Hallberg Robert

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  • 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.
  • Article
    Improving oceanic overflow representation in climate models : the Gravity Current Entrainment Climate Process Team
    (American Meteorological Society, 2009-05) Legg, Sonya ; Ezer, Tal ; Jackson, Laura ; Briegleb, Bruce P. ; Danabasoglu, Gokhan ; Large, William G. ; Wu, Wanli ; Chang, Yeon ; Ozgokmen, Tamay M. ; Peters, Hartmut ; Xu, Xiaobiao ; Chassignet, Eric P. ; Gordon, Arnold L. ; Griffies, Stephen M. ; Hallberg, Robert ; Price, James F. ; Riemenschneider, Ulrike ; Yang, Jiayan
    Oceanic overflows are bottom-trapped density currents originating in semienclosed basins, such as the Nordic seas, or on continental shelves, such as the Antarctic shelf. Overflows are the source of most of the abyssal waters, and therefore play an important role in the large-scale ocean circulation, forming a component of the sinking branch of the thermohaline circulation. As they descend the continental slope, overflows mix vigorously with the surrounding oceanic waters, changing their density and transport significantly. These mixing processes occur on spatial scales well below the resolution of ocean climate models, with the result that deep waters and deep western boundary currents are simulated poorly. The Gravity Current Entrainment Climate Process Team was established by the U.S. Climate Variability and Prediction (CLIVAR) Program to accelerate the development and implementation of improved representations of overflows within large-scale climate models, bringing together climate model developers with those conducting observational, numerical, and laboratory process studies of overflows. Here, the organization of the Climate Process Team is described, and a few of the successes and lessons learned during this collaboration are highlighted, with some emphasis on the well-observed Mediterranean overflow. The Climate Process Team has developed several different overflow parameterizations, which are examined in a hierarchy of ocean models, from comparatively well-resolved regional models to the largest-scale global climate models.
  • Article
    Sensitivity of the ocean state to the vertical distribution of internal-tide-driven mixing
    (American Meteorological Society, 2013-03) Melet, Angelique ; Hallberg, Robert ; Legg, Sonya ; Polzin, Kurt L.
    The ocean interior stratification and meridional overturning circulation are largely sustained by diapycnal mixing. The breaking of internal tides is a major source of diapycnal mixing. Many recent climate models parameterize internal-tide breaking using the scheme of St. Laurent et al. While this parameterization dynamically accounts for internal-tide generation, the vertical distribution of the resultant mixing is ad hoc, prescribing energy dissipation to decay exponentially above the ocean bottom with a fixed-length scale. Recently, Polzin formulated a dynamically based parameterization, in which the vertical profile of dissipation decays algebraically with a varying decay scale, accounting for variable stratification using Wentzel–Kramers–Brillouin (WKB) stretching. This study compares two simulations using the St. Laurent and Polzin formulations in the Climate Model, version 2G (CM2G), ocean–ice–atmosphere coupled model, with the same formulation for internal-tide energy input. Focusing mainly on the Pacific Ocean, where the deep low-frequency variability is relatively small, the authors show that the ocean state shows modest but robust and significant sensitivity to the vertical profile of internal-tide-driven mixing. Therefore, not only the energy input to the internal tides matters, but also where in the vertical it is dissipated.
  • Article
    Climate Process Team on internal wave–driven ocean mixing
    (American Meteorological Society, 2017-12-01) MacKinnon, Jennifer A. ; Zhao, Zhongxiang ; Whalen, Caitlin B. ; Waterhouse, Amy F. ; Trossman, David S. ; Sun, Oliver M. ; St. Laurent, Louis C. ; Simmons, Harper L. ; Polzin, Kurt L. ; Pinkel, Robert ; Pickering, Andrew I. ; Norton, Nancy J. ; Nash, Jonathan D. ; Musgrave, Ruth C. ; Merchant, Lynne M. ; Melet, Angelique ; Mater, Benjamin D. ; Legg, Sonya ; Large, William G. ; Kunze, Eric ; Klymak, Jody M. ; Jochum, Markus ; Jayne, Steven R. ; Hallberg, Robert ; Griffies, Stephen M. ; Diggs, Stephen ; Danabasoglu, Gokhan ; Chassignet, Eric P. ; Buijsman, Maarten C. ; Bryan, Frank O. ; Briegleb, Bruce P. ; Barna, Andrew ; Arbic, Brian K. ; Ansong, Joseph ; Alford, Matthew H.
    Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.
  • Article
    Challenges to understanding the dynamic response of Greenland's marine terminating glaciers to oceanic and atmospheric forcing
    (American Meteorological Society, 2013-08) Straneo, Fiamma ; Heimbach, Patrick ; Sergienko, Olga ; Hamilton, Gordon S. ; Catania, Ginny ; Griffies, Stephen M. ; Hallberg, Robert ; Jenkins, Adrian ; Joughin, Ian ; Motyka, Roman ; Pfeffer, W. Tad ; Price, Stephen F. ; Rignot, Eric ; Scambos, Ted ; Truffer, Martin ; Vieli, Andreas
    The recent retreat and speedup of outlet glaciers, as well as enhanced surface melting around the ice sheet margin, have increased Greenland's contribution to sea level rise to 0.6 ± 0.1 mm yr−1 and its discharge of freshwater into the North Atlantic. The widespread, near-synchronous glacier retreat, and its coincidence with a period of oceanic and atmospheric warming, suggests a common climate driver. Evidence points to the marine margins of these glaciers as the region from which changes propagated inland. Yet, the forcings and mechanisms behind these dynamic responses are poorly understood and are either missing or crudely parameterized in climate and ice sheet models. Resulting projected sea level rise contributions from Greenland by 2100 remain highly uncertain. This paper summarizes the current state of knowledge and highlights key physical aspects of Greenland's coupled ice sheet–ocean–atmosphere system. Three research thrusts are identified to yield fundamental insights into ice sheet, ocean, sea ice, and atmosphere interactions, their role in Earth's climate system, and probable trajectories of future changes: 1) focused process studies addressing critical glacier, ocean, atmosphere, and coupled dynamics; 2) sustained observations at key sites; and 3) inclusion of relevant dynamics in Earth system models. Understanding the dynamic response of Greenland's glaciers to climate forcing constitutes both a scientific and technological frontier, given the challenges of obtaining the appropriate measurements from the glaciers' marine termini and the complexity of the dynamics involved, including the coupling of the ocean, atmosphere, glacier, and sea ice systems. Interdisciplinary and international cooperation are crucial to making progress on this novel and complex problem.
  • Article
    NeverWorld2: an idealized model hierarchy to investigate ocean mesoscale eddies across resolutions
    (European Geosciences Union, 2022-09-01) Marques, Gustavo ; Loose, Nora ; Yankovsky, Elizabeth ; Steinberg, Jacob M. ; Chang, Chiung-Yin ; Bhamidipati, Neeraja ; Adcroft, Alistair ; Fox-Kemper, Baylor ; Griffies, Stephen M. ; Hallberg, Robert ; Jansen, Malte F. ; Khatri, Hemant ; Zanna, Laure
    We describe an idealized primitive-equation model for studying mesoscale turbulence and leverage a hierarchy of grid resolutions to make eddy-resolving calculations on the finest grids more affordable. The model has intermediate complexity, incorporating basin-scale geometry with idealized Atlantic and Southern oceans and with non-uniform ocean depth to allow for mesoscale eddy interactions with topography. The model is perfectly adiabatic and spans the Equator and thus fills a gap between quasi-geostrophic models, which cannot span two hemispheres, and idealized general circulation models, which generally include diabatic processes and buoyancy forcing. We show that the model solution is approaching convergence in mean kinetic energy for the ocean mesoscale processes of interest and has a rich range of dynamics with circulation features that emerge only due to resolving mesoscale turbulence.