Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

Rackow, Thomas; Sein, Dmitry V.; Semmler, Tido; Danilov, Sergey; Koldunov, Nikolay; Sidorenko, Dmitry; Wang, Qiang; Jung, Thomas

doi:10.5194/gmd-2018-192

Cited by 20 publications

(32 citation statements)

References 25 publications

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“…Areas to the south of the outcropping location are white (indicating no data). For animations of the bias development with a 10-year running window, see Supplement videos S1 and S2 (Rackow et al, 2018c).…”

Section: Discussionmentioning

confidence: 99%

“…10) is deep enough so that surface biases can reach the 31.8 and neighboring isopycnals, from where the signal is further advected towards the south. Eventually, the signal is advected towards the Equator, from where it propagates to the east as a Kelvin wave (Supplement video S1; Rackow et al, 2018c).…”

Section: Along-isopycnal Bias Propagation In the Atlanticmentioning

confidence: 99%

“…Meridional section at 30.5 • W through the Atlantic Ocean for the potential temperature bias in the five simulations. The difference compared to PHC is shown with colors for years 21-30 (left column) and years 91-100 (right column), illustrating the North Atlantic bias development along isopycnal layers (see animations S3 and S4 for LR and HR with a 10-year running window in the Supplement videos; Rackow et al, 2018c). The contours show σ 1 density contours that are representative for the deep ocean between 600 and 1000 m (gray and black; σ 1 = 31.6, 31.8, 32.0) and for the surface ocean until a maximum depth of about 300 m (red; σ 1 = 30.5, 30.8).…”

Section: Displacement and Tilt Of Simulated Isopycnalsmentioning

confidence: 99%

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Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

et al. 2019

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Abstract. Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) show substantial biases in the deep ocean that are larger than the level of natural variability and the response to enhanced greenhouse gas concentrations. Here, we analyze the influence of horizontal resolution in a hierarchy of five multi-resolution simulations with the AWI Climate Model (AWI-CM), the climate model used at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, which employs a sea ice–ocean model component formulated on unstructured meshes. The ocean grid sizes considered range from a nominal resolution of ∼1∘ (CMIP5 type) up to locally eddy resolving. We show that increasing ocean resolution locally to resolve ocean eddies leads to reductions in deep ocean biases, although these improvements are not strictly monotonic for the five different ocean grids. A detailed diagnosis of the simulations allows to identify the origins of the biases. We find that two key regions at the surface are responsible for the development of the deep bias in the Atlantic Ocean: the northeastern North Atlantic and the region adjacent to the Strait of Gibraltar. Furthermore, the Southern Ocean density structure is equally improved with locally explicitly resolved eddies compared to parameterized eddies. Part of the bias reduction can be traced back towards improved surface biases over outcropping regions, which are in contact with deeper ocean layers along isopycnal surfaces. Our prototype simulations provide guidance for the optimal choice of ocean grids for AWI-CM to be used in the final runs for phase 6 of CMIP (CMIP6) and for the related flagship simulations in the High Resolution Model Intercomparison Project (HighResMIP). Quite remarkably, retaining resolution only in areas of high eddy activity along with excellent scalability characteristics of the unstructured-mesh sea ice–ocean model enables us to perform the multi-centennial climate simulations needed in a CMIP context at (locally) eddy-resolving resolution with a throughput of 5–6 simulated years per day.

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Section: Discussionmentioning

confidence: 99%

Section: Along-isopycnal Bias Propagation In the Atlanticmentioning

confidence: 99%

Section: Displacement and Tilt Of Simulated Isopycnalsmentioning

confidence: 99%

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Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

et al. 2019

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“…For the unstructured‐mesh ocean and sea ice model component FESOM1.4 (Timmermann et al, ) we use the “CORE2” mesh with a resolution of ∼25 km in the Arctic and ∼1.27×10 5 surface nodes globally. Details on the influence of the model resolution of the two model components can be found in Sein et al () and Rackow et al (). The sea ice model (Danilov et al, ) includes an elastic‐viscous‐plastic rheology and a thermodynamical component based on Parkinson and Washington (), including a prognostic snow layer (Owens & Lemke, ).…”

Section: Methodsmentioning

confidence: 99%

Sea Ice Targeted Geoengineering Can Delay Arctic Sea Ice Decline but not Global Warming

Zampieri

Goessling

2019

Earth's Future

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To counteract global warming, a geoengineering approach that aims at intervening in the Arctic ice-albedo feedback has been proposed. A large number of wind-driven pumps shall spread seawater on the surface in winter to enhance ice growth, allowing more ice to survive the summer melt. We test this idea with a coupled climate model by modifying the surface exchange processes such that the physical effect of the pumps is simulated. Based on experiments with RCP 8.5 scenario forcing, we find that it is possible to keep the late-summer sea ice cover at the current extent for the next ∼60 years. The increased ice extent is accompanied by significant Arctic late-summer cooling by ∼1.3 K on average north of the polar circle (2021-2060). However, this cooling is not conveyed to lower latitudes. Moreover, the Arctic experiences substantial winter warming in regions with active pumps. The global annual-mean near-surface air temperature is reduced by only 0.02 K (2021-2060). Our results cast doubt on the potential of sea ice targeted geoengineering to mitigate climate change. contributed equally to this work. Key Points: • Sea ice targeted geoengineering allows to keep the late-summer sea ice cover at the current extent for the next ∼60 years • The Arctic summer cooling is not conveyed to lower latitudes and comes at the price of Arctic winter warming • Our results cast doubt on the potential of Arctic Ice Management to mitigate climate change Supporting Information: • Supporting Information S1

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“…All simulations are run with the Alfred Wegener Institute Climate Model version 1.1 (AWI-CM 1.1). AWI-CM has been described in Sidorenko et al (2015), Rackow et al (2018Rackow et al ( , 2019. The model was run in its low resolution CMIP6 set-up (LR).…”

Section: Experiments Setupmentioning

confidence: 99%

Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations

2020

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In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO 2 concentrations have been regionally increased in different latitudinal belts, namely in the Arctic, in the northern mid-latitudes, everywhere outside of the Arctic and globally, in a series of 150 year coupled model experiments with the AWI Climate Model. This method is applied to allow a decomposition of the response to increasing CO 2 concentrations in different regions. It turns out that CO 2 increase applied in the Arctic only is very efficient in heating the Arctic and that the energy largely remains in the Arctic. In the first 30 years after switching on the CO 2 forcing some robust atmospheric circulation changes, which are associated with the surface temperature anomalies including local cooling of up to 1 °C in parts of North America, are simulated. The synoptic activity is decreased in the mid-latitudes. Further into the simulation, surface temperature and atmospheric circulation anomalies become less robust. When quadrupling the CO 2 concentration south of 60° N, the March Arctic sea ice volume is reduced by about two thirds in the 150 years of simulation time. When quadrupling the CO 2 concentration between 30 and 60° N, the March Arctic sea ice volume is reduced by around one third, the same amount as if quadrupling CO 2 north of 60° N. Both atmospheric and oceanic northward energy transport across 60° N are enhanced by up to 0.1 PW and 0.03 PW, respectively, and winter synoptic activity is increased over the Greenland, Norwegian, Iceland (GIN) seas. To a lesser extent the same happens when the CO 2 concentration between 30 and 60° N is only increased to 1.65 times the reference value in order to consider the different size of the forcing areas. The increased northward energy transport, leads to Arctic sea ice reduction, and consequently Arctic amplification is present without Arctic CO 2 forcing in all seasons but summer, independent of where the forcing is applied south of 60° N. South of the forcing area, both in the Arctic and northern mid-latitude forcing simulations, the warming is generally limited to less than 0.5 °C. In contrast, north of the forcing area in the northern mid-latitude forcing experiments, the warming amounts to generally more than 1 °C close to the surface, except for summer. This is a strong indication that the influence of warming outside of the Arctic on the Arctic is substantial, while forcing applied only in the Arctic mainly materializes in a warming Arctic, with relatively small implications for non-Arctic regions.

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Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

Cited by 20 publications

References 25 publications

Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

Sensitivity of deep ocean biases to horizontal resolution in prototype CMIP6 simulations with AWI-CM1.0

Sea Ice Targeted Geoengineering Can Delay Arctic Sea Ice Decline but not Global Warming

Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations

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