Moum James N.

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James N.

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  • Article
    Nonlinear internal waves over New Jersey's continental shelf
    (American Geophysical Union, 2011-03-23) Shroyer, Emily L. ; Moum, James N. ; Nash, Jonathan D.
    Ship and mooring data collected off the coast of New Jersey are used to describe the nonlinear internal wave (NLIW) field and the background oceanographic conditions that formed the waveguide on the shelf. The subinertial, inertial, and tidal circulation are described in detail, and the background fluid state is characterized using the coefficients of the extended Korteweg–de Vries equation. The utility of this type of analysis is demonstrated in description of an amplitude-limited, flat wave. NLIWs observed over most of the month had typical displacements of −8 m, but waves observed from 17–21 August were almost twice as large with displacements near −15 m. During most of the month, wave packets occurred irregularly at a fixed location, and often more than one packet was observed per M2 tidal period. In contrast, the arrival times of the large-amplitude wave groups observed over 17–21 August were more closely phased with the barotropic tide. The time span in which the largest NLIWs were observed corresponded to neap barotropic conditions, but when the shoreward baroclinic energy flux was elevated. During the time of large NLIWs, near-inertial waves were a dominate contributor to the internal motions on the shelf and apparently regulated wave formation, as destructive/constructive modulation of the M2 internal tide by the inertial wavefield at the shelf break corresponded to stronger/weaker NLIWs on the shelf.
  • Article
    The tropical Atlantic observing system
    (Frontiers Media, 2019-05-10) Foltz, Gregory R. ; Brandt, Peter ; Richter, Ingo ; Rodriguez-fonseca, Belen ; Hernandez, Fabrice ; Dengler, Marcus ; Rodrigues, Regina ; Schmidt, Jörn Oliver ; Yu, Lisan ; Lefevre, Nathalie ; Cotrim Da Cunha, Leticia ; McPhaden, Michael J. ; Araujo, Moacyr ; Karstensen, Johannes ; Hahn, Johannes ; Martín-Rey, Marta ; Patricola, Christina ; Poli, Paul ; Zuidema, Paquita ; Hummels, Rebecca ; Perez, Renellys ; Hatje, Vanessa ; Luebbecke, Joke ; Polo, Irene ; Lumpkin, Rick ; Bourlès, Bernard ; Asuquo, Francis Emile ; Lehodey, Patrick ; Conchon, Anna ; Chang, Ping ; Dandin, Philippe ; Schmid, Claudia ; Sutton, Adrienne J. ; Giordani, Hervé ; Xue, Yan ; Illig, Serena ; Losada, Teresa ; Grodsky, Semyon A. ; Gasparin, Florent ; Lee, Tong ; Mohino, Elsa ; Nobre, Paulo ; Wanninkhof, Rik ; Keenlyside, Noel S. ; Garcon, Veronique Cameille ; Sanchez-Gomez, Emilia ; Nnamchi, Hyacinth ; Drevillon, Marie ; Storto, Andrea ; Remy, Elisabeth ; Lazar, Alban ; Speich, Sabrina ; Goes, Marlos Pereira ; Dorrington, Tarquin ; Johns, William E. ; Moum, James N. ; Robinson, Carol ; Perruche, Coralie ; de Souza, Ronald Buss ; Gaye, Amadou ; Lopez-Parages, Jorge ; Monerie, Paul-Arthur ; Castellanos, Paola ; Benson, Nsikak U. ; Hounkonnou, Mahouton Norbert ; Trotte Duha, Janice ; Laxenaire, Rémi ; Reul, Nicolas
    he tropical Atlantic is home to multiple coupled climate variations covering a wide range of timescales and impacting societally relevant phenomena such as continental rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric circulation in the equatorial Pacific. The tropical Atlantic also connects the southern and northern branches of the Atlantic meridional overturning circulation and receives freshwater input from some of the world’s largest rivers. To address these diverse, unique, and interconnected research challenges, a rich network of ocean observations has developed, building on the backbone of the Prediction and Research Moored Array in the Tropical Atlantic (PIRATA). This network has evolved naturally over time and out of necessity in order to address the most important outstanding scientific questions and to improve predictions of tropical Atlantic severe weather and global climate variability and change. The tropical Atlantic observing system is motivated by goals to understand and better predict phenomena such as tropical Atlantic interannual to decadal variability and climate change; multidecadal variability and its links to the meridional overturning circulation; air-sea fluxes of CO2 and their implications for the fate of anthropogenic CO2; the Amazon River plume and its interactions with biogeochemistry, vertical mixing, and hurricanes; the highly productive eastern boundary and equatorial upwelling systems; and oceanic oxygen minimum zones, their impacts on biogeochemical cycles and marine ecosystems, and their feedbacks to climate. Past success of the tropical Atlantic observing system is the result of an international commitment to sustained observations and scientific cooperation, a willingness to evolve with changing research and monitoring needs, and a desire to share data openly with the scientific community and operational centers. The observing system must continue to evolve in order to meet an expanding set of research priorities and operational challenges. This paper discusses the tropical Atlantic observing system, including emerging scientific questions that demand sustained ocean observations, the potential for further integration of the observing system, and the requirements for sustaining and enhancing the tropical Atlantic observing system.
  • Article
    Seasonality and buoyancy suppression of turbulence in the Bay of Bengal
    (American Geophysical Union, 2019-04-08) Thakur, Ritabrata ; Shroyer, Emily L. ; Govindarajan, Rama ; Farrar, J. Thomas ; Weller, Robert A. ; Moum, James N.
    A yearlong record from moored current, temperature, conductivity, and four mixing meters (χpods) in the northernmost international waters of the Bay of Bengal quantifies upper‐ocean turbulent diffusivity of heat (Kt) and its response to the Indian monsoon. Data indicate (1) pronounced intermittency in turbulence at semidiurnal, diurnal, and near‐inertial timescales, (2) strong turbulence above 25‐m depth during the SW (summer) and NE (winter) monsoon relative to the transition periods (compare Kt > 10−4 m2/s to Kt  ∼ 10−5 m2/s, and (3) persistent suppression of turbulence (Kt < 10−5 m2/s) for 3 to 5 months in the latter half of the SW monsoon coincident with enhanced near‐surface stratification postarrival of low‐salinity water from the Brahmaputra‐Ganga‐Meghna delta and monsoonal precipitation. This suppression promotes maintenance of the low‐salinity surface waters within the interior of the bay preconditioning the upper northern Indian Ocean for the next year's monsoon.
  • Article
    Mode 2 waves on the continental shelf : ephemeral components of the nonlinear internal wavefield
    (American Geophysical Union, 2010-07-02) Shroyer, Emily L. ; Moum, James N. ; Nash, Jonathan D.
    Shoreward propagating, mode 2 nonlinear waves appear sporadically in mooring records obtained off the coast of New Jersey in the summer of 2006. Individual mode 2 packets were tracked between two moorings separated by 1 km; however, packets could not be tracked between moorings separated by greater distances from one another (∼10 km). The inability to track individual packets large distances through the mooring array combined with detailed observations from a ship suggest that these waves are short lived. The evolution of the ship-tracked wave group was recorded using acoustic backscatter, acoustic Doppler current profilers, and turbulence profiling. The leading mode 2 wave quickly changed form and developed a tail of short, small-amplitude mode 1 waves. The wavelength of the mode 1 oscillations agreed with that expected for a copropagating tail on the basis of linear theory. Turbulent dissipation in the mixed layer and radiation of the short mode 1 waves contributed to rapid energy loss in the leading mode 2 wave, consistent with the observed decay rate and short life span of only a few hours. The energy in the leading mode 2 wave was 10–100 times smaller than the energy of mode 1 nonlinear internal waves observed during the experiment; however, the magnitudes of wave-localized turbulent dissipation were similar.
  • Article
    On the future of Argo: A global, full-depth, multi-disciplinary array
    (Frontiers Media, 2019-08-02) Roemmich, Dean ; Alford, Matthew H. ; Claustre, Hervé ; Johnson, Kenneth S. ; King, Brian ; Moum, James N. ; Oke, Peter ; Owens, W. Brechner ; Pouliquen, Sylvie ; Purkey, Sarah G. ; Scanderbeg, Megan ; Suga, Koushirou ; Wijffels, Susan E. ; Zilberman, Nathalie ; Bakker, Dorothee ; Baringer, Molly O. ; Belbeoch, Mathieu ; Bittig, Henry C. ; Boss, Emmanuel S. ; Calil, Paulo H. R. ; Carse, Fiona ; Carval, Thierry ; Chai, Fei ; Conchubhair, Diarmuid Ó. ; d’Ortenzio, Fabrizio ; Dall'Olmo, Giorgio ; Desbruyeres, Damien ; Fennel, Katja ; Fer, Ilker ; Ferrari, Raffaele ; Forget, Gael ; Freeland, Howard ; Fujiki, Tetsuichi ; Gehlen, Marion ; Geenan, Blair ; Hallberg, Robert ; Hibiya, Toshiyuki ; Hosoda, Shigeki ; Jayne, Steven R. ; Jochum, Markus ; Johnson, Gregory C. ; Kang, KiRyong ; Kolodziejczyk, Nicolas ; Körtzinger, Arne ; Le Traon, Pierre-Yves ; Lenn, Yueng-Djern ; Maze, Guillaume ; Mork, Kjell Arne ; Morris, Tamaryn ; Nagai, Takeyoshi ; Nash, Jonathan D. ; Naveira Garabato, Alberto C. ; Olsen, Are ; Pattabhi Rama Rao, Eluri ; Prakash, Satya ; Riser, Stephen C. ; Schmechtig, Catherine ; Schmid, Claudia ; Shroyer, Emily L. ; Sterl, Andreas ; Sutton, Philip J. H. ; Talley, Lynne D. ; Tanhua, Toste ; Thierry, Virginie ; Thomalla, Sandy J. ; Toole, John M. ; Troisi, Ariel ; Trull, Thomas W. ; Turton, Jon ; Velez-Belchi, Pedro ; Walczowski, Waldemar ; Wang, Haili ; Wanninkhof, Rik ; Waterhouse, Amy F. ; Waterman, Stephanie N. ; Watson, Andrew J. ; Wilson, Cara ; Wong, Annie P. S. ; Xu, Jianping ; Yasuda, Ichiro
    The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo’s global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.
  • Preprint
    The formation and fate of internal waves in the South China Sea
    ( 2015-03) Alford, Matthew H. ; Peacock, Thomas ; MacKinnon, Jennifer A. ; Nash, Jonathan D. ; Buijsman, Maarten C. ; Centurioni, 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 C. ; 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-Jang ; Paluszkiewicz, Theresa ; Tang, Tswen Yung
    Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they impact a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for manmade structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, posing severe challenges for their observation and their inclusion in numerical climate models, which are sensitive to their effects6-7. Over a decade of studies8-11 have targeted the South China Sea, where the oceans’ most powerful internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their generation mechanism, variability and energy budget, however, due to the lack of in-situ data from the Luzon Strait, where extreme flow conditions make measurements challenging. Here we employ new observations and numerical models to (i) show that the waves begin as sinusoidal disturbances rather than from sharp hydraulic phenomena, (ii) reveal the existence of >200-m-high breaking internal waves in the generation region that give rise to turbulence levels >10,000 times that in the open ocean, (iii) determine that the Kuroshio western boundary current significantly refracts the internal wave field emanating from the Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled and observed energy fluxes that enables the first observationally-supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.
  • Article
    Measurements of acoustic scattering from zooplankton and oceanic microstructure using a broadband echosounder
    (Oxford University Press, 2009-10-29) Lavery, Andone C. ; Chu, Dezhang ; Moum, James N.
    In principle, measurements of high-frequency acoustic scattering from oceanic microstructure and zooplankton across a broad range of frequencies can reduce the ambiguities typically associated with the interpretation of acoustic scattering at a single frequency or a limited number of discrete narrowband frequencies. With this motivation, a high-frequency broadband scattering system has been developed for investigating zooplankton and microstructure, involving custom modifications of a commercially available system, with almost complete acoustic coverage spanning the frequency range 150–600 kHz. This frequency range spans the Rayleigh-to-geometric scattering transition for some zooplankton, as well as the diffusive roll-off in the spectrum for scattering from turbulent temperature microstructure. The system has been used to measure scattering from zooplankton and microstructure in regions of non-linear internal waves. The broadband capabilities of the system provide a continuous frequency response of the scattering over a wide frequency band, and improved range resolution and signal-to-noise ratios through pulse-compression signal-processing techniques. System specifications and calibration procedures are outlined and the system performance is assessed. The results point to the utility of high-frequency broadband scattering techniques in the detection, classification, and under certain circumstances, quantification of zooplankton and microstructure.
  • Article
    Modification of upper-ocean temperature structure by subsurface mixing in the presence of strong salinity stratification
    (The Oceanography Society, 2016-06) Shroyer, Emily L. ; Rudnick, Daniel L. ; Farrar, J. Thomas ; Lim, Byungho ; Venayagamoorthy, Subhas K. ; St. Laurent, Louis C. ; Garanaik, Amrapalli ; Moum, James N.
    The Bay of Bengal has a complex upper-ocean temperature and salinity structure that is, in places, characterized by strong salinity stratification and multiple inversions in temperature. Here, two short time series from continuously profiling floats, equipped with microstructure sensors to measure subsurface mixing, are used to highlight implications of complex hydrography on upper-ocean heat content and the evolution of sea surface temperature. Weak mixing coupled with the existence of subsurface warm layers suggest the potential for storage of heat below the surface mixed layer over relatively long time scales. On the diurnal time scale, these data demonstrate the competing effects of surface heat flux and subsurface mixing in the presence of thin salinity-stratified mixed layers with temperature inversions. Pre-existing stratification can amplify the sea surface temperature response through control on the vertical extent of heating and cooling by surface fluxes. In contrast, subsurface mixing entrains relatively cool water during the day and relatively warm water during the night, damping the response to daytime heating and nighttime cooling at the surface. These observations hint at the challenges involved in improving monsoon prediction at longer, intraseasonal time scales as models may need to resolve upper-ocean variability over short time and fine vertical scales.
  • Article
    Shallow Water ’06 : a joint acoustic propagation/nonlinear internal wave physics experiment
    (Oceanography Society, 2007-12) Tang, Dajun ; Moum, James N. ; Lynch, James F. ; Abbot, Philip A. ; Chapman, Ross ; Dahl, Peter H. ; Duda, Timothy F. ; Gawarkiewicz, Glen G. ; Glenn, Scott M. ; Goff, John A. ; Graber, Hans C. ; Kemp, John N. ; Maffei, Andrew R. ; Nash, Jonathan D. ; Newhall, Arthur E.
    Since the end of the Cold War, the US Navy has had an increasing interest in continental shelves and slopes as operational areas. To work in such areas requires a good understanding of ocean acoustics, coastal physical oceanography, and, in the modern era, autonomous underwater vehicle (AUV) operations.
  • Article
    Biases in Thorpe-scale estimates of turbulence dissipation. Part I : Assessments from large-scale overturns in oceanographic data
    (American Meteorological Society, 2015-10) Mater, Benjamin D. ; Venayagamoorthy, Subhas K. ; St. Laurent, Louis C. ; Moum, James N.
    Oceanic density overturns are commonly used to parameterize the dissipation rate of turbulent kinetic energy. This method assumes a linear scaling between the Thorpe length scale LT and the Ozmidov length scale LO. Historic evidence supporting LT ~ LO has been shown for relatively weak shear-driven turbulence of the thermocline; however, little support for the method exists in regions of turbulence driven by the convective collapse of topographically influenced overturns that are large by open-ocean standards. This study presents a direct comparison of LT and LO, using vertical profiles of temperature and microstructure shear collected in the Luzon Strait—a site characterized by topographically influenced overturns up to O(100) m in scale. The comparison is also done for open-ocean sites in the Brazil basin and North Atlantic where overturns are generally smaller and due to different processes. A key result is that LT/LO increases with overturn size in a fashion similar to that observed in numerical studies of Kelvin–Helmholtz (K–H) instabilities for all sites but is most clear in data from the Luzon Strait. Resultant bias in parameterized dissipation is mitigated by ensemble averaging; however, a positive bias appears when instantaneous observations are depth and time integrated. For a series of profiles taken during a spring tidal period in the Luzon Strait, the integrated value is nearly an order of magnitude larger than that based on the microstructure observations. Physical arguments supporting LT ~ LO are revisited, and conceptual regimes explaining the relationship between LT/LO and a nondimensional overturn size are proposed. In a companion paper, Scotti obtains similar conclusions from energetics arguments and simulations.
  • Article
    The unpredictable nature of internal tides on continental shelves
    (American Meteorological Society, 2012-11) Nash, Jonathan D. ; Kelly, Samuel M. ; Shroyer, Emily L. ; Moum, James N. ; Duda, Timothy F.
    Packets of nonlinear internal waves (NLIWs) in a small area of the Mid-Atlantic Bight were 10 times more energetic during a local neap tide than during the preceding spring tide. This counterintuitive result cannot be explained if the waves are generated near the shelf break by the local barotropic tide since changes in shelfbreak stratification explain only a small fraction of the variability in barotropic to baroclinic conversion. Instead, this study suggests that the occurrence of strong NLIWs was caused by the shoaling of distantly generated internal tides with amplitudes that are uncorrelated with the local spring-neap cycle. An extensive set of moored observations show that NLIWs are correlated with the internal tide but uncorrelated with barotropic tide. Using harmonic analysis of a 40-day record, this study associates steady-phase motions at the shelf break with waves generated by the local barotropic tide and variable-phase motions with the shoaling of distantly generated internal tides. The dual sources of internal tide energy (local or remote) mean that shelf internal tides and NLIWs will be predictable with a local model only if the locally generated internal tides are significantly stronger than shoaling internal tides. Since the depth-integrated internal tide energy in the open ocean can greatly exceed that on the shelf, it is likely that shoaling internal tides control the energetics on shelves that are directly exposed to the open ocean.
  • Article
    Vertical heat flux and lateral mass transport in nonlinear internal waves
    (American Geophysical Union, 2010-04-24) Shroyer, Emily L. ; Moum, James N. ; Nash, Jonathan D.
    Comprehensive observations of velocity, density, and turbulent dissipation permit quantification of the nonlinear internal wave (NLIW) contribution to vertical heat flux and lateral mass transport over New Jersey's shelf. The effect of NLIWs on the shelf heat budget was significant. On average, heat flux in NLIWs was 10 times larger than background at the pycnocline depth. NLIWs were present at midshelf <10% of the time, yet we estimate that they contributed roughly one−half the heat flux across the pycnocline during the observation period, which was characterized by weak to moderate winds. Lateral transport distances due to the leading 3 waves in NLIW packets were typically inline equation(100 m) but ranged several kilometers. The month-averaged daily onshore transport (per unit alongshelf dimension) by NLIWs is estimated as 0.3 m2s−1. This is comparable to a weak downwelling wind, but sustained over an entire month.
  • Article
    Observations of broadband acoustic backscattering from nonlinear internal waves : assessing the contribution from microstructure
    (IEEE, 2010-11-30) Lavery, Andone C. ; Chu, Dezhang ; Moum, James N.
    In this paper, measurements of high-frequency broadband (160-590 kHz) acoustic backscattering from surface trapped nonlinear internal waves of depression are presented. These waves are ideal for assessing the contribution from oceanic microstructure to scattering as they are intensely turbulent. Almost coincident direct microstructure measurements were performed and zooplankton community structure was characterized using depth-resolved net sampling techniques. The contribution to scattering from microstructure can be difficult to distinguish from the contribution to scattering from zooplankton using a single narrowband frequency as microstructure and zooplankton are often colocated and can have similar scattering levels over a range of frequencies. Yet their spectra are distinct over a sufficiently broad frequency range, allowing broadband backscattering measurements to reduce the ambiguities typically associated with the interpretation of narrowband measurements. In addition, pulse compression signal processing techniques result in very high-resolution images, allowing physical processes that are otherwise hard to resolve to be imaged, such as Kelvin-Helmholtz shear instabilities. In this study, high-resolution acoustic observations of multiple nonlinear internal waves are presented and regions with distinct scattering spectra are identified. Spectra that decrease in level across the available frequency band were highly correlated to regions of intense turbulence and high stratification, and to Kevin-Helmholtz shear instabilities in particular. Spectra that increase in level across the available frequency band were consistent with scattering dominated by small zooplankton. Simple inversions for relevant microstructure parameters are presented. Limitations of, and improvements to, the broadband system and techniques utilized in this study are discussed.