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

Prospects for improving the representation of coastal and shelf seas in global ocean models
Prospects for improving the representation of coastal and shelf seas in global ocean models
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 through 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 identify and quantify 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 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. We demonstrate this through basin scale northern North Atlantic simulations and analysis of global profile data, which particularly shows the need for increased vertical resolution in shallower water. In terms of finer scale processes, we find that a 1/12° global model resolves the 1st baroclinic Rossby Radius for only ~?20?% of regions <?500?m deep, but this increases to ~?90?% for a 1/72° model, so to resolve these scales globally requires substantially finer resolution than the current state-of-the-art.

We consider a simple scale analysis and conceptual grid refining approach 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 2-way nesting approach). We put this analysis in the context of evolving computer systems, using the UK’s national research facility as an example. This doubles in peak performance every ~?1.2 years. Using a simple cost-model compared to a reference configuration (taken to be a 1/4° global model in 2011), 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 2024, the 2-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 today until 2027. Hence, we conclude that for computationally expensive models (e.g. for oceanographic research or operational oceanography), resolving scales to ~?1.5?km would be routinely practical in about a decade given substantial effort on numerical and computational development. For complex Earth System Models this extends to about two decades, suggesting the focus here needs to be on improved process parameterisation to meet these challenges.
1991-9603
499-523
Holt, Jason
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Hyder, Pat
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Ashworth, Mike
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Harle, James
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Hewitt, Helene T.
c6c30d10-905e-4fdb-a021-37f63c5e92a4
Liu, Hedong
c1aba27e-9255-4347-99ed-f124227583b4
New, Adrian L.
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Pickles, Stephen
b2e62281-bd10-4337-9658-65665ec7dbe2
Porter, Andrew
1fa1b618-0d61-4087-a311-81fe2dbdc532
Popova, Ekaterina
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Allen, J. Icarus
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Siddorn, John
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Wood, Richard
fa173eb1-9e26-4d9f-8d90-0c48d5586f94
Holt, Jason
6e0276a6-1a9b-4514-bc5f-9d04571b7687
Hyder, Pat
3ecf7b44-00f5-4b4d-b689-71aab9907d98
Ashworth, Mike
7997af65-3b5d-4001-9334-7197dd16c902
Harle, James
b59d8925-1e59-42d4-b08f-823fec3b701e
Hewitt, Helene T.
c6c30d10-905e-4fdb-a021-37f63c5e92a4
Liu, Hedong
c1aba27e-9255-4347-99ed-f124227583b4
New, Adrian L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Pickles, Stephen
b2e62281-bd10-4337-9658-65665ec7dbe2
Porter, Andrew
1fa1b618-0d61-4087-a311-81fe2dbdc532
Popova, Ekaterina
3ea572bd-f37d-4777-894b-b0d86f735820
Allen, J. Icarus
6a8016db-2a5a-4275-8cdf-63ddb7a51526
Siddorn, John
319d1da4-121a-4d1f-a825-db6a4c01068d
Wood, Richard
fa173eb1-9e26-4d9f-8d90-0c48d5586f94

Holt, Jason, Hyder, Pat, Ashworth, Mike, Harle, James, Hewitt, Helene T., Liu, Hedong, New, Adrian L., Pickles, Stephen, Porter, Andrew, Popova, Ekaterina, Allen, J. Icarus, Siddorn, John and Wood, Richard (2017) Prospects for improving the representation of coastal and shelf seas in global ocean models. Geoscientific Model Development, 10, 499-523. (doi:10.5194/gmd-10-499-2017).

Record type: Article

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 through 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 identify and quantify 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 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. We demonstrate this through basin scale northern North Atlantic simulations and analysis of global profile data, which particularly shows the need for increased vertical resolution in shallower water. In terms of finer scale processes, we find that a 1/12° global model resolves the 1st baroclinic Rossby Radius for only ~?20?% of regions <?500?m deep, but this increases to ~?90?% for a 1/72° model, so to resolve these scales globally requires substantially finer resolution than the current state-of-the-art.

We consider a simple scale analysis and conceptual grid refining approach 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 2-way nesting approach). We put this analysis in the context of evolving computer systems, using the UK’s national research facility as an example. This doubles in peak performance every ~?1.2 years. Using a simple cost-model compared to a reference configuration (taken to be a 1/4° global model in 2011), 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 2024, the 2-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 today until 2027. Hence, we conclude that for computationally expensive models (e.g. for oceanographic research or operational oceanography), resolving scales to ~?1.5?km would be routinely practical in about a decade given substantial effort on numerical and computational development. For complex Earth System Models this extends to about two decades, suggesting the focus here needs to be on improved process parameterisation to meet these challenges.

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More information

Accepted/In Press date: 6 July 2016
e-pub ahead of print date: 1 February 2017
Published date: 1 February 2017
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 404510
URI: http://eprints.soton.ac.uk/id/eprint/404510
ISSN: 1991-9603
PURE UUID: ed295028-235e-4533-987d-426337f62bda

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Date deposited: 10 Jan 2017 10:59
Last modified: 15 Mar 2024 04:09

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Contributors

Author: Jason Holt
Author: Pat Hyder
Author: Mike Ashworth
Author: James Harle
Author: Helene T. Hewitt
Author: Hedong Liu
Author: Adrian L. New
Author: Stephen Pickles
Author: Andrew Porter
Author: Ekaterina Popova
Author: J. Icarus Allen
Author: John Siddorn
Author: Richard Wood

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