,MOUNTAIN wave ,RICHARDSON number ,SHEAR flow ,VORTEX motion - Abstract
Tidal and low‐frequency flows interact with abrupt topographic features, giving rise to a variety of small‐scale phenomena including lee waves, vortical motions and turbulence. With the goal of identifying the processes that transfer momentum and energy between the larger‐scale and smaller‐scale flows, detailed tidally‐resolving shipboard surveys were conducted near a sharp and steep headland north of Velasco Reef, Palau, in the Western Pacific. We present velocity, microstructure and rapid‐cycling conductivity and temperature measurements, contextualized with a nearby 10‐month moored record, to examine wake and vortex structures. Observed flow near Velasco Reef was layered and multi‐directional in depth such that the "downstream" side of the headland depended on depth. Downstream of the headland, during a period where mean flow dominated over the tide in the top 100 m of the water column, turbulent kinetic energy dissipation rates were enhanced by up to three orders of magnitude relative to those upstream. During a period dominated by tides, the flow reversed periodically and wake eddies were associated with turbulent dissipation rates up to O10−5Wkg−1 $\mathcal{O}\left(1{0}^{-5}\right)\ \mathrm{W}\hspace*{.5em}\mathrm{k}{\mathrm{g}}^{-\mathrm{1}}$. Turbulent dissipation rates in the wake increased with inverse Richardson number for both tidal and mean flows past the headland, and were larger for stronger vorticity flows. Our analysis suggests that the eddies themselves lead to shear instabilities and subsequent turbulence, either through tilting or their limited vertical extent. We associate the enhanced downstream dissipation with a combination of breaking internal tides and either these eddy processes or a multi‐scaled turbulent wake. Plain Language Summary: Tall, steep underwater features such as ridges and headlands interact with tides and large currents to alter the flow downstream. Here, we present observations near Velasco Reef, Palau, an example of a sharp headland in the western Pacific. Turbulence in the wake of the headland is higher than upstream. During a time when the tides were strong the flow changed direction such that eddies were shed from both sides of the headland. These patches of rotating flow were associated with stronger turbulence than elsewhere around the headland. Shearing of the flow in the vertical direction by the eddies and the internal tides are possible mechanisms by which the turbulence is generated. Key Points: Direct observations of turbulent dissipation rates show enhancement downstream of a headland during mean flow and tidal flow regimesRegions of strong vorticity in the wake are associated with the highest turbulent dissipation ratesShear instabilities are a likely mechanism for the generation of turbulence in the wake [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
44. Redistribution of energy available for ocean mixing by long-range propagation of internal waves
- Author
-
Alford, Matthew H.
- Subjects
Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
Author(s): Matthew H. Alford (corresponding author) Ocean mixing, which affects pollutant dispersal, marine productivity and global climate [1], largely results from the breaking of internal gravity waves--disturbances propagating along the [...]
- Published
- 2003
- Full Text
- View/download PDF
45. Oceanic turbulence from a planktonic perspective.
- Author
-
Franks, Peter J. S., Inman, Bryce G., MacKinnon, Jennifer A., Alford, Matthew H., and Waterhouse, Amy F.
- Subjects
TURBULENCE ,OCEAN turbulence ,NUTRIENT uptake ,OCEAN dynamics ,MIXING height (Atmospheric chemistry) - Abstract
The potential influences of turbulence on planktonic processes such as nutrient uptake, grazing, predation, infection, and mating have been explored in hundreds of laboratory and theoretical studies. However, the turbulence levels used may not represent those experienced by oceanic plankton, bringing into question their relevance for understanding planktonic dynamics in the ocean. Here, we take a data‐centric approach to understand the turbulence climate experienced by plankton in the ocean, analyzing over one million turbulence measurements acquired in the open ocean. Median dissipation rates in the upper 100 m were < 10−8 W kg−1, with 99% of the observations < 10−6 W kg−1. Below mixed layers, the median dissipation rate was ~ 10−10 W kg−1, with 99% of the observations < 10−7 W kg−1. Even in strongly mixing layers the median dissipation rates rarely reached 10−5 W kg−1, decreasing by orders of magnitude over 10 m or less in depth. Furthermore, episodes of intense turbulence were transient, transitioning to background levels within 10 min or less. We define three turbulence conditions in the ocean: weak (< 10−8 W kg−1), moderate (10−8–10−6 W kg−1), and strong (> 10−6 W kg−1). Even the strongest of these is much weaker than those used in most laboratory experiments. The most frequent turbulence levels found in this study are weak enough for most plankton—including small protists—to outswim them, and to allow chemical plumes and trails to persist for tens of minutes. Our analyses underscore the primary importance of planktonic behavior in driving individual interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
46. Double Diffusion, Shear Instabilities, and Heat Impacts of a Pacific Summer Water Intrusion in the Beaufort Sea.
- Author
-
Fine, Elizabeth C., MacKinnon, Jennifer A., Alford, Matthew H., Middleton, Leo, Taylor, John, Mickett, John B., Cole, Sylvia T., Couto, Nicole, Boyer, Arnaud Le, and Peacock, Thomas
- Subjects
SALTWATER encroachment ,EDDIES ,SUMMER ,HEAT flux ,KINETIC energy - Abstract
Pacific Summer Water eddies and intrusions transport heat and salt from boundary regions into the western Arctic basin. Here we examine concurrent effects of lateral stirring and vertical mixing using microstructure data collected within a Pacific Summer Water intrusion with a length scale of ∼20 km. This intrusion was characterized by complex thermohaline structure in which warm Pacific Summer Water interleaved in alternating layers of O (1) m thickness with cooler water, due to lateral stirring and intrusive processes. Along interfaces between warm/salty and cold/freshwater masses, the density ratio was favorable to double-diffusive processes. The rate of dissipation of turbulent kinetic energy (ε) was elevated along the interleaving surfaces, with values up to 3 × 10−8 W kg−1 compared to background ε of less than 10−9 W kg−1. Based on the distribution of ε as a function of density ratio Rρ, we conclude that double-diffusive convection is largely responsible for the elevated ε observed over the survey. The lateral processes that created the layered thermohaline structure resulted in vertical thermohaline gradients susceptible to double-diffusive convection, resulting in upward vertical heat fluxes. Bulk vertical heat fluxes above the intrusion are estimated in the range of 0.2–1 W m−2, with the localized flux above the uppermost warm layer elevated to 2–10 W m−2. Lateral fluxes are much larger, estimated between 1000 and 5000 W m−2, and set an overall decay rate for the intrusion of 1–5 years. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
47. Advection-diffusion-settling of deep-sea mining sediment plumes. Part 1: Midwater plumes.
- Author
-
Ouillon, Raphael, Muñoz-Royo, Carlos, Alford, Matthew H., and Peacock, Thomas
- Subjects
ADVECTION ,OCEAN mining ,PLUMES (Fluid dynamics) ,FLUID dynamics ,PARAMETER estimation - Abstract
The evolution of midwater sediment plumes associated with deep-sea mining activities is investigated in the passivetransport phase using a simplified advection-diffusion-settling model. Key metrics that characterize the extent of plumes are defined based on a concentration threshold. Namely, we consider the volume flux of fluid that ever exceeds a concentration threshold, the furthest distance from and maximum depth below the intrusion where the plume exceeds the threshold, and the instantaneous volume of fluid in excess of the threshold. Formulas are derived for the metrics that provide insight into the parameters that most strongly affect the extent of the plume. The model is applied to a reference deep-sea mining scenario around which key parameters are varied. The results provide some sense of scale for deep-sea mining midwater plumes, but more significantly demonstrate the importance of the parameters that influence the evolution of midwater plumes. The model shows that the discharge mass flow rate and the concentration threshold play an equal and opposite role on setting the extent of the plume. Ambient ocean turbulence and the settling velocity distribution of particles play a lesser yet significant role on setting the extent, and can influence different metrics in opposing ways. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
48. Advection-diffusion settling of deep-sea mining sediment plumes. Part 2. Collector plumes.
- Author
-
Ouillon, Raphael, Muñoz-Royo, Carlos, Alford, Matthew H., and Peacock, Thomas
- Subjects
OCEAN mining ,PLUMES (Fluid dynamics) ,TURBULENT diffusion (Meteorology) ,OCEAN bottom ,NONLINEAR analysis - Abstract
We develop and investigate an advection-diffusion-settling model of deep-sea mining collector plumes, building on the analysis of midwater plumes in Part 1. In the case of collector plumes, deposition plays a predominant role in controlling the mass of sediment in suspension, and thus on setting the extent of the plume. We first discuss the competition between settling, which leads to deposition, and vertical turbulent diffusion, which stretches the plume vertically and reduces deposition. The time evolution of the concentration at the seabed is found to be a highly nonlinear function of time that depends non-trivially on the ratio of diffusion to settling time scales. This has direct implications for the three extent metrics considered, namely the instantaneous area of the seabed where a deposition rate threshold is exceeded, the furthest distance from the discharge where the plume exceeds a concentration threshold and the volume flux of fluid in the water column that ever exceeds a concentration threshold. Unlike the midwater plume, the particle velocity distribution of the sediment has the greatest influence on the extent metrics. The turbulence levels experienced by the plume also markedly affects its extent. Expected variability of turbulence and particle settling velocity yields orders of magnitude changes in the extent metrics. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
49. Data‐Driven Identification of Turbulent Oceanic Mixing From Observational Microstructure Data.
- Author
-
Couchman, Miles M. P., Wynne‐Cattanach, Bethan, Alford, Matthew H., Caulfield, Colm‐cille P., Kerswell, Rich R., MacKinnon, Jennifer A., and Voet, Gunnar
- Subjects
OCEANIC mixing ,TURBULENT mixing ,GENERAL circulation model ,OCEAN turbulence ,MICROSTRUCTURE ,MACHINE learning - Abstract
Characterizing how ocean turbulence transports heat is critically important for accurately parameterizing global circulation models. We present a novel data‐driven approach for identifying distinct regions of turbulent mixing within a microstructure data set that uses unsupervised machine learning to cluster fluid patches according to their background buoyancy frequency N, and turbulent dissipation rates of kinetic energy ϵ and thermal variance χ. Applied to data collected near the Velasco Reef in Palau, our clustering algorithm discovers spatial and temporal correlations between the mixing characteristics of a fluid patch and its depth, proximity to the reef and the background current. While much of the data set is characterized by the canonical mixing coefficient Γ = 0.2, elevated local mixing efficiencies are identified in regions containing large density fluxes derived from χ. Once applied to further datasets, unsupervised machine learning has the potential to advance community understanding of global patterns and local characteristics of turbulent mixing. Plain Language Summary: Turbulent fluid motions enhance the mixing of heat between different layers of the ocean, playing a critical role in driving large‐scale currents that influence the Earth's climate. Measurements of centimeter‐scale velocity and temperature fluctuations within the ocean, termed microstructure, are used to study the properties of turbulent mixing and characterize its variability in both space and time. We present a new technique for analyzing microstructure data that uses a machine learning algorithm to identify fluid regions with similar measured characteristics automatically, yielding insight into the underlying turbulent mechanisms driving mixing. Applied to a data set collected near the Velasco Reef in Palau, our algorithm highlights several distinct turbulent regions whose properties depend on their depth, proximity to the reef and the background current. Our findings demonstrate that machine learning is a valuable new technique for characterizing ocean turbulence that, applied to further data sets, has the potential to advance our understanding of global patterns and local characteristics of turbulent mixing. Key Points: Unsupervised machine learning is used to automatically cluster microstructure measurements collected off the Velasco Reef in PalauSeveral distinct turbulent regions are identified, highlighting strong spatial and temporal variability in the flowStrongly localized thermal gradients elevate the mixing coefficient above the canonical value 0.2 in a subset of the domain [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
50. Variability and Sources of the Internal Wave Continuum Examined from Global Moored Velocity Records.
- Author
-
Le Boyer, Arnaud and Alford, Matthew H.
- Subjects
- *
INTERNAL waves , *OCEAN turbulence , *GRAVITY waves , *SHEAR strain , *MESOSCALE eddies , *FREQUENCY spectra - Abstract
Energy for ocean turbulence is thought to be transferred from its presumed sources (viz., the mesoscale eddy field, near-inertial internal waves, and internal tides) to the internal wave continuum, and through the continuum via resonant triad interactions to breaking scales. To test these ideas, the level and variability of the oceanic internal gravity wave continuum spectrum are examined by computing time-dependent rotary spectra from a global database of 2260 current meter records deployed on 1362 separate moorings. Time series of energy in the continuum and the three "source bands" (near-inertial, tidal, and mesoscale) are computed, and their variability and covariability examined. Seasonal modulation of the continuum by factors of up to 5 is seen in the upper ocean, implicating wind-driven near-inertial waves as an important source. The time series of the continuum is found to correlate more strongly with the near-inertial peak than with the semidiurnal or mesoscale. The use of moored internal-wave kinetic energy frequency spectra as an alternate input to the traditional shear or strain wavenumber spectra in the Gregg–Henyey–Polzin finescale parameterization is explored and compared to traditional strain-based estimates. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
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