Investigating Solution Convergence in a Global Ocean Model Using a 2048-Processor Cluster of Distributed Shared Memory Machines

Up to 1920 processors of a cluster of distributed shared memory machines at the NASA Ames Research Center are being used to simulate ocean circulation globally at horizontal resolutions of 1/4, 1/8, and 1/16-degree with the Massachusetts Institute of Technology General Circulation Model, a finite volume code that can scale to large numbers of processors. The study aims to understand physical processes responsible for skill improvements as resolution is increased and to gain insight into what resolution is sufficient for particular purposes. This paper focuses on the computational aspects of reaching the technical objective of efficiently performing these global eddy-resolving ocean simulations. At 1/16-degree resolution the model grid contains 1.2 billion cells. At this resolution it is possible to simulate approximately one month of ocean dynamics in about 17 hours of wallclock time with a model timestep of two minutes on a cluster of four 512-way NUMA Altix systems. The Altix systems' large main memory and I/O subsystems allow computation and disk storage of rich sets of diagnostics during each integration, supporting the scientific objective to develop a better understanding of global ocean circulation model solution convergence as model resolution is increased.

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Impact of Resolution and Optimized ECCO Forcing on Simulations of the Tropical Pacific

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2007jtecho528.1 ◽

2008 ◽

Vol 25 (1) ◽

pp. 131-147 ◽

Cited By ~ 12

Author(s):

I. Hoteit ◽

B. Cornuelle ◽

V. Thierry ◽

D. Stammer

Keyword(s):

Ocean Circulation ◽

General Circulation ◽

Large Scale ◽

Circulation Model ◽

Tropical Pacific ◽

Global Ocean ◽

Massachusetts Institute Of Technology ◽

Model Domain ◽

Freshwater Fluxes ◽

The Tropical Pacific

Abstract The sensitivity of the dynamics of a tropical Pacific Massachusetts Institute of Technology (MIT) general circulation model (MITgcm) to the surface forcing fields and to the horizontal resolution is analyzed. During runs covering the period 1992–2002, two different sets of surface forcing boundary conditions are used, obtained 1) from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis project and 2) from the Estimating the Circulation and Climate of the Ocean (ECCO) assimilation consortium. The “ECCO forcing” is the “NCEP forcing” adjusted by a state estimation procedure using the MITgcm with a 1° × 1° global grid and the adjoint method assimilating a multivariate global ocean dataset. The skill of the model is evaluated against ocean observations available in situ and from satellites. The model domain is limited to the tropical Pacific, with open boundaries located along 26°S, 26°N, and in the Indonesian throughflow. To account for large-scale changes of the ocean circulation, the model is nested in the global time-varying ocean state provided by the ECCO consortium on a 1° grid. Increasing the spatial resolution to 1/3° and using the ECCO forcing fields significantly improves many aspects of the circulation but produces overly strong currents in the western model domain. Increasing the resolution to 1/6° does not yield further improvements of model results. Using the ECCO heat and freshwater fluxes in place of NCEP products leads to improved time-mean model skill (i.e., reduced biases) over most of the model domain, underlining the important role of adjusted heat and freshwater fluxes for improving model representations of the tropical Pacific. Combinations of ECCO and NCEP wind forcing fields can improve certain aspects of the model solutions, but neither ECCO nor NCEP winds show clear overall superiority.

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On the impact of sea ice in a global ocean circulation model

Annals of Glaciology ◽

10.3189/s0260305500013884 ◽

1997 ◽

Vol 25 ◽

pp. 111-115 ◽

Cited By ~ 3

Author(s):

Achim Stössel

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Ocean Circulation ◽

General Circulation ◽

Thermohaline Circulation ◽

Circulation Model ◽

Deep Ocean ◽

Global Ocean ◽

Convective Activity ◽

The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

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Multi-grid algorithm for passive tracer transport in the NEMO ocean circulation model: a case study with the NEMO OGCM (version 3.6)

Geoscientific Model Development ◽

10.5194/gmd-13-5465-2020 ◽

2020 ◽

Vol 13 (11) ◽

pp. 5465-5483

Author(s):

Clément Bricaud ◽

Julien Le Sommer ◽

Gurvan Madec ◽

Christophe Calone ◽

Julie Deshayes ◽

...

Keyword(s):

Spatial Resolution ◽

Ocean Circulation ◽

Circulation Model ◽

Ocean Model ◽

Ocean Dynamics ◽

Global Ocean ◽

Passive Tracer ◽

Tracer Transport ◽

Ocean Circulation Model ◽

Grid Algorithm

Abstract. Ocean biogeochemical models are key tools for both scientific and operational applications. Nevertheless the cost of these models is often expensive because of the large number of biogeochemical tracers. This has motivated the development of multi-grid approaches where ocean dynamics and tracer transport are computed on grids of different spatial resolution. However, existing multi-grid approaches to tracer transport in ocean modelling do not allow the computation of ocean dynamics and tracer transport simultaneously. This paper describes a new multi-grid approach developed for accelerating the computation of passive tracer transport in the Nucleus for European Modelling of the Ocean (NEMO) ocean circulation model. In practice, passive tracer transport is computed at runtime on a grid with coarser spatial resolution than the hydrodynamics, which reduces the CPU cost of computing the evolution of tracers. We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and discuss its performance on the basis of a series of sensitivity experiments with global ocean model configurations. Our experiments confirm that the spatial resolution of hydrodynamical fields can be coarsened by a factor of 3 in both horizontal directions without significantly affecting the resolved passive tracer fields. Overall, the proposed algorithm yields a reduction by a factor of 7 of the overhead associated with running a full biogeochemical model like PISCES (with 24 passive tracers). Propositions for further reducing this cost without affecting the resolved solution are discussed.

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Towards AOD1B RL07

10.5194/gstm2020-29 ◽

2020 ◽

Author(s):

Linus Shihora ◽

Henryk Dobslaw

Keyword(s):

General Circulation ◽

A Priori ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Temporal Variations ◽

Ocean Dynamics ◽

Global Ocean ◽

Ocean Bottom ◽

Data Set ◽

Priori Information

<p>The Atmosphere and Ocean De-Aliasing Level-1B (AOD1B) product provides a priori information about temporal variations in the Earth's gravity field caused by global mass variability in the atmosphere and ocean and is routinely used as background model in satellite gravimetry. The current version 06 provides Stokes coefficients expanded up to d/o 180 every 3 hours. It is based on ERA-Interim and the ECMWF operational model for the atmosphere, and simulations with the global ocean general circulation model MPIOM consistently forced with the fields from the same atmospheric data-set.</p> <p>We here present preliminary numerical experiments in the development towards a new release 07 of AOD1B. The experiments are performed with the TP10 configuration of MPIOM and include (I) new hourly atmospheric forcing based on the new ERA-5 reanalysis from ECMWF; (II) an improved bathymetry around Antarctica including cavities under the ice shelves; and (III) an explicit implementation of the feedback effects of self-attraction and loading to ocean dynamics. The simulated ocean bottom pressure variability is discussed with respect to AOD1B version 6 as well as in situ ocean observations. A preliminary timeseries of hourly AOD1B-like coefficients for the year 2019 that incorporate the above mentioned improvements will be made available for testing purposes.</p>

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A multi-year timeseries of observation-based 3D horizontal and vertical quasi-geostrophic global ocean currents

10.5194/essd-2020-73 ◽

2020 ◽

Author(s):

Bruno Buongiorno Nardelli

Keyword(s):

Ocean Circulation ◽

General Circulation ◽

Numerical Models ◽

Ocean Currents ◽

Ocean Dynamics ◽

Global Ocean ◽

Diagnostic Model ◽

Geostrophic Balance ◽

Consiglio Nazionale Delle Ricerche ◽

Marine Environment Monitoring

Abstract. Estimates of 3D ocean circulation are needed to improve our understanding of ocean dynamics and to assess its impact on marine ecosystems and Earth climate. Here we present the OMEGA3D product, an observation-based timeseries of (quasi) global 3D ocean currents covering the 1993–2018 period, developed by the Italian Consiglio Nazionale delle Ricerche within the European Copernicus Marine Environment Monitoring Service (CMEMS). This dataset was obtained by applying a diabatic quasi-geostrophic (QG) diagnostic model to CMEMS data-driven ARMOR3D weekly reconstruction of temperature and salinity and ERA-Interim fluxes. Outside the equatorial band, vertical velocities were retrieved in the upper 1500 m, at nominal ¼° resolution, and successively used to compute the horizontal ageostrophic components. Root mean square differences between OMEGA3D total horizontal velocities and totally independent drifter observations at two different depths (15 m and 1000 m) decrease with respect to corresponding estimates obtained from zero-order geostrophic balance, meaning that estimated vertical velocities can also be deemed reliable. OMEGA3D horizontal velocities are also closer to drifter observations than velocities provided by a set of re-analyses spanning a comparable time period, but based on data assimilation in ocean general circulation numerical models. The full OMEGA3D product (released on 31st of March 2020) is available upon free registration at https://doi.org/10.25423/cmcc/multiobs_glo_phy_w_rep_015_007. The reduced subset used here for validation and review purposes is openly available at https://doi.org/10.5281/zenodo.3696885 (Buongiorno Nardelli, 2020).

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Ocean-sea-ice coupling in a global ocean general circulation model

Annals of Glaciology ◽

10.3189/s0260305500013896 ◽

1997 ◽

Vol 25 ◽

pp. 116-120 ◽

Cited By ~ 7

Author(s):

S. Legutke ◽

E. Maier-Reimkr ◽

A. Stössel ◽

A. Hellbach

Keyword(s):

Sea Ice ◽

General Circulation Model ◽

Ocean Circulation ◽

General Circulation ◽

Circulation Model ◽

Ice Cover ◽

Ocean General Circulation Model ◽

Global Ocean ◽

Ocean General Circulation ◽

The Impact

A global ocean general circulation model has been coupled with a dynamic thermodynamic sea-ice model. This model has been spun-up in a 1000 year integration using daily atmosphere model data. Main water masses and currents are reproduced as well as the seasonal characteristics of the ice cover of the Northern and Southern Hemispheres. Model results for the Southern Ocean, however, show the ice cover as too thin, and there are large permanent polynyas in the Weddell and Ross Seas. These polynyas are due to a large upward oceanic heat flux caused by haline rejection during the freezing of sea ice. Sensitivity studies were performed to test several ways of treating the sea-surface salinity and the rejected brine. The impact on the ice cover, water-mass characteristics, and ocean circulation are described.

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A nested Atlantic-Mediterranean Sea general circulation model for operational forecasting

Ocean Science ◽

10.5194/os-5-461-2009 ◽

2009 ◽

Vol 5 (4) ◽

pp. 461-473 ◽

Cited By ~ 124

Author(s):

P. Oddo ◽

M. Adani ◽

N. Pinardi ◽

C. Fratianni ◽

M. Tonani ◽

...

Keyword(s):

Mediterranean Sea ◽

General Circulation Model ◽

Ocean Circulation ◽

General Circulation ◽

Circulation Model ◽

Ocean Model ◽

Global Ocean ◽

Lateral Boundary ◽

The Mediterranean ◽

The Impact

Abstract. A new numerical general circulation ocean model for the Mediterranean Sea has been implemented nested within an Atlantic general circulation model within the framework of the Marine Environment and Security for the European Area project (MERSEA, Desaubies, 2006). A 4-year twin experiment was carried out from January 2004 to December 2007 with two different models to evaluate the impact on the Mediterranean Sea circulation of open lateral boundary conditions in the Atlantic Ocean. One model considers a closed lateral boundary in a large Atlantic box and the other is nested in the same box in a global ocean circulation model. Impact was observed comparing the two simulations with independent observations: ARGO for temperature and salinity profiles and tide gauges and along-track satellite observations for the sea surface height. The improvement in the nested Atlantic-Mediterranean model with respect to the closed one is particularly evident in the salinity characteristics of the Modified Atlantic Water and in the Mediterranean sea level seasonal variability.

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Stability of the Global Ocean Circulation: Basic Bifurcation Diagrams

Journal of Physical Oceanography ◽

10.1175/jpo2726.1 ◽

2005 ◽

Vol 35 (6) ◽

pp. 933-948 ◽

Cited By ~ 31

Author(s):

Henk A. Dijkstra ◽

Wilbert Weijer

Keyword(s):

Ocean Circulation ◽

General Circulation ◽

Multiple Equilibria ◽

Stable Solution ◽

Circulation Model ◽

Ocean Model ◽

Global Ocean ◽

Freshwater Flux ◽

Surface Salinity ◽

Global Ocean Circulation

Abstract A study of the stability of the global ocean circulation is performed within a coarse-resolution general circulation model. Using techniques of numerical bifurcation theory, steady states of the global ocean circulation are explicitly calculated as parameters are varied. Under a freshwater flux forcing that is diagnosed from a reference circulation with Levitus surface salinity fields, the global ocean circulation has no multiple equilibria. It is shown how this unique-state regime transforms into a regime with multiple equilibria as the pattern of the freshwater flux is changed in the northern North Atlantic Ocean. In the multiple-equilibria regime, there are two branches of stable steady solutions: one with a strong northern overturning in the Atlantic and one with hardly any northern overturning. Along the unstable branch that connects both stable solution branches (here for the first time computed for a global ocean model), the strength of the southern sinking in the South Atlantic changes substantially. The existence of the multiple-equilibria regime critically depends on the spatial pattern of the freshwater flux field and explains the hysteresis behavior as found in many previous modeling studies.

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Multi-grid algorithm for passive tracer transport in NEMO ocean circulation model: a case study with NEMO OGCM (version 3.6)

10.5194/gmd-2019-341 ◽

2020 ◽

Cited By ~ 1

Author(s):

Clément Bricaud ◽

Julien Le Sommer ◽

Madec Gurvan ◽

Christophe Calone ◽

Julie Deshayes ◽

...

Keyword(s):

Spatial Resolution ◽

Ocean Circulation ◽

Circulation Model ◽

Ocean Model ◽

Ocean Dynamics ◽

Global Ocean ◽

Passive Tracer ◽

Tracer Transport ◽

Ocean Circulation Model ◽

Grid Algorithm

Abstract. Ocean biogeochemical models are key tools for both scientific and operational applications. Nevertheless the cost of running these models is often expensive because of the large number of biogeochemical tracers. This has motivated the development of multi-grid approaches where ocean dynamics and tracer transport are computed on grids of different spatial resolution. However, existing multi-grid approaches to tracer transport in ocean modelling do not allow to compute ocean dynamics and tracer transport simultaneously. This paper describes a new multi-grid approach developed for accelerating the computation of passive tracer transport in the NEMO ocean circulation model. In practice, passive tracer transport is computed at runtime on a grid with coarser spatial resolution than the hydrodynamics, which allows to reduce the CPU cost of computing the evolution of tracer. We describe the multi-grid algorithm, its practical implementation in the NEMO ocean model, and discuss its performance on the basis of a series of sensitivity experiments with global ocean model configurations. Our experiments confirm that the spatial resolution of hydrodynamical fields can be coarsened by a factor 3 in both horizontal directions without significantly affecting the resolved passive tracer fields. Overall, the proposed algorithm yields a reduction by a factor 7 of the overhead associated with running a full biogeochemical model like PISCES (with 24 passive tracers). Propositions for reducing further this cost without affecting the resolved solution are discussed.

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A multi-year time series of observation-based 3D horizontal and vertical quasi-geostrophic global ocean currents

Earth System Science Data ◽

10.5194/essd-12-1711-2020 ◽

2020 ◽

Vol 12 (3) ◽

pp. 1711-1723

Author(s):

Bruno Buongiorno Nardelli

Keyword(s):

Time Series ◽

Ocean Circulation ◽

General Circulation ◽

Numerical Models ◽

Ocean Currents ◽

Ocean Dynamics ◽

Global Ocean ◽

Diagnostic Model ◽

Geostrophic Balance ◽

Consiglio Nazionale Delle Ricerche

Abstract. Estimates of 3D ocean circulation are needed to improve our understanding of ocean dynamics and to assess their impact on marine ecosystems and Earth climate. Here we present the OMEGA3D product, an observation-based time series of (quasi-)global 3D ocean currents covering the 1993–2018 period, developed by the Italian Consiglio Nazionale delle Ricerche within the European Copernicus Marine Environment Monitoring Service (CMEMS). This dataset was obtained by applying a diabatic quasi-geostrophic (QG) diagnostic model to the data-driven CMEMS-ARMOR3D weekly reconstruction of temperature and salinity as well as ERA Interim fluxes. Outside the equatorial band, vertical velocities were retrieved in the upper 1500 m at 1∕4∘ nominal resolution and successively used to compute the horizontal ageostrophic components. Root mean square differences between OMEGA3D total horizontal velocities and totally independent drifter observations at two different depths (15 and 1000 m) decrease with respect to corresponding estimates obtained from zero-order geostrophic balance, meaning that estimated vertical velocities can also be deemed reliable. OMEGA3D horizontal velocities are also closer to drifter observations than velocities provided by a set of reanalyses spanning a comparable time period but based on data assimilation in ocean general circulation numerical models. The full OMEGA3D product (released on 31 March 2020) is available upon free registration at https://doi.org/10.25423/cmcc/multiobs_glo_phy_w_rep_015_007 (Buongiorno Nardelli, 2020a). The reduced subset used here for validation and review purposes is openly available at https://doi.org/10.5281/zenodo.3696885 (Buongiorno Nardelli, 2020b).

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