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1. Acute sensitivity of global ocean circulation and heat content to eddy energy dissipation time-scale

Author

Mak, Julian, Marshall, David P., Madec, Gurvan, and Maddison, James R.

Subjects
Physics - Atmospheric and Oceanic Physics, Physics - Fluid Dynamics
Abstract

The global ocean overturning circulation, critically dependent on the global density stratification, plays a central role in regulating climate evolution. While it is well-known that the global stratification profile exhibits a strong dependence to Southern Ocean dynamics and in particular to wind and buoyancy forcing, we demonstrate here that the stratification is also acutely sensitive to the mesoscale eddy energy dissipation time-scale. Within the context of a global ocean circulation model with an energy constrained mesoscale eddy parameterization, it is shown that modest variations in the eddy energy dissipation time-scale lead to significant variations in key metrics relating to ocean circulation, namely the Antarctic Circumpolar Current transport, Atlantic Meridional Overturning Circulation strength, and global ocean heat content, over long time-scales. The results highlight a need to constrain uncertainties associated with eddy energy dissipation for climate model projections over centennial time-scales, but also for paleoclimate simulations over millennial time-scales., Comment: 13 pages, 4 figures; preprint version; accepted by Geophysical Research Letters, post-print version to be made available at a later point

Published
2022
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7. The Future of Sea Ice Modeling : Where Do We Go from Here?

Author

Blockley, Ed, Vancoppenolle, Martin, Hunke, Elizabeth, Bitz, Cecilia, Feltham, Daniel, Lemieux, Jean-François, Losch, Martin, Maisonnave, Eric, Notz, Dirk, Rampal, Pierre, Tietsche, Steffen, Tremblay, Bruno, Turner, Adrian, Massonnet, François, Ólason, Einar, Roberts, Andrew, Aksenov, Yevgeny, Fichefet, Thierry, Garric, Gilles, Iovino, Doroteaciro, Madec, Gurvan, Rousset, Clément, Salas y Melia, David, and Schroeder, David

Published
2020

9. Thermodynamics Drive Post‐2016 Changes in the Antarctic Sea Ice Seasonal Cycle.

Author

Himmich, Kenza, Vancoppenolle, Martin, Stammerjohn, Sharon, Bocquet, Marion, Madec, Gurvan, Sallée, Jean‐Baptiste, and Fleury, Sara

Subjects
OCEAN temperature, SOLAR heating, WEATHER, SPRING, ANTARCTIC ice, SEA ice
Abstract

Antarctic sea ice extent has been persistently low since late 2016, possibly owing to changes in atmospheric and oceanic conditions. However, the relative contributions of the ocean, the atmosphere and the underlying mechanisms by which they have affected sea ice remain uncertain. To investigate possible causes for this sea‐ice decrease, we establish a seasonal timeline of sea ice changes following 2016, using remote sensing observations. Anomalies in the timing of sea ice retreat and advance are examined along with their spatial and interannual relations with various indicators of seasonal sea ice and oceanic changes. They include anomalies in winter ice thickness, spring ice removal rate due to ice melt and transport, and summer sea surface temperature. We find that the ice season has shortened at an unprecedented rate and magnitude, due to earlier retreat and later advance. We attribute this shortening to a winter ice thinning, in line with ice‐albedo feedback processes, with ice transport playing a smaller role. Reduced ice thickness has accelerated spring ice area removal as thinner sea ice requires less time to melt. The consequent earlier sea ice retreat has in turn increased ocean solar heat uptake in summer, ultimately delaying sea ice advance. We speculate that the observed winter sea ice thinning is consistent with previous evidence of subsurface warming of the Southern Ocean. Plain Language Summary: Following 2016, the Antarctic sea ice cover has been persistently low. To understand why, we retrace the seasonal timeline of sea ice and oceanic changes, using satellite observations. We find that the sea ice season has been significantly shorter following 2016, due to a later start and an earlier end. This shortening is likely caused by thinner sea ice in winter, accelerating sea ice melt in spring and causing sea ice to disappear earlier. In turn, this has caused the ice‐free ocean to absorb more solar heat in summer, and to take longer to cool down in the fall, ultimately delaying the ice season onset. Warmer waters beneath the Southern Ocean's surface, as evidenced by previous studies, could be a plausible cause of the observed thinning, by increasing the heat supply to sea ice. Key Points: The Antarctic sea ice season duration has undergone an unprecedented shortening since 2016The changes include thinner ice, faster melt, earlier retreat, larger ocean heat uptake, later advance, in line with the ice‐albedo feedbackThe near‐circumpolar ice thinning suggests a possible increase in sensible heat supply by the ocean [ABSTRACT FROM AUTHOR]

Published
2024
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12. Impacts of Vertical Convective Mixing Schemes and Freshwater Forcing on the 2016–2017 Maud Rise Polynya Openings in a Regional Ocean Simulation.

Author

Gülk, Birte, Roquet, Fabien, Naveira Garabato, Alberto C., Bourdallé‐Badie, Romain, Madec, Gurvan, and Giordani, Hervé

Subjects
FRESH water, POLYNYAS, OCEAN, MIXING height (Atmospheric chemistry), SEA ice, MODELS & modelmaking
Abstract

The correct representation of the Maud Rise open‐ocean polynya in the Weddell Sea remains a challenge for ocean models. Here we reproduce the most recent polynya openings in 2016–2017 using a regional configuration, and assess their dependencies on vertical convective mixing schemes and freshwater forcing, both separately and in combination. We test three vertical convective mixing schemes: the enhanced vertical diffusion (EVD), the Eddy‐Diffusivity Mass‐Flux (EDMF) parameterization, and a modified version of EDMF accounting for thermobaric effects. Using simulations for the period 2007–2017, we find that the modified EDMF reproduces the observed climatological evolution of the mixed layer depth better than the original EDMF and the EVD, but a polynya fails to open due to excessive freshwater forcing. We thus use the modified EDMF to perform sensitivity experiments with reduced precipitation during 2012–2017. The imposed freshwater forcing strongly affects the number of years with polynyas. The simulation with the best representation of the 2016–2017 polynyas is analyzed to evaluate the triggering mechanisms. The 2016 polynya was induced by the action of thermobaric instabilities on a weak ambient stratification. This opening preconditioned the water column for 2017, which produced a stronger polynya. By examining the impacts of the different convective mixing schemes, we show that the modified EDMF generates more realistic patterns of deep convection. Our results highlight the importance of surface freshwater forcing and thermobaricity in governing deep convection around Maud Rise, and the need to represent thermobaric instabilities to realistically model Maud Rise polynyas. Plain Language Summary: We investigate the impacts of representing numerical vertical mixing and surface freshwater forcing in a regional ocean model on polynyas (large openings in the pack ice) at Maud Rise, Southern Ocean. Maud Rise is prone to hosting polynyas, often associated with deep convection, which is a local vertical mixing process homogenizing the water column between surface and depths of several hundred meters. Numerical models often use simplistic strategies to represent this process, but improved parameterizations have recently become available. In this work, we test the impact of the representation of convective mixing in a particularly sensitive region. The last Maud Rise polynyas were observed in 2016 and 2017. Our regional simulation is capable of reproducing these polynyas, which has long been a challenge for ocean‐sea ice models. We show that the 2016 polynya resulted from the action of a vertical instability at depth acting on weak ambient stratification. This event preconditioned the stronger 2017 polynya and deep convection. We conclude that representing convective plumes as a sub‐grid scale process in models leads to a more realistic representation of open‐ocean polynyas and associated convection events. Key Points: The Eddy‐Diffusivity Mass‐Flux (EDMF) parameterization is tested in a regional simulation of the ocean around Maud RiseThermobaric effects on convective plumes are enabled by modifying the EDMF parameterizationSimulations of Maud Rise polynyas are highly sensitive to freshwater forcing and mixing schemes [ABSTRACT FROM AUTHOR]

Published
2024
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16. NEMO Ocean Engine Reference Manual

Author

Madec, Gurvan, Bell, Mike, Blaker, Adam, Bricaud, Clément, Bruciaferri, Diego, Castrillo, Miguel, Calvert, Daley, Jérômeme Chanut, Clementi, Emanuela, Coward, Andrew, Epicoco, Italo, Éthé, Christian, Ganderton, Jonas, Harle, James, Hutchinson, Katherine, Iovino, Doroteaciro, Lea, Dan, Lovato, Tomas, Martin, Matt, Martin, Nicolas, Mele, Francesca, Martins, Diana, Masson, Sébastien, Mathiot, Pierre, Mocavero, Silvia, Müller, Simon, Nurser, A.J. George, Paronuzzi, Stella, Peltier, Mathieu, Person, Renaud, Rousset, Clement, Rynders, Stefanie, Samson, Guillaume, Téchené, Sibylle, Vancoppenolle, Martin, and Wilson, Chris

Subjects
modelling, nemo-ocean, ComputerSystemsOrganization_COMPUTERSYSTEMIMPLEMENTATION, ocean, ocean-modelling, GeneralLiterature_MISCELLANEOUS, Physics::Atmospheric and Oceanic Physics, Physics::Geophysics
Abstract

The ocean engine of NEMO is a primitive equation model adapted to regional and global ocean circulation problems. It is intended to be a flexible tool for studying the ocean and its interactions with the others components of the earth climate system over a wide range of space and time scales. To cite this edition: Madec, G. and the NEMO System Team, 2023.NEMO Ocean Engine Reference Manual, Zenodo, https://doi.org/10.5281/zenodo.8167700

Published
2023
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19. Summer hydrography and circulation in Storfjorden, Svalbard, following a record low winter sea‐ice extent in the Barents Sea

Author

Vivier, Frédéric, Lourenço, Antonio, Michel, Elisabeth, Skogseth, Ragnheid, Rousset, Clément, Lansard, Bruno, Bouruet‐aubertot, Pascale, Boutin, Jacqueline, Bombled, Bruno, Cuypers, Yannis, Crispi, Olivier, Dausse, Dennis, Le Goff, Hervé, Madec, Gurvan, Vancoppenolle, Martin, Van Der Linden, Fanny, Waelbroeck, Claire, Vivier, Frédéric, Lourenço, Antonio, Michel, Elisabeth, Skogseth, Ragnheid, Rousset, Clément, Lansard, Bruno, Bouruet‐aubertot, Pascale, Boutin, Jacqueline, Bombled, Bruno, Cuypers, Yannis, Crispi, Olivier, Dausse, Dennis, Le Goff, Hervé, Madec, Gurvan, Vancoppenolle, Martin, Van Der Linden, Fanny, and Waelbroeck, Claire

Abstract

Storfjorden, Svalbard, hosts a polynya in winter and is an important source region of Brine-enriched Shelf Water (BSW) that, if dense enough, feeds the Arctic Ocean deep water reservoir. Changes in the BSW production may thus have far-reaching impacts. We analyze the water mass distribution and circulation in Storfjorden and the trough south of it, Storfjordrenna, using hydrographic sections occupied in July 2016, following a winter characterized by the lowest ice coverage recorded in the Barents Sea. These observations reveal an unusual hydrographic state, characterized at the surface by the near absence of Melt Water and Storfjorden Surface Water, replaced by a saltier water mass. At depth, BSW (maximum salinity of 34.95) was found from the bottom up to 90 m, above the 120-m deep sill at the mouth to Storfjordrenna. However, no gravity driven overflow was observed downstream of the sill: the dome of BSW remained locked over the depression in a cyclonic circulation pattern consistent with a stratified Taylor column. Observations further reveal a previously unreported intrusion of Atlantic Water far into the fjord, promoting isopycnal mixing with entrapped Arctic Water. This intrusion was possibly favored by positive wind stress curl anomalies over Svalbardbanken and Storfjordrenna. The bottom plume exiting Storfjordrenna was weak, carrying Polar Front Water rather than BSW, too light to sink underneath the Atlantic Water layer at Fram Strait. Whether Storfjorden switched durably to a new hydrographic state, following the observed Atlantification of the Barents Sea after 2005, remains to be established. Key Points Changes in the hydrography and circulation in Storfjorden a decade after a regime shift in the Barents Sea linked to its Atlantification The less saline Brine-enriched Shelf Water remained entrapped in Storfjorden within a cyclonic circulation pattern with no overflow Storfjorden was flooded with Atlantic Water, promoting isopycnal mixing with Arctic Water

Published
2023
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22. North Atlantic simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II). Part II: Inter-annual to decadal variability

Author

Danabasoglu, Gokhan, Yeager, Steve G., Kim, Who M., Behrens, Erik, Bentsen, Mats, Bi, Daohua, Biastoch, Arne, Bleck, Rainer, Böning, Claus, Bozec, Alexandra, Canuto, Vittorio M., Cassou, Christophe, Chassignet, Eric, Coward, Andrew C., Danilov, Sergey, Diansky, Nikolay, Drange, Helge, Farneti, Riccardo, Fernandez, Elodie, Fogli, Pier Giuseppe, Forget, Gael, Fujii, Yosuke, Griffies, Stephen M., Gusev, Anatoly, Heimbach, Patrick, Howard, Armando, Ilicak, Mehmet, Jung, Thomas, Karspeck, Alicia R., Kelley, Maxwell, Large, William G., Leboissetier, Anthony, Lu, Jianhua, Madec, Gurvan, Marsland, Simon J., Masina, Simona, Navarra, Antonio, Nurser, A.J. George, Pirani, Anna, Romanou, Anastasia, Salas y Mélia, David, Samuels, Bonita L., Scheinert, Markus, Sidorenko, Dmitry, Sun, Shan, Treguier, Anne-Marie, Tsujino, Hiroyuki, Uotila, Petteri, Valcke, Sophie, Voldoire, Aurore, Wang, Qiang, and Yashayaev, Igor

Published
2016
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23. Southern ocean carbon and heat impact on climate

Author

Sallée, Jean-Baptiste, Abrahamsen, E. P., Allaigre, C., Auger, Matthis, Ayres, H., Badhe, R., Boutin, Jacqueline, Brearley, J. A., de Lavergne, Casimir, ten Doeschate, A. M. M., Droste, E. S., Du Plessis, M. D., Ferreira, D., Giddy, I. S., Gülk, B., Gruber, N., Hague, M., Hoppema, M., Josey, S. A., Kanzow, T., Kimmritz, M., Lindeman, M. R., Llanillo, P. J., Lucas, N. S., Madec, Gurvan, Marshall, D. P., Meijers, A. J. S., Meredith, M. P., Mohrmann, M., Monteiro, P. M. S., Mosneron Dupin, Cosme, Naeck, Kirtana, Narayanan, A., Naveira Garabato, A. C., Nicholson, S. -A., Novellino, A., Ödalen, M., Østerhus, S., Park, W., Patmore, R. D., Piedagnel, Évéa, Roquet, Fabien, Rosenthal, H. S., Roy, T., Saurabh, Rathore, Silvy, Yona, Spira, T., Steiger, Nadine, Styles, A. F., Swart, S., Vogt, Linus, Ward, B., Zhou, S., Processus et interactions de fine échelle océanique (PROTEO), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Nucleus for European Modeling of the Ocean (NEMO R&D ), Océan et variabilité du climat (VARCLIM), and European Project: 821001,SO-CHIC(2019)

Subjects
[SDU]Sciences of the Universe [physics]
Abstract

International audience; The Southern Ocean greatly contributes to the regulation of the global climate by controlling important heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal timescales are therefore impacted by oceanic processes taking place in the Southern Ocean, yet too little is known about these processes. Limitations come both from the lack of observations in this extreme environment and its inherent sensitivity to intermittent processes at scales that are not well captured in current Earth system models. The Southern Ocean Carbon and Heat Impact on Climate programme was launched to address this knowledge gap, with the overall objective to understand and quantify variability of heat and carbon budgets in the Southern Ocean through an investigation of the key physical processes controlling exchanges between the atmosphere, ocean and sea ice using a combination of observational and modelling approaches. Here, we provide a brief overview of the programme, as well as a summary of some of the scientific progress achieved during its first half. Advances range from new evidence of the importance of specific processes in Southern Ocean ventilation rate (e.g. storm-induced turbulence, sea-ice meltwater fronts, wind-induced gyre circulation, dense shelf water formation and abyssal mixing) to refined descriptions of the physical changes currently ongoing in the Southern Ocean and of their link with global climate. This article is part of a discussion meeting issue `Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Published
2023

28. Summer hydrography and circulation in Storfjorden, Svalbard, following a record low winter sea‐ice extent in the Barents Sea

Author

Vivier, Frédéric, primary, Lourenço, Antonio, additional, Michel, Elisabeth, additional, Skogseth, Ragnheid, additional, Rousset, Clément, additional, Lansard, Bruno, additional, Bouruet‐Aubertot, Pascale, additional, Boutin, Jacqueline, additional, Bombled, Bruno, additional, Cuypers, Yannis, additional, Crispi, Olivier, additional, Dausse, Dennis, additional, Le Goff, Hervé, additional, Madec, Gurvan, additional, Vancoppenolle, Martin, additional, Van der Linden, Fanny, additional, and Waelbroeck, Claire, additional

Published
2023
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29. Drivers of Antarctic sea ice advance

Author

Himmich, Kenza, primary, Vancoppenolle, Martin, additional, Madec, Gurvan, additional, Sallée, Jean-Baptiste, additional, Holland, Paul, additional, and Lebrun, Marion, additional

Published
2023
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32. Variability and remote controls of the warm-water halo and Taylor cap at Maud rise

Author

Gülk, Birte, Roquet, Fabien, Naveira Garabato, Alberto C., Narayanan, Aditya, Rousset, Clément, and Madec, Gurvan

Abstract

The region of Maud Rise, a seamount in the Weddell Sea, is known for the occurrence of irregular polynya openings during the winter months. Hydrographic observations have shown the presence of a warmer water mass below the mixed layer along the seamount’s flanks, commonly termed the warm-water Halo, surrounding a colder region above the rise, the Taylor Cap. A combination of observational data sets, an eddy-permitting reanalysis product and a regional high-resolution configuration allows to investigate the properties of these features and shows a strong interannual variability. A warming of deep waters is observed in the Taylor Cap during the years preceding the opening of the Polynya in 2016 and 2017, starting in 2011. By analyzing regional simulations, we are able to demonstrate that most of the observed variability in the warm-water Halo is forced remotely by advection of Weddell Gyre deep waters in the region surrounding Maud Rise. Deep water anomalies found in the Halo are retroflected along the inner flank of the Halo and from there transported into the Taylor Cap by eddies within the next six months. In addition to the preconditioning of the ocean preceding the Polynya opening, we investigate the role of thermobaricity in the region of Maud Rise in the period before the Polynya opening by implementing the eddy-diffusivity mass-flux parameterization in 1D simulations and the regional configuration., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Published
2023

38. North Atlantic simulations in Coordinated Ocean-ice Reference Experiments phase II (CORE-II). Part I: Mean states

Author

Danabasoglu, Gokhan, Yeager, Steve G., Bailey, David, Behrens, Erik, Bentsen, Mats, Bi, Daohua, Biastoch, Arne, Böning, Claus, Bozec, Alexandra, Canuto, Vittorio M., Cassou, Christophe, Chassignet, Eric, Coward, Andrew C., Danilov, Sergey, Diansky, Nikolay, Drange, Helge, Farneti, Riccardo, Fernandez, Elodie, Fogli, Pier Giuseppe, Forget, Gael, Fujii, Yosuke, Griffies, Stephen M., Gusev, Anatoly, Heimbach, Patrick, Howard, Armando, Jung, Thomas, Kelley, Maxwell, Large, William G., Leboissetier, Anthony, Lu, Jianhua, Madec, Gurvan, Marsland, Simon J., Masina, Simona, Navarra, Antonio, George Nurser, A.J., Pirani, Anna, y Mélia, David Salas, Samuels, Bonita L., Scheinert, Markus, Sidorenko, Dmitry, Treguier, Anne-Marie, Tsujino, Hiroyuki, Uotila, Petteri, Valcke, Sophie, Voldoire, Aurore, and Wang, Qiang

Published
2014
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42. Stability and accuracy of Runge-Kutta based split-explicit time-stepping algorithms for free-surface ocean models

Author

Lemarié, Florian, Ducousso, Nicolas, Debreu, Laurent, Madec, Gurvan, Mathematics and computing applied to oceanic and atmospheric flows (AIRSEA), Inria Grenoble - Rhône-Alpes, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Université Grenoble Alpes (UGA)-Laboratoire Jean Kuntzmann (LJK), Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Service Hydrographique et Océanographique de la Marine (SHOM), Ministère de la Défense, Nucleus for European Modeling of the Ocean (NEMO R&D ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), and Lemarié, Florian

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, [SDU.OCEAN] Sciences of the Universe [physics]/Ocean, Atmosphere, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], [MATH.MATH-AP] Mathematics [math]/Analysis of PDEs [math.AP]
Abstract

International audience; Because of the Boussinesq assumption employed in the vast majority of oceanic models, the acoustic waves are filtered and the fast dynamics corresponds to the external gravity-wave propagation which is much faster than other (internal) processes. The fast and slow dynamics are traditionally split into separate subproblems where the fast motions are nearly independent of depth. It is thus natural to model these motions with a two-dimensional (barotropic) system of equations while the slow processes are modeled with a three-dimensional (baroclinic) system. However such splitting is inexact, the barotropic mode is not strictly depth-independent meaning that the separation of slow and fast modes is non-orthogonal, even in the linear case. A consequence is that there are some fast components contained in the slow motions which induce instabilities controlled by time filtering of the fast mode. In this talk we present an analysis of the stability and accuracy of the barotropic–baroclinic mode splitting in the case where the baroclinic mode is integrated using a Runge-Kutta scheme and the barotropic mode is integrated explicitly (i.e. the so-called split-explicit approach). By referring to the theoretical framework developed by Demange et al. (2019), the analysis is based on an eigenvector decomposition using the true (depth-dependent) barotropic mode. We investigate several strategies to achieve stable integrations whose performance is assessed first on a theoretical ground and then by idealized linear and nonlinear numerical experiments.

Published
2022

43. Acute Sensitivity of Global Ocean Circulation and Heat Content to Eddy Energy Dissipation Timescale

Author

Mak, Julian, Marshall, David P., Madec, Gurvan, Maddison, James R., Mak, Julian, Marshall, David P., Madec, Gurvan, and Maddison, James R.

Abstract

The global ocean overturning circulation, critically dependent on the global density stratification, plays a central role in regulating climate evolution. While it is well known that the global stratification profile exhibits a strong dependence to Southern Ocean dynamics and in particular to wind and buoyancy forcing, we demonstrate here that the stratification is also acutely sensitive to the mesoscale eddy energy dissipation timescale. Within the context of a global ocean circulation model with an energy constrained mesoscale eddy parameterization, it is shown that modest variations in the eddy energy dissipation timescale lead to significant variations in key metrics relating to ocean circulation, namely the Antarctic Circumpolar Current transport, Atlantic Meridional Overturning Circulation strength, and global ocean heat content, over long timescales. The results highlight a need to constrain uncertainties associated with eddy energy dissipation for climate model projections over centennial timescales and also for paleoclimate simulations over millennial timescales.

Published
2022

44. The Polar Transition from Alpha to Beta Regions Set by a Surface Buoyancy Flux Inversion

Author

Caneill, Romain, Roquet, Fabien, Madec, Gurvan, Nycander, Jonas, Caneill, Romain, Roquet, Fabien, Madec, Gurvan, and Nycander, Jonas

Abstract

The stratification is primarily controlled by temperature in subtropical regions (alpha ocean) and by salinity in subpolar regions (beta ocean). Between these two regions lies a transition zone, often characterized by deep mixed layers in winter and responsible for the ventilation of intermediate or deep layers. While of primary interest, no consensus on what controls its position exists yet. Among the potential candidates, we find the wind distribution, air-sea fluxes, or the nonlinear cabbeling effect. Using an ocean general circulation model in an idealized basin configuration, a sensitivity analysis is performed testing different equations of state. More precisely, the thermal expansion coefficient (TEC) temperature dependence is explored, changing the impact of heat fluxes on buoyancy fluxes in a series of experiments. The polar transition zone is found to be located at the position where the sign of the surface buoyancy flux reverses to become positive, in the subpolar region, while wind or cabbeling are likely of secondary importance. This inversion becomes possible because the TEC is reducing at low temperature, enhancing in return the relative impact of freshwater fluxes on the buoyancy forcing at high latitudes. When the TEC is made artificially larger at low temperature, the freshwater flux required to produce a positive buoyancy flux increases and the polar transition moves poleward. These experimets demonstrate the important role of competing heat and freshwater fluxes in setting the position of the transition zone. This competition is primarily influenced by the spatial variations of the TEC linked to meridional variations of the surface temperature.

Published
2022
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45. Unique thermal expansion properties of water key to the formation of sea ice on Earth

Author

Roquet, Fabien, Ferreira, David, Caneill, Romain, Schlesinger, Daniel, Madec, Gurvan, Roquet, Fabien, Ferreira, David, Caneill, Romain, Schlesinger, Daniel, and Madec, Gurvan

Abstract

The formation of sea ice in polar regions is possible because a salinity gradient or halocline keeps the water column stable despite intense cooling. Here, we demonstrate that a unique water property is central to the maintenance of the polar halocline, namely, that the thermal expansion coefficient (TEC) of seawater increases by one order of magnitude between polar and tropical regions. Using a fully coupled climate model, it is shown that, even with excess precipitations, sea ice would not form at all if the near-freezing temperature TEC was not well below its ocean average value. The leading order dependence of the TEC on temperature is essential to the coexistence of the mid/low-latitude thermally stratified and the high-latitude sea ice–covered oceans that characterize our planet. A key implication is that nonlinearities of water properties have a first-order impact on the global climate of Earth and possibly exoplanets.

Published
2022
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46. A Parallel Ocean Model for High Resolution Studies

Author

Guyon, Marc, Madec, Gurvan, Imbard, Maurice, Roux, François-Xavier, Amestoy, Patrick, editor, Berger, Philippe, editor, Daydé, Michel, editor, Ruiz, Daniel, editor, Duff, Iain, editor, Frayssé, Valérie, editor, and Giraud, Luc, editor

Published
1999
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48. Model of the Regional Coupled Earth system (MORCE): Application to process and climate studies in vulnerable regions

Author

Drobinski, Philippe, Anav, Alesandro, Lebeaupin Brossier, Cindy, Samson, Guillaume, Stéfanon, Marc, Bastin, Sophie, Baklouti, Mélika, Béranger, Karine, Beuvier, Jonathan, Bourdallé-Badie, Romain, Coquart, Laure, D'Andrea, Fabio, de Noblet-Ducoudré, Nathalie, Diaz, Frédéric, Dutay, Jean-Claude, Ethe, Christian, Foujols, Marie-Alice, Khvorostyanov, Dmitry, Madec, Gurvan, Mancip, Martial, Masson, Sébastien, Menut, Laurent, Palmieri, Julien, Polcher, Jan, Turquety, Solène, Valcke, Sophie, and Viovy, Nicolas

Published
2012
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