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An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation

An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation
An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation
The key physical parameters for the "eb_go_gs" configuration of version 2.7.4 of GENIE, an Earth system model of intermediate complexity (EMIC), are tuned using a multi-objective genetic algorithm. An ensemble of 90 parameter sets is tuned using two ocean and two atmospheric state variables as targets. These are "Pareto-optimal", representing a range of trade-offs between the four tuning targets. For the leading five parameter sets, simulations are evaluated alongside a simulation with untuned "default" parameters, comparing selected variables and diagnostics that describe the state of the atmosphere, ocean and sea ice. Further experiments are undertaken with these selected parameter sets to compare equilibrium climate sensitivities and transient climate responses. The pattern of warming under doubled CO2 is strongly shaped by changes in the Atlantic meridional overturning circulation (AMOC), while the pattern and rate of warming under rising CO2 is closely linked to changing sea ice extent. One of the five tuned parameter sets is identified as marginally optimal, and the objective function (error) landscape is further analysed in the vicinity of the tuned values of this parameter set. "Cliffs" along some dimensions motivate closer inspection of corresponding variations in the AMOC. This reveals that bifurcations in the AMOC are highly sensitive to parameters that are not typically associated with MOC stability. Specifically, the state of the AMOC is sensitive to parameters governing the wind-driven circulation and atmospheric heat transport. For the GENIE configuration presented here, the marginally optimal parameter set is recommended for single simulations, although the leading five parameter sets may be used in ensemble mode to admit a constrained degree of parametric uncertainty in climate prediction.
1991-9603
1729-1744
Marsh, R.
702c2e7e-ac19-4019-abd9-a8614ab27717
Sobester, Andras
096857b0-cad6-45ae-9ae6-e66b8cc5d81b
Hart, Elizabeth E.
7f26613c-7d19-4ee4-bd28-a5bb60729051
Oliver, K.I.C.
588b11c6-4d0c-4c59-94e2-255688474987
Edwards, Neil
e66fa35f-baf1-488e-ac1e-f19227087fd0
Cox, S.J.
0e62aaed-24ad-4a74-b996-f606e40e5c55
Marsh, R.
702c2e7e-ac19-4019-abd9-a8614ab27717
Sobester, Andras
096857b0-cad6-45ae-9ae6-e66b8cc5d81b
Hart, Elizabeth E.
7f26613c-7d19-4ee4-bd28-a5bb60729051
Oliver, K.I.C.
588b11c6-4d0c-4c59-94e2-255688474987
Edwards, Neil
e66fa35f-baf1-488e-ac1e-f19227087fd0
Cox, S.J.
0e62aaed-24ad-4a74-b996-f606e40e5c55

Marsh, R., Sobester, Andras, Hart, Elizabeth E., Oliver, K.I.C., Edwards, Neil and Cox, S.J. (2013) An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation. Geoscientific Model Development, 6, 1729-1744. (doi:10.5194/gmd-6-1729-2013).

Record type: Article

Abstract

The key physical parameters for the "eb_go_gs" configuration of version 2.7.4 of GENIE, an Earth system model of intermediate complexity (EMIC), are tuned using a multi-objective genetic algorithm. An ensemble of 90 parameter sets is tuned using two ocean and two atmospheric state variables as targets. These are "Pareto-optimal", representing a range of trade-offs between the four tuning targets. For the leading five parameter sets, simulations are evaluated alongside a simulation with untuned "default" parameters, comparing selected variables and diagnostics that describe the state of the atmosphere, ocean and sea ice. Further experiments are undertaken with these selected parameter sets to compare equilibrium climate sensitivities and transient climate responses. The pattern of warming under doubled CO2 is strongly shaped by changes in the Atlantic meridional overturning circulation (AMOC), while the pattern and rate of warming under rising CO2 is closely linked to changing sea ice extent. One of the five tuned parameter sets is identified as marginally optimal, and the objective function (error) landscape is further analysed in the vicinity of the tuned values of this parameter set. "Cliffs" along some dimensions motivate closer inspection of corresponding variations in the AMOC. This reveals that bifurcations in the AMOC are highly sensitive to parameters that are not typically associated with MOC stability. Specifically, the state of the AMOC is sensitive to parameters governing the wind-driven circulation and atmospheric heat transport. For the GENIE configuration presented here, the marginally optimal parameter set is recommended for single simulations, although the leading five parameter sets may be used in ensemble mode to admit a constrained degree of parametric uncertainty in climate prediction.

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Published date: 21 October 2013
Organisations: Physical Oceanography, Aeronautics, Astronautics & Comp. Eng

Identifiers

Local EPrints ID: 359348
URI: http://eprints.soton.ac.uk/id/eprint/359348
ISSN: 1991-9603
PURE UUID: 39fdaac8-59fd-463e-940e-8b52d95cbbc8
ORCID for Andras Sobester: ORCID iD orcid.org/0000-0002-8997-4375

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Date deposited: 28 Oct 2013 13:27
Last modified: 09 Jul 2020 00:28

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