Marsh Robert

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Marsh
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Robert
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  • Article
    A review of the role of the Atlantic meridional overturning circulation in Atlantic multidecadal variability and associated climate impacts
    (American Geophysical Union, 2019-04-29) Zhang, Rong ; Sutton, Rowan ; Danabasoglu, Gokhan ; Kwon, Young-Oh ; Marsh, Robert ; Yeager, Stephen G. ; Amrhein, Daniel E. ; Little, Christopher M.
    By synthesizing recent studies employing a wide range of approaches (modern observations, paleo reconstructions, and climate model simulations), this paper provides a comprehensive review of the linkage between multidecadal Atlantic Meridional Overturning Circulation (AMOC) variability and Atlantic Multidecadal Variability (AMV) and associated climate impacts. There is strong observational and modeling evidence that multidecadal AMOC variability is a crucial driver of the observed AMV and associated climate impacts and an important source of enhanced decadal predictability and prediction skill. The AMOC‐AMV linkage is consistent with observed key elements of AMV. Furthermore, this synthesis also points to a leading role of the AMOC in a range of AMV‐related climate phenomena having enormous societal and economic implications, for example, Intertropical Convergence Zone shifts; Sahel and Indian monsoons; Atlantic hurricanes; El Niño–Southern Oscillation; Pacific Decadal Variability; North Atlantic Oscillation; climate over Europe, North America, and Asia; Arctic sea ice and surface air temperature; and hemispheric‐scale surface temperature. Paleoclimate evidence indicates that a similar linkage between multidecadal AMOC variability and AMV and many associated climate impacts may also have existed in the preindustrial era, that AMV has enhanced multidecadal power significantly above a red noise background, and that AMV is not primarily driven by external forcing. The role of the AMOC in AMV and associated climate impacts has been underestimated in most state‐of‐the‐art climate models, posing significant challenges but also great opportunities for substantial future improvements in understanding and predicting AMV and associated climate impacts.
  • Article
    The surface-forced overturning of the North Atlantic : estimates from modern era atmospheric reanalysis datasets
    (American Meteorological Society, 2014-05-15) Grist, Jeremy P. ; Josey, Simon A. ; Marsh, Robert ; Kwon, Young-Oh ; Bingham, Rory J. ; Blaker, Adam T.
    Estimates of the recent mean and time varying water mass transformation rates associated with North Atlantic surface-forced overturning are presented. The estimates are derived from heat and freshwater surface fluxes and sea surface temperature fields from six atmospheric reanalyses—the Japanese 25-yr Reanalysis (JRA), the NCEP–NCAR reanalysis (NCEP1), the NCEP–U.S. Department of Energy (DOE) reanalysis (NCEP2), the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-I), the Climate Forecast System Reanalysis (CFSR), and the Modern-Era Reanalysis for Research and Applications (MERRA)—together with sea surface salinity fields from two globally gridded datasets (World Ocean Atlas and Met Office EN3 datasets). The resulting 12 estimates of the 1979–2007 mean surface-forced streamfunction all depict a subpolar cell, with maxima north of 45°N, near σ = 27.5 kg m−3, and a subtropical cell between 20° and 40°N, near σ = 26.1 kg m−3. The mean magnitude of the subpolar cell varies between 12 and 18 Sv (1 Sv ≡ 106 m3 s−1), consistent with estimates of the overturning circulation from subsurface observations. Analysis of the thermal and haline components of the surface density fluxes indicates that large differences in the inferred low-latitude circulation are largely a result of the biases in reanalysis net heat flux fields, which range in the global mean from −13 to 19 W m−2. The different estimates of temporal variability in the subpolar cell are well correlated with each other. This suggests that the uncertainty associated with the choice of reanalysis product does not critically limit the ability of the method to infer the variability in the subpolar overturning. In contrast, the different estimates of subtropical variability are poorly correlated with each other, and only a subset of them captures a significant fraction of the variability in independently estimated North Atlantic Subtropical Mode Water volume.
  • Article
    Lagrangian ocean analysis : fundamentals and practices
    (Elsevier, 2017-11-24) van Sebille, Erik ; Griffies, Stephen M. ; Abernathey, Ryan ; Adams, Thomas P. ; Berloff, Pavel S. ; Biastoch, Arne ; Blanke, Bruno ; Chassignet, Eric P. ; Cheng, Yu ; Cotter, Colin J. ; Deleersnijder, Eric ; Döös, Kristofer ; Drake, Henri F. ; Drijfhout, Sybren ; Gary, Stefan F. ; Heemink, Arnold W. ; Kjellsson, Joakim ; Koszalka, Inga M. ; Lange, Michael ; Lique, Camille ; MacGilchrist, Graeme ; Marsh, Robert ; Mayorga-Adame, Claudia G. ; McAdam, Ronan ; Nencioli, Francesco ; Paris, Claire B. ; Piggott, Matthew D. ; Polton, Jeff ; Rühs, Siren ; Shah, Syed H.A.M. ; Thomas, Matthew D. ; Wang, Jinbo ; Wolfram, Phillip J. ; Zanna, Laure ; Zika, Jan D.
    Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.