A Partial Coupling Method to Isolate the Roles of the Atmosphere and Ocean in Coupled Climate Simulations

Garuba, O. A.; Rasch, Philip J.

doi:10.1029/2019ms002016

Cited by 6 publications

(2 citation statements)

References 71 publications

(148 reference statements)

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“…Cael and Jansen 2020;Todd et al 2020). While Garuba and Klinger (2018) found evidence of weakening in an ocean-only model study, subsequent work using coupled simulations found that heat fluxes rather than freshwater fluxes drive AMOC weakening (Garuba and Rasch 2020). Recent studies employing an idealised doubling of southern hemisphere westerly wind stress magnitude have shown AMOC strengthening (Lüschow et al 2021), as well as a transient AMOC strengthening and subsequent return to a weakened state (Lohmann et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

et al. 2022

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The effect of anthropogenic climate change in the ocean is challenging to project because atmosphere-ocean general circulation models (AOGCMs) respond differently to forcing. This study focuses on changes in the Atlantic Meridional Overturning Circulation (AMOC), ocean heat content ($$\Delta$$ Δ OHC), and the spatial pattern of ocean dynamic sea level ($$\Delta \zeta$$ Δ ζ ). We analyse experiments following the FAFMIP protocol, in which AOGCMs are forced at the ocean surface with standardised heat, freshwater and momentum flux perturbations, typical of those produced by doubling $$\hbox {CO}_{{2}}$$ CO 2 . Using two new heat-flux-forced experiments, we find that the AMOC weakening is mainly caused by and linearly related to the North Atlantic heat flux perturbation, and further weakened by a positive coupled heat flux feedback. The quantitative relationships are model-dependent, but few models show significant AMOC change due to freshwater or momentum forcing, or to heat flux forcing outside the North Atlantic. AMOC decline causes warming at the South Atlantic-Southern Ocean interface. It does not strongly affect the global-mean vertical distribution of $$\Delta$$ Δ OHC, which is dominated by the Southern Ocean. AMOC decline strongly affects $$\Delta \zeta$$ Δ ζ in the North Atlantic, with smaller effects in the Southern Ocean and North Pacific. The ensemble-mean $$\Delta \zeta$$ Δ ζ and $$\Delta$$ Δ OHC patterns are mostly attributable to the heat added by the flux perturbation, with smaller effects from ocean heat and salinity redistribution. The ensemble spread, on the other hand, is largely due to redistribution, with pronounced disagreement among the AOGCMs.

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Section: Introductionmentioning

confidence: 99%

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

et al. 2022

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“…A partially coupled experiment wherein the impact of ocean circulation changes on the air‐sea interaction is suppressed is further used to access the role of the coupling between the atmosphere and ocean in augmenting or curtailing the atmosphere‐ and ocean‐driven sea ice volume changes. The formulation and validation of the partial coupling method are described in detail in the study of Garuba and Rasch (2020) (hereafter GR20). By comparing the evolving Arctic sea ice volume budget and frazil/ocean‐ice heat components in the fully and partially coupled experiments, we discern the time‐evolving roles of the atmosphere, ocean, and the coupling between them in driving sea ice loss in the Arctic.…”

Section: Introductionmentioning

confidence: 99%

Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO₂ Increases

Garuba

Singh

Hunke

et al. 2020

J Adv Model Earth Syst

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A novel decomposition of the ocean heat energy that contributes to sea ice melt and growth (ocean-ice and frazil heat) into components that are driven by surface heat flux and ocean circulation changes is used to isolate the evolving roles of the atmosphere and ocean in the Arctic sea ice loss from CO 2 increases. A sea ice volume budget analysis is used to separate the impacts of the anomalous frazil/ocean-ice heat from those of atmosphere-ice heat on the evolving Arctic sea ice volume. The role of atmosphere-ocean coupling in augmenting or curtailing the atmosphere-and ocean-driven sea ice losses is further isolated by comparing the ice volume budget and the anomalous frazil/ocean-ice heat components in partially and fully coupled experiments. Atmosphere-ice heat fluxes drive most of Arctic sea ice loss in the first decade following CO 2 increase by increasing the sea ice top face melt in summer, while ocean circulation changes drive the loss over the longer term through the anomalous increase of heat transport into the Arctic, which drive decreases in frazil ice growth and sea ice extent in winter. Atmosphere-ocean coupling in the subpolar Atlantic further supports a negative feedback that attenuates the ocean-driven sea ice losses over time; by accelerating the weakening of the Atlantic meridional overturning circulation, it causes a large cooling of the subpolar Atlantic and attenuation of the anomalous heat transport into the Arctic in winter, allowing for a seasonal Arctic sea ice in the fully coupled experiment, while the Arctic completely becomes ice free in the partially coupled experiment. Plain Language Summary The interactions between the atmosphere, ocean, and sea ice are disentangled in order to isolate their individual roles in driving Arctic sea ice losses and how these roles change over time. We introduce a new decomposition of the ocean heat that contributes to melting and growing sea ice into parts that are caused by changes in the surface heat input into the ocean and ocean circulation. We analyze the contributions of the ocean heat and atmosphere heat to the overall Arctic sea ice volume changes, both in an experiment where a two-way interaction between the atmosphere and ocean is allowed and in another where this two-way interaction is not allowed. Our results suggest that the atmosphere causes most of Arctic sea ice loss (within a decade) by increasing sea ice top face melt, while the ocean causes the long-term sea ice changes in the Arctic by decreasing winter bottom face growth. The interactions between the atmosphere and ocean further enhance the ocean circulation weakening and surface cooling in the subpolar Atlantic and thereby stop the winter heat transport increase into the Arctic and eventually curtail the ocean-driven sea ice loss and prevent the total loss of Arctic sea ice. Anomalous atmospheric heat fluxes at the top surface of the ice are determined by atmospheric radiative and turbulent flux changes, which are, in turn, influenced by changing atmospheric energy transport, rad...

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Revisiting the equatorial Pacific sea surface temperature response to global warming

Li,

Luo,

et al. 2023

Clim Dyn

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The relative roles of the oceanic and atmospheric processes in the pattern formation of the equatorial Pacific sea surface temperature (SST) response to global warming is investigated using a set of climate model experiments embedded with a novel partial coupling technique.The modeling results show that the SST response experiences a transition from a La Niña-like warming pattern at the initial stage to an El Niño-like warming pattern at the quasi-equilibrium stage. By decomposing anomalous equatorial Pacific SST into atmosphere-forced passive component and ocean dynamically induced active component, it is found that the SST warming pattern at both stages is entirely induced by its active component. Specifically, the meridional and vertical ocean circulation changes play a dominant role in forming the La Niña-like SST warming pattern at the initial stage, and the zonal and meridional ocean circulation changes are responsible for the formation of the El Niño-like SST warming pattern at the quasi-equilibrium stage. In contrast, the passive SST at both stages is characterized by a zonally uniform warming along the equator, which can be explained by a balance between the total effect of the heat transport divergence associated with the mean ocean circulation and the effect of the passive surface heat flux change. In addition, this study finds that it is the slowdown of the Pacific subtropical cells during the transition period that controls the evolution of the equatorial SST warming pattern by changing the meridional and vertical ocean heat transports.

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A Partial Coupling Method to Isolate the Roles of the Atmosphere and Ocean in Coupled Climate Simulations

Cited by 6 publications

References 71 publications

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO₂ Increases

Revisiting the equatorial Pacific sea surface temperature response to global warming

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A Partial Coupling Method to Isolate the Roles of the Atmosphere and Ocean in Coupled Climate Simulations

Cited by 6 publications

References 71 publications

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

Greenhouse-gas forced changes in the Atlantic meridional overturning circulation and related worldwide sea-level change

Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO2 Increases

Revisiting the equatorial Pacific sea surface temperature response to global warming

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About

Disentangling the Coupled Atmosphere‐Ocean‐Ice Interactions Driving Arctic Sea Ice Response to CO₂ Increases