The North Atlantic subpolar circulation in an eddy-resolving global ocean model

Marzocchi, Alice; Hirschi, Joël; Holliday, N. Penny; Cunningham, Stuart A.; Blaker, Adam T.; Coward, Andrew C.

doi:10.1016/j.jmarsys.2014.10.007

Cited by 177 publications

(220 citation statements)

References 81 publications

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“…Colder SSTs in the sub-polar North Atlantic for all models are not uncommon and likely due to the coarse resolution (e.g. Marzocchi et al, 2015a). This can be seen by comparing HadCM3B and HadCM3BL, which are models that differ most in their ocean resolution.…”

Section: Sea Surface Temperaturementioning

confidence: 94%

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

et al. 2017

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Abstract. Understanding natural and anthropogenic climate change processes involves using computational models that represent the main components of the Earth system: the atmosphere, ocean, sea ice, and land surface. These models have become increasingly computationally expensive as resolution is increased and more complex process representations are included. However, to gain robust insight into how climate may respond to a given forcing, and to meaningfully quantify the associated uncertainty, it is often required to use either or both ensemble approaches and very long integrations. For this reason, more computationally efficient models can be very valuable tools. Here we provide a comprehensive overview of the suite of climate models based around the HadCM3 coupled general circulation model. This model was developed at the UK Met Office and has been heavily used during the last 15 years for a range of future (and past) climate change studies, but has now been largely superseded for many scientific studies by more recently developed models. However, it continues to be extensively used by various institutions, including the BRIDGE (Bristol Research Initiative for the Dynamic Global Environment) research group at the University of Bristol, who have made modest adaptations to the base HadCM3 model over time. These adaptations mean that the original documentation is not entirely representative, and several other relatively undocumented configurations are in use. We therefore describe the key features of a number of configurations of the HadCM3 climate model family, which together make up HadCM3@Bristol version 1.0. In order to differentiate variants that have undergone development at BRIDGE, we have introduced the letter B into the model nomenclature. We include descriptions of the atmosphere-only model (HadAM3B), the coupled model with a low-resolution ocean (HadCM3BL), the high-resolution atmosphere-only model (HadAM3BH), and the regional model (HadRM3B). These also include three versions of the land surface scheme. By comparing withPublished by Copernicus Publications on behalf of the European Geosciences Union. observational datasets, we show that these models produce a good representation of many aspects of the climate system, including the land and sea surface temperatures, precipitation, ocean circulation, and vegetation. This evaluation, combined with the relatively fast computational speed (up to 1000 times faster than some CMIP6 models), motivates continued development and scientific use of the HadCM3B family of coupled climate models, predominantly for quantifying uncertainty and for long multi-millennial-scale simulations.

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Section: Sea Surface Temperaturementioning

confidence: 94%

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

et al. 2017

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“…Barnier et al, 2006;Penduff et al, 2007Penduff et al, , 2010Treguier et al, 2014;Marzocchi et al, 2015). The FRM at 1/4 • horizontal resolution is referred to here as ORCA025 and has 46 z levels, with thickness ranging from 6 m at the surface to 250 m at the ocean bottom.…”

Section: Free-running Modelsmentioning

confidence: 99%

South Atlantic meridional transports from NEMO-based simulations and reanalyses

2018

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Abstract. The meridional heat transport (MHT) of the South Atlantic plays a key role in the global heat budget: it is the only equatorward basin-scale ocean heat transport and it sets the northward direction of the global cross-equatorial transport. Its strength and variability, however, are not well known. The South Atlantic transports are evaluated for four state-of-the-art global ocean reanalyses (ORAs) and two free-running models (FRMs) in the period 1997-2010. All products employ the Nucleus for European Modelling of the Oceans (NEMO) model, and the ORAs share very similar configurations. Very few previous works have looked at ocean circulation patterns in reanalysis products, but here we show that the ORA basin interior transports are consistently improved by the assimilated in situ and satellite observations relative to the FRMs, especially in the Argo period. The ORAs also exhibit systematically higher meridional transports than the FRMs, which is in closer agreement with observational estimates at 35 and 11 • S. However, the data assimilation impact on the meridional transports still greatly varies among the ORAs, leading to differences up to ∼ 8 Sv and 0.4 PW in the South Atlantic Meridional Overturning Circulation and the MHTs, respectively. We narrow this down to large inter-product discrepancies in the western boundary currents (WBCs) at both upper and deep levels explaining up to ∼ 85 % of the inter-product differences in MHT. We show that meridional velocity differences, rather than temperature differences, in the WBCs drive ∼ 83 % of this MHT spread. These findings show that the present ocean observation network and data assimilation schemes can be used to consistently constrain the South Atlantic interior circulation but not the overturning component, which is dominated by the narrow western boundary currents. This will likely limit the effectiveness of ORA products for climate or decadal prediction studies.

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“…Marzocchi et al, 2015;Duchez et al, 2014) as a reference grid and bathymetry. This is a tri-polar grid with a coarsest resolution of 9.3 km, but decreasing to minimum values of 1.8 km in the Southern Ocean and 1.3 km in the Canadian archipelago.…”

Section: Coastal Ocean Process Scales In a Global Contextmentioning

confidence: 99%

“…To illustrate what might be achieved through higher resolution, introducing tides and sophisticated mixing schemes in the context of the coastal ocean, we consider runs of the global ORCA12 (Marzocchi et al, 2015;Duchez et al, 2014) and the northern North Atlantic (NNA; Holt et al, 2014) NEMO models. Both use the same NEMO code base (v3.5) and have 75 z partial step layers in the vertical.…”

Section: An Example Of Improved Resolution and Process Representationmentioning

confidence: 99%

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Prospects for improving the representation of coastal and shelf seas in global ocean models

et al. 2017

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Abstract. Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth system science. They are regions of immense societal importance through the goods and services they provide, hazards they pose and their role in global-scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution, we aim to briefly characterise the problem, and then to identify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape.We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions, e.g. nominal 1/12 • , and still reasonably well resolved at 1/4 • ; here, the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. In terms of finer-scale processes, we find that a 1/12 • global model resolves the first baroclinic Rossby radius for only ∼ 8 % of regions < 500 m deep, but this increases to ∼ 70 % for a 1/72 • model, so resolving scales globally requires substantially finer resolution than the current state of the art.We quantify the benefit of improved resolution and process representation using 1/12 • global-and basin-scale northern North Atlantic nucleus for a European model of the ocean (NEMO) simulations; the latter includes tides and a k-ε vertical mixing scheme. These are compared with global stratification observations and 19 models from CMIP5. In terms of correlation and basin-wide rms error, the high-resolution models outperform all these CMIP5 models. The model with tides shows improved seasonal cycles compared to the highresolution model without tides. The benefits of resolution are particularly apparent in eastern boundary upwelling zones.To explore the balance between the size of a globally refined model and that of multiscale modelling options (e.g. finite element, finite volume or a two-way nesting approach), we consider a simple scale analysis and a conceptual grid refining approach. We put this analysis in the context of evolving computer systems, discussing model turnaround time, scalability and resource costs. Using a simple cost model compared to a reference configuration (taken to be a 1/4 • global model in 2011) and the increasing performance of the UK Research Councils' computer facility, we estimate an unstructured mesh multiscale approach, resolving process scales down to 1.5 km, would use a comparable share of the computer resource by 2021, the two-way nested multiscale approach by 2022, and a 1/72 • global model by 2026. However, we also note that a 1/12 • global model would not have a comparable computational cost to a 1 • global model in 2017 until 2027. Hence, we conc...

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The North Atlantic subpolar circulation in an eddy-resolving global ocean model

Cited by 177 publications

References 81 publications

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

The BRIDGE HadCM3 family of climate models: HadCM3@Bristol v1.0

South Atlantic meridional transports from NEMO-based simulations and reanalyses

Prospects for improving the representation of coastal and shelf seas in global ocean models

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